sustainability

Review Characterization of Technological Innovations in Photovoltaic Rural Electrification, Based on the Experiences of Bolivia, Peru, and Argentina: Third Generation Solar Home Systems

Miguel H. Fernandez-Fuentes 1,2,* , Andrea A. Eras-Almeida 1 and Miguel A. Egido-Aguilera 1

1 Instituto de Energía Solar, ETSI Telecomunicación, Universidad Politécnica de Madrid, 28040 Madrid, Spain; [email protected] (A.A.E.-A.); [email protected] (M.A.E.-A.) 2 ENERGETICA Foundation, La Paz, Cochabamba E-573, Bolivia * Correspondence: [email protected]; Tel.: +591-71-735-123

Abstract: The electrification of isolated homes in rural areas without access to the electric grid has been achieved in part using solar energy transformed into electricity through Photovoltaic (PV) equipment known as Solar Home Systems (SHSs), which has been widely disseminated throughout the world. The use of SHSs in rural electrification projects has been studied from 1980 to date, they have been incorporating advances and technological innovations successively. Through the review of documents on PV projects, articles, and technical reports, it has been possible to identify the changes in the main components of the SHS and the typical configurations, systematizing them in a discrete



 timeline. Thereby, this article characterizes three generations of SHSs and highlights their differences. The first generation is fully valid between 1980–1995, the second generation in 1995–2010, and the Citation: Fernandez-Fuentes, M.H.; third generation from 2005 to date, which overlaps the beginning. In any case, the time limits in each Eras-Almeida, A.A.; Egido-Aguilera, period are only referential. The later generation, Third Generation Solar Home Systems (3G-SHSs), M.A. Characterization of is highly efficient, uses LED lamps, lithium batteries, microelectronic control, and plug and play Technological Innovations in connections. Indeed, this equipment can be self-managed by the user and reflects the technology’s Photovoltaic Rural Electrification, Based on the Experiences of Bolivia, high reliability by a minimum maintenance service in situ. Furthermore, their lower costs make Peru, and Argentina: Third access to electricity more affordable for the last mile population. The present research offers a detailed Generation Solar Home Systems. technological and operational characterization of the 3G-SHSs to show the most relevant aspects of Sustainability 2021, 13, 3032. support to project developers, planners, and decision-makers to achieve the Sustainable Development https://doi.org/10.3390/su13063032 Goal (SDG) 7.

Academic Editor: Aritra Ghosh Keywords: universal access to energy; off-grid electrification; third generation solar home systems; rural electrification Received: 7 February 2021 Accepted: 3 March 2021 Published: 10 March 2021 1. Introduction Publisher’s Note: MDPI stays neutral The 17 Sustainable Development Goals (SDGs), agreed by the United Nations Confer- with regard to jurisdictional claims in ence at the Paris 2015 meeting, mark the international commitments to eradicate poverty published maps and institutional affil- and improve people’s quality of life [1]. Objective number seven, SDG 7, determines that by iations. 2030 all the planet inhabitants should have clean, modern, and safe energy services. Energy is essential to improve the quality of life of the population, generate synergies, and promote social, economic, health, education, and environmental achievements [2–5]. However, having a connection to the electricity grid does not automatically imply access to quality, Copyright: © 2021 by the authors. reliable, safe and economical energy in line with the achievement of SDG 7. Ayaburi et al. Licensee MDPI, Basel, Switzerland. (2020) estimated that 3.5 billion people have an electrical connection but suffer frequent and This article is an open access article long-term interruptions, which would qualify the electrical service as unreliable and of low distributed under the terms and quality [6]. In practice, this population does not meet the conditions required by SDG 7. In conditions of the Creative Commons this sense, ensuring access to energy implies more than a physical connection to an energy Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ source, it also implies a quality supply. In particular, the lack of access to electric power 4.0/). in 2019 affected 10% of the world population (771 million people) [7] who have affected

Sustainability 2021, 13, 3032. https://doi.org/10.3390/su13063032 https://www.mdpi.com/journal/sustainability Sustainability 2021, 13, 3032 2 of 23 Sustainability 2021, 13, x FOR PEER REVIEW 2 of 25

their development possibilitiesaccess to electric [8 ].power The in majority 2019 affected of 10 this% of population the world populati is locatedon (771 million in rural people) areas, especially in sub-Saharan[7] who Africahave affected (578 their million development people possibi withoutlities [8]. access The majority to electricity), of this population India, is located in rural areas, especially in sub-Saharan Africa (578 million people without ac- regions of Asia, and tocess a to lesser electricity), extent, India, the regions Middle of Asia, East and andto a lesser North extent, Africa the Middle (see FigureEast and1 North). For the Latin America andAfrica the (see Caribbean Figure 1). For (LAC) the Latin region, America the an electricityd the Caribbean coverage (LAC) region, has the increased electricity to 98.31%, consideringcoverage it one of has the increased regions to 98.31%, withthe considering highest it one electrical of the regions coverage with the on highest the planet. elec- trical coverage on the planet. However, there are still 11 million people without access to However, there are stillelectricity 11 million in this region people [9]. without access to electricity in this region [9].

Figure 1. Rural populationFigure with 1. Rural access population to electricity with access in to 2019electricity [7]. in 2019 [7].

However, it is now crucial to observe the effect of the COVID-19 pandemic that has However, it is nowsignificantly crucial affected to observe energy access, the effect slowing of down the COVID-19the efforts being pandemic made by directing that has significantly affectedresources energy primarily access, for slowing health care down[10]. In LAC, the effortsthe pandemic being forced made them byto take directing health resources primarily forprotection health measures care [ 10that]. drastically In LAC, reduce the pandemicd economic forcedactivity. The them electricity to take demand health protection measuresfell that between drastically 6% and 32% reduced in these economic countries [11], activity. affecting Thethe coverage electricity expansion demand projects. fell By 2019, except for Haiti (38.7%) and Honduras (81.1%), LAC countries have covered between 6% and 32%the in population these countries with electricity [11], between affecting 92.4% the to 99.9% coverage [7]. The expansioncoverage levels projects. of electric- By 2019, exceptity for have Haiti been (38.7%) increasing and in the Honduras LAC region, (81.1%), but the difficulty LAC countries of achieving have total coverage covered the population with electricityis also greater. between For instance, 92.4% in the to Bolivian 99.9% [case,7].The the electricity coverage coverage levels increases of electricity very fast, and for 2019 reached 93.2% when the urban level was 99.3%, and the rural was 79.3%. have been increasingPeru in the reported LAC a region,total coverage but theof 97.0% difficulty and at the of rural achieving level, 86.3%. total Argentina, coverage although is also greater. For instance,it in reports the Bolivian 98.8% total case, coverage the and electricity rural coverage coverage of 84.9% increases [7], with a verypopulation fast, of and 44.56 for 2019 reached 93.2% whenmillion, the in 2018, urban it reported level was that 120,000 99.3%, rural and families the rural still did was not 79.3%.have access Peru to electricity reported (0.8% of the population) [12]. For this region, Figure 2 shows the growth of electricity cov- a total coverage of 97.0%erage between and at 1998 the ruraland 2018 level, and allows 86.3%. the Argentina,appreciation that although the electrification’s it reports annual 98.8% total coverage and ruralrate decreases. coverage Reaching of 84.9% the last [7], mile with of arural population electrification of is 44.56 difficult million, and expensive in 2018, it reported that 120,000[13,14]. rural families still did not have access to electricity (0.8% of the population) [12]. For this region, Figure2 shows the growth of electricity coverage between 1998 and 2018 and allows the appreciation that the electrification’s annual rate decreases. Sustainability 2021, 13, x FOR PEER REVIEW 3 of 25 Reaching the last mile of rural electrification is difficult and expensive [13,14].

0.80

0.70

0.60

0.50

0.40

0.30

0.20

0.10 Annual Electrification Rate (%) Electrification Annual 0.00 90.46 91.09 91.45 92.05 92.63 92.76 93.25 93.59 94.28 94.54 95.26 95.42 95.98 96.25 96.61 96.90 97.07 97.34 97.55 97.88 98.33 Total Electric Coverage 1998 - 2018 (%)

Figure 2. Annual electrification rate vs. total electric coverage in the Latin America and the Carib- Figurebean (LAC) 2. region,Annual 1998–2018. electrification Based on data rate from vs. the totalWorld electricBank [15]. coverage in the Latin America and the Caribbean (LAC) region, 1998–2018. Based on data from the World Bank [15]. The high level of LAC coverage is the result of sustained actions in the energy sector by the countries, in correspondence with a global development agenda, which allows the active presence of multilateral funds and the active participation of civil society [16]. Like- wise, the actors of the public and private electricity sector are regulated, and there is a context of economic growth and democracy [17]. A common aspect to all countries in LAC is that the people without access to electric- ity are mostly located in rural areas and have limitations to access to all services provided by a modern source of energy such as communication, information, and lighting [18,19]. Furthermore, the electric grid’s extension reaches a cost-efficient limit, and the low density of households in rural areas without electricity makes it impossible to expand the grid. This situation is also aggravated by the high poverty level that reduces electricity access conditions, typical characteristics of isolated and dispersed rural populations in the LAC region [20]. In this context, decentralized solutions based on solar energy such as Solar Home Systems (SHSs) have been an extended option in many countries of the world since the beginning of the 1980s [21–23]. The Off-Grid Solar Market Trends Report 2020, for the period 2010–2019, estimated 84 million SHSs in the world at an operational level [24]. In different countries of LAC such as Brazil, Argentina, Peru, and Bolivia, etc., pro- jects with Photovoltaic (PV) technology are implemented with different scales [17,25]. For instance: • The “Light for All” program in Brazil, which began in 2003 until April 2018, has reached 16.2 million inhabitants of the rural area [26] through concessionaire electric companies directly. In the Amazon, due to the dispersed population, the most wide- spread solution was large SHSs [27]. • Argentina identified, in 2015, that there were still 145,000 isolated families without access to electricity [28], and this was the goal of PERMER II (Renewable Energy Pro- ject in Rural Markets), which launched an international tender in March 2018 to buy 120,000 SHSs to close the gap of existing electricity coverage. • Peru, through a tariff scheme for isolated electric services, still executing its program of half-million SHSs, and in Bolivia is expected to reach 15,500 rural families with SHSs (and 14,500 families with grid extension) in the framework of the Infrastructure for Decentralized Rural Transformation—IDTR II project financed by the World Bank [29]. Sustainability 2021, 13, 3032 3 of 23

