17 June 2008

The Waltz of the Mirrors

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If less than 1% of the world’s deserts were used to concentrate solar power, enough electricity could be produced to supply the entire planet

90% of the world’s population lives less than 2,700 km from a desert. If less than 1% of the world’s deserts were used to concentrate solar power, enough electricity could be produced to supply the entire planet.

These two facts – the rise in cost of fossil fuels and their increasing environmental impact – makes solar energy a genuine alternative for producing renewable, clean electricity on a large scale.

The most advanced example of the emergence of solar power in Europe is Sanlucar, near Seville in the south of Spain. Here, the biggest solar power plant in Europe is located in one of the sunniest, desertlike regions of the continent. It has a double mission: to produce clean electricity starting today, and to develop new solutions to expand the commercial applications of solar power for tomorrow. When construction is completed in 2013, it will have a total nominal capacity of 300 MW for all its systems combined. This is one of the only spots on earth where every form of solar technology is in use.

These different technologies all have two things in common: they use mirrors to concentrate sunlight and they optimize the energy gathered at all times with a sun-tracking system. These movable mirrors are called heliostats.

There are two major techniques based on this principle. Photovoltaics transforms sunlight into electricity with semiconductor panels. This electricity is rectified into alternative current and injected directly into the power supply. Sanlucar produces 1230 kW of photovoltaic energy concentrated by its mirrors. The main inconvenience with photovoltaics, besides manufacturing costs and the environmental impact of the panels, is that the energy produced can’t be stored.

Solar thermal power concentrates sunlight to heat a fluid and produce steam to fuel an electric generator. The PS10 solar power tower and its field of heliostats uses this technology and, since 2006, has produced enough electricity to supply 6,000 households. A second tower is under construction – the PS20, with double the capacity of PS10.

Parabolic collectors, long trough-shaped mirrors, also work on the same principle. They focus light onto a fluid that is heated to 400 C° and then fuels a generator. The The parabolic troughs at Sanlucar should in time produce 50 MW.

Research plays an important role in the development of Sanlucar. A network of researchers and engineers backed by the EU are working to improve power storage and electrical yield while reducing manufacturing costs in order to make solar energy more appealing. A new technology with high yield, parabolic mirrors with Stirling engines, is currently being tested. The concentrated sunlight expands a gas which fuels a special engine. This engine transforms solar energy into mechanical energy. Each parabolic mirror functions autonomously, offering a flexible system adapted to all types of surfaces.

In time, the Sanlucar plant should provide power for 150,000 homes and save 180,000 tons of CO2 per year, in other words the equivalent of what’s emitted by 100,000 vehicles. It could very well herald the beginning of the solar era in Europe.

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