In the desert of southern Spain, 20 miles outside Seville, more than 1,000 mirrors are being carefully positioned. Each is about half the size of a tennis court, so the adjustments will take time. But when they are complete in a few weeks, it will mark a major moment in the quest for renewable energy.
The mirrors are part of the world’s biggest solar tower plant, a technology that reflects sunlight to superheat water at a central tower. Once this €80m (£67m) plant is inaugurated in January, it will generate 20MW of electricity, enough to power 11,000 Spanish homes.
Concentrated solar power (CSP) technology, as it is known, is seen by many as a simpler, cheaper and more efficient way to harness the sun’s energy than other methods such as photovoltaic (PV) panels. But CSP only works in places with clear skies and strong sunshine.
Abengoa has already built a smaller version of the tower technology to test that the idea works. The 11MW PS10 system has been generating electricity for almost two years. Its new design uses an area larger than 100 football pitches, with 1,255 mirrors, called heliostats, each with a collecting area of 120 sq m. These track the sun as it moves through the day and reflect the energy to the top of a 160-metre tower at the centre of the field. Here, the concentrated light is used to heat water to more than 260C, producing steam that can turn an electricity generating turbine.
When switched on, the new plant will be the world’s largest commercial CSP plant feeding electricity into a national grid. It will be also be a significant step for tower technology, seen as a candidate for the large-scale solar plants of the future.
Spanish firms are charging ahead with CSP: more than 50 solar projects around Spain have been approved for construction by the government and, by 2015, the country will generate more than 2GW of power from CSP, comfortably exceeding current national targets. The companies are also exporting their technology to Morocco, Algeria and the US.
The country’s clean energy targets are in line with the EU’s plan to source 20% of primary energy from renewables by 2020, which means that 30% of electricity would have to come from carbon-free sources. A new EU renewables directive would increase that electricity target to 40%, but García said Spain could easily reach for more, up to 50%.
The 20MW solar tower is also a forerunner for an even more ambitious idea, one that Abascal hopes will become a standard for CSP plants in future – a 50MW version that could generate electricity around the clock. “During the day, you’d use 50% of your electricity to produce electricity and 50% to heat molten salt. During the night you use the molten salt to produce electricity.”
Molten salt technology is in its early stages but Abengoa is testing the idea at a power plant in Granada. So far the company has demonstrated that it is possible to store up to eight hours of solar energy by heating tanks containing 28,000 tonnes of salt to more than 220C. “This will make it possible to have almost constant production or at least it will be able to produce energy for most of the day,” said Abascal.
– from guardian. 24 Nov 2008