The abstract for the paper is as follows:
In the SOLGATE project, a solar-hybrid gas turbine system was developed, built and tested (ORMAT et al., 2005). The concept involves gas turbine systems in which air is first compressed, then heated through a combination of concentrated solar radiation and gas combustion, and finally passed through a turbine to generate power. The hybrid nature of the system enables savings on fuel and emissions, but also power delivery when the sun is not shining. The exhaust from the gas turbines is very hot, and therefore suitable for some kind of bottoming cycle to boost the output.Recently, the author (Barton, 2012) analysed a new bottoming cycle based on evaporative cooling of hot air at reduced pressure. This concept is called the Expansion-Cycle Evaporation Turbine (ECET). Barton showed that the ECET can typically boost the output of utility-scale open-cycle gas turbines by around 20%, without any extra fuel consumption or emissions, and at a specific capital cost expected to be no more than that for the upstream gas turbine. With these attributes, the ECET is expected to be suitable for peak duty in the electricity grid.
The present work investigates the suitability of the ECET to boost the power output of solar-hybrid gas turbines such as in the SOLGATE project. Power boosts of approximately 20% are expected. The Levelised Electricity Cost (LEC) with ECET boost is also compared to that for two other bottoming cycles – the Rankine steam cycle (which gives the solar-hybrid combined-cycle gas turbine) and an Air Heat Recovery Turbine Unit (AHRTU, Romanov et al., 2010). In these comparisons, the three bottoming cycles give a 10-14% reduction in the LEC when compared to the original solar-hybrid gas turbine. The LEC for the ECET-boosted system is marginally lower than that for the Rankine-boosted system, which in turn is marginally lower than that for the AHRTU-boosted system. The percentage by which the LEC is improved by the bottoming cycles does not depend strongly on the capacity factor.
This study provides a preliminary assessment of the benefits of three bottoming cycles when used in conjunction with solar-hybrid gas turbines for power generation. According to this analysis, all three cycles clearly lead to benefits; the output is boosted by around 17-22%, the levelised electricity cost is reduced by around 10-14%, and CO2 emissions are reduced by around 14-18%.
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