2014

Ivanpah Solar Electric Generating System

Imagine that you want to collect sunlight. A lot of sunlight. So much sunlight, and so much heat, that you can power a small city with it. That is what this huge heliostat array near Las Vegas is doing starting in 2014. Owned by Google, NRG Energy, and BrightSource Energy, it is an engineered structure of immense proportions.

The basic idea is so simple: Take a flat mirror and use it to reflect sunlight toward a tower. Now scale up that flat mirror so it is 75 square feet (7 square meters) in size. Now put two of these mirrors on a moving axis—this assembly is called a heliostat. Now install 173,000 of these heliostats pointing at three different towers. That is the scale of operation at the Ivanpah Solar Electric Generating station.

The purpose of a heliostat is to track the sun. A heliostat can tilt and rotate the mirrors so they are always reflecting sunlight toward the tower. That would be a fairly easy task, except for the wind. Imagine that you stick your hand out of the window of a car traveling at 60 miles an hour. There is a lot of drag. Now imagine sticking a sheet of plywood out the window—the wind force is immense. The heliostat is holding two mirrors equaling roughly five sheets of plywood in size. Each heliostat has to be quite powerful to deal with that kind of wind loading and keep the mirror pointing properly on a windy day.

Inside the three towers there are custom boilers that turn the sun’s heat into steam. The steam drives a steam turbine just as it would in a conventional power plant.

Consider that the sun delivers about 1 kilowatt of energy per square meter of the Earth’s surface. Consider that this site has about 2.5 million square meters of mirror. That is 2.5 million kilowatts of heat being collected. About half of that heat is lost in the process of focusing it on the tower. It then converts to electricity at roughly 30 percent efficiency. So the site is able to produce about 400 megawatts when the sun is shining brightly—approximately 7 hours a day. If electricity sells for 10 cents per kilowatt-hour, that’s about $100 million of electricity annually.

SEE ALSO Steam Turbine (1890), Light Water Reactor (1946), CANDU Reactor (1971).

Aerial view of the solar electric generating system in the Mojave Desert.