The high level of LAC coverage is the result of sustained actions in the energy sector by the countries, in correspondence with a global development agenda, which allows the active presence of multilateral funds and the active participation of civil society [16]. Likewise, the actors of the public and private electricity sector are regulated, and there is a context of economic growth and democracy [17]. A common aspect to all countries in LAC is that the people without access to electricity are mostly located in rural areas and have limitations to access to all services provided by a modern source of energy such as communication, information, and lighting [18,19]. Furthermore, the electric grid’s extension reaches a cost-efficient limit, and the low density of households in rural areas without electricity makes it impossible to expand the grid. This situation is also aggravated by the high poverty level that reduces electricity access conditions, typical characteristics of isolated and dispersed rural populations in the LAC region [20]. In this context, decentralized solutions based on solar energy such as Solar Home Systems (SHSs) have been an extended option in many countries of the world since the beginning of the 1980s [21–23]. The Off-Grid Solar Market Trends Report 2020, for the period 2010–2019, estimated 84 million SHSs in the world at an operational level [24]. In different countries of LAC such as Brazil, Argentina, Peru, and Bolivia, etc., projects with Photovoltaic (PV) technology are implemented with different scales [17,25]. For instance: • The “Light for All” program in Brazil, which began in 2003 until April 2018, has reached 16.2 million inhabitants of the rural area [26] through concessionaire elec- tric companies directly. In the Amazon, due to the dispersed population, the most widespread solution was large SHSs [27]. • Argentina identified, in 2015, that there were still 145,000 isolated families without access to electricity [28], and this was the goal of PERMER II (Renewable Energy Project in Rural Markets), which launched an international tender in March 2018 to buy 120,000 SHSs to close the gap of existing electricity coverage. • Peru, through a tariff scheme for isolated electric services, still executing its program of half-million SHSs, and in Bolivia is expected to reach 15,500 rural families with SHSs (and 14,500 families with grid extension) in the framework of the Infrastructure for Decentralized Rural Transformation—IDTR II project financed by the World Bank [29]. • Bolivia, in 2012 reported officially 31,544 families that have access to electricity through SHSs [30], as a result of different projects. For the period 2012–2015, different agencies reported new projects with more than 30,000 installations [31,32]. However, the SHS, while representing a widely accepted solution at a global level, was technically not always the same. Over time, the evolution of technology produced successive configurations in these systems and their components. The innovations, which have been carried out since the 1980s, have resulted in overcoming problems, difficulties, and generating impacts on rural families that use them. Therefore, the main contribution of this research is to help understand how the SHS configuration gradually changed due to technological advances and how these changes impacted the technical, economic, operational, and sustainability aspects of the SHS in rural areas. In this line, this article states the following research questions: • What are the technological innovations in SHSs? • Is it possible to identify these innovations in different periods and achieve a functional characterization? • Will there be a new standard for photovoltaic electrification? • What will be the implications for rural PV electrification actions? This paper is organized as follows: Section2 summarizes an initial discussion on rural electrification with SHSs; Section3 describes the materials and methods used; Section4 presents the evolution of SHSs technology; Section5 presents the results obtained, and finally, Section6 summarizes the main conclusions. Sustainability 2021, 13, 3032 4 of 23

2. Rural Electrification with SHSs: Insights and Barriers The experiences, benefits, difficulties, and access models to electricity for the small and medium-size village, with a mini-grid based on decentralized technologies, have been studied by many authors. This solution involves planning, regulation, and specific policies for improving their impacts [33]. The mini-grids, additionally, need an optimal configuration to reach economic results and expand this option as a feasible solution [34,35], with a technically correct field operation [36]. In the case of stand-alone systems for individual use such as SHSs, many researchers have reviewed their applications worldwide. The experiences of 20 World Bank’s projects in different countries, such as Bangladesh, China, Vietnam, Sri Lanka, Argentina, Benin, Togo, Dominican Republic, and India, were evaluated, showing aspects such as business models, difficulties operating, and technical performance [37]. Nieuwenhout et al. (2001) carried out an extensive inventory of experiences of small PV systems projects, analyzing the cost, components quality, and access schemes for 104 projects from Africa, Asia, and LAC between 1992 to 2000 [22]. The main recommendation is the need of service infrastructure to make projects viable. Similarly, the field implementation, impacts, technical performance, and lessons learned from African SHSs projects were reported by Van Der Vleuten et al. (2007), showing that for a massive deployment of SHSs, among other aspects, active participation of public-private alliances is necessary and that rural entrepreneurs can be a key to sustainability [38]. On the other hand, several authors reported benefits and problems in the SHS use, as well as the management and financing models used in India [23], Bangladesh [39], and the evaluation of prices, financing structure, and the success in Bangladesh during the period 2002–2012 [40]. Focused on LAC, the rural electrification with decentralized applications of renewable energy and their impact was studied by different authors [21,41,42]. SHSs are undoubtedly an alternative to facilitate access to energy for rural populations without access to the electrical grid. However, its successful dissemination depends on a management system that integrally involves technical quality aspects, financing mechanisms appropriate for users’ payment capacity, and clear roles of the actors involved. Aligned to this, different technical analyses of SHSs components installed since 1990 to 2005 and focused on the quality of components [43,44] determine the need to apply quality programs to ensure technical sustainability and develop solar markets [45]. These reports also showed that the lead-acid batteries had been the weakest and the most ex- pensive system component and are critical to achieving economic savings for end-user satisfaction [46]. A similar situation was already identified in 1999 in Kenya [47], in 2000 in India [48], in 2004 in Zambia [49], and for Bolivia, Brazil, Peru, and Argentina in 2006 [50]. For solar systems operators, the low reliability of lead-acid batteries has resulted in an expensive SHS operation and maintenance service [49]. In some cases, where governments regulate solar operators, these high costs may require high levels of subsidy. For instance, in Jujuy (Argentina), the end-user pays only 12.5% of the full tariff (USD 26.59/month) and requires an operating subsidy of 87.5% [36]. For users, SHSs owners, these systems are inoperable after a few years, and solving small flaws or changing batteries is simply impossible [51]. Conversely, the PV module has proved to be the most reliable component technically with guarantees of at least 10 years and a lifetime of 20 years [47,48]. The most isolated families have no access to SHSs since the initial investment is too high for the target group: Rural low-income families with seasonal incomes and without access to financial services [52,53]. The need for periodic maintenance, which must be done by trained technicians, also implies an additional cost. The technical configuration for SHSs used for rural electrification was similar in different countries of the world (Kenya, Philippines, China, Mexico, etc.), the components were a solar panel, a lead-acid battery, a regulator, loads, and accessories. The medium size of the SHS was 50 Wp [54]. In LAC countries, the typical structure of SHSs in the mid-1990s was based on a photovoltaic module of around 50 Wp, an 8 Ampere (A) charge controller, a lead-acid battery of 100 Ampere hours (Ah), and three fluorescent lamps on Sustainability 2021, 13, 3032 5 of 23

average 18 W each, plus a DC (12 V) outlet for radio or TV [22,44]. However, during the last 20 years, significant technological innovations have been developed to introduce a new generation of photovoltaic systems. For instance, in the mid-2000 years, a series of technologies called pico PV broke out. With solar panels from 1 to 5 Wp integrated as a format of solar lanterns and rechargeable batteries, these small photovoltaic systems grew rapidly [55,56]. As a consequence, field tests, market tests, etc. were carried out, studying the acceptance of these pico PV by certain strata of the population [57–60]. The Alliance for Rural Electrification [61] already incorporates the pico PV as a complementary option to SHSs, also, to calling for the use of more efficient equipment as a way to reduce the energy demand and size of photovoltaic systems [62,63]. In a fast process of evolution, the manufacturers of pico PV equipment incorporated in their designs new elements, such as Light-Emitting Diode (LED) lamps, microelectronics for control, rechargeable NiMh batteries, lithium-ion, lithium iron phosphate (coexisting with lead-acid batteries), showing a broad and diversified offer [64] and installation in rural areas of the world [65]. The International Finance Corporation (IFC) already shows a classification of three groups of equipment [66]: Rechargeable solar lanterns, solar kits, and Sustainability 2021, 13, x FOR PEER REVIEW 6 of 25 the classic SHSs (see Figure3).

Typical power 3 Wp Typical power 10 Wp Typical power 50 Wp Power range 1–5 Wp Power range 5–10 Wp Power range 20–150 Wp 6–60 USD 100–150 USD 300–500 USD

Figure 3. Solar rechargeable systems for lighting and electricity supply in homes [66]. Figure 3. Solar rechargeable systems for lighting and electricity supply in homes [66]. In the market, the penetration of these new types of equipment was fast. At the end of In the market,2017, it was the estimated penetration that 4.14 ofmillion these solar new lighting types equipment of equipment or pico PV systems was fast. are At the end of providing services to rural families [67]. It is worth mentioning that the presence of this 2017, it wasequipment estimated produces that tension 4.14 millionfor the project solar developers lighting and, especially, equipment for decision-makers. or pico PV systems are providing servicesThe wide and to ruralvaried offer, families few technical [67]. refere It isnts worth of performance, mentioning and absence that of standards the presence of this equipment produces(compared to tension traditional for SHSs) the generate project technical developers doubts about and, their especially, quality. On the for other decision-makers. hand, low costs, and the association with the idea of small systems that have less energy, The wide andreinforce varied a space offer, of fewuncertainty technical that prevents referents them from of performance, seeing it as part of anda valid absence option of standards (compared tofor traditional providing the same SHSs) services generate and from technical reducing the doubtsgap in universal about access their [56,68]. quality. On the other hand, low costs,3. Materials and and the Methods association with the idea of small systems that have less energy, reinforce a spaceThis of article uncertainty seeks to systematize that prevents the technological them fromchanges seeing and innovations it as part of SHSs of a valid option for providingover the the same last 30 servicesyears through and a bibliographic from reducing review of the experiences gap in of universal PV electrification access [56,68]. projects. Moreover, it identifies the main components and operational and functional as- pects (PV generator, energy storage systems, charge control, and electrical connection of components). Projects of several world regions, technical reports, and articles available on Sustainability 2021, 13, 3032 6 of 23

