Traditionally, flat solar panels, usually made out of a dark absorbent material, have and continue to soak up the sun’s heat to generate electricity. This traditional technology can be seen on a small-scale such as on the roofs of houses and businesses around the world. However, newer technology has taken this concept and intensified it multiple times over. Instead of absorbing heat into solar cells and converting it right away into electricity, concentrated solar power (CSP) redirects sunlight light using reflective surfaces and tracking systems into one small, concentrated area, thus amplifying its effect on producing energy. Projecting concentrated light into one small area intensifies the heat and allows for more energy to be produced at one time. Sunlight naturally generates heat and this technology simply intensifies the original intention. A huge feat of ingenuity, CSP technology has the capability of storing energy to generate electricity even after the sun has gone down. Traditional solar panels are only capable of creating solar electricity while the sun is shining.
Depending on the system design, different designs are used to turn that concentrated solar heat into electricity. Let’s explore the three main designs:
1. Parabolic Trough- This design incorporates a lengthy, linear parabolic trough on the ground shaped like a “U”. This design concentrates the light that is reflected from the surface of the trough onto a hollow bar in the center. This bar is usually filled with a fluid that is good at conducting and transferring heat. Newer models use molten salt because of its ability to transfer heat effectively; however oil has been predominantly used in the past, making it a hybrid design. This bar is heated to 150-350 degrees C (or 302-662 degrees F). This heats flows to a receiver creating steam which ultimately powers the generator to create electricity. These troughs are positioned in a north-south orientation so that throughout the course of a day, the trough can move according to the rise and setting of the sun. Click here to see a visual diagram: www.solarpaces.org/CSP_Technology/csp_technology.htm
2. Dish Sterling- For the sake of visualizing, sterling dishes have a similar physique to satellite TV dishes. They are large, circular and are uniquely parabolic. This means the inside of the dish is curved like a bowl. It can also move to follow the sun’s position in the sky and projects solar light with mirrors onto a receiver mounted a short distance in front of the dish. The heat that is collected by the receiver is handled with a heat engine mounted on the receiver itself. Click here to see a visual diagram: www.solarpaces.org/CSP_Technology/csp_technology.htm
3. Solar Power Tower- This design incorporates a field of moveable mirrors, or heliostats, and a tower high above them which collects the heat from the projected light. Throughout the day, these mirrors move inch by inch, tracking the sun’s movement across the sky, and reflect the light onto a receiver at the top of tower. The light generates heat at the receiver, warming a heat-transfer fluid (usually water) inside. This fluid then generates steam which turns a turbine and generates electricity. The steam can be stored for later electricity generation, even when there is no sunlight. Click here to see a visual diagram: www.solarpaces.org/CSP_Technology/csp_technology.htm
Contextualizing successful CSP around the world:
The first CSP plant was designed and built in Sant’Ilario, near Genoa, Italy in 1968 by a Genoese, Professor Giovanni Francia. Since then there have been many more designs drafted, many more plants erected and even more renewable electricity generated. There are multiple regions across the globe that have built successful and fully operational CSP plants and varying designs of the technology. According to the International Energy Agency (IEA), in 2010, the total energy capacity of entire global effort in generating solar power topped out at 1 GW. There are now dozens of CSP projects under construction in China, India, Morocco, Spain and the United States and they are expected to top out at 15 GW of solar electricity produced. 1 GW is equal to 1000 MW and 1 MW is equal to 1,000,000 watts. To put this into context, an average light bulb in the U.S. is 60 watts.
Boulder City, Nevada, USA and “Parabolic Troughs”- The Nevada Solar One CSP plant went into operation in 2007 and was the world’s third largest solar plant. There are 760 parabolic troughs at this site, with the estimated capability of supplying 134 million kilowatt hours of energy per year. It has a normal capacity of 64 MW and maximum capacity of 75 MW. One of the issues with parabolic troughs being known as completely renewable energy sources was that they were partly hybrids by design. The solar plant is 98 percent concentrated solar and two percent natural gas (the liquid is located in the hollow tube).
-9 parabolic troughs have been operating in the Mojave Desert located in California since 1984. Combined, they have a capacity of 354MW.
-Click here to view statuses/statistics on projects through out the United States: (AZ (3), CA (26), CO (1), NV (5), NM (1), HI (1), FL(1)):
Seville, Spain and “Solar Power Towers”- Seville’s PS10 (Planta Solar 10), has a 115m tall tower standing above a field of 624 mirrors fully equipped with tracking systems to follow the movement of the sun. Upon its opening in 2006, it was capable of producing 11 MW of energy, enough for 5,000 homes. In another adjacent field, PS20 (Planta Solar 20) began its construction in 2006 and was fully operational in 2009. PS20’s tower is 165m tall and stands above a field of 1,255 heliostats (nearly twice the size of PS10). Upon its opening in 2009, it was capable of producing 20MW, enough for 10,000 homes. That is enough energy to avoid the emission of approximately 12,000 tons of carbon dioxide (CO2) into the atmosphere. According to Bellona, it is projected that by 2013 that Seville’s solar towers will produce 300 MW of electricity, from the sun. That is enough electricity to power the total number of households in the area (180,000 of them). This would remove 600,000 tons of CO2 from the atmosphere each year. Reference to Seville’s PS10 and PS20 projects is located in Bellona’s 101 Solutions to Climate Change magazine, solution #12. Click here to view the PDF: www.bellona.org/filearchive/fil_101_solution.pdf
-Click here to view the statistics of other operational/ developing projects in Spain. There are (30):
Links to projects in other countries:
Algeria currently has one single project under construction. It is a parabolic trough system: www.nrel.gov/csp/solarpaces/project_detail.cfm/projectID=44
Egypt has one single project under construction. It is a parabolic trough system: www.nrel.gov/csp/solarpaces/project_detail.cfm/projectID=65
Morocco has one single project under construction. It is a parabolic trough system: www.nrel.gov/csp/solarpaces/project_detail.cfm/projectID=43
Italy has one single project in operation. It is a parabolic trough system:
United Arab Emirates has one single project under development. It is a parabolic trough system: www.nrel.gov/csp/solarpaces/project_detail.cfm/projectID=69
By Michelle Lanning, www.bellona.org