(791b) Dynamics of Pumped Heat Energy Storage Systems

The eventual success and widespread utilization of photovoltaic and wind energy generation will depend on the availability of efficient and economical storage capability. The current technology for long term (diurnal), high efficiency large scale energy storage of electrical energy appears to have been limited to Pumped Hydroelectric Storage (PHS) and Compressed Air Storage (CAES).  Both of them are dependent of the availability of geological features such as elevated lakes or empty deep mines for PHS or caverns for the CAES. This features are not available everywhere and other technologies such flow batteries while capable of large scale storage are limited in their power output.

Pumped heat energy storage systems can provide a valuable alternative PHS or CAES. The proposed process uses a Brayton cycle where during the loading cycle heat is pumped to heat up a high pressure thermal regenerator while a low pressure thermal regenerator is cooled down to a low temperature. During the unloading period the gas circulation is reversed. Cold gas from the low pressure regenerator is compressed and heated in the high pressure regenerator to be then expanded to the low pressure vessel.  Electrical energy storage capacities in the 30-50kWh/m³ range appear possible and are comparable to lead acid batteries (25-50 kWh/m³).

Analysis and optimization of these systems are complicated by the difficult dynamics of thermal regenerators. A novel matrix algorithm is proposed that allows us to directly calculate cyclic steady state as well as transients. The effects of different design parameters such as pressure ratios, compressor and expander efficiencies, type of gases, solid heat capacities and gas solid heat transfer coefficients are explored. Possible synergistic integration with natural gas combustion combined cycles will be discussed.