3. Materials and Methods This article seeks to systematize the technological changes and innovations of SHSs over the last 30 years through a bibliographic review of experiences of PV electrification projects. Moreover, it identifies the main components and operational and functional aspects (PV generator, energy storage systems, charge control, and electrical connection of components). Projects of several world regions, technical reports, and articles available on online dating from the 1980s were reviewed, and documented references on the LAC region and specifically on Bolivia, Peru, and Argentina were searched and reviewed. Since the 2000s, sources of information such as the International Renewable Energy Agency (IRENA), the Global Off-Grid Lighting Association (GOGLA), the Lighting for Africa, and the Lighting Global are institutions that are adding information and sys- tematizing it, so their reports are considered in this study. Therefore, to have sufficient Sustainability 2021, 13documentation, x FOR PEER REVIEW on the countries under study, the information available7 of 25 on photovoltaic

electrification programs implemented on a massive scale and the participation of gov- ernments and cooperation agencies has been considered. As a reference, in Argentina, online dating from the 1980s were reviewed, and documented references on the LAC re- the Projectgion of and Renewable specifically on EnergiesBolivia, Peru, for and RuralArgentina Markets were searched (PERMER) and reviewed. works since 1999 and is executed bySince the the government, 2000s, sources of reaching information around such as the 100,000 International SHSs Renewable installations Energy until 2018 [69]. Agency (IRENA), the Global Off-Grid Lighting Association (GOGLA), the Lighting for With theAfrica, project and the named Lighting Infrastructure Global are institutions for that Decentralized are adding information Rural and systema- Transformation (IDTR), Bolivia supportstizing it, so their the reports installation are considered of 19,000 in this study. SHSs Therefore, [31]. to Finally, have sufficient in Peru, docu- different projects developedmentation by the on Ministry the countries of under Energy study, and the information Mines (MEM) available through on photovoltaic the General elec- Directorate of trification programs implemented on a massive scale and the participation of govern- Rural Electricityments and (DGER)cooperation reachedagencies has near been 20,000considered. SHSs As a installationsreference, in Argentina, in 2013 the [70,71]. WithProject the of review Renewable of Energies official for Rural information Markets (PERMER) (reports, works evaluations,since 1999 and is exe- terms of reference), cuted by the government, reaching around 100,000 SHSs installations until 2018 [69]. With technologicalthe project and named configuration Infrastructure for changes Decentralized in the Rural SHSs Transformation are identified, (IDTR), Bolivia selecting structurally importantsupports components the installation (energy of 19,000 storage, SHSs [31]. loadFinally, control, in Peru, different lighting, projects and developed electrical connections). The identifiedby the Ministry changes of Energy and theand Mines problems (MEM) andthrough challenges the General Directorate are analyzed of Rural and systematized, Electricity (DGER) reached near 20,000 SHSs installations in 2013 [70,71]. locating themWith in the homogeneous review of official periodsinformation to (r theeports, reviewed evaluations, projects. terms of reference), Finally,technological to characterize and configuration the typechanges of in accessthe SHSs toareelectricity identified, selecting that structurally households have in differ- important components (energy storage, load control, lighting, and electrical connections). ent regionsThe andidentified social changes and and economic the problems realities,and challenges a technologicallyare analyzed and systematized, neutral and progressive multilevellocating standard them incomparison homogeneous pe baseriods to called the reviewed Access projects. Tiers will be used [72]. Starting from a basic level, theFinally, ascent to characterize to the the successive type of access steps to electricity depends that households on the have supply in different attributes that satisfy regions and social and economic realities, a technologically neutral and progressive multi- an increasinglevel standard use of comparison electrical base equipment. called Access Tiers We will will be used use [72]. this Starting internationally from a basic accepted base to comparelevel, the the ascent different to the successive SHSs access steps depend generationss on the supply analyzed. attributes that Figure satisfy an4 showsin- the detail of creasing use of electrical equipment. We will use this internationally accepted base to com- each level.pare the different SHSs access generations analyzed. Figure 4 shows the detail of each level.

Figure 4. Access tiers. Matrix for measuring the access to household electricity [72]. Figure 4. Access tiers. Matrix for measuring the access to household electricity [72]. Sustainability 2021, 13, x FOR PEER REVIEW 8 of 25

4. Technological Evolution of Solar Home Systems

Sustainability 2021, 13, 3032 4.1. SHSs in the Period 1980–1995 7 of 23 SHSs used in isolated rural electrification made their appearance in the 1970s as demonstration projects. In 1978, PV systems for the rural application installed in the USA and4. Technological other countries Evolution was reported, of Solar Homewith a Systems module cost of USD 14.7 to 18.3/Wp [73]. In the 1980s,4.1. SHSs the in projects the Period had 1980–1995 a small-scale diffusion, and in the 1990s, large-scale dissemination [74]. SHSs used in isolated rural electrification made their appearance in the 1970s as demonstrationIn Latin America, projects. Inthe 1978, first PV photovoltaic systems for the electrification rural application projects installed for infamilies the USA began in theand 1980s. other countriesSHSs for wasrural reported, electrification, with a module with a costcommercial of USD 14.7 presence to 18.3/Wp in the [73 market]. In since thethe 1980s, 1980s, thebasically projects constituted had a small-scale a hybrid diffusion, techno andlogy in that the used 1990s, both large-scale the 12 dissemina-V DC technology oftion cars [74 and]. Alternating Current (AC) equipment adapted such as fluorescent lamps. These systemsIn Latin operate America, at 12 theV DC. first Problems photovoltaic with electrification the fluorescent projects tubes for were families reported began inas a short lifetimethe 1980s. (9 SHSs months), for rural flickering electrification, and interference with a commercial with radio presence were in also the market identified since [75]. the A sim- 1980s, basically constituted a hybrid technology that used both the 12 V DC technology of ilar situation arose with the charge regulators that controlled the batteries, which in prin- cars and Alternating Current (AC) equipment adapted such as fluorescent lamps. These ciplesystems used operate the same at 12 Vconcept DC. Problems of protection with the of fluorescent automobiles, tubes with were electromechanical reported as a short relays forlifetime the protection (9 months), of flickering the battery and and interference fuses for with automotive radio were use. also Finally, identified the [batteries75]. A used tosimilar store situationenergy were arose lead with theacid charge of automoti regulatorsve type that controlled[76]. Although the batteries, these systems which in compo- nentsprinciple were used initially the same the concept product of protectionof local adaptations, of automobiles, gradually, with electromechanical with the expansion relays of the market,for the protection the production of the battery of components and fuses for specific automotiveally for use. SHSs Finally, is standardized. the batteries used Acceptance to testsstore and energy technology were lead on acid SHSs of automotive are reported type since [76]. Although1986 in Peru these [21]. systems The componentsfirst trials for what wouldwere initially later be the the product projects of local promoted adaptations, by the gradually, German with Cooperation the expansion in the of the region market, are given. the production of components specifically for SHSs is standardized. Acceptance tests and In Bolivia, the Program for the Diffusion of Renewable Energies in Bolivia (PROPER), technology on SHSs are reported since 1986 in Peru [21]. The first trials for what would later supportedbe the projects by the promoted German by Cooperation the German Cooperation (GTZ), promote in the regiona technology are given. transfer In Bolivia, process for localthe Program production for the of Diffusion ballasts offo Renewabler fluorescent Energies lamps, in Boliviaelectronic (PROPER), charge supportedregulators, by and the manufacturethe German Cooperation of solar batteries (GTZ), promote of lead a acid technology [50] with transfer the processpremise for of local ensuring production quality. In thisof ballasts period, for international fluorescent lamps, products electronic also charge began regulators, to position and themselves the manufacture in a global of solar market, suchbatteries as the of leadMorning acid [50 Star] with in the premiseUSA (a ofcompany ensuring founded quality. In in this 1993, period, remains international active) [77] or Stecaproducts in Germany also began (a to company position themselves founded inin a1976), global a market, pioneer such in supply as the Morning charge Starregulators in in thethe 1990s USA (a in company LAC [78]. founded in 1993, remains active) [77] or Steca in Germany (a company founded in 1976), a pioneer in supply charge regulators in the 1990s in LAC [78]. The mentioned characteristic for the SHSs installed in rural electrification projects The mentioned characteristic for the SHSs installed in rural electrification projects betweenbetween 19801980 and and 1995 1995 had had a typical a typical configuration, configuration, named named in this article in this the article 1st Generation the 1st Genera- tionSolar Solar Home Home Systems Systems (1G-SHSs), (1G-SHSs), a diagram a diagram of 1G-SHSs of 1G-SHSs is shown inis Figureshown5. in Figure 5.

FigureFigure 5. Scheme of of the the 1st 1st generation generation solar solar home home systems systems (1G-SHSs). (1G-SHSs). Despite the technical problems that the 1G-SHS had, its main achievement was to placeDespite a technology the technical that came fromproblems space applicationsthat the 1G on-SHS the had, ground, its tomain be used achievement to electrify was to placefamilies a technology in rural areas that worldwide came from without space access applicat to conventionalions on the ground, energy sources. to be used to electrify families in rural areas worldwide without access to conventional energy sources. Sustainability 2021, 13, x FOR PEER REVIEW 9 of 25 Sustainability 2021, 13, 3032 8 of 23

