IMPACT OF BATTERY AND WATER STORAGE ON THE TRANSITION TO AN INTEGRATED 100% RENEWABLE ENERGY POWER SYSTEM FOR SAUDI ARABIA Upeksha Caldera and Christian Breyer Lappeenranta University of Technology E-mail:
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Motivation & Purpose of Work
Main Objectives
Saudi Arabia can transition to a 100% renewable energy (RE) power sector from the current fossil-based power sector by 2050, optimised through the integration of the power and desalination sectors [1]. The system LCOE is estimated to be 38 €/MWh. Single-axis tracking photovoltaics (PV) dominate the power sector contributing to 77% of the total installed capacities. Battery storage contributes up to 48% of the total electricity demand. The dominance of PV and supporting battery storage is attributed to the steep reduction in capital costs of the technologies. In the study, desalination plants offer limited flexibility to the power sector, reducing the need for battery and power-to-gas storage. Saudi Arabia is the world’s largest producer of desalinated water and desalination will remain vital to the country’s future water supply. In addition, the Saudi government has called for an increase in strategic water storage from 0.4 days to 3 days by 2020. Motivated by the increasing demand for water storage and transition towards 100% RE power systems, this study poses the following question: How do the technical and financial parameters of battery and water storage influence the least cost transition path to a 100% RE based power system in Saudi Arabia?
• To understand the interplay of battery storage, desalination plants and water storage that will enable the least cost transition pathway to a 100% RE based power sector. This study is done for Saudi Arabia. Methodology
Power Sector Transition (2015 - 2050) Fig. 2 Top: Variation in levelised cost of electricity (LCOE) during the energy transition. The LCOE decreases from 129 €/MWh in 2015 to 35 €/MWh in 2050. Saudi Arabia achieves a 100% RE system by 2040 with an LCOE of 43 €/MWh.
Fig. 2 Bottom: Installed capacities of different power plants required for the energy transition. Single-axis tracking PV accounts for 408 GW out of the total power plant capacity of 622 GW. Battery storage provides a total output of 413 TWhel that accounts for 44% of the electricity demand.
Results (Impacts of SWRO Capex)
Fig. 4 Top: Variation of SWRO FLH with the SWRO Capex for years 2030 and 2050 Bottom: Variation of battery output with the SWRO Capex for year 2030 and 2050. Expected SWRO capex are 725 and 415 €/(m3∙day) for 2030 and 2050 respectively. The battery capex are 150 and 75 €/kWh for 2030 and 2050 respectively. The decrease in SWRO capex has less impact than in 2030.
LUT Energy Model
• The energy transition from the current fossil based power system in Saudi Arabia to a 100% RE based power system is found. In addition to the power and seawater reverse osmosis (SWRO) desalination sector discussed in [1], the current study accounts for multiple effect distillation (MED) desalination capacities and non-energetic industrial gas demand sectors of Saudi Arabia [2]. • The LUT energy model, illustrated in Fig.1, is used to identify the optimal power system for the transition from 2015 – 2050, in 5 year time steps. • A sensitivity analysis is done, by varying SWRO capex and re-running the transition, to understand the relationship between battery and water storage.
Input data used • • • • • • • • • •
historical weather data for: solar irradiation, wind speed and precipitation available sustainable resources for biomass and geothermal energy potential of areas with geologies favorable to A-CAES load data for Saudi Arabia seawater desalination demand from 2015 up to 2050 installed power plant and seawater desalination capacities by 2015 efficiency/yield characteristics of RE plants and seawater desalination efficiency of energy conversion processes capex, opex, lifetime for all energy resources min and max capacity limits for all RE resources
Fig. 1: Schematic composition of the LUT energy model including energy resources, conversion technologies, storage options, major end-use categories and all energy sectors [3]. The model determines the optimal combination of the components that meets the electricity demand of every hour from 2015 to 2050, in 5-year time steps.
Desalination Sector Transition (2015 - 2050) Results (2030 Sensitivity Analysis) Fig. 3 Top: Water desalination capacities required to meet the desalination demand from 2015 to 2050. SWRO desalination is the preferred technology due to the low electricity consumption. By 2050, there is 58,718,000 m3/day of SWRO plants and 214,100 m3 of water storage. The water storage accounts for 0.4% of the daily desalination demand. Fig. 3 Bottom: The variation in the water storage for 2050. The water storage fluctuates on a daily basis, although not with large variation. The full load hours (FLH) of the SWRO desalination plants is estimated to be 8745 hours, which is baseload operation.
Table 1. Key observations for the transition year 2030 when SWRO capex is reduced (WACC assumed is 7%)
Key insights • As the SWRO capex decreases, the water storage increases and full load hours (FLH) of the desalination plants decrease • Battery output decreases as the water storage increases. However, the decrease is 5.3% when SWRO capex is halved. Resulting annualised system cost only decreases by 2.5%
Discussion • The decrease in SWRO capex enables the SWRO plants to be run at lower FLH while maintaining the water production costs • When there is excess energy, it may be more economical to store the excess as water and utilize the water when there is not enough renewable energy in the system. This in turn leads to a decrease in the requirement for battery storage as illustrated in Table 1. • The parameters in Table 1 displayed similar behavior in 2050. However, when 2050 SWRO capex is halved, the decrease in battery storage output is 0.4% and the annualised total system cost is 2.4%. • The results indicate that the cost of SWRO plants have to reduce substantially for the plants to operate in a flexible manner. This maybe attributed to the relatively larger SWRO capex than battery storage. • Fig 4 illustrates that the decrease in FLH of the SWRO plants and battery output is more significant in 2030 than in 2050. When the SWRO capex was halved in 2030, the battery storage output was reduced by 5.3%. In contrast, in 2050, the battery storage output was reduced by 0.4%. • The lower impact of the reducing the SWRO capex in 2050 can be explained by the relatively steeper decrease in capex of battery storage and single-axis tracking PV between 2030 and 2050. It is more cost effective to keep the SWRO plants at higher FLH and implement more battery storage.
Conclusion • A least cost pathway for Saudi Arabia to achieve a 100% renewable energy system through the integration of the power, desalination and non-energetic industrial gas sectors is presented. • Reduction in SWRO capex enables desalination plants to run on lower FLH, enabling an increase in water storage and therefore a decrease in battery storage output. This leads to a decrease in the annualised system costs of the transition. • However, the SWRO capex has to decrease sharply if there is to be a significant impact on the flexibility of the power system. It is more lucrative to have PV and battery storage rather than run capex-intensive SWRO plants at lower FLH. • A drastic decrease in capex by about 50% (which is not foreseeable) by 2050 would lead to a reduction of 2.5% in the total annualized energy system cost. 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 first author would like to thank Reiner Lemoine-Foundation for the valuable scholarship.
References [1] Caldera U, Bogdanov D, Afanasyeva S, Breyer Ch,2016, Integration of reverse osmosis seawater desalination in the power sector, based on PV and wind energy, for the Kingdom of Saudi Arabia, 32nd European Photovoltaic Solar Energy Conference, Munich, June 20 – 24, http://bit.ly/2iVKP97 [2] Caldera U, Bogdanov D, Afanasyeva S, Breyer C, 2017, Role of seawater desalination in the management of an integrated water and 100% renewable energy based power sector in Saudi Arabia, submitted [3] Bogdanov D. and Breyer Ch., 2016. North-East Asian Super Grid for 100% Renewable Energy supply: Optimal mix of energy technologies for electricity, gas and heat supply options, Energy Conversion and Management, 112, 176-190.
