Combined steam based high-temperature heat and power storage with an Organic Rankine Cycle, an efficient mechanical electricity storage technology

Today, mechanical energy storages are getting more important than before as the share of fluctuating renewable energies are dramatically increasing in the global energy matrix. Steam-based high-temperature heat and power storage is one of the very recent mechanical energy storage technologies introduced. This system stores electricity as heat in a packed bed of rocks and then, co-generates heat and electricity through a conventional Rankine cycle when discharging. This system presents an electricity and heat efficiencies of about 33–35% and 60–65%, meaning an overall efficiency in the range of 93–98%. As the major production of the system is heat, it is only appropriate for countries with district heating systems. As not all countries have heat networks, and according to the fact that, electricity is getting much pricier than heat everywhere, a modification of this technology in order for offering a better electricity efficiency could be highly advantageous. This study proposes the hybridization of a steam-based high-temperature heat and power storage with a small-scale Organic Rankine Cycle (with three different working fluids) to improve its electricity efficiency. The hybrid system is comprehensively analyzed and compared to its conventional design. The results prove the electricity efficiency of 42.6–46.3% is obtained for the hybrid systems which are 24–35% higher than that of the conventional design.