Storage and discharge efficiency of small-temperature-difference CO2 hydrate batteries with cyclopentane accelerators

Abstract

We developed a battery system that stores and discharges electricity using a gas hydrate heat cycle due to the formation and dissociation process of CO2 hydrate (CHD). Cyclopentane (CP) is known as one of the used catalysts in the formation of CHD. The overall efficiency of the proposed system obtained from the sum of a CHD generation process (energy storage mode) and dissociation and power generation processes (power generation mode), where the energy storage mode corresponds to the charging operation, and the power generation mode corresponds to the discharging operation. The details of the overall efficiency of the battery systems with CHD heat cycles in which CP is added to increase the generation rate are still unclear. Thus, in this work, the efficiency of the generation and dissociation processes of a CP-enhanced CHD heat cycle and the power generation efficiency of an actuator using dissociated expansion gas were experimentally investigated to determine the overall efficiency of the proposed system. Generally, CHD heat cycles have a power density that is about eight times greater than that of pneumatic energy storage and pumped storage systems. However, the energy density of CHD heat cycles needs further improvement. Moreover, compared with most batteries and fuel cells, CHD heat cycles neither use rare metals, such as precious metals, nor toxic chemicals and flammable fluids, making them cheap, safe, and environmentally friendly battery systems.