4.2. SHSs in the Period 1995–2010 4.2. SHSs in the Period 1995–2010 Between 1995 to 2000, an evolution process of PV technology produces a new gener- ation Betweenof SHSs 1995perceived. to 2000, It anis the evolution use of processequipment, of PV components, technology producesand electronics a new specifi- genera- tion of SHSs perceived. It is the use of equipment, components, and electronics specifically cally designed to use solar energy. Achieving an optimal use of the energy generated with designed to use solar energy. Achieving an optimal use of the energy generated with photovoltaic panels defines this trend, and rural electrification projects incorporate SHSs photovoltaic panels defines this trend, and rural electrification projects incorporate SHSs as a formal alternative [40,79]. as a formal alternative [40,79]. Concerns about the quality of components, their efficiency, and how to carry out the Concerns about the quality of components, their efficiency, and how to carry out the installations impulse the development and use of technical standards and protocols. In installations impulse the development and use of technical standards and protocols. In this context, the Universal Technical Standard for Photovoltaic Systems [80] was used reg- this context, the Universal Technical Standard for Photovoltaic Systems [80] was used ularly in LAC. In the Bolivian case, it served as a guide for the formulation of the Bolivian regularly in LAC. In the Bolivian case, it served as a guide for the formulation of the Standard NB 1056 that regulated the installation of SHSs up to 5000 Wp [81]. In parallel, Bolivian Standard NB 1056 that regulated the installation of SHSs up to 5000 Wp [81]. In other initiatives such as the Global Approval Program for Photovoltaics (GAPPV) high- parallel, other initiatives such as the Global Approval Program for Photovoltaics (GAPPV) lighted the need to ensure quality in photovoltaic systems [82]. highlighted the need to ensure quality in photovoltaic systems [82]. TheThe global global acceptance acceptance of of the the technology technology as as well well as as the the most most common common technical technical prob- prob- lemslems are are identified identified through through technical technical field field eval evaluations,uations, intending intending to to know know the the specific specific per- per- formanceformance of of the the technology technology in in different different countr countriesies of the world world such as Bangladesh [43,46] [43,46] andand Kenya Kenya [45]. [45]. The The level level of ofenergy energy consumption consumption of rural of rural households households that thatuse SHSs use SHSs is also is analyzedalso analyzed [83]. Finally, [83]. Finally, the promotion the promotion of differen of differentt PV applications PV applications [84] is [ 84part] is of part the of tech- the nologytechnology diffusion diffusion task taskduring during this period. this period. AsAs a a result of the technical recommendations, the solar industry gradually changed thethe SHSs SHSs components components until until reaching reaching the the following following configuration: configuration: Photovoltaic Photovoltaic panels panels of crystallineof crystalline technology, technology, solid-state solid-state electronic electronic charge charge regulators regulators (including (including automatic automatic reset andreset electronic and electronic fuses), fuses), Compact Compact Fluorescent Fluorescent Lamps Lamps (CFL) (CFL) manufactured manufactured for 12 for V 12DC, V and DC, lead-acidand lead-acid batteries batteries adapted adapted for specific for specific use in use solar in solar systems systems (with (with terminals terminals specially specially de- signeddesigned to prevent to prevent their their automotive automotive use). use). An integral An integral part partof the of system the system was a was DC-DC a DC-DC volt- agevoltage adapter adapter for forradio radio (to (toallow allow radio radio connection connection of ofdifferent different voltages voltages below below 12 12 V V (DC), (DC), andand a a socket for charge cellphones based on the car type (built around 2005, since the mobilemobile phone phone grew grew in coverage). Finally, Finally, in in areas areas with access to a television signal, the demanddemand for for this this equipment equipment also also increased increased the the offer offer of of efficient efficient Televisions Televisions (TVs) (TVs) in in 12 12 V. V. These changes made a structure of 2nd GenerationGeneration Solar HomeHome SystemsSystems (2G-SHSs).(2G-SHSs). A schemescheme of of 2G-SHSs 2G-SHSs can can be be seen in Figure 66..

FigureFigure 6. 6. SchemeScheme of of 2nd 2nd generation generation solar solar home home systems (2G-SHSs).

InIn Bolivia, Bolivia, the consolidationconsolidation ofof schemescheme of of 2G-SHSs 2G-SHSs becomes becomes clear clear in in 2004 2004 with with a tendera ten- derto finance to finance 15,000 15,000 SHSs SHSs for the for World the World Bank [Ba85]nk successfully [85] successfully implemented implemented (a poster (a usedposter to usedpromote to promote SHSs can SHSs be seencan be in Figureseen in7 Figure). Later 7). in Later 2010, in the 2010, Decentralized the Decentralized Electricity Electricity Project for Universal Access [31] launched a tender of 7067 SHSs. The technical specification of SHSs incorporates for the first time two LED lamps (over five lamps). It includes a Sustainability 2021, 13, x FOR PEER REVIEW 10 of 25

Sustainability 2021, 13, 3032 9 of 23

Project for Universal Access [31] launched a tender of 7067 SHSs. The technical specifica- tion of SHSs incorporates for the first time two LED lamps (over five lamps). It includes a solarsolar lanternlantern ofof 1600 1600 pico pico PV PV with with the the condition condition that that the the equipment equipment was was on on the the Lighting Lighting GlobalGlobal product product quality quality list. list. The The LightingLighting Global Global support support from from the the World World Bank Bank works works with with manufacturers,manufacturers, distributors,distributors, governments,governments, andand other other development development partners partners to to build build and and growgrow a a modern modern off-grid off-grid solar solar energy energy market market with with a widelya widely applicable applicable and and rigorous rigorous Quality Qual- Assuranceity Assurance framework. framework.

FigureFigure 7. 7.Poster Poster ofof a a 2G-SHSs 2G-SHSs used used in in Bolivian Bolivian projects projects [ 86[86].].

InIn 2013, 2013, in in Peru, Peru, one one of of the the largest largest LAC LAC tenders tenders was was launched, launched, which which was was intended intended to installto install 500,000 500,000 photovoltaic photovoltaic installations installations [71 [71]] and and incorporate incorporate LED LED lamps lamps [ 87[87].]. Whereas, Whereas, inin Argentina, Argentina, the the PERMER PERMER project project involved involved more more than than 100,000 100,000 SHSs SHSs installations installations [69 ,[88],88], launched[69], launched two tenders two tenders in 2016: in One 2016: for One 6500 for SHSs 6500 (LPN SHSs no. (LPN 02/2016 no. in02/2016 August) in andAugust) another and foranother 7500 SHSsfor 7500 (LPN SHSs no. (LPN 03/2016 no. in03/2016 October). in October). What is more,What theseis more, 2G-SHSs these 2G-SHSs have already have startedalready to started incorporate to incorporate LED lamps LED [12 lamps]. [12]. TheThe 2G-SHS 2G-SHS was was the the mature mature expression expression of the of PV the electrification PV electrification technology technology for homes, for withhomes, equipment with equipment specifically specifically designed designed to optimize to optimize solar energy solar use, energy mobilizing use, mobilizing the genera- the tiongeneration of internationally of internationally accepted accepted norms andnorms standards. and standards. Training Training materials materials for technicians for tech- andnicians designers and designers were also were developed, also developed, as well asas thewell standardization as the standardization of bidding of bidding documents. doc- Alluments. these elementsAll these madeelements the 2G-SHSmade the to 2G-SHS be considered to be considered as a robust andas a acceptedrobust and solution accepted to supplysolution electricity to supply in electricity rural areas. in rural areas. 4.3. SHSs in the Period 2010—Until Now 4.3. SHSs in the Period 2010—Until Now In the period 2005–2015, SHSs components had an accelerated change: On storage of In the period 2005–2015, SHSs components had an accelerated change: On storage of energy (with the introduction of lithium batteries in replacement of lead-acid batteries) [64]; energy (with the introduction of lithium batteries in replacement of lead-acid batteries) lighting (incorporation of LED lamps more efficient, more compact, and long life service); [64]; lighting (incorporation of LED lamps more efficient, more compact, and long life ser- use of microelectronics in the control system (introducing small touch screen); and last by vice); use of microelectronics in the control system (introducing small touch screen); and not least, the interconnection of the components had an upgrade with the introduction last by not least, the interconnection of the components had an upgrade with the intro- of plug and play connections [61]. The equipment named pico PV incorporates, in a duction of plug and play connections [61]. The equipment named pico PV incorporates, progressive form, these innovations. in a progressive form, these innovations. The pico PV offers a point of light and the capacity to charge a cell phone with solar panels below 10 Wp [89]. However, a pico PV does not represent a substitution to the classic 2G-SHSs, which is considered the base configuration of PV electrification. Instead, a Sustainability 2021, 13, x FOR PEER REVIEW 11 of 25

Sustainability 2021, 13, 3032 The pico PV offers a point of light and the capacity to charge a cell phone with 10solar of 23 panels below 10 Wp [89]. However, a pico PV does not represent a substitution to the classic 2G-SHSs, which is considered the base configuration of PV electrification. Instead, apico pico PVPV representsrepresents aa stepstep beforebefore thethe installationinstallation of an SHS due to to the the benefits benefits it it provides provides toto the the end-user, end-user, as as identified identified by by Feron Feron (2016) (2016) and and other other authors authors [61,64,66,90,91]. [61,64,66,90,91]. However, However, withoutwithout a adoubt, doubt, getting getting households households to tohave have acce accessss to a to pico a pico PV that PV thatprovides provides lighting lighting and theand capacity the capacity to charge to charge mobile mobile phones phones makes makes them them enter enter Tier Tier1 on 1 the on thescale scale of access of access to electricityto electricity [72] [and72] andmarks marks the difference the difference between between not having not having access access to electricity to electricity and start- and ingstarting the electrification the electrification process. process. TheThe load load commonly commonly covered covered by by 2G-SHSs 2G-SHSs is isassociated associated with with the the electricity electricity needs needs of ofa rurala rural family: family: Three Three points points of light of light for for3 h/day 3 h/day (with (with CFL CFL from from 7 to 7 11 to W), 11 W), useuse of radio of radio (8 h/day),(8 h/day), TV and TV DVD and DVDplayer player (27 W (27for W3 h/day), for 3 h/day), and charge and at charge least one at least cell phone one cell (6 phoneW for 2(6 h/day). W for The 2 h/day). total demand The total can demand reach 280 can Wh/day reach 280[92]. Wh/day In this period [92]. (2005–2015), In this period techno- (2005– logical2015), advances technological were advances migrating were from migrating pico PV to from larger pico and PV more to larger efficient and moreapplications, efficient allowingapplications, a new allowing type of SHSs a new to type be configured of SHSs to. beFor configured. instance, the For introduction instance, the ofintroduction LED lamps andof LED the electricity lamps and demand the electricity reduction demand was reductionanalyzed for was different analyzed countries for different in sub-Saharan countries in Africasub-Saharan and South Africa Asia, and impacting South Asia, the impactingSHSs size theand SHSs its cost size reduction and its cost [93]. reduction [93]. OnceOnce more more efficient efficient technologiestechnologies were were defined defined as as a need,a need, the the same same benefits benefits of 2G-SHSs of 2G- SHSscould could be covered be covered with 90with Wh/day 90 Wh/day (using (using a 3 W a LED 3 W lamp,LED lamp, 11 W flat-screen11 W flat-screen TV with TV a with built- ain built-in DVD player, DVD player, and 3 W and USB 3 W cell USB phone cell charger).phone charger). In 2015, In a study2015, a by study the Lawrence by the Lawrence Berkeley BerkeleyNational National Laboratory Laboratory showed showed that it was that possible it was possible to cover to the cover demand the demand of a conventional of a con- ventionalSHS (600 SHS lumens (600 oflumens illumination of illumination for 4 h/day, for 4 19-inchh/day, 19-inch TV 4 h/day, TV 4 h/day, small radiosmall 6radio h/day, 6 h/day,charge charge one cell one phone cell phone per day) per day) with with a super-efficient a super-efficient SHS SHS of only of only 25 Wp 25 Wp [94 ],[94], with with the theconsequent consequent reduction reduction in costs,in costs, as shownas shown in Figurein Figure8. 8.

