Spain and the US, are the current world leaders in concentrated solar power (CSP). Spain’s latest installation, the 550,000 square metre La Florida plant at Alvarado, Badajoz, can generate 50MW. This national total, for CSP and photovoltaics combined, is currently only broadly equivalent to the output of one nuclear power station, but it is growing fast. Spain’s solar industry association Protermosolar projects a six-fold increase over the next three years, a growth rate far outstripping other modes.
La Florida’s plant uses sun-tracking trough-shaped parabolic mirrors to focus reflected sunlight on to a central tube. The fluid in the tube heats up, turning water into steam to drive the turbines. Over in Italy, meanwhile, a new CSP plant claims to be the first in the world to use molten salt as its heat transfer fluid. Sicily’s Archimede plant, recently opened by energy company Enel, is little more than a twentieth of the size of La Florida, and can generate only 5MW of electricity.
But its technology has attracted attention because the mixture of sodium nitrates and potassium is particularly good at retaining heat. The ability to ‘store’ solar power in this way, and deliver it outside peak sunshine hours, would give CSP the added value of flexibility. Another ‘first’ for the Archimede plant is its integration with the adjacent gas-fired power station, where the solar-powered steam shares the task of turning the turbines with steam heated by fossil fuel.