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Steam turbines in solar thermal power plants experience a much greater number of starts than those operating in baseload plants. In order to preserve the lifetime of the turbine while still allowing fast starts, it is of great interest to find ways to maintain the turbine temperature during idle periods. A dynamic model of a solar steam turbine has been elaborated, simulating both the heat conduction within the body and the heat exchange with the gland steam, main steam and the environment, allowing prediction of the temperatures within the turbine during off-design operation and standby. The model has been validated against 96 h of measured data from the Andasol 1 power plant, giving an average error of 1.2% for key temperature measurements. The validated model was then used to evaluate a number of modifications that can be made to maintain the turbine temperature during idle periods. Heat blankets were shown to be the most effective measure for keeping the turbine casing warm, whereas increasing the gland steam temperature was most effective in maintaining the temperature of the rotor. By applying a combination of these measures the dispatchability of the turbine can be improved significantly: electrical output can be increased by up to 9.5% after a long cooldown and up to 9.8% after a short cooldown.

The present study analyzes the influence that market conditions have on determining optimum molten salt solar tower plants with storage that maximizes profits (in terms of plant configuration, sizing, and operation) for a location in South Africa. Three different scenarios based on incentive programs and local wholesale electricity prices are considered. A multi-objective optimization modeling approach was followed, showing the tradeoff curves between minimizing investment and maximizing profits when varying critical size-related parameters (such as nameplate capacity, solar multiple (SM), and storage capacity) together with power-cycle design and operating specifications including dynamic startup curves and different storage dispatchability strategies. Results are shown by means of a comparative analysis between optimal plants found for each scenario, highlighting the value that storage has under the current two-tier tariff scheme and the relevance of designing a suitable policy for technology development. Finally, a final analysis is performed with regard to the indicators used for economic evaluation of power plants, by comparing the differences between optimum designs found when using the levelized cost of electricity (LCoE) solely as performance indicator instead of cash-flows and profit-based indicators, such as the internal rate of return (IRR).