FigureFigure 8. 8. RetailRetail prices prices for for three three types types of of solar solar house house systems systems (SHSs) (SHSs) with with identical identical benefits benefits [94]. [94].

DueDue to to the greater efficiencyefficiency achieved achieved in in lighting lighting with with LED LED technology technology [63 ],[63], LCD LCD TVs, TVs,radios radios of lower of lower consumption, consumption, and moreand more efficient efficient cell phones, cell phones, a significant a significant reduction reduction of the ofneed the need for electricity for electricity in new in new SHSs SHSs was was achieved, achieved, which which avoids avoids unnecessary unnecessary oversizing oversizing of ofSHSs SHSs and and reduces reduces the the investment investment cost. cost. On On the th othere other hand, hand, in in recent recent years, years, the the increase increase in inappliances’ appliances’ efficiency efficiency has has been been impressive impressive [95 ,[95,96].96]. Increased Increased efficiencies efficiencies in televisions, in televisions, fans, fans,and refrigeratorsand refrigerators will allow will allow future future growth growth in off-grid in off-grid households’ households’ energy services,energy services, allowing allowingmore services more withservices smaller with SHSs, smaller and rethinkingSHSs, and therethinking Access Tiers’the Access reference Tiers’ power reference ranges. powerThe ranges. use of high-efficient applications, the incorporation of lithium batteries, and the innovationsThe use of detected high-efficient allows applications, a new configuration the incorporation for SHSs of with lithium significant batteries, differences and the innovationsin respect to detected 2G-SHSs. allows These a new configuration SHSs are named for 3rdSHSs Generation with significant Solar Home differences Systems in (3G-SHSs), as shown in Figure9. Sustainability 2021, 13, x FOR PEER REVIEW 12 of 25

Sustainability 2021, 13, 3032 11 of 23 respect to 2G-SHSs. These new SHSs are named 3rd Generation Solar Home Systems (3G- SHSs), as shown in Figure 9.

FigureFigure 9. Scheme 9. Scheme of 3rdof generation 3rd generation solar home solar systems home (3G-SHSs). systems (3G-SHSs).

In Inthis this context, context, a 3G-SHS a 3G-SHS incorporates incorporates technological technological innovations in a innovations comprehensive, in a comprehensive, efficient,efficient, and and compact compact design, design, as detailed as below: detailed below: • Use of rechargeable batteries of high density and small size, essentially lithium iron • phosphate,Use of rechargeablereplacing lead-acid batteries batteries. of high density and small size, essentially lithium iron • Microelectronicsphosphate, replacingcontrol is incorporated lead-acid batteries.in the same battery. The system does not • requireMicroelectronics an electronic charge control controller is incorporated as a separate in theequipment samebattery. and has Theadditional system does not require capabilitiesan electronic associated charge with controllera microprocesso as ar separate(communication, equipment data storage, andhas and additionaldis- capabilities play). • Useassociated of LED lamps with as an a integral microprocessor part of the equipment (communication, to make efficient data storage,use of energy and display). • in Uselighting, of LED and availability lamps as anof outputs integral for part powering of the equipment equipment with to the make standard efficient use of energy USBin port. lighting, and availability of outputs for powering equipment with the standard • A USBcompact port. integrated design, lighting, easy to install, and no need to make electrical connections (plug and play logic). • A compact integrated design, lighting, easy to install, and no need to make electrical As an example, the configuration of 3G-SHSs used in Bolivia is shown in Figure 10. Sustainability 2021, 13, x FOR PEER REVIEW connections (plug and play logic). 13 of 25

As an example, the configuration of 3G-SHSs used in Bolivia is shown in Figure 10.

FigureFigure 10. 10.PosterPoster of 3G-SHSs of 3G-SHSs used in Bolivian used in projects Bolivian [97]. projects [97].

The use of 3G-SHSs was reported almost 10 years ago, and with clear advantages over 2G-SHSs in economic, technical, and logistical aspects. Eras-Almeida et al. reported expe- riences in Mexico, Peru, and Bolivia in 2019 [98], where additionally business models to fa- cilitate the implementation of 3G-SHSs are tackled. The authors concluded that 3G-SHSs are the most suitable solution in terms of economic, social, and environmental efficiency. Undoubtedly, the 3G-SHSs have a singular configuration: Compact dimensions, high-efficient components, and capacity for interaction through microelectronics that gives multiple possibilities of operability to provide access to electricity in the most remote locations in LAC.

5. Results and Discussion 5.1. Time Sequence of SHSs Components Innovation Over the last 30 years, there have been different technological innovations in SHSs. An analysis of these changes, disaggregated by SHS components, allows structural modifica- tions to be identified in four components: (a) The energy storage, (b) lighting technology and new energy demands, (c) the electronic control system, and (d) the connections and installation form of the systems. All these identified modifications are described below.

5.1.1. Energy Storage The 1G-SHSs used automotive car batteries due to the lack of technology of energy storage for solar systems. While 2G-SHSs use lead-acid batteries specially adapted for so- lar use (open or sealed) with modifications in terms of dimensions (due mainly to the increase in the plates’ thickness). The change of terminals prevents automotive use. In Sustainability 2021, 13, 3032 12 of 23

The use of 3G-SHSs was reported almost 10 years ago, and with clear advantages over 2G-SHSs in economic, technical, and logistical aspects. Eras-Almeida et al. reported experiences in Mexico, Peru, and Bolivia in 2019 [98], where additionally business models to facilitate the implementation of 3G-SHSs are tackled. The authors concluded that 3G-SHSs are the most suitable solution in terms of economic, social, and environmental efficiency. Undoubtedly, the 3G-SHSs have a singular configuration: Compact dimensions, high- efficient components, and capacity for interaction through microelectronics that gives multiple possibilities of operability to provide access to electricity in the most remote locations in LAC.

5. Results and Discussion 5.1. Time Sequence of SHSs Components Innovation Over the last 30 years, there have been different technological innovations in SHSs. An analysis of these changes, disaggregated by SHS components, allows structural modifi- cations to be identified in four components: (a) The energy storage, (b) lighting technology and new energy demands, (c) the electronic control system, and (d) the connections and installation form of the systems. All these identified modifications are described below.

5.1.1. Energy Storage

Sustainability 2021, 13, x FOR PEER REVIEWThe 1G-SHSs used automotive car batteries due to the lack of technology of energy14 of 25 storage for solar systems. While 2G-SHSs use lead-acid batteries specially adapted for solar use (open or sealed) with modifications in terms of dimensions (due mainly to the increase in the plates’ thickness). The change of terminals prevents automotive use. In addition, 3G-SHSsaddition, use3G-SHSs lithium use rechargeable lithium rechargeable batteries of batteries different of configurations different configurations with big advantages with big inadvantages lifespan, lowerin lifespan, weight, lower minimum weight, maintenance,minimum maintenance, and lower and costs lower [99]. costs In this [99]. sense, In this it issense, possible it is topossible leap the to classicleap the lead-acid classic lead-acid accumulator accumulator to use portable to use portable rechargeable rechargeable lithium batterieslithium batteries [100]. Figure [100]. 11 Figure shows 11 the shows changes the changes in energy in storage energy forstorage SHSs. for SHSs.

(a) (b) (c)

FigureFigure 11.11. ChangesChanges inin batteriesbatteries forfor energyenergy storagestorage inin SHSsSHSs [[100].100]. (a)) 1G-SHSs: Lead-acid automotive battery, ((bb)) 2G-SHSs:2G-SHSs: Lead-acidLead-acid solarsolar battery,battery, ( c(c)) 3G-SHSs: 3G-SHSs: Lithium Lithium battery battery (Phocos, (Phocos, Germany). Germany).

5.1.2.5.1.2. Lighting and New ChargesCharges TheThe firstfirst installationsinstallations of of 1G-SHSs 1G-SHSs used used fluorescent fluorescent tubes tubes of of 18 18 W W which which was was a standard a stand- forard photovoltaicfor photovoltaic electrification. electrification. These These fluorescent fluorescent lamps lamps manufactured manufactured to to workwork withwith reactorsreactors inin 220220 VV ACAC werewere usedused toto workwork withwith electronicelectronic ballastsballasts thatthat mademade itsits useuse possiblepossible atat 1212 VV DC.DC. Whereas,Whereas, 2G-SHSs 2G-SHSs used used Compact Compac Fluorescentt Fluorescent Lamps Lamps (CFL) (CFL) designed designed for for 12 12 V DCV DC with with specific specific characteristics characteristics to to extend extend their their useful useful life life (preheating (preheatingand and temperaturetemperature control),control), thethe highhigh efficiency, efficiency, and and the the use use of of the the E47 E47 thread thread as aas universal a universal connection connection format, for- quicklymat, quickly displaced displaced the use the of use fluorescent of fluorescent tubes. tubes. However, However, the new the technologicalnew technological leap usesleap LED,uses LED, given given the high the high efficiency efficiency and lowand energylow energy consumption, consumption, its long its life,long and life, downwardand down- costsward [costs101], [101], making making their usetheir mandatory use mandator in 3G-SHSs.y in 3G-SHSs. Figure Figure 12 shows 12 shows the the evolution evolution of lightingof lighting technologies technologies graphically graphically for for SHSs. SHSs.

(a) (b) (c) Figure 12. Changes in lighting technologies used in SHS [100]. (a) 1G-SHSs: Fluorescent tubes of 18 W; (b) 2G-SHSs: CFL lamps (8 to 15 W); (c) 3G-SHSs: Light-emitting diode (LED) lamps (3 to 5 W).

Other types of equipment such as cell phones, DVD players, or flat-screen TVs have also improved their efficiency, and many require USB connections.

