The Sun is the ultimate renewable energy resource. Just a tiny fraction of the solar radiation that hits the Earth (around a hundredth of a millionth of a percent) can provide all our power needs many times over. Unfortunately, capturing this energy is not that simple. Now a new technology offers hope for efficient and affordable solar power, perhaps enabling people in cloudier, cooler climes to tap in to this valuable resource.
Fresnel technology, a joint development between MAN Ferrostaal and Solar Power Group, uses parallel lines of flat mirrors to reflect sunlight up onto a water-filled pipe above. Each line of mirrors can be tilted to maximize the rays they reflect. Inside the pipe the water is heated to 450 °C to produce steam, which is then converted to electrical energy over a steam turbine.
Compared to other solar energy harvesting devices Fresnel collectors exhibit a number of advantages. Their simple flat mirrors are easy and inexpensive to make and, unlike other devices, there is no danger of combustable or toxic fluid leaking from the pipe. Because the structure is low to the ground it is immune to problems from high winds. But perhaps most important of all, Fresnel collectors are highly efficient at what they do. "They have a much higher energy harvest per ground surface area than parabolic trough," Rüdiger Wolf, of Solar Power Group in Essen, Germany, told environmentalresearchweb.
Currently Fresnel technology is still at the research and development stage. There are three demo power plants – one in Australia, one in Spain and one in Belgium. Over the last few years Wolf and his colleagues have been tweaking and improving the design, to maximize the energy returns. Now they think they have a product that could be useful to huge numbers of people.
In addition to being used in large-scale solar thermal power plants, it's envisaged that Fresnel technology could play a more domestic role. "We now have the option of integrating it into the urban environment, for example on roof-tops and above parking lots," said Wolf. This flexibility, along with the simplicity of the product, makes it very appealing.
In theory, small clusters of houses or businesses could meet a significant portion of their energy demands, for both heat and electricity, from a bank of Fresnel mirrors on the rooftops. In regions like Almeria, on the south coast of Spain, which receives 3000 hours of sunshine per year, Fresnel technology could be ideal.
Because Fresnel technology is more efficient at gathering the Sun's energy it may make solar power viable in regions that have traditionally been assumed to be too cloudy or at too high a latitude. However, Fresnel technology can't overcome one fundamental problem: the Sun doesn't shine at night. Like other forms of solar energy harvesters, integrating the technology with other sources of power is the only way to ensure that the lights stay on.