Lab helps develop hybrid power plant

One of the frequently mentioned pitfalls of renewable energy sources such as wind turbines and solar panels is their inconsistency. They can’t make power if the wind isn’t blowing, or if the sun isn’t shining.

But Idaho National Laboratory researchers might have a solution to that problem. A recently completed INL research project helped combine three clean energy sources in a Nevada power plant that can churn out large amounts of electricity, day and night. INL’s Dan Wendt, a leading national researcher on geothermal and hybrid power plants, said the Stillwater facility in Fallon, Nev., is the first of its kind anywhere in the world.

The desert facility combines two types of solar power technology alongside a geothermal plant to produce a maximum of 61 megawatts of electricity — enough to power roughly 45,000 homes. It is operated by an Italian company, Enel Green Power. Wendt said the plant’s success — it began operating last year — shows that renewable energy sources can be paired together to generate power that matches up with customer demand.

“The lessons we are learning at this advanced geothermal-solar facility will be key to the development of other hybrid plants throughout the world,” Enel’s CEO Francesco Starace said at a plant dedication in March. The lab first examined hybrid renewable technology in 2012, Wendt said. Then in 2014, it signed onto a cooperative research agreement with Enel and the National Renewable Energy Laboratory to help develop the Stillwater facility.

Enel needed help from INL with computer modeling and other technical research to optimize the performance of Stillwater, Wendt said.

Stillwater has three components. It includes 89,000 photovoltaic solar panels, which convert sunlight directly into electricity. There is also a smaller field of solar thermal panels, which use mirrors to reflect the sun and create electricity by boiling a fluid. And the final piece is a geothermal plant, which makes energy using heat stored naturally deep inside the Earth’s crust.

The three technologies work together to produce a steady supply of electricity, Wendt said. INL researchers were focused on optimizing the relationship between the solar thermal and geothermal technologies, he said. Pumps bring hot water out of the ground and into the geothermal plant, which is “essentially a big machine that converts heat into electricity,” Wendt said.

The solar thermal panels improve the geothermal plant’s performance by making the water it pumps out of the ground even hotter. Geothermal plants naturally perform best in cooler temperatures, often at night, while solar technology thrives during sunny, hot times of day. “Adding the solar heat at that point in time can give the (geothermal) plant performance a boost when it needs it the most,” Wendt said.

Energy demand also happens to often be highest during the day, when air conditioning and various other household appliances are running. “There’s an excellent synergy there, matching up the power generation with the demand,” Wendt said of the relationship between the geothermal and solar panels.

With funding from DOE’s Geothermal Technologies Office, Wendt said he will continue to dig into different types of hybrid renewable energy technologies, and study whether plants similar to Stillwater could be built elsewhere.

Idaho could be an ideal candidate for a future hybrid plant, he said, considering its geothermal energy resources and abundant sunshine. Yet economic challenges for developers looking to build such complicated plants will be one big hurdle to overcome.

“I don’t think in the immediate future there will be a huge number of (hybrid plants),” Wendt said. “But as the costs of the solar collectors continue to decline, there may be more built.”

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