Advances in thermochemical energy storage and fluidised beds for domestic heat

Abstract

Thermochemical energy storage (TCES) has a vital role to play in a future where 100 % of our domestic energy needs are generated by renewables. Heating and cooling represent 51 % of total energy consumption, and as such contribute highly to greenhouse gas emissions. As a society, we have effective solutions for this in the form of renewable energy sources, the primary two being: solar thermal heat and wind power. However, one issue plagues these energy sources, that is their intermittency. Specifically, their seasonal deficit which represents a significant energy surplus in the summer months and significant energy dearth in the winter months. Effective seasonal heat storage is needed to solve this problem. At present, one of the best candidates to solve this issue TCES. Both sorption and reaction present many interesting chemical pairings which optimise various different important parameters, including: Energy density, cycle stability, turning temperature, capital and running costs, power output, charging and discharging speed. However, due to hazardous high temperatures and chemicals associated with reaction based TCES, it can be all but ruled out from domestic application. Sorption TCES presents many different promising subcategories, but salt based composite TCES materials are emerging as the most likely category to succeed in a domestic market. Sorption TCES faces one key issue though, that is its power output.Fluidised bed reactors (FBRs), both bubbling fluidised beds and circulating fluidised beds, have been used extensively in industry to increase the heat and mass transfer of various industrial processes. They have been used in the context of TCES to assist in the charging and discharging of various concentrating solar power plant energy storage systems. And, they have shown to effectively improve the power output of these systems, as well as in other high temperature energy storage systems (sensible energy storage, phase-change energy storage). Overall, it is clear that FBRs have the potential to be applied to domestic sorption TCES to improve its power output, priming it for domestic applications. It is also worth noting that very few studies exist investigating FBRs in the context of domestic TCES, and there is limited knowledge and understanding one how FBRs will affect domestic TCES systems.