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Energy Storage in Global and Transcontinental Energy Scenarios: A Critical Review
Available online at www.sciencedirect.com
ScienceDirect Energy Procedia 99 (2016) 53 – 63
10th International Renewable Energy Storage Conference, IRES 2016, 15-17 March 2016, Düsseldorf, Germany
Energy Storage in Global and Transcontinental Energy Scenarios: A Critical Review Otto Koskinena, Christian Breyera,* a
Lappeenranta University of Technology, Skinnarilankatu 34, Lappeenranta 53850, Finland
Abstract There are a fast growing number of global energy scenarios based on high shares of renewable energy (RE). However, many of them lack comprehensive analyses of energy storage systems. A review of global scenarios reveals that energy storage systems are assessed mainly qualitatively; quantitative assessments of global energy storage demand are scarce. The possible future roles of energy storage systems are plentiful: they can be used in short-term control (e.g. in power grid frequency control), as a mediumterm balance mechanism (to shift daily production to meet demand), as long-term storage (seasonal shift), or to substitute grid extensions. Typically, only power storage is considered, if energy storage is assessed at all. Scenario-makers do not always assess the dynamics and synergies of energy storage systems in the power, heat and mobility sectors. To date, publications of the dynamics between continent-wide renewable energy production, transmission grids and energy storage capacities are not numerous. The existing body of research indicates that transmission lines connecting individual countries are regarded as a key component in enabling RE-based, low-cost energy systems. However, various issues could restrain the implementation of proposed grid connections. These barriers could be overcome by partially substituting energy grid reinforcements with energy storage solutions. Furthermore, less storage related curtailment of renewable energy could lead to improved energy system efficiency and cost. Therefore, energy scenarios that capture quantitatively different configurations of international energy exchange and its influence on regional storage systems are needed. High spatial and temporal resolution energy system models are needed to assess scenarios for high share of renewable energy supply and demand for energy storage. © 2016 2016The TheAuthors. Authors. Published Elsevier © Published by by Elsevier Ltd.Ltd. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of EUROSOLAR - The European Association for Renewable Energy. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of EUROSOLAR - The European Association for Renewable Energy Keywords: storage; energy scenarios; global
* Corresponding author. Tel.: +358-50-443-1929 E-mail address: [email protected]
1876-6102 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of EUROSOLAR - The European Association for Renewable Energy doi:10.1016/j.egypro.2016.10.097
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1. Introduction Climate change, optimal resource use and desire to better understand aspects of large-scale renewable energy (RE) deployment have motivated scenario-makers to explore pathways to and aspects of high RE futures [1]. Substantial growth in RE deployment in recent years undoubtedly has spurred increased attention to high RE scenarios. Over the mid-term, Intended Nationally Determined Contributions (INDCs) can set light on the current ambition level of RE uptake. Cumulative RE supply levels in Brazil, China, the European Union and Indonesia are set to increase from 7980 TWh/year in 2012 to 14,830 TWh/year (86% increase) in 2030 according to a recent report [2] based upon INDCs. Renewable electricity generation in Brazil, India, Mexico and the United States is set to increase from 630 TWh/year in 2012 to 2250 TWh/year (257 % increase) in 2030. The substantial RE growth indicated in INDCs is in line with leading institutional projections of rapid RE deployment in the years to come [3]. Moreover, partly excluded and partly included in INDCs, growing number of subnational and corporate targets show even more stringent greenhouse gas (GHG) reduction and RE deployment goals [4,5,6]. Significant health benefits, job creation and reduced cost of imported fuels have been estimated to result from more ambitious renewable energy deployment [7]. Nomenclature CAES CCGT DSM EUMENA H2 HVDC PHS RE RPM V2G VLS-PV
Compressed Air Energy Storage Combined Cycle Gas Turbine Demand Side Management Europe-Middle-East-North-Africa Hydrogen High Voltage Direct Current Pumped Hydro Storage Renewable Energy Renewable Power Methane Vehicle to Grid Very Large Scale-Photovoltaics
Several studies suggest that on the European level the further integration of electricity transfer capacities would deliver cost savings in the total system. Grid integration is argued to be an economically beneficial measure in achieving long-term energy and climate policy targets: integrating high shares of renewables, increasing competition in the market, thus leading to lower electricity prices, and increasing security of supply. A recent study found the cost savings ranging between 2 – 21% compared to a scenario without grid expansion [8]. In a concept study several opportunities enabled by a global grid were identified: smoothing out electricity supply and demand, minimizing power reserves, reducing storage demand and reducing volatility of electricity prices. Power system security could be on the one hand reduced (reliance on overseas source of energy) and on the other enhanced (relief of congestion) [9]. Thinking broader, current energy systems are already heavily dependent on fuels imported from thousands of kilometers away [10], and a global grid could actually reduce the dependence on overseas energy. Some of the targets above could be at least partly addressed by energy storage as well, thus the research questions of this study arise: Is the role of energy storage assessed in influential global energy scenarios? What is the quantified demand for energy storage in global scenarios? To some extent the issue of building supergrids has already departed the academic circles and been taken on by various initiatives in Europe and applications in Asia; ten years after the ground-breaking TRANS-CSP study by the DLR [11], industry rooted initiative Dii [12] and non-profit civil society initiative Desertec Foundation [13] are carrying on the concept of importing solar power from North Africa to Europe. The North Sea grid project co-funded by European Union (EU) is yet another example [14]. In Asia, the State Grid Corporation of China is poised to construct about 160 GW of high voltage connections by 2016 (116 GW had been constructed by the end of 2014) [15]. According to the Global Energy Storage Database [16], the grid connected energy storage capacity installed in China amounted to 33.3 GW in 2015, mainly based on pumped hydro storage.
