Annual performance of the solar hybrid STIG cycle

Abstract

The solar hybrid Steam Injection Gas turbine (STIG) cycle uses both recuperated heat and solar heat in order to generate steam at a low temperature and pressure, and inject it into the cycle in order to augment the power output. An annual performance analysis of the Solar STIG cycle is presented for sites in Israel and India, with moderate and high annual direct insolation. The cycle operation was simulated in two modes: constant power output and variable power output following the variation of solar input. The solar contribution to the electricity production of the hybrid cycle and the solar to electricity efficiency were calculated, where the conventional reference system was either a conventional STIG or a conventional recuperated Brayton cycle. Results show annual solar fraction of up to 31% in constant power mode and up to 33% in variable power mode. The annual solar to electricity efficiency was in the range of 22–26% when the reference efficiency was based on the recuperated Brayton cycle, and 12–16% when the reference efficiency was based on an optimal conventional STIG cycle. These values are similar to or higher than the annual efficiency of current solar thermal power technologies, even though the hybrid STIG cycle uses low-grade solar heat at only 200°C.