Thermo Economic Optimization of Hybridization Options for Solar Retrofitting of Combined Cycle Power Plants

Abstract

A thermoeconomic optimization model of an integrated solar combinedcycle (ISCC) has been developed to evaluate the performance of an existing combinedcycle gas turbine (CCGT) plant when retrofitted with solar trough collectors. The model employs evolutionary algorithms to assess the optimal performance and cost of the power plant. To define the tradeoffs required for maximizing gains and minimizing costs (and to identify â€کoptimal’ hybridization schemes), two conflicting objectives were considered, namely, minimum required investment and maximum net present value (NPV). Optimization was performed for various feedin tariff (FIT) regimes, with tariff levels that were either fixed or that varied with electricity pool prices. It was found that for the given combinedcycle power plant design, only small annual solar shares (∼1.2% annual share, 4% of installed capacity) could be achieved by retrofitting. The integrated solar combinedcycle design has optimal thermal storage capacities that are several times smaller than those of the corresponding solaronly design. Even with strong incentives to shift the load to periods in which the prices are higher, investment in storage capacity was not promoted. Nevertheless, the levelized costs of the additional solargenerated electricity are as low as 10 c€/kWh, compared to the 17–19 c€/kWh achieved for a reference, nonhybridized, “solaronlyâ€‌ concentrating solar power plant optimized with the same tools and cost dataset. The main reasons for the lower cost of the integrated solar combinedcycle power plant are improved solartoelectric efficiency and the lower level of required investment in the steam cycle. The retrofitting of combinedcycle gas turbine plants to integrated solar combinedcycle plants with parabolic troughs represents a viable option to achieve relatively lowcost capacity expansion and strong knowledge building regarding concentrating solar power.