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2. Methodology Global and transcontinental energy scenarios were chosen for this meta-analysis. The latter include studies having geographical scopes of Europe, Middle-East, North Africa, North and South America and South-East Asia. We review quantitative and qualitative assessments of energy storage in the scenarios. In a qualitative analysis we look for existence of storage technologies in the scenarios, storage technology descriptions, discussions of the relevance of energy storage in the scenarios and different roles that energy storage could have. In a quantitative analysis we look for energy storage capacities in terms of power and energy and relative shares of energy storage on the demand side. The results of the analysis for global scenarios are presented in Table 1 and for continental and transcontinental scenarios in Table 2. 3. Review of energy scenarios Comparisons of various energy scenarios provide wide viewpoints on alternative energy systems. Such metaanalysis with global scope had been done earlier in [1,17]. The authors of these two review studies have polarized conclusions: the previous shows that renewable energy sources can play a large role in future power systems, and the latter summarizes that scenarios for renewable energy dominance in the world’s energy supply by mid-century assume unrealistic technical potentials and implementation times. A review of International Energy Agency’s (IEA) past World Energy Outlooks (WEO) suggests that assuming linear growth of wind power and solar PV leads to systematic underestimation of the deployment of these technologies [3]. Historically, the more progressive projections made by Greenpeace and Bloomberg New Energy Finance (BNEF) have more accurately captured the real RE technology deployment compared to the conservative IEA outlooks [18]. It can be argued that energy scenarios are not meant to be predictions of the future; they can be used as a tool to evaluate alternative outcomes and their sensitivities. Despite this, in a review [19] by Citigroup it was found that fossil fuel industry businesses use IEA’s New Policy Scenarios as forecasts to base their strategies on. Citigroup analysts suggest that investors should also take into account IEA’s 450, which is more skeptical on fossil fuels and a bit more optimistic on RE, or compatible scenarios. Furthermore, it should be noted that when scenario-makers create scenarios, in effect they limit the possibility space (what is perceived as possible or credible) within chosen boundaries. Our view is that energy scenarios have an influence on people’s mindsets, including researchers, investors, politicians, industry representatives, NGOs and general public, and can set the frame in which policies are made and actions are based upon. In essence, influential energy scenarios could have a self-fulfilling mechanism on different levels in the society. The spectrum of different scenario types is wide, thus the purposes and applications differ from each other, and a useful decision-makers’ guideline can be found in [20]. 3.1. Energy storage in global energy scenarios 3.1.1. Quantitative assessments The IEA notes in its energy and climate change special issue [21] that global installations of energy storage could amount to 400 GW by 2050. It is stated that over the mid-term, energy storage can alleviate transmission constraints. In contrast, in a study where a global decentralized renewable energy system was investigated, using load demand for the year 2010 and cost basis of the year 2020, energy storage demand for batteries only was found to be 1500 GWh [22]. Assuming an energy to power ratio of six, this would represent 250 GW of battery capacity demand over the short term in the over 160 countries assessed in the study. Optimal mixes of solar and wind power generation were investigated in [23]. In addition, minimum storage capacity was determined with different amounts of installed capacity of solar and wind. It was found that while the seasonal storage capacity has to be two orders of magnitude larger than required capacity of the storage for daily cycle, the sum of stored energy during one year is almost equal for long and short term storage. In a closer look for Europe, long term storage amounted to 146.2 TWh and short term 4.1 TWh. The latter would represent capacity of 683 GW applying the energy to power ratio above. Note that in this scenario 30% of power capacity is wind and 70% PV power, and they are used to supply annual demand of 3956 TWh (weather year 2009). Another dissertation [24] investigated the dynamics of storage and transmission. It was found that if wind power was available, local excess was transferred
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inter-regionally to meet demand, whereas if excess solar PV was available, it was stored locally. Global energy storage demand was found up to 60 TWh without grid extensions and 20 TWh with optimized grid extensions in a scenario where solar PV, wind power and concentrated solar power (CSP) comprised 90% of global electricity generation, with wind contributing a 30% share (this represents a mix of technologies where the high end of storage demand was found). In a sensitivity analysis, 40% reduction in investment costs lead to energy reservoirs of 130 TWh and 30 TWh, respectively. Delucchi and Jacobson [25] determined the demand for decentralized electricity storage to be in the range of 2.7 – 11 GWh (measured in battery charge input) in the vehicle to grid (V2G) concept. 3.1.2. Qualitative assessments Energy storage is not mentioned in Energy Watch Group’s [26], Massachusetts Institute of Technology‘s (MIT) [27], BP’s [28] and ExxonMobil’s [29] energy outlooks. However, in BP’s technology outlook [30] RE is put into different perspective. First, it is shown that RE sources cover 75% of technically recoverable primary energy sources in 2050. It is then argued that intermittency of solar and wind could be solved with storage technologies, demand response, flexible generation and increased connectivity, but at the expense of higher costs and lower efficiencies. All in all, it is acknowledged that energy storage represents disruptive technology to the current energy supply. In Statoil’s Renewal scenario [31], constructed to be 2-degree target compatible, solar power capacity is expected to grow to 2500 GW in 2030 and 4500 GW in 2040, and wind power to 1800 GW and 2300 GW, respectively. Solar and wind power would then produce 6000 TWh electricity each in 2040. RE in total would cover 57% of power sector, and energy storage would be one of the solutions to handle intermittency of generation. The World Energy Council (WEC) regards energy storage as a solution to intermittency as well [32]. On a side note, implementing a large PV power plant project in a relatively short period of time might in some cases rule out grid extension and favor local storage [33]. Statoil and the Stockholm Environment Institute (SEI) [34] state that energy storage is needed for achieving higher shares of renewable energy in the system. However, scenario-makers have different conceptions of “high” penetration of renewables. In IIASA’s global energy assessment (GEA) [10] energy storage is identified as a solution for reaching renewable electricity shares over 20 – 50%. In turn, World Wide Fund for Nature (WWF) regards 60% share of variable renewable electricity as a limit after which energy storage, grid enforcements and demand side management are needed. In German Advisory Council’s (WBGU) study [35] a 450 ppm compatible scenario was studied considering strict sustainability constraints, qualitatively stating a need for energy storage in the future. Shell Lens envisions hydrogen infrastructure build-up from 2020 onwards, and about half of the cars using electricity and hydrogen by mid-century [36]. Greenpeace’s report [37] includes an overview of a wide range of storage technologies, and the need of energy storage in a fully renewable energy system is emphasized, but the demand is not quantified in the report. In an updated report [38] the authors state that they implicitly assume that required smart grids, fast expansion of transmission grids, storage and load balancing capacities are implemented. It is expected that synthetic methane produced with renewables will enter a commercial phase between 2015 and 2020. In the Advanced scenario hydrogen is converted to synthetic hydrocarbons, which replace fossil fuels in heavy duty vehicles and air transportation, and between 2040 and 2050 remaining gas consumption in industry and energy sectors is replaced with hydrogen. Table 1. Energy storage in global scenarios. Study (year) IEA WEO Special (2015)
Energy storage assessment Total demand of 400 GW by 2050. Increasing level of variable renewables requires conventional power plants, energy storage and demand response.
Temporal resolution Yearly*
Remarks Renewable share in primary energy grows from 1% (2013) to 5% (2030), excl. hydro and bio. Energy storage could alleviate transmission constraints. Solar and wind power are given an availability factor based on hourly generation and load profiles. *Power generation curve based on hourly data
Type of study Report [21]
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BP Energy Outlook 2035 (2015)
-
1+ years
Intermittency seen as constraint for RE growth
Report [28]
Statoil Energy Perspectives (2015)
Intermittency of solar and wind power is overcome with energy storage, smart-grids and natural gas turbines
1+ years
10% RE (excl. hydro and bio) in primary energy in 2040
Report [31]
Troendle (2014)
Europe 150 TWh (3.8% of the el. demand), Australia 13 TWh (4.9%), South America 45 TWh (4.3%), North America 113.8 TWh (2.2%), New Zealand 2.4 TWh (5.4%), Asia 172 TWh (1.9%), Africa 35.7 TWh (5.6%)
Hourly
100% renewable el. system, Europe 70/30
Dissert. [23]
Plessman et al. (2014)
RPM 1960 TWh, Thermal energy storage 73.6 TWh, Battery 1.5 TWh
Hourly
100% renewable el. system with 2020 cost and 2010 demand basis, 50/50 PV/Wind power ratio
Article [22]
ExxonMobil The Outlook for Energy 2040 (2014)
-
1+ years
Gas-fired power plants seen necessary back-up for wind and solar
Report [29]
MIT Energy and Climate Outlook 2050 (2014)
-
1+ years
Fossil fuels and nuclear account for 91% of primary energy in 2050
Report [27]
IEA-PVPS (2013)
On-grid storage can be faster than grid reinforcement, thus essential for completing a VLS-PV project in time
1+ years
PV and VLS-PV provide 22 – 25% of global primary energy need in 2100. PV capacity 133 TW in 2100, of which 50% is VLS.
