Longer heat retention of salts means plant can operate overnight and in intermittent sunshine
What is claimed to be the world’s first solar thermal concentration plant to use molten salt as the heat transfer fluid has been opened by Italian energy company Enel in Sicily.
The 5MW Archimede plant – named after the rows of huge parabolic mirrors used to capture the sun's rays – is also claimed to be the first to integrate a combined-cycle gas facility and a solar thermal power plant for electricity generation.
The solar thermal power plant comprises a field of about 30,000m2 of mirrors that concentrate sunlight on to 5.4km of pipe carrying the molten salt fluid. The thermal energy harvested by the system produces high-pressure steam that is channelled into the turbines of the power plant to produce electricity, reducing the consumption of fossil fuels and, as a result, enhancing the environmental performance of the combined-cycle plant.
The solar collectors (the parabolic mirrors and pipes or receivers), together with a steam generator and two heat storage tanks – one cold and one hot – make up the solar portion of the system.
When the sun shines, the thermal fluid drawn from the cold tank is circulated through the network of parabolic collectors, where it is heated to a temperature of 550°C and injected into the hot tank, where the thermal energy is stored. The fluid is then drawn from the hot reservoir to produce steam at high pressure and temperature, which is sent to Enel’s nearby combined-cycle plant, where it contributes to electricity generation.
The molten salts used in the system are a mixture of sodium nitrates and potassium, which can retain heat for prolonged periods. This enables the plant to generate electricity at any time of the day and in all weather conditions until the stored energy is depleted.
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