Off-design performance of a hybrid renewable compressed air energy storage system: Dynamic simulation and thermo-economic analysis

This research proposes a novel co-simulation model for analyzing the time dependent performance of a compressed air energy storage (CAES) system driven by the renewable excess electricity. In particular, the system layout of the considered CAES includes: a compression train, an expansion train and a compressed air tank. All these components are modelled in MATLAB by suitable algorithms. The developed CAES is also coupled with a renewable plant supplying electricity to a plurality of users. The overall simulation model of the renewable plant, including the CAES, is developed in TRNSYS. The compressions train includes two centrifugal compressors and one reciprocating compressor. The expansion train includes three radial turbines. This model is designed for assessing the time dependent performance of the compressed air energy storage tracking the excess electricity in charging phase and the load in discharging phase. The models of the compressors and turbines are developed using the manufacturer maps approach. The selected user is a residential user including 50 buildings located in Naples, South of Italy. The proposed renewable plant consists of a compression train, featured by an overall capacity of 3.5 MW, a 1.5 MW expansion train and a 250 m3 compressed air tank at 350 bar. This system is integrated with a 6.30 MW photovoltaic field and 2000 m2 solar field of evacuated collectors. The photovoltaic electricity firstly meets the demand of the district users. The excess renewable electricity is used to drive the compressed air energy storage system. This system also includes a suitable waste heat management system, designed for storing the waste heat due to compression and reducing the air temperature at the inlet of each compressor. Such waste heat is used for heating the air delivered to the turbines. The thermal energy provided by the evacuated collector solar field is used for increasing the turbines inlet temperature. The proposed system achieves promising energy results, being able to reduce by 59 % the primary energy demand of the selected residential district. Moreover, the compressed air energy storage system meets about 14 % of the district load. The proposed system shows a limited economic profitability with a payback period of 21 years, due to the high capital cost of the technologies involved in such plant.