5.1.3. Control System The 1G-SHSs used load controllers based on electromechanical components, such as relays, automotive fuses that were the most widespread security element, cylindrical type initially and then of bayonet type. 2G-SHSs use the electronic solid-state regulators and have LED lights indicators, clearly differentiated connection ports, and electronic self-reset fuses. The next change (3G-SHSs) has incorporated microelectronics in control, small circuits with high control capabilities, aimed at controlling lithium batteries, which require more specific cell control than the case of lead-acid batteries. Regulators are currently integrated into the lithium batteries and incorporate a small high-definition screen with user-friendly icono- graphy that shows information about the state of charge, connections, and remaining hours Sustainability 2021, 13, x FOR PEER REVIEW 14 of 25

addition, 3G-SHSs use lithium rechargeable batteries of different configurations with big advantages in lifespan, lower weight, minimum maintenance, and lower costs [99]. In this sense, it is possible to leap the classic lead-acid accumulator to use portable rechargeable lithium batteries [100]. Figure 11 shows the changes in energy storage for SHSs.

(a) (b) (c) Figure 11. Changes in batteries for energy storage in SHSs [100]. (a) 1G-SHSs: Lead-acid automotive battery, (b) 2G-SHSs: Lead-acid solar battery, (c) 3G-SHSs: Lithium battery (Phocos, Germany).

5.1.2. Lighting and New Charges The first installations of 1G-SHSs used fluorescent tubes of 18 W which was a stand- ard for photovoltaic electrification. These fluorescent lamps manufactured to work with reactors in 220 V AC were used to work with electronic ballasts that made its use possible at 12 V DC. Whereas, 2G-SHSs used Compact Fluorescent Lamps (CFL) designed for 12 V DC with specific characteristics to extend their useful life (preheating and temperature control), the high efficiency, and the use of the E47 thread as a universal connection for- mat, quickly displaced the use of fluorescent tubes. However, the new technological leap uses LED, given the high efficiency and low energy consumption, its long life, and down- Sustainability 2021, 13, 3032 ward costs [101], making their use mandatory in 3G-SHSs. Figure 12 shows13 the of 23 evolution of lighting technologies graphically for SHSs.

(a) (b) (c)

Figure 12. FigureChanges 12. Changes in lighting in lighting technologies technologies used used in inSHS SHS [100]. [100]. (a)) 1G-SHSs:1G-SHSs: Fluorescent Fluorescent tubes tubes of 18 W; of (18b) 2G-SHSs:W; (b) 2G-SHSs: CFL CFL lamps (8 tolamps 15 W); (8 to(c 15) 3G-SHSs: W); (c) 3G-SHSs: Light-emitting Light-emitting diode diode (LED) (LED) lamps lamps (3 (3 to to 5 W).5 W).

Other types of equipment such as cell phones, DVD players, or flat-screen TVs have Otheralso improved types of their equipment efficiency, andsuch many as cell require phones, USB connections. DVD players, or flat-screen TVs have also improved their efficiency, and many require USB connections. 5.1.3. Control System 5.1.3. ControlThe 1G-SHSs System used load controllers based on electromechanical components, such as relays, automotive fuses that were the most widespread security element, cylindrical type Theinitially 1G-SHSs and then used of bayonet load controllers type. 2G-SHSs based use theon electronicelectromechanical solid-state regulators components, and such as relays,have automotive LED lights fuses indicators, that clearly were differentiatedthe most widespread connection ports, security and electronicelement, self-reset cylindrical type Sustainability 2021, 13, x FOR PEER REVIEWfuses. The next change (3G-SHSs) has incorporated microelectronics in control, small 15 of 25 initially and then of bayonet type. 2G-SHSs use the electronic solid-state regulators and have LED lightscircuits indicators, with high control clearly capabilities, differentiated aimed atconnec controllingtion lithiumports, and batteries, electron whichic requireself-reset fuses. more specific cell control than the case of lead-acid batteries. Regulators are currently The nextintegrated change into (3G-SHSs) the lithium has batteries incorporated and incorporate microelectronics a small high-definition in control, screen small with circuits with ofhigh autonomy, controluser-friendly capabilities, recalculated iconography aimed automatically. that at shows controlling information Thes lithiume regulators about batteries, the state are of anwhich charge, important require connections, component more specific of 3G-SHSs.cell controland remainingFigure than the13 hours shows case ofof the autonomy, lead-acid identified recalculated batteries. changes Regulators automatically. in regulators. are These currently regulators integrated are an into the lithiumimportant batteries component and incorporate of 3G-SHSs. a Figure small 13 high shows-definition the identified screen changes with in user-friendly regulators. icono- graphy that shows information about the state of charge, connections, and remaining hours

(a) (b) (c) Figure 13. FigureChange 13. inChange SHS inload SHS regulators load regulators [100]. [100 (].a) ( a1G-SHSs:) 1G-SHSs: Electromechanical load load regulator; regulator; (b) 2G-SHSs: (b) 2G-SHSs: Electronic Electronic solid-state solid-stateregulator; regulator; (c) 3G-SHSs: (c) 3G-SHSs: Microelectronic Microelectronic regulator. regulator.

5.1.4. 5.1.4.Connections Connections and and Installation Installation The evolution of electric connections is possible to see in Figure 14. The electrical Theconnections evolution of 1G-SHSs of electric were normallyconnections made throughis poss splicesible to in see the conductorsin Figure that 14. had The to electrical connectionsbe isolated of later1G-SHSs (the Bolivian were standardnormally NB1056 made included through an annexsplices on thein the best conductors way to make that had to be splices).isolated For later 2G-SHSs, (the Bolivian generic connectors standard are NB1056 incorporated included as a standard an annex of installations, on the best way to make eliminatingsplices). For splices 2G-SHSs, and insulating generic tape, connectors thus reducing are the incorporated points of failure. as On a standard the contrary, of installa- 3G-SHSs use connectors specifically designed under a plug and play logic. Thus, it is tions, easyeliminating to interconnect splices modules, and insulating loads, batteries, tape, using thus universal reducing ports. the This points makes of 3G-SHSs failure. On the contrary,installations 3G-SHSs much use faster connectors and extremely specifically safe, avoiding designed errors, under and making a plug self-installation and play logic. Thus, it is easypossible to interconnect without a specialized modules, technician. loads, batteries, using universal ports. This makes 3G- SHSs installations much faster and extremely safe, avoiding errors, and making self-in- stallation possible without a specialized technician.

(a) (b) (c) Figure 14. Changes in the way electrical connections are made in SHS [100]. (a) 1G-SHSs: Splices in electrical wires; (b) 2G-SHSs: Connectors for electrical use; (c) 3G-SHSs: Plug and play connectors.

Under these four aspects, it is possible to appreciate the technological changes, which occur progressively and coincidentally in certain periods, allowing SHSs to be classified into three generations of SHSs. From which, the most efficient configuration, 3G-SHSs, has resulted in a fast deployment of installations to supply electricity demand in the hard- est-to-reach rural areas, as a consequence of shorter installation times, the possibility of installation by non-specialized personnel, the simplicity of operation, and, above all, the absence of the need for periodic maintenance. Moreover, the battery’s microcontroller opens possibilities for regulation, control, data collection, and an online connection to add a mobile payment system. The combination of all these technological innovations and their consequent changes in economic aspects, useful life, operation, and maintenance, opens the possibilities of developing new business models oriented to the population without access to energy at the base of the pyramid.

5.2. Technical Characterization of 3G-SHSs and Differences A systematization of the technical characteristics of the three generations of SHSs is carried out, considering the following technological variables: Power generation, lighting, Sustainability 2021, 13, x FOR PEER REVIEW 15 of 25

of autonomy, recalculated automatically. These regulators are an important component of 3G-SHSs. Figure 13 shows the identified changes in regulators.

(a) (b) (c) Figure 13. Change in SHS load regulators [100]. (a) 1G-SHSs: Electromechanical load regulator; (b) 2G-SHSs: Electronic solid-state regulator; (c) 3G-SHSs: Microelectronic regulator.

5.1.4. Connections and Installation The evolution of electric connections is possible to see in Figure 14. The electrical connections of 1G-SHSs were normally made through splices in the conductors that had to be isolated later (the Bolivian standard NB1056 included an annex on the best way to make splices). For 2G-SHSs, generic connectors are incorporated as a standard of installa- tions, eliminating splices and insulating tape, thus reducing the points of failure. On the contrary, 3G-SHSs use connectors specifically designed under a plug and play logic. Thus, it is easy to interconnect modules, loads, batteries, using universal ports. This makes 3G- Sustainability 2021, 13, 3032 SHSs installations much faster and extremely safe, avoiding errors, and making self-in-14 of 23 stallation possible without a specialized technician.

(a) (b) (c)

FigureFigure 14.14. ChangesChanges inin thethe wayway electricalelectrical connectionsconnections areare mademade inin SHSSHS [[100].100]. ((aa)) 1G-SHSs:1G-SHSs: SplicesSplices inin electricalelectrical wires;wires; ((b)) 2G-SHSs:2G-SHSs: ConnectorsConnectors forfor electricalelectrical use;use; ((cc)) 3G-SHSs:3G-SHSs: PlugPlug andand playplay connectors.connectors.

Under these four aspects, it is possible to appreciate the technological changes,changes, whichwhich occur progressivelyprogressively andand coincidentallycoincidentally in certaincertain periods,periods, allowingallowing SHSsSHSs toto bebe classifiedclassified intointo threethree generationsgenerations ofof SHSs.SHSs. From which,which, thethe mostmost efficientefficient configuration,configuration, 3G-SHSs,3G-SHSs, has resulted in in a afast fast deployment deployment of ofinstallations installations to supply to supply electricity electricity demand demand in the in hard- the hardest-to-reachest-to-reach rural rural areas, areas, as a asconsequence a consequence of shorter of shorter installation installation times, times, the the possibility possibility of ofinstallation installation by bynon-specialized non-specialized personnel, personnel, the thesimplicity simplicity of operation, of operation, and, and, above above all, all,the theabsence absence of the of the need need for for periodic periodic maintenance. maintenance. Moreover, Moreover, the the battery’s microcontroller opens possibilities forfor regulation,regulation, control,control, datadata collection,collection, andand anan onlineonline connectionconnection toto addadd a mobilemobile paymentpayment system. system. The The combination combination of allof theseall these technological technological innovations innovations and their and consequenttheir consequent changes changes in economic in economic aspects, aspects, useful useful life, operation, life, operatio andn, maintenance, and maintenance, opens theopens possibilities the possibilities of developing of developing new business new bu modelssiness orientedmodels oriented to the population to the population without accesswithout to access energy to at energy the base at ofthe the base pyramid. of the pyramid. 5.2. Technical Characterization of 3G-SHSs and Differences 5.2. Technical Characterization of 3G-SHSs and Differences A systematization of the technical characteristics of the three generations of SHSs is A systematization of the technical characteristics of the three generations of SHSs is carried out, considering the following technological variables: Power generation, lighting, carried out, considering the following technological variables: Power generation, lighting, energy storage, regulation, wiring and connections, installation, operation and maintenance. In each item, a detail of specific topics exists with values or short descriptions, which allows us to appreciate the changes incorporated in each generation of SHSs. A synthesis of detected changes in the different generations of SHSs is shown in Table1.

