Solar Power Tower is one of the most important technologies of the emerging clean energy economy. I believe that over the next few years power towers will be one of the fastest growing and most important forms of solar energy generation.
Last year I went to sourthern Spain to visit PS10 the world’s first commercial solar power tower.
PS10 (Plataforma Solar 10) is located within Abengoa Solar’s Solúcar Solar Park, located about 16 miles (25 km) northwest of Seville. The complex is as ambitious a solar project as exists anywhere in the world. By the time Abengoa Solar is finished building Solúcar it will have a capacity of 300 MW and generate enough electricity to power a city the size of Seville.
The PS10 tower has a height of 330 feet (110 m) PS10 tower and has a generating capacity of 11MW. Launched in the fall of 2006, it generates 24.3 GWh of electricity per year—about enough to fully power 5,500 homes.
Concentrating Solar Power
When most people think about solar power, they think of photovoltaic (PV) panels on the roof of a house or building. PV converts photons directly into electricity. PS10 and other CSP (Concentrating Solar Power) plants use the sun’s energy to generate power in a different way. It uses the sun’s heat to heat a fluid (water) to generate steam which then drives a turbine to generate electricity.
If you’ve ever used a magnifying glass or better yet a concave mirror to focus sunlight and burn a hole in a piece of paper, you get the idea. Use thousands (or millions) of square meters of mirrors (not PV panels!) to reflect that same sunlight on a single point, and you can heat a fluid flowing past it up to several hundred degrees Celsius and use that superheated fluid to drive an industrial-scale turbine.
Mirrors not PV
The mirrors are called heliostats. Heliostats can be of any size but Abengoa engineers decided to use 120 m2 (1,292 ft2) mirrors - sides measure 10 m (30 ft) by 12 m (36 ft). The more mirrors the more sunshine is focuse on the tower and the more power it can generate. PS10 has 640 heliostats for a total mirror surface of 74,800 m2 (800,000 ft2.)
Tony Seba PS10 Tower and Heliostats.
At PS10 they use water as the main transfer fluid. Water goes up one side of the tower and gets heated to about 250 ºC (500 ºF) and pressurized to 40 bar (580 psi) as it runs through the receiver on top of the tower. The receiver is actually composed of four large panels set in a semi-circular fashion inside a square ‘hole’ or ‘cavity’ on top of the tower. Each one of these panels is 5.5 m (18 ft) wide and 12 m (39 ft) tall. The cavity is 11 m (33 ft) by 11 m (33t), slightly larger than one helliostat.
Once the water is super-heated within this cavity it goes down on the other side of the tower where it generates electricity the old fashioned way: by driving a turbine. (Large fossil fuel- and nuclear power plants use the same principle: heat water to run a turbine which generates electricity. The main difference with power towers is that they use the sun as fuel. )
Thermal Energy Storage
PS10 also has about 1 hour of energy storage. This means that this solar plant can deliver steady power to the grid even when there are cloud covers or high winds that interrupt the steady generation of steam. In fact, when I visited PS10 high the plant operators had to shut down the heliostats for a few minutes due to high wind conditions.
The plant kept generating power despite this drop in solar energy input.
PS20, the taller tower in the video, opened a few months after my January 2009 visit. It is 50% taller (165 meters or 540 feet) and users 1,255 heliostats (about twice as many as PS10). PS20 has nearly twice the heliostat mirror surface and a generation capacity of 20 MW or about twice the generation capacity of PS10.
Future of Solar – Desert Power
The smaller towner between PS10 and PS20 is a research tower. Dubbed Eureka, this tower allows Abengoa Solar to experiment with materials and technologies at ever higher temperatures – beyond 1000 ºC (1832 º F). The higher the receiver temperature the more power a tower can generate with the same solar input. Compare this with surface temperature of the sun which is about 5505 °C (9941 °F) .
As we move forward to a clean energy economy, Solar Power Tower will generate a increasing part of our power around the world. This technology works best in high solar radiation desert-type conditions. There are new solar power towers being built or planned around the globe – from the Mojave desert in California to the Sahara desert; from Spain to Israel; from Australia to South Africa .
