Energy storage in Spain: Forecasting electricity excess and assessment of power-to-gas potential up to 2050

Innovative technologies and strategies to decarbonize electricity generation, transport, and heat supply sector are key factors to achieve the global climate targets set by international organizations. One of these strategies implies a significant increase of the share of renewable electricity in the energy mix. Given the intermittent behaviour of renewable energy sources (RES), a detailed assessment of future energy scenarios is required to estimate the potential surplus in electricity production. To facilitate the penetration of renewable energy sources up to significant shares, massive long-term electricity storage technologies must be considered. Among these technologies, power-to-gas (PtG) systems may foster the fossil fuels switch by providing storage of surplus renewable electricity in the form of hydrogen or synthetic natural gas. Thus, this energy carrier could be reconverted to electrical power to cover peak demand periods. In this work, a study of the prospective Spanish scenario is presented and the potential of PtG technology is assessed in terms of expected renewable surplus. We found that the annual electricity surplus for 2050 might vary between 1.4 TWh and 13.5 TWh, and the required PtG capacity would be in the range 7.0–19.5 GW, depending on the renewable production pattern and the increment of demand

Operation maps in calcium looping thermochemical energy storage for concentrating solar power plants

Calcium Looping (CaL) process used as thermochemical energy storage system in concentrating solar plants has been extensively investigated in the last decade and the first large-scale pilot plants are now under construction. Existing research focuses on improving global efficiencies under steady-state and single modes of operation: energy storage or energy retrieval. However, TCES systems will operate under different operation points to adapt the load of its reactors to the solar availability and the energy demand from the power cycle. A thorough analysis of the operation modes provides an extremely large number of potential situations to operate the system. In this study, operation maps which maximize thermal energy availability and energy storage efficiency are defined. Furthermore, a novel approach for the management of partially carbonated solids is examined to reduce the circulation of inert material in the system based on preliminary experimental results which allows for a partial separation of carbonated solids. Two threshold scenarios are analysed: (i) no solids separation as considered in most CaL TCES studies and (ii) ideal total solids separation. The aims of this work are to set methodological criteria to define the optimal operation map and to assess the effect of partially carbonated solids separation on the energy penalties and equipment size. The inclusion of a solid separation stage leads to a maximum increase of energy storage efficiency of 26 % and a size reduction between 53 and 74 % of those heat exchangers affected by solids streams

Optimized Ca-looping thermochemical energy storage under dynamic operation for concentrated solar power

The massive deployment of renewable energy sources and carbon capture technologies are required to achieve net zero emissions target by 2050. Calcium Looping (CaL) is a promising Thermochemical Energy Storage (TCES) system which improves the dispatchability of Concentrating Solar Power (CSP) plants. CaL TCES configurations found in literature focus on a steady-state analysis of thermal-to-electric efficiency of the CSP plants. In this work, the operation of the CaL TCES system for a CSP plant is economically optimized taking into account the seasonal and daily variations of solar resource and electricity prices. The defined methodology determines the operating performance of the CaL TCES which maximize the economic incomes of the CSP and the daily profiles of energy production and storage for representative days of the different seasons/periods of the year. Results show that it is possible to obtain good economic results and operate the CSP + storage for a daily maximization of incomes. Obtained results are also useful for the final design of the system and for the definition of the size required for the storage equipment

Power to gas-oxyfuel boiler hybrid systems

One of the main future energy challenges is the management of electrical supply and demand, mainly motivated by the increase of share renewable energy in electricity mix. Thus, energy storage represents a crucial line of research and innovative solutions are currently being proposed. Power to Gas is a technology which stores excess of electrical energy in form of synthetic natural gas through the methanation of hydrogen produced by electrolysis. Methanation requires a source of CO2 which could be provided from the flue gas of an oxyfuel boiler. A further advantage of this hybridization comes from the supply of the oxygen generated by electrolysis to the oxyfuel combustion. In this study the concept is simulated using Aspen Plus® software and the performance of the combined system is analysed through the definition of a size ratio, ¿¿¿¿, that relates the flow of renewable hydrogen produced in electrolyser and the thermal output of the boiler. This variable has allowed defining different ranges of operation for a PtG- oxycombustion hybridized plant. Thus, for ¿¿¿¿ of 1.33, the air separation unit required as an auxiliary element for the oxyfuel boiler becomes unnecessary while if this ratio is increased up to 2.29, flue gas is completely consumed in the methanation plant and converted to synthetic natural gas

Power to gas-electrochemical industry hybrid systems: A case study

Several researchers have proposed in literature different Power to Gas (PtG) hybridizations to improve the efficiency of this energy storage technology. Some of the synergies of this hybrid systems are already being tested under real conditions (e.g. PtG-Amine scrubbing, PtG-wastewater treatment) while others have only been studied through numerical simulations (e.g., PtG-oxyfuel combustion). Here, a novel hybridization between Power to Gas and electrochemical industries is proposed for the first time. This PtG-Electrochemical hybridization avoids to implement the typical water electrolysis stage of PtG since hydrogen is already available in the plant. This study thoroughly analyzes the implementation of Power to Gas in a real electrochemical plant that sub-produces hydrogen from the lines of production of chlorate, chlorine, and potassium hydroxide. It is shown that the required carbon dioxide for methanation can be captured from the flue gas of the factory''s boilers without additional energy penalty thanks to energy integration. The methanation plant has been designed according to the H2 and CO2 availability, taking into account the number of operating hours and the degree of usage of by-products. Results show that this PtG hybridization could operate more than 6000 h per year at large scale concepts (nominal H2 inputs of 2000 m3/h (NTP)), which represents 2000 h more than pilot/commercial demonstrations of classic PtG concepts. Besides, a detailed economic analysis demonstrates the economic feasibility of the system under current scenarios. It is shown that the capital investment would be recovered in 8 years, generating a 4.8 M€ NPV at the end of the project lifetime. Thus, this work presents a suitable way to avoid the subsidy dependency that current PtG research projects have