Table 1. Synthesis matrix of detected changes.

First Generation Second Generation Third Generation Component Variable 1980–1995 1995–2010 2010– Mono or Poly Crystalline Mono or Poly Crystalline Mono or Poly Crystalline Technology Generation Photovoltaic Panels Photovoltaic Panels Photovoltaic Panels Capacity 50 Wp 50–80 Wp 20–50 Wp Compact Fluorescent Type Fluorescent (TL) LED (CFL) Required power 18 W 7–11 W 3 W

Lightning Life Spam 5000 to 8000 h 8000 to 10,000 h 50,000 h Efficiency 4 lm/W 60 lm/W 100 lm/W Lamp with E47 thread (for Lamp with E47 thread (for Electronic Tubes with electronic ballast a conventional socket) and a conventional socket) and electronic incorporated electronic incorporated Lithium-Ion and Lithium Type Lead Acid—Automotive Lead Acid—Solar Iron Phosphate—Solar Life cycles 1000 1500 2500–3000 Storage 30% normal, 50% Discharge depth 30% normal, 50% maximum 100% (nominal) maximum Typical capacity 100–120 Ah 100–120 Ah 6–10 Ah Energy density 30–35 Wh/kg 35–40 Wh/kg 90–125 Wh/kg Sustainability 2021, 13, 3032 15 of 23

Table 1. Cont.

First Generation Second Generation Third Generation Component Variable 1980–1995 1995–2010 2010– Type Electromechanics Solid-state electronics Microelectronics Information by LEDs of Fault relays open the circuit. Icons, with clear User interface different states of charge Regulator Restitution by the user information to the user and troubles Electronic fuses for Fully integrated internal Protections Automotive fuses automatic restitution protection Type Bicolor Bicolor Armored Follow technical rules for Follow technical rules for Pre-set lengths, with a Cabling design installations installations switch already connected Cabling and Direct connection with Splices and twisted leads, Connectors are used connectors Connection methods specific terminals (plug insulation with electric tapes instead of splices and play) Observe polarity, problems in Each terminal is specific Polarity Observe polarity short-term splices for its use Equipment weight 50 kg 50 kg 6 kg Need specialized Installation Complexity Need specialized technician Minimum technician Human resource Specialized Specialized End-user Manuals and explanation to Manuals and explanation Posters, manuals, detailed Training the user to the user explanation to the user SHS operation End-user End-user End-user Connection made only by Connection made only by Connect/disconnect by Connections technicians technicians end-user Operation Use of adjustable DC-DC Fixed outputs in 12 and Adapters adapters depending on 5 V (USB) the load Short circuit hazards on Short circuit hazards on Risk No particular danger battery terminals. Polarity battery terminals. Polarity Training the user to take the component that fails Training Training a technician Training a technician and carry it to the technical center Module Cleaning Cleaning Cleaning Regulator Cleaning and adjustments Cleaning and adjustments Maintenance Cleaning added Battery Cleaning added distilled water Cleaning distilled water Charges Cleaning and adjustments Cleaning and adjustments Cleaning Adapters Cleaning and adjustments In case of failure, bring the In case of failure, call the In case of failure, call the Consideration component to the technician technician technician 3 point of light (CFL 7 W, 3 point of light (LED 3 W, 3 point of light (TL 18 W, 9 h/d total) 9 h/d total) 9 h/d total) 1 radio (10 W, 6 h/d) 1 radio (4 W, 6 h/d) Energy Services 1 radio (12 W, 6 h/d) 1 TV flat DC—Color 1 TV flat DC—Color 1 TV DC Black and White Energy Services 14 inch (14 W, 3 h/d) 15.6 inch (10 W, 3 h/d) 12 inch (20 W, 2h/d) Offered in Bolivian Charge Cell Phone Charge Cell Phone projects [31,32,86] Wh/day 274 183 96 Access Tier 2 Tier 2 Tier 2 Tiers Source: Own elaboration. Sustainability 2021, 13, x FOR PEER REVIEW 17 of 25

3 point of light (CFL 7 W, 9 h/d total) 3 point of light (LED 3 W, 9 h/d total) 3 point of light (TL 18 W, 9 h/d total) 1 radio (10 W, 6 h/d) 1 radio (4 W, 6 h/d) 1 radio (12 W, 6 h/d) Energy Services 1 TV flat DC—Color 1 TV flat DC—Color 15.6 inch (10 W, 1 TV DC Black and White 14 inch (14 W, 3 h/d) 3 h/d) 12 inch (20 W, 2h/d) Charge Cell Phone Charge Cell Phone Wh/day 274 183 96 jects [31,32,86] [31,32,86] jects SustainabilityAccess2021 , 13, 3032 16 of 23 Energy Services Of- Services Energy Tier 2 Tier 2 Tier 2 fered in Bolivian pro- Tiers Source: Own elaboration.

It can see thatIt can the see three that generations the three generations of SHSs offer of SHSsthe same offer energy the same services energy corre- services corre- sponding tosponding Tier 2. Likewise, to Tier 2. the Likewise, increase the in increaseefficiency in is efficiency observed, is which observed, for the which same for the same services goesservices from 274 goes Wh/day from 274 with Wh/day the 1G-SHS with the to 183 1G-SHS Wh/day to 183 with Wh/day 2G-SHS with and 2G-SHS finally and finally at 96 Wh/dayat 96with Wh/day 3G-SHSs. with By 3G-SHSs. the way, the By component the way, the costs component for the three costs generations for the three of generations SHS have beenof SHS compiled have been from compiled projects carried from projects out in Bolivia carried [31,32,86]. out in Bolivia Following [31,32 ,the86]. line Following the of analysis lineof Phadke of analysis [94], ofFigure Phadke 15 shows [94], Figure the results 15 shows obtained the results that validate obtained the that cost validate re- the cost duction attributedreduction to the attributed 3G-SHS. to the 3G-SHS.

Lights Battery PV BOS Appliances

1G - SHS (2000)

2G - SHS (2010)

3G - SHS (2015)

0 100 200 300 400 500 600 700 800

Figure 15. CostFigure of components 15. Cost forof components three generations for three of SHSs generations in Bolivia of toSHSs satisfy in Bolivia demands to satisfy of Tier demands 2, with data of Tier of [31 ,32,86]. 2, with data of [31,32,86]. Reviewing the technical characteristics of 3G-SHSs concerning their previous versions, Reviewingthe positive the technical differences characteristics and advantages of 3G-SHSs lead us concerning to think that their the photovoltaic previous ver- electrification sions, the positivefor rural differences households and must advantages necessarily lead turn us to towards think that a wide the usephotovoltaic of 3G-SHSs elec- (with quality trification forcertification), rural households becoming must a new necessarily standard turn for thistowards application. a wide It use is important of 3G-SHSs to emphasize (with qualitythat certification), the systems’ becoming quality is a vital new to standard comply withfor this the application. services offered. It is important to emphasize thatWhen the systems’ the deployment qualityof is 3G-SHSsvital to comply began, somewith the organizations, services offered. such as the International When Electrotechnicalthe deployment Commissionof 3G-SHSs began, (IEC), workedsome organizations, on quality assurance. such as the The Interna- result was a series tional Electrotechnicalof documents Commission for renewable (IEC), hybrid work systemsed on quality dedicated assurance. to rural The electrification, result was a IEC 61257- series of documents9-5 [102]. for Aligned renewable to this, hybrid the international systems dedicated program to Lightingrural electrification, Global [103] IEC has published 61257-9-5 [102].a standard Aligned named to this, Solar the international Home System program Kits Quality Lighting Standards Global [103] [104 ]has based pub- on the IECs lished a standardpublications named and Solar considering Home System its verification Kits Quality procedure. Standards In February [104] based 2020, on Lighting the Global, IECs publicationsthe Collaborative and considering Labeling its verification and Appliance procedure. Standards In February Program 2020, (CLASP), Lighting and the Schatz Global, the EnergyCollaborative Research Labeling Center and launched Appliance VeraSol, Standards an evolved Program quality (CLASP), assurance and the program for Schatz Energymodern Research off-grid Center solar launched solutions, VeraSol, providing an evolved product quality certifications assurance that program meet international for modernstandards off-grid solar [105], solutions, and will continueprovidin withg product the work certifications of Lighting that Global. meet interna- tional standardsThe [105], quality and will assurance continue must with guarantee the work thatof Lighting the technical Global. conditions specified in the products are met under international standards that ensure the useful life and efficiency. However, it must also ensure that the products respond to the population’s needs, achieving social acceptance [98]. Finally, it must protect the consumer in aspects such as transparency of information and compliance of companies’ guarantees. The products that meet the standard are listed on their website [106]; for October 2021, in the category solar energy kits, exist as 57 brands and 189 kits certified with different sizes and capabilities. However, GOGLA (2020) indicates that out of 30.6 million SHSs products sold in 2018, only 7.6 million were affiliated companies’ to GOGLA [24,107]. Along these lines, defining a standard similar to the Universal Technical Standard for Photovoltaic Systems Sustainability 2021, 13, x FOR PEER REVIEW 18 of 25

The quality assurance must guarantee that the technical conditions specified in the products are met under international standards that ensure the useful life and efficiency. However, it must also ensure that the products respond to the population’s needs, achiev- ing social acceptance [98]. Finally, it must protect the consumer in aspects such as trans- parency of information and compliance of companies’ guarantees. Sustainability 2021, 13, 3032 17 of 23 The products that meet the standard are listed on their website [106]; for October 2021, in the category solar energy kits, exist as 57 brands and 189 kits certified with differ- ent sizes and capabilities. However, GOGLA (2020) indicates that out of 30.6 million SHSs products sold in 2018,but orientedonly 7.6 million to 3G-SHSs, were affiliated with compan broadies’ applicability, to GOGLA [24,107]. and setting Along these up morelines, laboratories and definingtest centers, a standard are asimilar pending to the challenge.Universal Technical Standard for Photovoltaic Systems but oriented to 3G-SHSs, with broad applicability, and setting up more laboratories and test5.3. centers, Operational are a pending Characterization challenge. of 3G-SHSs 5.3. OperationalAdopting Charac LEDterization technology of 3G-SHSs for lighting decreases the energy consumption, which adds to theAdopting increasing LED technology efficiency for of lighting loads decr sucheases as flat-screenthe energy consumption, televisions, which compact radios, and addscell phones,to the increasing making efficiency a less of need loads for such energy as flat-screen storage televisions, [94]. A compact lower radios, electricity requirement and(using cell veryphones, efficient making loads)a less need allows for en theergy use storage of smaller [94]. A lower PV modules, electricity facilitatingrequire- transport and ment (using very efficient loads) allows the use of smaller PV modules, facilitating transportinstallation, and installation, and the weight and the weight reduction reduction of 3G-SHSs. of 3G-SHSs. The The interactions interactions between between the innovative thecomponents innovative components of 3G-SHSs of 3G-SHSs are shown are shown in Figure in Figure 16. 16.

