ENEL opens "world's first" molten-salt/solar plant

Rome – Italian power group Enel has inaugurated its Archimede solar thermal power plant at Priolo Gargallo, in Syracuse, Sicily. The 5MW facility, it said, is the first in the world to use molten salts as the heat transfer fluid and is also the first in the world to integrate a combined-cycle gas facility and a solar thermal power plant for electricity generation.

The plant is designed to collect and store the heat of the sun for many hours in order to use it to generate electricity at night or in overcast conditions. This allows to overcome the common limitation of this renewable source, namely that you can use it only when nature makes it available.

Solar thermodynamic technology uses a set of parabolic mirrors to concentrate the sun’s rays on pipes carrying a fluid. The latter, collected in special tanks, can be used to power a steam generator. The high-temperature steam and pressure drives the turbine in the adjacent combined-cycle power plant to generate electricity when needed, reducing consumption of fossil fuels.

The molten salts used in the system are a mixture of sodium nitrates and potassium, which can accumulate heat for prolonged periods.

The solar thermal power plant consists of a field of about 30,000 square metres of mirrors that concentrate sunlight onto 5,400 metres 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 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.

This system, said ENEL, enables the plant to generate electricity at any time of the day and in all weather conditions until the stored energy is depleted.

The plant is called “Archimede” after the rows of huge parabolic mirrors used to capture the sun’s rays, which recall the “burning mirrors” that Archimedes is said to have used to set fire to the Roman ships besieging Syracuse during the Punic War of 212 BC.