Energy Efficiency of Low Voltage Direct Current Supplies Including PV Sources Anis Ammous1, Ammar Assaidi1, Abdulrahman Alahdal1 and Kaiçar Ammous2 1Department of Electrical Engineering, College of Engineering and Islamic Architecture, Umm Al-Qura University, K.S.A. 2Department of Electrical Engineering, National School of Engineers of Sfax, University of Sfax, Tunisia Keywords: Renewable Energy, Power Electronics, LVDC, Energy Efficiency. Abstract: The low Voltage Direct Current (LVDC) system concept has been growing in the recent times due to its characteristics and advantages like renewable energy source compatibility, more straightforward integration with storage utilities through power electronic converters and distributed loads. This paper presents the energy efficiency performances of a proposed LVDC supply concept and others classical PV chains architectures. A PV source was considered in the studied nanogrids. The notion of Relative Saved Energy (RSE) was introduced to compare the studied PV systems energy performances. The obtained results revealed that the employment of the LVDC chain supply concept is very interesting and the use of DC loads as an alternative to AC loads, when a PV power is generated locally, is more efficient. The installed PV power source in the building should be well sized regarding to the consumed power in order to register a high system RSE. 1 INTRODUCTION integration of modern energy resources in comparison to conventional AC systems. The photovoltaic electricity was primarily Direct use of DC power would reduce many established for standalone applications deprived of power conversion losses by exploiting self- any connection to a power grid. Such was the case of consumption of the energy produced on site and satellites or isolated habitations. Currently, PV's are decreasing imports of electricity from the grid. DC found in many power applications like personal loads used in households and office buildings, also calculators, watches and other objects of daily use, operate on DC, heating/cooling systems and larger they can supply many individual DC loads without equipment used in industry such as variable difficulty. The main objective of this paper is to frequency drives have also adopted DC motors. investigate the energy efficiency performance of a Direct current power systems are essentially more proposed Low-Voltage Direct Current (LVDC) PV efficient than their AC counterparts; since in DC system regarding to a classical LVDC architecture systems do not suffer from skin effect or reactive and classical PV systems using AC loads. All the power (Leonardo et al., 2016; IEC, 2016; D. Kumar studied PV chains are on-grid ones and are supposed et al., 2017; Gyuyoung Yoon et al., 2019). supplying offices. A literature research has exposed the study of the In general, electric energy consumption in office first system analysis explored the use of very low applications and housing is achieved by using the voltage (<120 V) in small-size systems, particularly alternative current plugs even for Grid Tie PV panel residential dwellings (J Pellis, 1997). systems. In this case the use of AC's can increase Subsequently, Lasseter R.H proposed the system losses especially when DC current is used at concept of the DC Microgrid as a low voltage the load levels. distribution network. This concept was projected as LVDC systems have been gaining more interest the future low voltage distribution systems which during the past few years both in academia and were facing revolutionary variations at the time due industry. LVDC systems offer many advantages to emanation of distributed generation and market covering higher energy efficiency and easier liberalization. The basic idea behind this concept is to combine micro sources and loads into one entity 188 Ammous, A., Assaidi, A., Alahdal, A. and Ammous, K. Energy Efficiency of Low Voltage Direct Current Supplies Including PV Sources. DOI: 10.5220/0010471001880195 In Proceedings of the 10th International Conference on Smart Cities and Green ICT Systems (SMARTGREENS 2021), pages 188-195 ISBN: 978-989-758-512-8 Copyright c 2021 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved Energy Efficiency of Low Voltage Direct Current Supplies Including PV Sources which could be interpreted as a single dispatch-able Through review of the available literature load that could respond in short time to meet the (Leonardo et al., 2016), (Gyuyoung Yoon et al., transmission system needs (R. H. Lasseter, 2002). 