Solar Farms in 15 Images

1. Concentrated solar power plants
Concentrated solar power (CSP) plants use mirrors to concentrate the Sun's rays and heat a fluid, producing steam, which drives a turbine to generate power. They should not be confused with photovoltaic (PV) solar power plants, which produce electricity directly. This photo shows the three "solar power towers" of the Ivanpah power plant in California.

1. Concentrated solar power plants
Concentrated solar power (CSP) plants use mirrors to concentrate the Sun's rays and heat a fluid, producing steam, which drives a turbine to generate power. They should not be confused with photovoltaic (PV) solar power plants, which produce electricity directly. This photo shows the three "solar power towers" of the Ivanpah power plant in California.

2. Tens of thousands of mirrors
Located in California's Mojave Desert, near Las Vegas, the Ivanpah plant has nearly 175,000 mirrors mounted on the ground. Known as heliostats, these mirrors can be moved to track the Sun's path and more effectively capture its rays. This solar energy is reflected onto a central tower, which gives the sites their circular form.

3. A heat-transfer fluid to turn water to steam
The central tower houses a receiver and tubes containing a flowing heat-transfer fluid, or heat carrier, which is generally made up of molten salt. This fluid serves to heat a network of water within the tower, producing steam, which drives a turbine as in conventional thermal power plants.

4. The water issue
At the Ivanpah plant, once the steam has passed through the turbine, it is cooled by large fans, the backs of which can be seen in this photo. The use of an air-cooled system helps save water, a key concern in desert regions. Water is also needed occasionally to clean the dust and other debris off the mirrors.

5. Parabolic trough power plants
The second category of concentrated solar technology – and currently most widespread – is the parabolic trough power plant (PTPP), which is made up of long, semi-circular mirrors, or troughs, that rotate on a horizontal axis to track the Sun. This type of solar farm has a rectangular form, not a circular one. The Noor 1 power plant in Ouarzazate, Morocco, seen here, has 500,000 mirrors spread over 4.8 square kilometers – the equivalent of 600 football fields!

6. Storage capabilities
In parabolic trough power plants, sunlight is focused onto a horizontal black tube running above the center of the mirror. Through this tube flows the heat-transfer fluid, which can reach temperatures of up to 500°C. The heat is then transported and concentrated through a network of pipes to drive a turbine in the power generation unit. One of the advantages of concentrated solar power plants is that the heat can be stored for a few hours before being used to produce electricity at peak demand times.

7. Farms in the desert
Parabolic trough power plants, like their solar power tower equivalents, are best suited to extremely sunny wide-open spaces, such as deserts. The largest PTPPs are located in the United States, Morocco and the Gulf states, like the Shams 1 power plant in the United Arab Emirates (seen here), with its 258,000 mirrors spread over 2.5 square kilometers.

8. Linear Fresnel reflectors
One variant of the parabolic trough power plant is the linear Fresnel reflector (LFR) system. Invented by a French scientist in the early 19th century, this technology has been around for some time and is used in most lighthouses. In this photo, a Tokyo University professor and researcher for Japanese electronics giant Sharp is shown presenting a model of these flat mirrors for solar power generation.

9. Less expensive but also less efficient technology
In linear Fresnel reflector systems, the flat mirrors rotate on a horizontal axis and tilt slightly to concentrate the Sun's rays onto a stationary tube above, as shown in this photo taken at a plant in Galicia, in western Spain. Flat mirrors are less expensive than their parabolic equivalents, but they are also less efficient. This technology is also used in the 12-megawatt Alba Nova plant in Ghisonaccia, Corsica.

10. Parabolic dishes
While parabolic dish systems look like satellite dishes, this technology uses mirrors to capture the Sun's rays and send them back toward a Stirling engine located at the focus of the parabola. First conceived in the early 19th century, the Stirling engine operates using fluctuations in the pressure of a gas. Each parabolic dish is a stand-alone unit. In Phoenix, Arizona, 60 such units have been grouped together to offer a combined capacity of 1.5 megawatts.

11. Photovoltaic solar power
Photovoltaic (PV) systems are by far the most common solar farms worldwide and significantly cheaper to build than concentrated solar power plants. They are based on PV cells assembled into panels, which capture the sunlight and convert it directly into electricity. The largest plants can be found in desert regions, such as the one shown here in Chile's Atacama Desert.

12. The world's largest solar farms
The most powerful photovoltaic plants are today found in China, the United States and India. Four, located in Tamil Nadu, India and in California, have capacities of more than 500 megawatts. France boasts Europe's largest PV power plant, situated in Cestas in the southeast of the country. This photo shows the California Valley Solar Ranch north of Los Angeles, which is built over nearly 800 hectares and has a capacity of 250 megawatts.

13. Sun-tracking panels
The California Valley Solar Ranch uses 90,000 rotating systems to pivot the panels toward the sun for greater efficiency. This makes it possible to concentrate production in the middle of the day, when electricity demand is at its highest, particularly for air conditioning.

14. DC to AC
Photovoltaic panels generate direct current (DC) electricity, which must be converted to alternating current (AC) before it can be fed into the power grid. Shown here is a transformer substation at the Nanao PV power plant in Japan.

15. Sophisticated control rooms
Larger solar farms require careful management. The Ivanpah concentrated solar power plant, for example, is divided into three sites, each consisting of a round cluster of heliostats facing a tower. The facility as a whole is coordinated from a control room, seen here.