# A first-of-its-kind project makes energy from a triple whammy: Hot rocks, solar panels and mirrors

In a few weeks, a first-of-its kind power plant — which uses energy from hot rocks deep in the earth, combined with the heat and light from the sun — will start producing power from all three sources at a site in Churchill County, Nevada, about a two-hour drive east of Reno. The project is called the Stillwater Geothermal/Solar Hybrid plant, and Enel Green Power North America, an American division of the huge Italian power company Enel, is now hard at work finishing construction on the solar portion that collects the sun’s heat using large concave mirrors that concentrate the sunlight by 75 times.

A geothermal plant at the site went online in 2009, and a sprawling solar panel field — using 89,000 panels across 110 acres — started delivering energy in 2012. But on Monday, during a tour of the plant, Bill Price, Enel’s VP of geothermal engineering and construction, said that before the end of the month a portion of the 2 MW solar thermal field is supposed to start producing solar power, and the entire solar thermal site will be fully operational by the third quarter of this year. All together, the geothermal plant (33 MW), the solar panels (26 MW) and solar thermal site (2 MW) will make enough renewable energy to ensure that the nearby town of Fallon is running completely on clean power.

Price, who is lauded by his peers for getting the unique hybrid plant up and running, says when he walks down the street in Fallon, he looks up at the street lights with a sense of pride. The entire hybrid project “used a lot of serial number one” technologies, says Price. For example, when the geothermal pump was installed in 2009, it was the first time that that technology had been used.

## Clean energy innovation

Churchill County and the city of Fallon aren’t exactly used to being at the forefront of cutting-edge technology. The mostly rural county has a population of 25,000 and it’s filled with agriculture; farmers grow crops like alfalfa, cantaloupes and onions. Abandoned houses are common sights. If you drive too fast through Fallon, you can easily miss the tiny downtown strip on — of course — Maine St. (However, Fallon is also home to a Naval Air Station that houses the Top Gun training program).

But Nevada — with its natural geothermal environment and hot, sunny terrain — is one of the leading states when it comes to installing new types of clean power. Clean power projects from Enel Green Power alone generated 308,000 MWh of green electricity in Nevada last year. Nevada has thousands of MW of geothermal plants under development (45 total projects under development), including many that are using a newer type of geothermal technology called a “binary system.”

Apple(s AAPL) built its data center in northern Nevada, partly to tap into these types of clean power sources. Tesla (s TSLA) is looking at a spot just outside of Reno for its massive battery factory, and plans to use significant renewable energy. All of a sudden, Reno and the surrounding areas — long depressed and associated with casinos — find themselves at the center of an emerging clean energy tech explosion. This week the National Geothermal Summit will kick off at the Grand Sierra Resort, a casino in Reno, bringing hundreds of geothermal execs to the city.

The technology at the Stillwater plant is so new that it’s actually somewhat experimental for Enel. The company recently signed a cooperative R&D agreement with the National Renewable Energy lab and the Idaho National Lab to share data about how the system works over the coming years, and what the benefits are of using these three technologies in tandem. Price says the $15 million it took to build the solar thermal project came out of Enel’s R&D budget. The geothermal plant, which was built first in 2009, is the core of the site and produces electricity that is sold in a power purchase agreement to NV Energy. Enel Green Power added on the two types of solar to enhance and aid the geothermal project. The first solar panel project worked so well in tandem that the team decided to add the solar thermal subsequently, says Price. The solar panels produce electricity that power the geothermal project’s switch gear. When the geothermal tech is working its hardest during the blazing hot afternoon, the solar panels are producing their max electricity. The idea behind the solar thermal tech is that it will produce heat that will boost the temperature of some of the cooler fluid that runs through the geothermal pipelines. The geothermal project isn’t dependent on either the panels or mirrors to run, but uses these solar technologies to add efficiency and operate better. ## Hot rocks and the hot sun The geothermal project uses newer tech all on its own: a binary cycle that taps two systems to get the heat from the underground rocks to the turbine to generate electricity. In a binary system, pumps are used to pump the underground hot water (at this site, it’s 300 degrees) from a geothermal well to the surface of the earth and through a series of heat exchangers. The heat exchangers capture the heat, and the geothermal brine (the water from the well) cools and is returned to the well (to be reheated and recycled again and again). At the same time, another liquid with a low boiling point is pumped at high pressure through the heat exchanger, where it vaporizes and then powers a turbine. The benefit of this tech is that it has two separate closed loop systems, so nothing is added into the ground and nothing is consumed in the process. Proponents of geothermal say this technology makes it the cleanest and most environmentally safe clean power in the world. Other geothermal tech, like that built around the geysers in Napa, California, inject water into the reservoirs of rocks and use the steam created to drive turbines. Those are the most common projects in operation, but binary systems are being in used in many new and under construction projects. The geothermal plant at Stillwater looks the way you’d expect a large industrial power plant with lots of pipes to look. There are pipes all over the place that push geothermal brine and the second liquid — in this case, isobutanol — around, and a large tank that’s the vaporizer. Long pipes extend off the 240 acres to tap the geothermal well and bring it to the power plant. By comparison, Stillwater’s solar thermal plant looks a lot more modern. Twenty-two rows of 20-foot mirrors are tucked inside a see-through mesh fence that protects the site from wind and stops the reflection of the sun from affecting nearby residents. Each mirror is a parabolic trough that tracks the sun as it moves across the sky during the day, and concentrates the sunlight by 75 times onto a long tube that stretches across the rows. The tube is filled with water that is heated, and the steam runs a turbine. The technology is made by SkyFuel. Other companies that make solar thermal tech include BrightSource and Abengoa. Larger plants are beginning to employ a next-generation solar thermal tech based on a solar tower design, like at Ivanpah just outside of Las Vegas. The only site we didn’t visit during the tour was the solar panels. They cost$60 million to build (four times the cost of the much smaller solar thermal plant). The omission is testament to how commonplace solar panels are these days — they’re no longer next-gen tech. (It was also raining a lot that day.)

The drawback of such a system, compared to say natural gas or coal, of course, is cost. The companies didn’t disclose the levelized cost of the energy of the plants, but geothermal, solar thermal and solar panels, can commonly be more expensive than fossil fuel based power. However, that’s starting to change with state renewable portfolio standards, the coming regulations from the Environmental Protection Agency, introduction of newer lower cost technology and the availability of other types of incentives. For example, the Stillwater solar panel project used \$40 million in federal tax support from the U.S. government’s stimulus program in 2009.

But ultimately, the Stillwater plant is interesting because of what can be discovered when all three technologies are combined. The result of the clean energy hybrid, across 240 acres, could offer key insights about how these three renewable energy sources can work together, rather than in competition with each other.

Most energy execs agree that there won’t be one clean energy solution. Instead, a half-dozen options will be used where they fit best in the given environment. If these technologies can work in cooperation, then they could be deployed even more quickly, and potentially at a lower cost.

Updated to correct the number of total geothermal projects in Nevada.