Book [33]
Shell New Lens (2013)
H2 infrastructure for storing and transporting energy implemented after 2020
1+ years
Primarily reformed from gas, by 2060 60% of passenger cars use electricity and H2 as fuel
Report [36]
WEC World Energy Scenarios (2013)
Storage seen as solution to intermittency of RE
Seasonal and daynight
26% renewable el. generation in 2050 (symphony scenario, excl. hydro and bio)
Report [32]
Aboumahboub (2012)
Restricted grid scenario: 60 TWh energy storage or 130 TWh in case costs are reduced 40%
Hourly**
Near 100% renewable share in el. sector 2050, 60 – 80% of produced el. inter-regionally transported. Storage can reduce transcontinental transmission capacity from total of 10 TW to 7 TW. **The total year is represented by 6-13 weeks
Dissert. [24]
IIASA GEA (2012)
Storage one solution for accommodating over 20 – 50% renewable el. generation
5 years
30 – 75% share of RE in primary energy by 2050, in some regions over 90%
Report [10]
SEI Global Scenarios (2012)
Storage will be key to achieve high renewable el. penetration
Yearly
28% RE share in primary energy in 2050 (excl. hydro and bio)
Report [34]
PV/Wind power ratio, 10% excess production capacity results in 50% storage reduction
3.2. Energy storage in continental and transcontinental scenarios 3.2.1. Quantitative assessments A 100% renewable electricity system in Europe, Middle East and North Africa (EUMENA) was studied in [40], [41]. In the later publication self-supply constraint was dropped to 80% from 100% used before. In the later study, however, electricity demand in 2050 was raised to 6250 TWh from 4122 TWh. This resulted in doubling the needed storage discharge power to about 1030 GW from 530 GW. Czisch [42] studied a fully renewable system consisting of Europe, NA and parts of Asia connected via HVDC grid. Hydrogen storage need was addressed in a restricted transmission scenario, and the assessment implied that especially Central Europe would need hydrogen storage. In a
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scenario where geothermal power was scaled-up tenfold, required solar thermal and fuel cell capacities were greatly reduced [42]. Minimum generation capacity of PV and storage dispersed over a large geographical region was investigated in [43]. Providing constant demand of 400 GW would require 8 – 35 TW generation capacity of PV and a storage of 8.4 – 9.7 TWh, using ten PV generation sites located in EU27. Widening the geographical region to cover seven sites in EUMENA would require 4.2 – 12.6 TW generation capacity and 6.1 – 8.7 TWh storage, respectively. Grossmann et al. [43] identified significant benefits in terms of reduced generation and storage capacity in case connecting the two hemispheres. Consequently, a Pan-American transmission network was studied later in [44], and required storage was determined to be around 100 TWh. An hourly resolution analysis for the electricity system in South and Central America identified the needed storage for synthetic methane to be around 64 TWh for a fully renewable, HVDC connected system [45]. High renewable contributions for the energy system in Europe have been studied in [46,47,48], in which demand for energy storage is lower due to flexibility provided by the remaining fossil fuels in the system, and fully renewable electricity in [49,50,51]. Costs of electricity are low in [49], in the range of 69 – 83 €/MWh in 2050, whereas in [50] it was projected that in a 100% renewable electricity scenario the levelized cost of electricity rises 5 – 10% compared to baseline (which is on par with the 80% RES scenario assuming CO2 price of 20 – 30 € per ton), resulting in cost of electricity in the range of 85 – 105 €/MWh in 2030. In [51] the importance of a short-term (6h) high-efficient storage was underlined; the required average wind and solar generation in relation to average load demand was reduced from 1.52 to 1.15, and lossless 6h storage combined with 25 TWh low-efficient long-term storage requires an average generation of solar and wind power of 1.03 times the average load. Eurasia was studied in [52], and as in the case of South America [45], very good hydro resources greatly reduced the need for energy storage in a fully renewable electricity system. In both studies, further flexibility was provided by non-energy industry gas demand and demand for desalination. Electricity systems based on a high renewable share in the US have been studied in [53,54]. In addition to a maximum storage capacity of 160 GW, up to 48 GW of demand side management (DSM) was deployed. A fully renewable electricity system for the US was studied in [55], and on par with results described above for Europe, it was found that a slight over-generation is more cost-effective than building more storage capacity. However, it was noted that this excess could be used in covering almost all consumer and commercial heating demand. Furthermore, a close to 100% renewable electricity system in the US in 2030 was found to be at cost parity with today’s fossil based system [55]. Two thirds of the Southeast Asian electricity demand could be met with solar energy, half of which would be indigenous and half imported from Australia [56]. A fully renewable electricity system for Northeast Asia was studied [57] and updated model results can be found in [58]. Overall results confirmed that a transnational HVDC grid plays an important role in a fully renewable electricity system; it enables utilization of best resource sites, decreases required capacity and capital for energy storage and reduces required generation capacities. However, about 80% of the system is still in a distributed and decentralized structure, since only slightly more than 20% is exchanged via the HVDC grid. The study also identified new possible operation methods for storage technologies; batteries were used to charge power-to-gas during night to maximize the stored energy the following day, and in PV dominated regions power-togas was discharged during daytime to charge batteries, which would cover demand at nighttime. 3.2.2. Qualitative assessments The European Renewable Energy Council (EREC) stated that storage technologies are needed to accelerate the deployment of PV across Europe [59]. However, as noted in [53], flexibility can be increased using a broad spectrum of supply and demand side measures: flexible generation capacity, grid storage, demand-side technologies and expansion of transmission infrastructure. Several studies contribute to examining the possibility of solar power imports from MENA to Europe [46,47,48,49,50], and especially CSP is given an important role. However, as Grossmann et al. [43] and Afanasyeva et al. [60] note, rapidly improving economics of PV and storage technologies could make them more economical than CSP. IRENA’s report [61] devoted to the use of renewables in manufacturing states that low- and medium-temperature heat accounts for 45% of industrial process heat use, thus solar thermal systems have a large potential (currently solar thermal plants for industrial process heating cover under 1% of total global demand).
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In [49] it is acknowledged that even though transmission lines can be a crucial element for renewable based electricity supply, enabling geographical balance effect and utilization of the best resource sites, opposed political agendas can restrict full implementation of such transmission grids. It was found in [57] that transnational HVDC power lines substitute short-term storage in particular. Thus, restrictions exposed by political agendas could increase demand for local short-term storage, such as battery storage. In [50] it is noted that when using hydrogen or V2G storage, the cost-optimized generation mix is comprised of onshore and offshore wind. In the case of using centralized storage, generation is more diversified between solar PV, onshore and offshore wind. It is argued that the higher cost for centralized storage leads to higher diversification of electricity generation, especially weighting offshore wind. Table 2. Energy storage in continental and transcontinental scenarios. Study
Energy storage assessment
Temporal resolution
Remarks
Type of study
Barbosa et al. (2016)
Synthetic gas 63.8 TWhth, PHS 0.001 TWh, centralized battery 0.0013 TWh, decentralized battery 0.0041 TWh, CAES 0.008 TWh
Hourly
100% renewable el. system in South and Central America in 2030 (weather year 2005). Area-wide scenario: countries are connected by a HVDC grid
Article [45]
Bogdanov et al. (2016)
Synthetic gas 407.6 TWhth, PHS 0.1 TWh, centralized battery 1.5 TWh, decentralized battery 1.9 TWh
Hourly
100% renewable el. system in Northeast Asia in 2030 (weather year 2005). Area-wide scenario: countries are connected by a HVDC grid
Article [58]
Bussar et al. (2015)
CCGT 550 GW (800 TWh), hydro turbines 190 GW (2.7 TWh), battery 320 GW (1.6 TWh)
Hourly
100% renewable el. system in EUMENA in 2050, 60/40 PV/Wind power ratio, at least 80% self-supply constraint
Conf. proc. [41]
Bogdanov et al. (2015)
Synthetic gas 62.6 TWhth, PHS 0.009 TWh, centralized battery 0.009 TWh, decentralized battery 0 TWh
Hourly
100% renewable el. system in Eurasia in 2030 (weather year 2005). Area-wide scenario: countries are connected by a HVDC grid
Conf. proc. [52]
Grossmann et al. (2014)
US 110 – 129 TWh storage capacity derived from constant demand load of 4.7 TW, North and South America connected 100 – 117 TWh with constant demand of 8.5 TW
Hourly
100% renewable energy system in 2100. PanAmerican network meets combined demand of the two continents (74 750 TWh annually) with same amount of generation capacity needed for isolated North America alone.
