Both parabolic and Fresnel collectors focus sunlight directly incident on linear absorber in which a liquid is heated. But what if you had rather focus all rays at a single point? This is precisely the principle of solar tower power plants.
If you drive on the motorway from Seville to Cordoba, could believe half way to have a vision. Surrounded by fields of sunflowers stands there, a 140 meter high tower, which glows brightly gleaming. Gemasolar, that means that so far the world's largest solar power tower in Fuentes de Andalucia. In May, the first electricity fed into the grid. Power Plant Director Santiago Arias from Torresol Energy companies currently monitors the transition into regular operations.
"The solar field at the foot of the tower consists of 2500 heliostats, each with 110 square meters of mirror surface. 300 000 square meters of mirrors to focus sunlight on the steeple."
The heliostats are distributed concentrically around the tower. Its huge mirror resting on massive pillars.
"Every 20 seconds, small motors to correct the alignment of the mirrors at a fraction of a degree. This precision is necessary because the extreme levels are almost a kilometer away from the tower."
"Up there it is hot as hell. To transport the heat, we derive molten salt by thousands thin absorber tubes. The heated salt is stored in large tanks in order to steam for a turbine to generate electricity. And then, when he used is - even if seems not the sun. "
The 16 meter high tower absorber ring at the tip consists of special heat-resistant pipes. The focus of the mirror they are about 700 degrees hot, and shine so brightly that have pilots who flew dozens of kilometers away, was wondering. The salt melt, the cooled tubes, consists of potassium and sodium nitrate - and in exactly the same mixture as in the heat storage of the parabolic trough power plants. But the Solar Tower, the salt is heated much more strongly - to 565 degrees.
A heat exchanger at the foot of the tower to 550 degrees hotter steam is generated at 100 bar: Optimal conditions for the 20-megawatt turbine from Siemens, which runs in the machine hall.
"Our key advantage is that we operate at higher temperatures than other solar thermal power plants and the higher the temperature, the more efficiently can be heat into electricity - are the laws of thermodynamics We can also use more efficiently by the high temperatures and our salt storage.. . We are 8000 tons of molten salt and thus can stash enough heat for 15 hours at full load have. "
The power tower is as good as base load - an important consideration for utilities. 110 gigawatt hours per year to produce Gemasolar, enough for 25,000 households. According to the first service experience could be even more in there. Santiago Arias is therefore convinced that the solar towers are the future.
"This is the first solar tower power plant of this magnitude. But I think soon there will be dozens of them. Other companies are waiting in the wings. We, of Torresol Energy, have plans for much larger power plants in Spain, Abu Dhabi and the U.S. ".
Even for Solar Millennium, which has specialized in parabolic trough German rivals, you have got the charm of the tower technology and explores the potential of currently.