Energy Integration of High and Low Temperature Solid Sorbents for CO2 Capture

It is crucial to reduce the energy penalties related to CO2 capture processes if CCS is to be implemented at industrial scale. In this context, gas-solid sorption has become a relevant technology. The absence of large amounts of water when using dry solid sorbents and their high heat capacity reduce the energy requirements in the gas-solid sorption CO2 capture process. Depending on the sorbent composition, the gas-solid sorption process carries out at high or low temperatures. High temperature sorbents allow the utilization of waste energy while energy requirements in low temperature processes will be less demanding. This study is focused on the assessment and comparison of the final energy penalty of low-temperature (amine impregnated alumina-based solid particles) and high-temperature solid sorbents capture process (calcium oxide)

Power to Gas-biomass oxycombustion hybrid system: Energy integration and potential applications

A promising hybridization which increases the chances of deployment of Power to Gas technology is found in the synergy with oxycombustion of biomass. This study assesses the efficiency of an energy integrated system under different sizes and potential applications. District heating and industrial processes are revealed as the most suitable potential applications for this hybrid technology. Global efficiency of the combined system may be increased through thermal energy integration. The relative increment of efficiency achieved for those designs which avoid the requirement of an air separation unit and for those which completely consumed the generated CO2, are 24.5% and 29.7% respectively. A 2 MWth district heating case study is also analysed, revealing that 81.2% of the total available heat from the PtG–oxy system could be integrated raising the global efficiency up to 78.7% at the adequate operational point. Further ‘full-fuel-cycle’ analysis will be required prior to decide the interest of the concept under a specific scenario in comparison to other available energy storage technologies

Power to Gas projects review: Lab, pilot and demo plants for storing renewable energy and CO2

Power to Gas (PtG) processes have appeared in the last years as a long-term solution for renewable electricity surplus storage through methane production. These promising techniques will play a significant role in the future energy storage scenario since it addresses two crucial issues: electrical grid stability in scenarios with high share of renewable sources and decarbonisation of high energy density fuels for transportation. There is a large number of pathways for the transformation of energy from renewable sources into gaseous or liquid fuels through the combination with residual carbon dioxide. The high energy density of these synthetic fuels allows a share of the original renewable energy to be stored in the long-term. The first objective of this review is to thoroughly gather and classify all these energy storage techniques to define in a clear manner the framework which includes the Power to Gas technologies. Once the boundaries of these PtG processes have been evidenced, the second objective of the work is to detail worldwide existing projects which deal with this technology. Basic information such as main objectives, location and launching date is presented together with a qualitative description of the plant, technical data, budget and project partners. A timeline has been built for every project to be able of tracking the evolution of research lines of different companies and institutions

Techno-economic assessment of an industrial carbon capture hub sharing a cement rotary kiln as sorbent regenerator

The concept of CCS cluster brings together multiple CO2 industrial emitters using shared capture and/or transportation infrastructure and offers several advantages for network partners compared with point-to-point individual projects. It reduces costs for CCS, and enables CO2 capture from small volume industrial facilities. The proposed concept connects a cluster of industrial sites with significant heat demands with a cement plant through the implementation of a Ca-looping CCS system. This system treats the flue gas from all the industrial emitters in independent boiler/carbonators while uses the kiln furnace as calciner for the cement and the capture plant. The carbonator reactors located in each one of the industry sites are fed by CaO from the cement plant to capture the CO2 content of their own flue gas. After carbonation reaction, the exhaust sorbent is transported back to the cement plant for regeneration in the kiln furnace. The aim of this work is to analyse the techno-economic feasibility of the proposed Ca-looping CCS cluster. The economic assessment, assuming 20 euro/ton CaO and carbon market 30 euro/ton CO2 points out the feasibility of this kind of centralized carbon capture system to handle the carbon from small emitters. Results show that the operating costs of small companies that use coal or natural gas reduce from 21.3 Meuro to 18.8 Meuro or from 25.5 to 23.0 Meuro. For the cement industry this income lessens its operating costs 1.9 Meuro lower than a reference situation where CCS is only implemented in cement plant

Reducing cycling costs in coal fired power plants through power to hydrogen

The increase of renewable share in the energy generation mix makes necessary to increase the flexibility of the electricity market. Thus, fossil fuel thermal power plants have to adapt their electricity production to compensate these fluctuations. Operation at partial load means a significant loss of efficiency and important reduction of incomes from electricity sales in the fossil power plant. Among the energy storage technologies proposed to overcome these problems, Power to Gas (PtG) allows for the massive storage of surplus electricity in form of hydrogen or synthetic natural gas. In this work, the integration of a Power to Gas system (50 MWe) with fossil fuel thermal power plants (500 MWe) is proposed to reduce the minimum complaint load and avoid shutdowns. This concept allows a continuous operation of power plants during periods with low demand, avoiding the penalty cost of shutdown. The operation of the hybrid system has been modelled to calculate efficiencies, hydrogen and electricity production as a function of the load of the fossil fuel power plant. Results show that the utilisation of PtG diminishes the specific cost of producing electricity between a 20% and 50%, depending on the framework considered (hot, warm and cold start-up). The main contribution is the reduction of the shutdown penalties rather than the incomes from the sale of the hydrogen. At the light of the obtained results, the hybrid system may be implemented to increase the cost-effectiveness of existing fossil fuel power plants while adapting the energy mix to high shares of variable renewable electricity sources