Article [44]
Bussar et al. (2014)
H2 320 GW discharge (245 TWh), Pumped hydro 160 GW (2.3 TWh), Battery 50 GW (0.3 TWh)
Hourly
100% renewable el. system in EUMENA in 2050, 60/40 PV/Wind power ratio
Conf. proc. [40]
Mai et al. (2014)
160 GW grid storage (not specified)
Hourly
90% renewable el. system in US in 2050, 20/80 PV/Wind power ratio
Article [53]
Trieb (2013)
Additional 30 GW by 2030. Storage alternative with HVDC links
Hourly
90% renewable el. share in Germany, which has HVDC connection with NA
Report [48]
Grossmann et al. (2013)
EUMENA 56 – 62.4 GWh, Northern and Southern America 14 GWh, China-Mongolia 26.4 GWh, Australia 13.9 GWh, Pan-AsiaAustralia 21 GWh
Hourly
Solar PV based el. system. Results for storage are derived from constant generic demand of 1 GW throughout the year. The emphasis in the study is to investigate effect on required storage with generation located across large geographic areas
Article [43]
Budischak et al. (2013)
H2 58 GW (2.899 TWh) or central batteries 58 GW (0.362 TWh) or grid integrated vehicles 52 GW (0.891 TWh)
Hourly
99.9% renewable el. system in US in 2030
Article [55]
Dii (2012)
118 GW additional balancing power in case no connections between EU-MENA. 59 GW PHS in 2050. CH4 and H2 produced with renewable power seen appropriate for providing the last 5% in a 100% RE system
Hourly
80% renewable el. in EUMENA in 2050 (excl. hydro and bio). Storage addressed implicitly considering power generation in reference and connected scenarios
Report [47]
(Year)
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Scholz (2012)
No transmission: PHS 2.5, CAES 1.6, H2 182 TWh. No transmission restriction: PHS 4.2, CAES 0.2, H2 203 TWh
Hourly
100% renewable power supply in most regions in Europe and NA in 2050, storage input 7.2/ 30% of total power generation in connected/ isolated grids scenarios
Dissert . [49]
NREL (2012)
Cumulative storage capacity of 100 – 152 GW.
Hourly
80% renewable el. in US in 2050. Majority of new storage capacity comes from CAES installations
Report [54]
Blakers et al. (2012)
Southeast Asia: 0.7 TWh storage discharge (50% of daily demand)
Daily
33% of el. demand supplied with indigenous solar, 33% imported from Australia, 33% produced with conventional power
Article [56]
Rasmussen et al. (2012)
Short-term storage (6h) 2.2 TWh and seasonal storage (H2) 25 TWh. Highly efficient shortterm storage significantly reduces needed capacity for variable renewable production
Hourly
100% renewable el. in Europe. Ave. solar and wind power generation is 1.03 times the ave. load. PV/wind ratio 44/56.
Article [51]
ECF (2010)
Additional 125 GW storage capacity (50 TWh). Storage capacity in scenario that transmission lines are substantially restricted
Hourly
100% renewable el. scenario for EU with connection to Northern Africa in 2050 (15% CSP import from NA)
Report [50]
EREC (2010)
Storage capacities needed to accelerate deployment of variable RES
Yearly
96% renewable share in final energy consumption in EU in 2050
Report [59]
Trieb (2006)
6 – 18 h thermal storage in CSP plants, which would provide el. for both base load and balancing power
Hourly
80% renewable el. in Europe in 2050, of which 15% are CSP imports from NA (115 GW HVDC lines from/ to MENA). The remaining fossil fuel capacity is for providing peak demand (+25% reserve).
Report [11]
Czisch (2005)
PHS 28.1 GW, 259 GW fuel cell installed power (729 TWh yearly generation). Geothermal power utilization could reduce fuel cell demand by about 30%, and solar thermal demand by about 65%
3h
100% renewable electricity scenario for Europe, parts of Asia and NA connected with HVDC. Restricted transmission between countries; H2 accounts for 18% of total electricity consumption, and rises up to 60% in areas where hydro power is limited. Origin of H2 not defined.
Dissert . [42]
4. Conclusion Hourly analyses and real weather based cost-optimized simulations imply that no real technical and economic barriers exist in implementing an energy system based on renewable sources. Studies that have high spatial and temporal resolution and take into account the energy demands from the heat and transport sectors are scarce. Integrating heat and transport sectors into high renewable energy modeling would provide further insights on overall system cost-optimization and cost-optimal system operation, due to a higher degree of flexibility in the entire energy system. Further benefits can be reached by the integration of non-energy sectors. For example, desalination and nonenergy industry gas use could provide further flexibility services on the demand side. The demand for energy storage depends on the level of renewable electricity deployment. High renewable electricity shares require various flexibility measures, thus increasing demand for energy storage significantly. Global estimates expect several hundred gigawatts discharge capacity for energy storage on varying timescales. The order of magnitude for global capacity for storing energy ranges from tens of terawatt-hours to over a thousand terawatt-hours, based on studies in which a fully renewable electricity system was investigated. Studies indicate that in regions where a high direct normal irradiation is present, CSP with thermal energy storage can provide solar energy around the clock. However, rapid decline in costs of PV and battery storage technologies could make them more cost competitive in the power sector than CSP on large scale. The potential of low or medium temperature heat provided with CSP for industrial non-energy use remains largely uncharted so far. The body of research has identified continent wide HVDC grids as a key solution for deploying high shares of renewable energy in a cost-efficient manner. Political barriers could restrict the full implementation of such grids, and thus increase the demand for local energy storage. In addition, energy storage can reduce the amount of curtailed electricity generated by RE technologies.
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To conclude, hourly simulations with high spatial resolution are needed to verify the technical feasibility of high RE scenarios. If electricity generation is based on variable renewables, some of the flexibility previously provided by a fuel is lost. The needed flexibility can be derived from energy storage, flexible power generation, weather dependent generation spread over large areas, diversification of energy sources, DSM and from renewable, synthetic fuels. Acknowledgements The authors gratefully acknowledge the public financing of Tekes, the Finnish Funding Agency for Innovation, for the “Neo-Carbon Energy” project under the number 40101/14. The authors would like to thank Michael Child for proofreading.
