Concept of the hybridization of solar tower plants
The receiver is operated with a variable mass flow to maintain the design hot air temperature of approx. 680°C. In operation, first the thermal storage is charged to a certain level to have a backup for compensation of less or no solar radiation. In times of high solar radiation the receiver provides enough heat to charge the storage and to produce steam. To charge the storage the excess hot air mass flow enters the storage from the top and dissipates its heat to the storage mass. When the receiver is generating less hot air than required (e. g. due to cloud transients) the differential hot air flow is provided by a discharge flow through the storage entering at the bottom [3].
The concept of a hybrid tower plant is shown in Fig. 1. To achieve the gas parameters at the inlet of the HRSG for nominal load even by less solar radiation a channel burner is included. The burner heats up
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the preheated air from the receiver to the desired temperature. Instead of using a channel burner a gas turbine can be combined with the system. The gas turbine is in a parallel position to the receiver. The exhaust gas of the gas turbine is mixed with the air from the receiver to get the nominal mass flow at a high temperature. After the HRSG the exhaust gas is recirculated to the receiver or can be passed to a stack. This hybridisation concept has the advantages of combined cycles, like a high efficiency, and an additional power production by the gas turbine. As fuel natural gas or biogas (to maintain the status of the plant using renewable energies) can be used. In addition the hybridisation concepts can be used in different operation modes. The burner or the gas turbine can be operated parallel or in turn with the solar air receiver. Parallel means that on a day with less solar radiation both components can provide the heat for the HRSG at the same time. In the other operation mode the hybrid component is only switched on in the night or at times of no solar radiation.
