energies Article Hydrogen as a Long-Term Large-Scale Energy Storage Solution to Support Renewables Subodh Kharel and Bahman Shabani * School of Engineering, RMIT University, Melbourne 3083, Australia; [email protected] * Correspondence: [email protected]; Tel.: +61-3-9925-4353 Received: 21 September 2018; Accepted: 16 October 2018; Published: 19 October 2018 Abstract: This paper presents a case study of using hydrogen for large-scale long-term storage application to support the current electricity generation mix of South Australia state in Australia, which primarily includes gas, wind and solar. For this purpose two cases of battery energy storage and hybrid battery-hydrogen storage systems to support solar and wind energy inputs were compared from a techno-economical point of view. Hybrid battery-hydrogen storage system was found to be more cost competitive with unit cost of electricity at $0.626/kWh (US dollar) compared to battery-only energy storage systems with a $2.68/kWh unit cost of electricity. This research also found that the excess stored hydrogen can be further utilised to generate extra electricity. Further utilisation of generated electricity can be incorporated to meet the load demand by either decreasing the base load supply from gas in the present scenario or exporting it to neighbouring states to enhance economic viability of the system. The use of excess stored hydrogen to generate extra electricity further reduced the cost to $0.494/kWh. Keywords: renewable energy; solar and wind; battery storage; hydrogen-based energy storage; hybrid energy systems; South Australia 1. Introduction In efforts towards reducing the greenhouse gas emissions and mitigating the impact of climate change, countries around the globe have started to shift towards energy production through renewables. Energy generation from renewable sources such as wind and solar can help mitigate emissions produced through using traditional fossil fuel-based energy generation. However, renewable energy generation is highly weather-dependent and lacks the possibility of achieving a continuous supply on their own due to their inherent intermittency [1]. This can lead to issues, such as energy curtailment and wastage of energy and, hence, mismatching between supply and demand. While employing multiple generation systems as backups or demand management measures initiated by the end users could be the possible options, employing an optimally designed and sized energy storage system can be the most viable and sustainable solution [2]. Energy storage solutions can even be also employed in gird connected area (with or without renewables) for peak shaving or fill the reliability gap of the grids where reliability is of significant importance [3–5]. One of the technologies to store excess energy produced by renewable energy sources is generation and storage of hydrogen. This system includes the major components of an electrolyser, hydrogen storage tank, and a fuel cell system. The excess from the renewable sources (i.e., solar and wind) is directed towards an electrolyser to generate hydrogen by electrolysing water into hydrogen and oxygen. The hydrogen is stored in the storage tank and when the renewable sources fall short in meeting the demand, the fuel cell draws on this stored hydrogen and generates electricity (usually by taking oxygen from air) [6,7]. Energies 2018, 11, 2825; doi:10.3390/en11102825 www.mdpi.com/journal/energies Energies 2018, 11, 2825x FOR PEER REVIEW 22 of of 17 Hydrogen-based energy storage has high power rates (i.e., in the range of 10 MW) and is suitableHydrogen-based for meeting long-term energy storage (seasonal) has high energy power storage rates (i.e.,requirements in the range [8]. of Pumped 10 MW) andhydroelectric is suitable storagefor meeting system long-term (PHS) has (seasonal) limited energyscope for storage further requirements development [8 in]. long-term Pumped hydroelectric storage applications storage duesystem to its (PHS) specific has geographical limited scope requirements for further and development possible environmental in long-term impacts storage applications[9]. Batteries that due canto its be specific considered geographical as another requirements energy storage and soluti possibleon are environmental efficient as impactsshort-term [9]. energy Batteries storage that solutions;can be considered however, asdue another to their energy uncertain storage lifetime, solution and are quick efficient degradation as short-term (i.e., due energy to charging storage cycles),solutions; sensitivity however, to due environmental to their uncertain conditions lifetime, (e.g., and temperature), quick degradation self-discharge, (i.e., due and to charging limited storagecycles), sensitivitycapacity (per to environmentalunit volume and conditions mass), batteries (e.g., temperature), are not perfect self-discharge, candidates and for limitedlong-term storage and bulkcapacity energy (per storage unit volume applications and mass), [10–13]. batteries are not perfect candidates for long-term and bulk energy storageThis applications paper investigates [10–13]. the scope of application of hydrogen as a long-term large-scale energy storageThis solution paper investigatesthrough a case the st scopeudy for of state application of South of Australia hydrogen (SA) as ain long-term Australia large-scalefor hybrid energy inputstorage from solution solar throughphotovoltaic a case (PV) study and for wind state turb of Southines to Australia meet the (SA) state’s in Australia load demand. for hybrid The energy energy generationinput from mix solar has photovoltaic evolved in (PV)SA with and the wind increase turbines in topenetration meet the state’sof renewable load demand. energy. TheAt the energy end ofgeneration 2016, registered mix has local evolved generation in SA withcomprised the increase of 48.4% in penetrationrenewable energy of renewable generation energy. with At wind the and end solarof 2016, energy registered contributing local generation 39.2% and comprised 9.2% respective of 48.4%ly renewable[14]. Moreover, energy the generation total of 1515 with MW wind solar and andsolar 3178 energy MW contributing of additional 39.2% wind and generation 9.2% respectively on existing [14]. Moreover,1698 MW thewas total either of 1515committed MW solar or proposedand 3178 MWas of of1 July additional 2017 [14]. wind In generation2016–2017, onSA’s existing electricity 1698 generation MW was either capacity committed from gas or was proposed 49.1% ofas oftotal 1 Julycapacity, 2017 [14with]. In the 2016–2017, increase in SA’s solar electricity and wind generation capacity capacity such that from the gascombined was 49.1% generation of total capacitycapacity, from with these the increase sources inwould solar reach and wind 58% while capacity gas suchwould that contribute the combined 35% in generation total capacity capacity [14]. Hence,from these as sourcessynchronous would generation reach 58% whilecapacity gas dec wouldreases contribute and intermittent 35% in total renewable capacity [14generation]. Hence, increases,as synchronous more storage generation capacity capacity will decreases be required and to intermittent maintain the renewable stability of generation the grid. increases,Figure 1 shows more thestorage map capacity of SA. The will total be required renewable to maintain energy thegenerati stabilityng capacity of the grid. as per Figure the1 targetshows set the by map the of state SA. governmentThe total renewable would reach energy to generating1515 MW of capacity solar ener asgy per and the 4876 target MW set of by wind the state energy. government However, would apart fromreach 100 to 1515 MW MWof Tesla’s of solar battery energy storage and 4876 installati MWon, of wind there energy. are no However,significant apartstorage from options 100 MW being of investedTesla’s battery for the storage state. installation,Hence, lack there of a areconcrete no significant energy storagestorage optionstarget and being increase invested in for renewable the state. energyHence, generation lack of a concrete target can energy result storage in instability target andin the increase grid and in power renewable cuts. energyThis case generation study will target help understandcan result in the instability storage in capacity the grid and and design power cuts.requir Thisements case to study support will helpthe SA’s understand renewable the storageenergy targetcapacity (RET). and design requirements to support the SA’s renewable energy target (RET). Figure 1. Map of South Australia highlighted. SA SA has has an area of 983,482 square km. and monthly average loadload demanddemand is is 1,321,549 1,321,549 kWh kWh in in which which 560,600 560,600 is the is basethe base load load supplied supplied by gas by or gas coal or power coal powerplants andplants monthly and monthly average averag renewablee renewable supply supply is 760,499 is 760,499 kWh. kWh. Energies 2018, 11, 2825 3 of 17 Limited studies are available in the literature on real world application of hydrogen as a large-scale energy storage solution in multiple renewable energy input scenarios. Most of the studies available in the literature focus on either small scale or medium size system (e.g., households or small communities). Zoulias et al. [15] in 2007 carried out a techno-economic analysis on a hydrogen-based energy storage system to replace batteries and diesel generator of an existing PV/diesel generator stand-alone system. The investigation was done