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ScienceDirect Energy Procedia 99 (2016) 53 – 63
10th International Renewable Energy Storage Conference, IRES 2016, 15-17 March 2016, Düsseldorf, Germany
Energy Storage in Global and Transcontinental Energy Scenarios: A Critical Review Otto Koskinena, Christian Breyera,* a
Lappeenranta University of Technology, Skinnarilankatu 34, Lappeenranta 53850, Finland
Abstract There are a fast growing number of global energy scenarios based on high shares of renewable energy (RE). However, many of them lack comprehensive analyses of energy storage systems. A review of global scenarios reveals that energy storage systems are assessed mainly qualitatively; quantitative assessments of global energy storage demand are scarce. The possible future roles of energy storage systems are plentiful: they can be used in short-term control (e.g. in power grid frequency control), as a mediumterm balance mechanism (to shift daily production to meet demand), as long-term storage (seasonal shift), or to substitute grid extensions. Typically, only power storage is considered, if energy storage is assessed at all. Scenario-makers do not always assess the dynamics and synergies of energy storage systems in the power, heat and mobility sectors. To date, publications of the dynamics between continent-wide renewable energy production, transmission grids and energy storage capacities are not numerous. The existing body of research indicates that transmission lines connecting individual countries are regarded as a key component in enabling RE-based, low-cost energy systems. However, various issues could restrain the implementation of proposed grid connections. These barriers could be overcome by partially substituting energy grid reinforcements with energy storage solutions. Furthermore, less storage related curtailment of renewable energy could lead to improved energy system efficiency and cost. Therefore, energy scenarios that capture quantitatively different configurations of international energy exchange and its influence on regional storage systems are needed. High spatial and temporal resolution energy system models are needed to assess scenarios for high share of renewable energy supply and demand for energy storage. © 2016 2016The TheAuthors. Authors. Published Elsevier © Published by by Elsevier Ltd.Ltd. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of EUROSOLAR - The European Association for Renewable Energy. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of EUROSOLAR - The European Association for Renewable Energy Keywords: storage; energy scenarios; global
* Corresponding author. Tel.: +358-50-443-1929 E-mail address: [email protected]
1876-6102 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of EUROSOLAR - The European Association for Renewable Energy doi:10.1016/j.egypro.2016.10.097
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1. Introduction Climate change, optimal resource use and desire to better understand aspects of large-scale renewable energy (RE) deployment have motivated scenario-makers to explore pathways to and aspects of high RE futures [1]. Substantial growth in RE deployment in recent years undoubtedly has spurred increased attention to high RE scenarios. Over the mid-term, Intended Nationally Determined Contributions (INDCs) can set light on the current ambition level of RE uptake. Cumulative RE supply levels in Brazil, China, the European Union and Indonesia are set to increase from 7980 TWh/year in 2012 to 14,830 TWh/year (86% increase) in 2030 according to a recent report [2] based upon INDCs. Renewable electricity generation in Brazil, India, Mexico and the United States is set to increase from 630 TWh/year in 2012 to 2250 TWh/year (257 % increase) in 2030. The substantial RE growth indicated in INDCs is in line with leading institutional projections of rapid RE deployment in the years to come [3]. Moreover, partly excluded and partly included in INDCs, growing number of subnational and corporate targets show even more stringent greenhouse gas (GHG) reduction and RE deployment goals [4,5,6]. Significant health benefits, job creation and reduced cost of imported fuels have been estimated to result from more ambitious renewable energy deployment [7]. Nomenclature CAES CCGT DSM EUMENA H2 HVDC PHS RE RPM V2G VLS-PV
Compressed Air Energy Storage Combined Cycle Gas Turbine Demand Side Management Europe-Middle-East-North-Africa Hydrogen High Voltage Direct Current Pumped Hydro Storage Renewable Energy Renewable Power Methane Vehicle to Grid Very Large Scale-Photovoltaics
Several studies suggest that on the European level the further integration of electricity transfer capacities would deliver cost savings in the total system. Grid integration is argued to be an economically beneficial measure in achieving long-term energy and climate policy targets: integrating high shares of renewables, increasing competition in the market, thus leading to lower electricity prices, and increasing security of supply. A recent study found the cost savings ranging between 2 – 21% compared to a scenario without grid expansion [8]. In a concept study several opportunities enabled by a global grid were identified: smoothing out electricity supply and demand, minimizing power reserves, reducing storage demand and reducing volatility of electricity prices. Power system security could be on the one hand reduced (reliance on overseas source of energy) and on the other enhanced (relief of congestion) [9]. Thinking broader, current energy systems are already heavily dependent on fuels imported from thousands of kilometers away [10], and a global grid could actually reduce the dependence on overseas energy. Some of the targets above could be at least partly addressed by energy storage as well, thus the research questions of this study arise: Is the role of energy storage assessed in influential global energy scenarios? What is the quantified demand for energy storage in global scenarios? To some extent the issue of building supergrids has already departed the academic circles and been taken on by various initiatives in Europe and applications in Asia; ten years after the ground-breaking TRANS-CSP study by the DLR [11], industry rooted initiative Dii [12] and non-profit civil society initiative Desertec Foundation [13] are carrying on the concept of importing solar power from North Africa to Europe. The North Sea grid project co-funded by European Union (EU) is yet another example [14]. In Asia, the State Grid Corporation of China is poised to construct about 160 GW of high voltage connections by 2016 (116 GW had been constructed by the end of 2014) [15]. According to the Global Energy Storage Database [16], the grid connected energy storage capacity installed in China amounted to 33.3 GW in 2015, mainly based on pumped hydro storage.
