Thermochemical Energy Storage for enhancing dispatchability of Solar Photovoltaics

Abstract

Solar photovoltaics (PV) plants are today a competitive alternative to power plants based on fossil fuels. Cost reduction in PV modules, scalability (from kW to MW) and ease of installation of PV plants are enabling a rapid expansion of the technology throughout the world. Nevertheless, PV dispatchability still remains as the major challenge to be overcome due to intrinsic variability of solar energy. Most of the current PV facilities lack energy storage while those with storage systems rely on expensive batteries. Batteries are based on elements such as nickel, lithium or cadmium whose scarcity hinder the sustainability of batteries for storing energy in the large scale. This manuscript presents a novel concept to integrate thermochemical energy storage in PV plants. Furthermore, the concept is also directly adaptable to wind power plants in order to store surplus energy. In particular, this paper analyses the suitability of the Calcium-Looping (CaL) process as thermochemical energy storage system applied to large scale PV facilities. The PV-CaL integration works as follows: a part of power produced in the PV plant provides electricity to the grid while the rest is used to supply heat to carry out the calcination of CaCO3. After calcination, the products of the reaction (CaO and CO2) are stored separately. When power production is required, the stored products are brought together in a carbonation reactor wherein the exothermic reaction releases energy for power production. The overall system is simulated in order to estimate the process behaviour and results show that storage efficiencies of ~40% can be achieved. Moreover, an economic analysis is developed to compare the proposed system with batteries. Due to the low price of natural CaO precursors such as limestone and the longer lifetime of equipment than batteries, the CaL process can be considered as a promising alternative to increase dispatchability in PV plants. Moreover, limestone is abundant and nontoxic, which is an essential requirement for the storage of energy in massive amounts