PREFORMANCE OF THE SOLAR HYBRID STEAM INJECTION GAS TURBINE (STIG) CYCLE WITH PCM HEAT STORAGE

Guy Polonsky

Department of Mechanical and Manufacturing Engineering, Tel Aviv University.

The solar hybrid STIG cycle utilizes solar energy to generate steam at medium temperature heat, around 200°C. The steam is then superheated by the residual heat from the gas turbine exhaust and injected to the combustion chamber to increase the turbine output. Previous work on this cycle analyzed the peak performance of the cycle using a thermodynamic simulation. This work analyzes the annual performance of a solar STIG plant based on the GE LM2500 gas turbine with nominal steam to air ratio (SAR) of 0.7. The plant is designed to condense and recapture water, and sized to operate at zero annual water consumption. Two operation modes were investigated: constant power output, and variable solar dependent power output. The analysis was done for two sites in Israel using climatic hourly data (direct normal irradiance, temperature and relative humidity). The plant performance was computed separately for each hour and summed to produce the annual values. The incremental contribution of solar power was evaluated in reference to two reference fossil-only cycles: a conventional STIG without a solar contribution, and a recuperated gas turbine. The solar incremental performance in reference to the recuperated gas turbine was: solar to electric efficiency up to 24.5%, solar capacity factor (SCF) 11%. In reference to conventional STIG the efficiency is up to 15.8%, and SCF 7.2%. This is good performance compared to another solar hybrid cycle, the integrated solar combined cycle (ISCC), which was reported to have a similar solar to electric efficiency of 21.5%-27.3% and a much smaller SCF of up to 2.4%. Finally, an ideal four-hour phase change material heat storage was added, leading to an increase of SCF to 17.2% while maintaining good efficiency