Investigation of the thermodynamic and economic feasibility of cold Pumped Thermal Energy Storage using Oceanic Temperature Difference

The significant future penetration of variable renewable energy will require energy storage to stabilize the electric grids and pumped thermal energy storage (PTES) is an attractive solution preferable to electrochemical storage for long-duration applications. Particularly, Thermally Integrated-PTES (TI-PTES), represents an improvement of this technology. This paper introduces a novel TI-PTES concept exploiting the temperature difference between surface and deep oceanic water in tropical areas. The system comprises a chiller, phase change material (PCM) cold storage, and an organic Rankine cycle. In the charging phase, the chiller operates between the cold seawater and the thermal storage, converting electric energy into a cooling effect, with an Energy Efficiency Ratio (EER) in the range of 4.6–9.0 due to the deep seawater's low temperature. During the discharge phase, the organic Rankine cycle operates between the hot surface and the storage to produce electricity. A model of the system was defined in Aspen Hysys, and an optimization to maximize the round-trip efficiency was performed. Several storage temperatures were also compared. Results show that the round-trip efficiency ranges from 0.30 to 0.52, while the specific cost of this technology is still high at 1910 €/kWh, mainly due to the low efficiency of the discharge phase.