2019), (Kiran and Hassan, 2020), (Yu Zhang et al., For many years, The LVDC system has been 2020), local DC grids are a promising option for developed for specific applications like aerospace, buildings to link natural DC power sources such as automotive and marine (A. Ghareeb et al., 2013), photovoltaic power systems with DC loads like (Ahmed T et al., 2015), (Jifei Du et al., 2019). lighting applications and data centers (Tomm Literature review reveals that over the last decades, Aldridge, 2009), (Kiran and Hassan, 2020). LVDC systems are growing rapidly for industrial (A. AMMOUS and H. Morel, 2014) reported that applications, essentially in the telecommunication DC microgrids are alternatives promising to industry, ships and buildings. Adopting Direct conventional AC distribution networks especially for Current in data centers improve efficiency, decrease the integration of renewable energies. They allow, capital cost, increase reliability and boost power for example, to reduce consumption energy of 25% quality (AlLee et al., 2012). In data centers, LVDC when supplying buildings directly from sectors and architectures have been widely studied. Various by photovoltaic panels. leader projects have been installed in Europe, the The majority works on DC distribution grids United States, Oceania and Asia. From these assume that converters are installed at each projects it was registered that the profit of DC in household, which connect the local DC or AC data-centers are about 10% to 30% reduction in nanogrids (Patwa and Saxena, 2020) ,(X. Yue et energy consumption, about 15% lower capital costs, al.,2018). In case of distributed energy resources, simpler design, potential increase in reliability, less nanogrids in buildings could be functioned physical area requirements, a smaller carbon separately from the main grid in islanding mode (X. footprint and less cooling demand (Tomm Aldridge, Yue et al.,2018) and typical low voltage subsystems 2009), (Brian Fortenbery, 2011). like 48V, 24V, or 12 V can be applied (Rodriguez- The most significant challenge that DC Diaz et al., 2016). They could, for example, be used distribution systems face today is the lack of for low power LED lighting or for connecting loads standardization inducing varied architectures and by USB Type-C connector and USB Power operations of DC distribution systems (Kiran and Delivery. Hassan, 2020), (Paul, Robert and Sean, 2010). In the first part of the paper, we focused our The work presented in (V. Vossos et al., 2014) study on the state of the art related to the use of the was accomplished in many various locations through LVDC supply concept and the proposition of an on- the country, with different types of system grid LVDC PV chain. The disadvantage of the use topologies. Further, distribution topologies were of classical on-Grid PV systems and of using AC carried out for both two cases with and without plugs to supply electric DC loads are shown. The energy storage. used average model of power converters is then Studies conducted in (V. Vossos et al., 2014), presented in the second part. This model allows the (Paul, Robert and Sean, 2010) aim to accomplish 25- evaluation of the different converters efficiencies in 30% of energy savings. The environment the studied PV chains. The last part of the paper conditioning loads are very significant part in treats the energy efficiency performances of the Buildings and should be explored in further studies. proposed LVDC system compared to others classical The authors in (Patterson, B. T, 2012) reported ones. For this purpose, offices loads are considered that the majority of electricity used in on office and Jeddah location (in KSA) was chosen in our building passes through power converters enclosing study. further conversions. Average conversion efficiency is closed 68%. When using high quality electronics, only a 10% loss from each stage of conversion is 2 THE PROPOSED LVDC PV considered as generous number. The DC power is directly produced from SYSTEM residential solar panels and inverter is commonly added to supply AC loads. Electronic appliances, such as computers, gaming Despite that the multi-stage conversion is basic consoles, printers, economic LED lights, televisions to extract power from the solar panel into the server; and so on need DC supplies. Additional AC to DC losses resulting from these conversions are expected converters are needed in such equipment. to be between 10% and 25%. 189 SMARTGREENS 2021 - 10th International Conference on Smart Cities and Green ICT Systems Figure1 shows one of classical chain used to connect PV panels to the low voltage grid with a transformerless solution. The DC/DC converter, Converter #1, allows the extraction of the maximum power from the PV panels when climatic conditions changes. The Maximum Power Point Tracking (MPPT) algorithm is used to act on this DC/DC converter control. The DC/AC converter, Converter #2, transfers the PV generated power to the grid and ensures the regulation of the DC voltage value (400 V) of the Figure 2: Possible LVDC classical architecture (syst2). inverter input. This DC value is mainly used value for single phase PV systems allowing to obtain The last converter allows the transfer of power from easily the standard 230 V AC. The injected current PV panels to the inverter when the generated power to the grid has a quasi-sinusoidal waveform. is higher than the consumed power. This reversible converter works as a Buck converter in the case when the consumed power is higher than the PV generated one.