Figure 16. 16. Inter-relationshipsInter-relationships identified identified between LED, between microelectronics, LED, microelectronics, and lithium batteries. and lithium batteries.

InIn the the same same line, line,the high the charge high density charge of density lithium batteries, of lithium their batteries, large number their of large number of charge and and discharge discharge cycles, cycles, and their and depth their of discharge depth of in dischargeregular use of in almost regular 100%, use of almost 100%, implies the use of smaller and more compact batteries [108,109], which additionally do notimplies require the periodic use of maintenance. smaller and However, more compactlithium batteries’ batteries complexity [108,109 of ],charge which con- additionally do not trolrequire would periodic not have been maintenance. possible to achiev However,e in operational lithium terms batteries’ without microelectron- complexity of charge control icswould and microprocessors. not have been Microprocessors possible to achieveand a high-resolution in operational screen terms make it without possible microelectronics and microprocessors. Microprocessors and a high-resolution screen make it possible to use icons, symbols, and display information dynamically and easily to understand by the final user. Furthermore, the application of integrality concepts, modularity, and easy connections show a completely different functionality from 2G-SHSs. Analyzing the operation of a 3G-SHS is possible to identify the following advantages: • Smaller and more efficient systems. • Lightweight systems: A 3G-SHS weighs 6 kg (a traditional SHS, weighs over 50 kg), which results in easier transport logistics. • Lower cost: The price of a system of this type is less than 50% of a conventional 2G-SHS (USD 900). • Longer lifespan: The system’s operational lifetime could be between 8 and 10 years with a lithium iron phosphate battery between 2500 to 3000 charge/discharge cycles (already available in the market) and LED lamps with 50,000 h of use. • Minimal after-sales service: The low probability of failures makes that the systems not require operation and maintenance services by specialized technicians in situ and, rather, makes the user interact much more with the equipment. • Self-installation by the user: An installation by specialized technicians is not necessary, and thus, the same end-user can do it with an adequate training process. Sustainability 2021, 13, 3032 18 of 23

Undoubtedly, it can be seen that the sum of radical and incremental innovations, in this case, have achieved a superior version of the product [110,111]. Therefore, it can be said that it is a new generation of SHSs. A 3G-SHS is not only more efficient, compact, lightweight, and cheap. It is also a friendly and intelligent system since the microprocessor allows, beyond the handling of information to the user, the consumption record and the possibility of interacting remotely with a suitable interface. Through the connection with cellular networks, it can operate microcredit or innovative payment systems known as Pay As You Go (PAYG) which, for certain contexts such as Sub-Saharan Africa, are rapidly expanding access to this technology [112,113]. In LAC, the population without access to energy lives in regions without access to cell phone services and very high dispersion. The application of the PAYG business model is limited since it requires communication technologies as a condition [114]. However, the capabilities of 3G-SHSs to manage equipment access locks are used for initiatives such as the rent-to-own of Quetsol in Guatemala [115] and sales of equipment on credit in Bolivia [32]. In both cases, users pay their fees periodically, and the unlock is done manually and not online. With this solution, collection costs and risks are minimized. Three aspects such as: The possibility of self-installation by the user, the absence of need for periodic maintenance of 3G-SHSs by technicians, and the long useful life of the components (lithium battery, LED lamps, and PV panel), reduce the need to provide Operation and Maintenance (O&M) services with periodically home visits (as it is done with 2G-SHSs). As these, in situ services, are unnecessary, an important component of operating costs in the system’s life cycle is minimized. However, it is necessary to change the logic of technicians visiting houses by having fixed technical assistance centers when the user takes his equipment for repair. All these elements will impact on the actions in massive PV electrification projects since the 3G-SHSs allow optimizing investment resources, improving the technical and economic sustainability of access to energy and facilitating the logistics and implementa- tion conditions of the projects, and, finally, it rethinks the traditional ways of executing photovoltaic electrification projects for homes. Over the last 20 years, installations of SHS for rural households have grown in LAC. Reviewing the statistics available for the isolated photovoltaic capacity installed in rural homes in LAC and the number of people who use them [116], Figure 17 has been con-

Sustainability 2021, 13, x FOR PEER REVIEWstructed, which shows the relationship between the installed power20 of 25 in the SHS for the period 2007–2017 by year, and also shows the presence of 2G-SHS and 3G-SHS.

FigureFigure 17. Installed 17. Installed capacity capacity of photovoltaic of photovoltaic (PV) off-grid in (PV) LAC off-grid2007-2017. in Elaborated LAC 2007-2017. with data Elaborated with data of [116].of [116 ].

6. Conclusions This research reviews the information from 1980 to date on PV rural electrification, showing that most of the people without access to electricity, especially in LAC, live in rural, isolated, and dispersed areas. In addition, the lack of electricity seriously limits the quality of life in terms of lighting, communication, and education services. For these pop- ulations, decentralized solutions based on renewable energy and specifically solar energy are a realistic option. For supplying energy to isolated households, SHS is a widely used alternative throughout the world, with a success level that has been improving over time due to pro- gressive technological innovations in different components of SHSs. When these sets of innovations become disruptive, they affect the SHS functionality and produce a new SHS version. In this review, three generations of SHSs have been clearly identified. During the transition time from one generation to another, the current generation tends to coexist with the improved version, generating hybrid versions with a short validity time. The last technological innovations (LED lighting, lithium batteries, microelectronic control, and plug and play connection systems) integrated into the SHS are called 3G-SHS, which have achieved technological safety and a long useful life in all components (about 10 years). The 3G-SHSs are easy to operate, require minimum maintenance, and have lower costs than the previous generations. With 3G-SHSs, operational issues such as transport and installation are no longer a barrier since the end-user can perform them. With minimal maintenance requirements, technicians do not need to visit users periodi- cally, and after-sales service costs drop dramatically. The 3G-SHSs allow overcoming the barriers of the traditional SHS: High initial in- vestment, need of specialized technicians for installation and maintenance, high costs of battery replacement, and, particularly in LAC, logistics, transport, and execution are be- coming more complex and expensive due to the dispersion of users and inaccessible areas. Moreover, the technological advances in 3G-SHSs allow new business models and insti- tutional forms that manage the universal access to electricity to be developed. It is im- portant to identify the experiences generated in a broad and accelerated manner in Sub- Saharan Africa and, considering LACs particularities, to select those that can be used suc- cessfully. Sustainability 2021, 13, 3032 19 of 23

6. Conclusions This research reviews the information from 1980 to date on PV rural electrification, showing that most of the people without access to electricity, especially in LAC, live in rural, isolated, and dispersed areas. In addition, the lack of electricity seriously limits the quality of life in terms of lighting, communication, and education services. For these populations, decentralized solutions based on renewable energy and specifically solar energy are a realistic option. For supplying energy to isolated households, SHS is a widely used alternative through- out the world, with a success level that has been improving over time due to progressive technological innovations in different components of SHSs. When these sets of innovations become disruptive, they affect the SHS functionality and produce a new SHS version. In this review, three generations of SHSs have been clearly identified. During the transition time from one generation to another, the current generation tends to coexist with the improved version, generating hybrid versions with a short validity time. The last technological innovations (LED lighting, lithium batteries, microelectronic control, and plug and play connection systems) integrated into the SHS are called 3G- SHS, which have achieved technological safety and a long useful life in all components (about 10 years). The 3G-SHSs are easy to operate, require minimum maintenance, and have lower costs than the previous generations. With 3G-SHSs, operational issues such as transport and installation are no longer a barrier since the end-user can perform them. With minimal maintenance requirements, technicians do not need to visit users periodically, and after-sales service costs drop dramatically. The 3G-SHSs allow overcoming the barriers of the traditional SHS: High initial invest- ment, need of specialized technicians for installation and maintenance, high costs of battery replacement, and, particularly in LAC, logistics, transport, and execution are becoming more complex and expensive due to the dispersion of users and inaccessible areas. More- over, the technological advances in 3G-SHSs allow new business models and institutional forms that manage the universal access to electricity to be developed. It is important to identify the experiences generated in a broad and accelerated manner in Sub-Saharan Africa and, considering LACs particularities, to select those that can be used successfully. From the point of view of progress in universal access to energy, SDG 7, using the Multi Tiers framework, the 3G-SHS allows covering the Tier 1 and Tier 2 with clear advantages over 2G-SHS. Another important variable to consider is the technological advances of household appliances’ increasing efficiency (TVs, fans, and refrigerators). In other words, less and less energy needs to obtain the same services. Disregarding these advances can lead to oversizing and unnecessary costs of SHSs. Given the difficulties in promoting universal access in LAC and other regions of the world, 3G-SHSs are strategically a recommended solution to achieve this global goal.

Author Contributions: Conceptualization, M.H.F.-F., A.A.E.-A., and M.A.E.-A.; methodology, M.H.F.- F., A.A.E.-A., and M.A.E.-A.; investigation, M.H.F.-F.; resources, M.H.F.-F., A.A.E.-A., and M.A.E.-A.; writing—original draft preparation, M.H.F.-F.; writing—review and editing, M.H.F.-F., A.A.E.-A., and M.A.E.-A.; supervision, M.A.E.-A. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by ENERGETICA through the projects: The Microfranchises for Access to Clean Energy in Rural Areas, and Deploying New Solar Technologies for Isolated Rural Areas: Supporting their Adoption in the LAC Region. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Data applied in this study is well-cited throughout the text, and no new data were created. Conflicts of Interest: The authors declare no conflict of interest. Sustainability 2021, 13, 3032 20 of 23

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