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2. Methodology Global and transcontinental energy scenarios were chosen for this meta-analysis. The latter include studies having geographical scopes of Europe, Middle-East, North Africa, North and South America and South-East Asia. We review quantitative and qualitative assessments of energy storage in the scenarios. In a qualitative analysis we look for existence of storage technologies in the scenarios, storage technology descriptions, discussions of the relevance of energy storage in the scenarios and different roles that energy storage could have. In a quantitative analysis we look for energy storage capacities in terms of power and energy and relative shares of energy storage on the demand side. The results of the analysis for global scenarios are presented in Table 1 and for continental and transcontinental scenarios in Table 2. 3. Review of energy scenarios Comparisons of various energy scenarios provide wide viewpoints on alternative energy systems. Such metaanalysis with global scope had been done earlier in [1,17]. The authors of these two review studies have polarized conclusions: the previous shows that renewable energy sources can play a large role in future power systems, and the latter summarizes that scenarios for renewable energy dominance in the world’s energy supply by mid-century assume unrealistic technical potentials and implementation times. A review of International Energy Agency’s (IEA) past World Energy Outlooks (WEO) suggests that assuming linear growth of wind power and solar PV leads to systematic underestimation of the deployment of these technologies [3]. Historically, the more progressive projections made by Greenpeace and Bloomberg New Energy Finance (BNEF) have more accurately captured the real RE technology deployment compared to the conservative IEA outlooks [18]. It can be argued that energy scenarios are not meant to be predictions of the future; they can be used as a tool to evaluate alternative outcomes and their sensitivities. Despite this, in a review [19] by Citigroup it was found that fossil fuel industry businesses use IEA’s New Policy Scenarios as forecasts to base their strategies on. Citigroup analysts suggest that investors should also take into account IEA’s 450, which is more skeptical on fossil fuels and a bit more optimistic on RE, or compatible scenarios. Furthermore, it should be noted that when scenario-makers create scenarios, in effect they limit the possibility space (what is perceived as possible or credible) within chosen boundaries. Our view is that energy scenarios have an influence on people’s mindsets, including researchers, investors, politicians, industry representatives, NGOs and general public, and can set the frame in which policies are made and actions are based upon. In essence, influential energy scenarios could have a self-fulfilling mechanism on different levels in the society. The spectrum of different scenario types is wide, thus the purposes and applications differ from each other, and a useful decision-makers’ guideline can be found in [20]. 3.1. Energy storage in global energy scenarios 3.1.1. Quantitative assessments The IEA notes in its energy and climate change special issue [21] that global installations of energy storage could amount to 400 GW by 2050. It is stated that over the mid-term, energy storage can alleviate transmission constraints. In contrast, in a study where a global decentralized renewable energy system was investigated, using load demand for the year 2010 and cost basis of the year 2020, energy storage demand for batteries only was found to be 1500 GWh [22]. Assuming an energy to power ratio of six, this would represent 250 GW of battery capacity demand over the short term in the over 160 countries assessed in the study. Optimal mixes of solar and wind power generation were investigated in [23]. In addition, minimum storage capacity was determined with different amounts of installed capacity of solar and wind. It was found that while the seasonal storage capacity has to be two orders of magnitude larger than required capacity of the storage for daily cycle, the sum of stored energy during one year is almost equal for long and short term storage. In a closer look for Europe, long term storage amounted to 146.2 TWh and short term 4.1 TWh. The latter would represent capacity of 683 GW applying the energy to power ratio above. Note that in this scenario 30% of power capacity is wind and 70% PV power, and they are used to supply annual demand of 3956 TWh (weather year 2009). Another dissertation [24] investigated the dynamics of storage and transmission. It was found that if wind power was available, local excess was transferred
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inter-regionally to meet demand, whereas if excess solar PV was available, it was stored locally. Global energy storage demand was found up to 60 TWh without grid extensions and 20 TWh with optimized grid extensions in a scenario where solar PV, wind power and concentrated solar power (CSP) comprised 90% of global electricity generation, with wind contributing a 30% share (this represents a mix of technologies where the high end of storage demand was found). In a sensitivity analysis, 40% reduction in investment costs lead to energy reservoirs of 130 TWh and 30 TWh, respectively. Delucchi and Jacobson [25] determined the demand for decentralized electricity storage to be in the range of 2.7 – 11 GWh (measured in battery charge input) in the vehicle to grid (V2G) concept. 3.1.2. Qualitative assessments Energy storage is not mentioned in Energy Watch Group’s [26], Massachusetts Institute of Technology‘s (MIT) [27], BP’s [28] and ExxonMobil’s [29] energy outlooks. However, in BP’s technology outlook [30] RE is put into different perspective. First, it is shown that RE sources cover 75% of technically recoverable primary energy sources in 2050. It is then argued that intermittency of solar and wind could be solved with storage technologies, demand response, flexible generation and increased connectivity, but at the expense of higher costs and lower efficiencies. All in all, it is acknowledged that energy storage represents disruptive technology to the current energy supply. In Statoil’s Renewal scenario [31], constructed to be 2-degree target compatible, solar power capacity is expected to grow to 2500 GW in 2030 and 4500 GW in 2040, and wind power to 1800 GW and 2300 GW, respectively. Solar and wind power would then produce 6000 TWh electricity each in 2040. RE in total would cover 57% of power sector, and energy storage would be one of the solutions to handle intermittency of generation. The World Energy Council (WEC) regards energy storage as a solution to intermittency as well [32]. On a side note, implementing a large PV power plant project in a relatively short period of time might in some cases rule out grid extension and favor local storage [33]. Statoil and the Stockholm Environment Institute (SEI) [34] state that energy storage is needed for achieving higher shares of renewable energy in the system. However, scenario-makers have different conceptions of “high” penetration of renewables. In IIASA’s global energy assessment (GEA) [10] energy storage is identified as a solution for reaching renewable electricity shares over 20 – 50%. In turn, World Wide Fund for Nature (WWF) regards 60% share of variable renewable electricity as a limit after which energy storage, grid enforcements and demand side management are needed. In German Advisory Council’s (WBGU) study [35] a 450 ppm compatible scenario was studied considering strict sustainability constraints, qualitatively stating a need for energy storage in the future. Shell Lens envisions hydrogen infrastructure build-up from 2020 onwards, and about half of the cars using electricity and hydrogen by mid-century [36]. Greenpeace’s report [37] includes an overview of a wide range of storage technologies, and the need of energy storage in a fully renewable energy system is emphasized, but the demand is not quantified in the report. In an updated report [38] the authors state that they implicitly assume that required smart grids, fast expansion of transmission grids, storage and load balancing capacities are implemented. It is expected that synthetic methane produced with renewables will enter a commercial phase between 2015 and 2020. In the Advanced scenario hydrogen is converted to synthetic hydrocarbons, which replace fossil fuels in heavy duty vehicles and air transportation, and between 2040 and 2050 remaining gas consumption in industry and energy sectors is replaced with hydrogen. Table 1. Energy storage in global scenarios. Study (year) IEA WEO Special (2015)
Energy storage assessment Total demand of 400 GW by 2050. Increasing level of variable renewables requires conventional power plants, energy storage and demand response.
Temporal resolution Yearly*
Remarks Renewable share in primary energy grows from 1% (2013) to 5% (2030), excl. hydro and bio. Energy storage could alleviate transmission constraints. Solar and wind power are given an availability factor based on hourly generation and load profiles. *Power generation curve based on hourly data
Type of study Report [21]
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BP Energy Outlook 2035 (2015)
-
1+ years
Intermittency seen as constraint for RE growth
Report [28]
Statoil Energy Perspectives (2015)
Intermittency of solar and wind power is overcome with energy storage, smart-grids and natural gas turbines
1+ years
10% RE (excl. hydro and bio) in primary energy in 2040
Report [31]
Troendle (2014)
Europe 150 TWh (3.8% of the el. demand), Australia 13 TWh (4.9%), South America 45 TWh (4.3%), North America 113.8 TWh (2.2%), New Zealand 2.4 TWh (5.4%), Asia 172 TWh (1.9%), Africa 35.7 TWh (5.6%)
Hourly
100% renewable el. system, Europe 70/30
Dissert. [23]
Plessman et al. (2014)
RPM 1960 TWh, Thermal energy storage 73.6 TWh, Battery 1.5 TWh
Hourly
100% renewable el. system with 2020 cost and 2010 demand basis, 50/50 PV/Wind power ratio
Article [22]
ExxonMobil The Outlook for Energy 2040 (2014)
-
1+ years
Gas-fired power plants seen necessary back-up for wind and solar
Report [29]
MIT Energy and Climate Outlook 2050 (2014)
-
1+ years
Fossil fuels and nuclear account for 91% of primary energy in 2050
Report [27]
IEA-PVPS (2013)
On-grid storage can be faster than grid reinforcement, thus essential for completing a VLS-PV project in time
1+ years
PV and VLS-PV provide 22 – 25% of global primary energy need in 2100. PV capacity 133 TW in 2100, of which 50% is VLS.
