One of the world's largest renewable energy projects can be found in the Mojave Desert near the California-Nevada border: the Ivanpah solar thermal facility. Located on the Ivanpah Dry Lake, this giant project uses solar thermal technology and it covers 3500 acres of public desert land near Las Vegas. This area is equivalent to four times the size of Central Park in New York City. It produces 377 megawatts (MW) of  solar power at its peak capacity, powering more than 140,000 homes.

Power to the Tower

Solar thermal power is a very distant cousin of photovoltaics (PV), the mainstay of residential solar power systems. While PV systems use both the direct and diffuse component of solar radiation, solar thermal systems only use the direct component. That is to say, PV systems can still eek out some production on cloudy days but solar thermal systems need clear skies to generate power. While photovoltaics can convert incoming solar radiation into electricity directly, solar thermal systems operate quite differently.

Ivanpah consists of three "power towers" that use concentrated solar rays to generate steam in order to rotate a turbine, much like conventional power plants that use natural gas or coal. The sun's rays are collected using hundreds of thousands of mirrors (also called heliostats) and then reflected onto a receiver full of water. This intense heat creates high temperature steam which is then used to rotate a turbine. The resulting technology is awe inspiring: the sun's rays reflected onto a single focal point, surrounded by thousands of shimmering mirrors.

Aerial view of the three towers

Aerial view of the three towers (credit: Brightsource Energy)

...but not without any problems

On October 27, 2010, the then California Governor Arnold Schwarzenegger launched the construction of the project. After more than three years of construction, Ivanpah was completed on February 13, 2014. The total cost is reported at $2.2 billion, and $1.6 billion of this amount was financed through a loan guaranteed by the U.S. Department of Energy. The remaining amount was financed by NRG Energy, BrightSource Energy and Google. However, in November 2011, Google withdrew from the project citing the steep declines in the prices of photovoltaics, a more conventional way to harness solar energy. The federal loan guarantee also generated some tension, as it was criticized by a Republican senator as irresponsible fiscal management by the U.S. government.

Although the project is located on a desert, its impact to local wildlife also caused controversy. Desert tortoises living in the area had to be relocated, and a few migratory birds were reported dead due to the intense heat of the mirrors surrounding the towers.

Despite all these challenges, Ivanpah is now fully operational, and it will continue to produce energy with virtually no greenhouse gas emissions for the next 25 years. While the impact on the local environment should not be dismissed, it is a very small price to pay to generate large amounts of clean power.

Making sense of the numbers

Let's take a quick look at the numbers related to this project. As expected, the solar resource in the area is abundant. Sunmetrix Discover gives a solar score of 75 for the area, making it one of the top spots of solar energy potential in the US (you can see a list of top 10 US cities here). But what about the generation capacity of Ivanpah at 377 megawatts? This is a giant number, especially for a renewable energy project.

In comparison, the capacity of a nuclear power plant in the US ranges anywhere between 500 megawatts to nearly 4,000 megawatts according to the US Energy Information Administration. So is it safe to say that Ivanpah can replace a nuclear power plant, even if it's on the smaller side? Unfortunately not, as capacity is one thing, but "capacity factor" another. As we highlighted in a previous article, the capacity factor of nuclear power is in the 85-90% range. According to NREL, the capacity factor of Ivanpah is in the range of 28% - around a third of nuclear power plants. Thus, the 377 megawatt of solar thermal capacity is roughly equivalent to about 120 megawatts of nuclear power capacity.

Detailed view of a tower (credit: Brightsource Energy)

Detailed view of a tower (credit: Brightsource Energy)

Our verdict: sunny skies ahead for solar thermal

In many ways, Ivanpah is a very significant milestone in the evolution of solar energy. It is living proof that large scale solar projects are viable, relatively cost-efficient and much faster to deploy than nuclear energy. Since this was a pioneering project, it was full of many technical and economic risks. The loan guarantee of the U.S. Department of Energy and the initial involvement of Google certainly helped surmount some of these risks. Future projects can benefit greatly from these lessons learned and decrease the costs even further. Can you beat Ivanpah's solar score of 75? Click here to play the Sunmetrix Solar Challenge!