Latest developments on TES and CSP technologies – Energy and environmental issues, applications and research trends

Abstract

The concentrating solar power (CSP) technology is promising especially for countries having an abundance of solar resources in order to secure their energy supply, reduce their carbon footprint and consequently achieve sustainable development goals. Furthermore, the thermal energy storage (TES), when combined with CSP plants, offers the opportunity to make these plants economically competitive and reliable during their operation and could balance supply and demand of energy by reducing the undesirable impacts of the solar energy intermittency. This paper presents a review on TES systems and an update of the latest developments of different technologies of TES that are commercially available or under investigation. Various aspects are discussed including the limits of each technology, different new concepts to enhance the heat transfer efficiency, the principal applications and the environmental issues associated with the integration of TES in solar thermal CSP plants. The results of the current review have revealed that despite the important thermo-physical characteristics of latent heat and thermo-chemical heat storage systems, such as high TES density, they are still at a laboratory level and their development is still far from any proven design and material to be transferred to a commercial scale, especially for high temperature applications. In contrast, the liquid sensible heat storage (SHS) systems are the most mature and the most used in CSP plants. Indeed, according to a census survey that we carried out, based on data compiled by the National Renewable Energy Laboratory (NREL) and Global Energy Observatory (GEO) about CSP projects around the world that are either operational or under development, 45.5% of the operational CSP plants worldwide (i.e. 45.1% of the total installed capacity) are equipped with TES and 95.6% of them (i.e. 99.8% of the total installed capacity) use liquid SHS materials due to their reliability, low cost and easy operation. Economically, the integration of TES systems into large scale CSP plants is a cost-effective way for the widespread deployment of CSP technology, by reducing the levelized cost of electricity (LCOE), especially for solar power tower (SPT) technology over parabolic trough collector (PTC) one, thanks to the high temperature differential occurred in the storage system that reduces the amount of required TES materials. However, owing to its longer commercial operational experience and less technical and financial risks, the PTC is currently the most commonly used technology in CSP plants. Regarding the environmental side, a case study about Moroccan CSP has quantitatively highlighted the environmental potential of integrating TES in CSP plants for electricity production in order to mitigate significantly the greenhouse gases emissions.