Book [33]
Shell New Lens (2013)
H2 infrastructure for storing and transporting energy implemented after 2020
1+ years
Primarily reformed from gas, by 2060 60% of passenger cars use electricity and H2 as fuel
Report [36]
WEC World Energy Scenarios (2013)
Storage seen as solution to intermittency of RE
Seasonal and daynight
26% renewable el. generation in 2050 (symphony scenario, excl. hydro and bio)
Report [32]
Aboumahboub (2012)
Restricted grid scenario: 60 TWh energy storage or 130 TWh in case costs are reduced 40%
Hourly**
Near 100% renewable share in el. sector 2050, 60 – 80% of produced el. inter-regionally transported. Storage can reduce transcontinental transmission capacity from total of 10 TW to 7 TW. **The total year is represented by 6-13 weeks
Dissert. [24]
IIASA GEA (2012)
Storage one solution for accommodating over 20 – 50% renewable el. generation
5 years
30 – 75% share of RE in primary energy by 2050, in some regions over 90%
Report [10]
SEI Global Scenarios (2012)
Storage will be key to achieve high renewable el. penetration
Yearly
28% RE share in primary energy in 2050 (excl. hydro and bio)
Report [34]
PV/Wind power ratio, 10% excess production capacity results in 50% storage reduction
3.2. Energy storage in continental and transcontinental scenarios 3.2.1. Quantitative assessments A 100% renewable electricity system in Europe, Middle East and North Africa (EUMENA) was studied in [40], [41]. In the later publication self-supply constraint was dropped to 80% from 100% used before. In the later study, however, electricity demand in 2050 was raised to 6250 TWh from 4122 TWh. This resulted in doubling the needed storage discharge power to about 1030 GW from 530 GW. Czisch [42] studied a fully renewable system consisting of Europe, NA and parts of Asia connected via HVDC grid. Hydrogen storage need was addressed in a restricted transmission scenario, and the assessment implied that especially Central Europe would need hydrogen storage. In a
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scenario where geothermal power was scaled-up tenfold, required solar thermal and fuel cell capacities were greatly reduced [42]. Minimum generation capacity of PV and storage dispersed over a large geographical region was investigated in [43]. Providing constant demand of 400 GW would require 8 – 35 TW generation capacity of PV and a storage of 8.4 – 9.7 TWh, using ten PV generation sites located in EU27. Widening the geographical region to cover seven sites in EUMENA would require 4.2 – 12.6 TW generation capacity and 6.1 – 8.7 TWh storage, respectively. Grossmann et al. [43] identified significant benefits in terms of reduced generation and storage capacity in case connecting the two hemispheres. Consequently, a Pan-American transmission network was studied later in [44], and required storage was determined to be around 100 TWh. An hourly resolution analysis for the electricity system in South and Central America identified the needed storage for synthetic methane to be around 64 TWh for a fully renewable, HVDC connected system [45]. High renewable contributions for the energy system in Europe have been studied in [46,47,48], in which demand for energy storage is lower due to flexibility provided by the remaining fossil fuels in the system, and fully renewable electricity in [49,50,51]. Costs of electricity are low in [49], in the range of 69 – 83 €/MWh in 2050, whereas in [50] it was projected that in a 100% renewable electricity scenario the levelized cost of electricity rises 5 – 10% compared to baseline (which is on par with the 80% RES scenario assuming CO2 price of 20 – 30 € per ton), resulting in cost of electricity in the range of 85 – 105 €/MWh in 2030. In [51] the importance of a short-term (6h) high-efficient storage was underlined; the required average wind and solar generation in relation to average load demand was reduced from 1.52 to 1.15, and lossless 6h storage combined with 25 TWh low-efficient long-term storage requires an average generation of solar and wind power of 1.03 times the average load. Eurasia was studied in [52], and as in the case of South America [45], very good hydro resources greatly reduced the need for energy storage in a fully renewable electricity system. In both studies, further flexibility was provided by non-energy industry gas demand and demand for desalination. Electricity systems based on a high renewable share in the US have been studied in [53,54]. In addition to a maximum storage capacity of 160 GW, up to 48 GW of demand side management (DSM) was deployed. A fully renewable electricity system for the US was studied in [55], and on par with results described above for Europe, it was found that a slight over-generation is more cost-effective than building more storage capacity. However, it was noted that this excess could be used in covering almost all consumer and commercial heating demand. Furthermore, a close to 100% renewable electricity system in the US in 2030 was found to be at cost parity with today’s fossil based system [55]. Two thirds of the Southeast Asian electricity demand could be met with solar energy, half of which would be indigenous and half imported from Australia [56]. A fully renewable electricity system for Northeast Asia was studied [57] and updated model results can be found in [58]. Overall results confirmed that a transnational HVDC grid plays an important role in a fully renewable electricity system; it enables utilization of best resource sites, decreases required capacity and capital for energy storage and reduces required generation capacities. However, about 80% of the system is still in a distributed and decentralized structure, since only slightly more than 20% is exchanged via the HVDC grid. The study also identified new possible operation methods for storage technologies; batteries were used to charge power-to-gas during night to maximize the stored energy the following day, and in PV dominated regions power-togas was discharged during daytime to charge batteries, which would cover demand at nighttime. 3.2.2. Qualitative assessments The European Renewable Energy Council (EREC) stated that storage technologies are needed to accelerate the deployment of PV across Europe [59]. However, as noted in [53], flexibility can be increased using a broad spectrum of supply and demand side measures: flexible generation capacity, grid storage, demand-side technologies and expansion of transmission infrastructure. Several studies contribute to examining the possibility of solar power imports from MENA to Europe [46,47,48,49,50], and especially CSP is given an important role. However, as Grossmann et al. [43] and Afanasyeva et al. [60] note, rapidly improving economics of PV and storage technologies could make them more economical than CSP. IRENA’s report [61] devoted to the use of renewables in manufacturing states that low- and medium-temperature heat accounts for 45% of industrial process heat use, thus solar thermal systems have a large potential (currently solar thermal plants for industrial process heating cover under 1% of total global demand).
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In [49] it is acknowledged that even though transmission lines can be a crucial element for renewable based electricity supply, enabling geographical balance effect and utilization of the best resource sites, opposed political agendas can restrict full implementation of such transmission grids. It was found in [57] that transnational HVDC power lines substitute short-term storage in particular. Thus, restrictions exposed by political agendas could increase demand for local short-term storage, such as battery storage. In [50] it is noted that when using hydrogen or V2G storage, the cost-optimized generation mix is comprised of onshore and offshore wind. In the case of using centralized storage, generation is more diversified between solar PV, onshore and offshore wind. It is argued that the higher cost for centralized storage leads to higher diversification of electricity generation, especially weighting offshore wind. Table 2. Energy storage in continental and transcontinental scenarios. Study
Energy storage assessment
Temporal resolution
Remarks
Type of study
Barbosa et al. (2016)
Synthetic gas 63.8 TWhth, PHS 0.001 TWh, centralized battery 0.0013 TWh, decentralized battery 0.0041 TWh, CAES 0.008 TWh
Hourly
100% renewable el. system in South and Central America in 2030 (weather year 2005). Area-wide scenario: countries are connected by a HVDC grid
Article [45]
Bogdanov et al. (2016)
Synthetic gas 407.6 TWhth, PHS 0.1 TWh, centralized battery 1.5 TWh, decentralized battery 1.9 TWh
Hourly
100% renewable el. system in Northeast Asia in 2030 (weather year 2005). Area-wide scenario: countries are connected by a HVDC grid
Article [58]
Bussar et al. (2015)
CCGT 550 GW (800 TWh), hydro turbines 190 GW (2.7 TWh), battery 320 GW (1.6 TWh)
Hourly
100% renewable el. system in EUMENA in 2050, 60/40 PV/Wind power ratio, at least 80% self-supply constraint
Conf. proc. [41]
Bogdanov et al. (2015)
Synthetic gas 62.6 TWhth, PHS 0.009 TWh, centralized battery 0.009 TWh, decentralized battery 0 TWh
Hourly
100% renewable el. system in Eurasia in 2030 (weather year 2005). Area-wide scenario: countries are connected by a HVDC grid
Conf. proc. [52]
Grossmann et al. (2014)
US 110 – 129 TWh storage capacity derived from constant demand load of 4.7 TW, North and South America connected 100 – 117 TWh with constant demand of 8.5 TW
Hourly
100% renewable energy system in 2100. PanAmerican network meets combined demand of the two continents (74 750 TWh annually) with same amount of generation capacity needed for isolated North America alone.
