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Stored and concentrated: Storage systems for CSP

Advanced storage solutions involving salt and concrete are opening up the possibilities for concentrated solar power plants.

Storage systems for CSP
Storage systems for CSP

Since the world’s first molten salt concentrating solar power demonstration plant, Archimede, was unveiled in the summer of 2010, developments in combining energy storage technology with CSP have moved forward dramatically.

Collecting and storing the sun’s heat for many hours at a time, the plant opened up the idea of saving and distributing energy both overnight and when the sun isn’t shining.

The plant in Scilly introduced the CSP sector to the concept of salt storage systems. It was the world’s first to use molten salts as the heat transfer fluid and the first to use molten-salt technology integrated with a combined-cycle plant.

The plant consists of a field of around 30,000 sqm of mirrors (paraboliccollectors) that concentrate sunlight onto 5,400m of pipe carrying the molten salt fluid. The molten salts used in the system are a mixture of sodium nitrates and potassium, which can accumulate heat for prolonged periods.

The thermal energy harvested by the system produces high pressure steam that is channelled into the turbines of the power plant to produce electricity. 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 a nearby combined-cycle plant, where it contributes to electricity generation. This enables the plant to generate electricity at any time of the day and in all weather conditions until the stored energy is depleted.

At the time, Italian developer ENEL said that the plant overcame “the common limitation of this [solar power] renewable source, namely that you can use it only when nature makes it available.”

But Archimede also paved the way for other projects using salt storage systems with CSP and, over two years on, other developers are carrying on from where ENEL left off.