Article [44]
Bussar et al. (2014)
H2 320 GW discharge (245 TWh), Pumped hydro 160 GW (2.3 TWh), Battery 50 GW (0.3 TWh)
Hourly
100% renewable el. system in EUMENA in 2050, 60/40 PV/Wind power ratio
Conf. proc. [40]
Mai et al. (2014)
160 GW grid storage (not specified)
Hourly
90% renewable el. system in US in 2050, 20/80 PV/Wind power ratio
Article [53]
Trieb (2013)
Additional 30 GW by 2030. Storage alternative with HVDC links
Hourly
90% renewable el. share in Germany, which has HVDC connection with NA
Report [48]
Grossmann et al. (2013)
EUMENA 56 – 62.4 GWh, Northern and Southern America 14 GWh, China-Mongolia 26.4 GWh, Australia 13.9 GWh, Pan-AsiaAustralia 21 GWh
Hourly
Solar PV based el. system. Results for storage are derived from constant generic demand of 1 GW throughout the year. The emphasis in the study is to investigate effect on required storage with generation located across large geographic areas
Article [43]
Budischak et al. (2013)
H2 58 GW (2.899 TWh) or central batteries 58 GW (0.362 TWh) or grid integrated vehicles 52 GW (0.891 TWh)
Hourly
99.9% renewable el. system in US in 2030
Article [55]
Dii (2012)
118 GW additional balancing power in case no connections between EU-MENA. 59 GW PHS in 2050. CH4 and H2 produced with renewable power seen appropriate for providing the last 5% in a 100% RE system
Hourly
80% renewable el. in EUMENA in 2050 (excl. hydro and bio). Storage addressed implicitly considering power generation in reference and connected scenarios
Report [47]
(Year)
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Otto Koskinen and Christian Breyer / Energy Procedia 99 (2016) 53 – 63
Scholz (2012)
No transmission: PHS 2.5, CAES 1.6, H2 182 TWh. No transmission restriction: PHS 4.2, CAES 0.2, H2 203 TWh
Hourly
100% renewable power supply in most regions in Europe and NA in 2050, storage input 7.2/ 30% of total power generation in connected/ isolated grids scenarios
Dissert . [49]
NREL (2012)
Cumulative storage capacity of 100 – 152 GW.
Hourly
80% renewable el. in US in 2050. Majority of new storage capacity comes from CAES installations
Report [54]
Blakers et al. (2012)
Southeast Asia: 0.7 TWh storage discharge (50% of daily demand)
Daily
33% of el. demand supplied with indigenous solar, 33% imported from Australia, 33% produced with conventional power
Article [56]
Rasmussen et al. (2012)
Short-term storage (6h) 2.2 TWh and seasonal storage (H2) 25 TWh. Highly efficient shortterm storage significantly reduces needed capacity for variable renewable production
Hourly
100% renewable el. in Europe. Ave. solar and wind power generation is 1.03 times the ave. load. PV/wind ratio 44/56.
Article [51]
ECF (2010)
Additional 125 GW storage capacity (50 TWh). Storage capacity in scenario that transmission lines are substantially restricted
Hourly
100% renewable el. scenario for EU with connection to Northern Africa in 2050 (15% CSP import from NA)
Report [50]
EREC (2010)
Storage capacities needed to accelerate deployment of variable RES
Yearly
96% renewable share in final energy consumption in EU in 2050
Report [59]
Trieb (2006)
6 – 18 h thermal storage in CSP plants, which would provide el. for both base load and balancing power
Hourly
80% renewable el. in Europe in 2050, of which 15% are CSP imports from NA (115 GW HVDC lines from/ to MENA). The remaining fossil fuel capacity is for providing peak demand (+25% reserve).
Report [11]
Czisch (2005)
PHS 28.1 GW, 259 GW fuel cell installed power (729 TWh yearly generation). Geothermal power utilization could reduce fuel cell demand by about 30%, and solar thermal demand by about 65%
3h
100% renewable electricity scenario for Europe, parts of Asia and NA connected with HVDC. Restricted transmission between countries; H2 accounts for 18% of total electricity consumption, and rises up to 60% in areas where hydro power is limited. Origin of H2 not defined.
Dissert . [42]
4. Conclusion Hourly analyses and real weather based cost-optimized simulations imply that no real technical and economic barriers exist in implementing an energy system based on renewable sources. Studies that have high spatial and temporal resolution and take into account the energy demands from the heat and transport sectors are scarce. Integrating heat and transport sectors into high renewable energy modeling would provide further insights on overall system cost-optimization and cost-optimal system operation, due to a higher degree of flexibility in the entire energy system. Further benefits can be reached by the integration of non-energy sectors. For example, desalination and nonenergy industry gas use could provide further flexibility services on the demand side. The demand for energy storage depends on the level of renewable electricity deployment. High renewable electricity shares require various flexibility measures, thus increasing demand for energy storage significantly. Global estimates expect several hundred gigawatts discharge capacity for energy storage on varying timescales. The order of magnitude for global capacity for storing energy ranges from tens of terawatt-hours to over a thousand terawatt-hours, based on studies in which a fully renewable electricity system was investigated. Studies indicate that in regions where a high direct normal irradiation is present, CSP with thermal energy storage can provide solar energy around the clock. However, rapid decline in costs of PV and battery storage technologies could make them more cost competitive in the power sector than CSP on large scale. The potential of low or medium temperature heat provided with CSP for industrial non-energy use remains largely uncharted so far. The body of research has identified continent wide HVDC grids as a key solution for deploying high shares of renewable energy in a cost-efficient manner. Political barriers could restrict the full implementation of such grids, and thus increase the demand for local energy storage. In addition, energy storage can reduce the amount of curtailed electricity generated by RE technologies.
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To conclude, hourly simulations with high spatial resolution are needed to verify the technical feasibility of high RE scenarios. If electricity generation is based on variable renewables, some of the flexibility previously provided by a fuel is lost. The needed flexibility can be derived from energy storage, flexible power generation, weather dependent generation spread over large areas, diversification of energy sources, DSM and from renewable, synthetic fuels. Acknowledgements The authors gratefully acknowledge the public financing of Tekes, the Finnish Funding Agency for Innovation, for the “Neo-Carbon Energy” project under the number 40101/14. The authors would like to thank Michael Child for proofreading.
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