RICHLAND, Wash. — Solar power remains a hard sell in the United States, but researchers in Washington have developed a way to harness the heat of the sun to boost the efficiency of conventional power plants.
The new technology allows a natural gas-fired plant to generate 25 percent more electricity from the same amount of fuel. And it also reduces greenhouse-gas emissions, says Robert Wegeng, the Pacific Northwest National Laboratory engineer who's leading the project.
Wegeng and his colleagues are testing the system this summer on the PNNL campus near the Columbia River, where it's not uncommon for the blistering sun to drive temperatures into triple digits.
On a morning when the high was forecast to hit 100 degrees, team members gathered around their apparatus to explain how it operates.
"It will work best in a dry, sunny environment," Wegeng said. "In Eastern Washington our sun is pretty good."
The flashiest part of the device is a mirrored, parabolic dish that concentrates the sun's rays onto the business end of the operation: a sleek pod about 4 feet long crammed with wiring and machinery.
When the sun is shining, temperatures inside the pod approach 1,500 degrees — hot enough, with an assist from a catalyst, to blast apart the chemical bonds in a mixture of natural gas and water. The result is another fuel, called syngas, which burns better and releases more energy than natural gas.
Climate-altering carbon dioxide emissions drop because a power plant equipped with a solar-booster wouldn't have to burn as much fuel.
"Of all the projects I've worked on at PNNL, this is probably the most economically viable," said systems engineer Rick Cameron. "No matter what the price (of natural gas) is, you can improve the energy value."
But as with all energy technologies, the system's commercial fate will hinge on cost and practicality, which have yet to be demonstrated.
"It's a development effort, and it's a stretch to get there," Wegeng said.
The PNNL approach builds on what's called solar thermal energy production. Instead of relying on photovoltaic cells to directly convert sunlight into energy, solar thermal plants use mirrored, parabolic troughs or dishes to concentrate sunlight and tap the resulting heat to drive steam turbines.
One complex in the Mojave Desert covers more than 1,600 acres and has a capacity of 350 megawatts. Another being built in the same area will have a capacity of 400 MW.
The PNNL system takes advantage of the solar heat to drive a chemical reaction instead of using it to create steam.
Wegeng and his colleagues estimate a 500-megawatt solar-gas hybrid plant — with enough capacity to power about 350,000 homes — would require about 3,000 mirrored dishes equipped with the podlike chemical reactors.
Cara Libby, project manager for environment and renewable energy at the Electric Power Research Institute, called the PNNL system "intriguing." But while the cost of photovoltaic cells has dropped sharply in recent years, the price of mirrored solar concentrators is still high, she pointed out.
That means a steep upfront investment for any new natural-gas plant that might consider the solar-booster technology. "You're adding cost by putting a solar component into the project," she said.
With natural-gas prices so low, operators aren't likely to spend that extra cash.
Solar-gas hybrids might make more sense in places, like Washington, that require utilities to include renewable power sources in their mix, Libby said.
"If a system like this can provide a more economic solar resource than a stand-alone solar project, then I think it would be attractive to utilities trying to meet those mandates," she said.
Another advantage over an all-solar plant is that a hybrid facility could continue operating when the sun isn't shining, by switching to natural gas.
Wegeng and his colleagues are working with industry and academic experts at Oregon State University to reduce the cost of their system and develop ways to mass-produce it. The challenge is to produce a system that's reliable, high-performing and economically competitive with natural gas.
"We think we really have a good shot at it," Wegeng said.
The project was launched with $750,000 in federal stimulus money. The experimental phase is funded with about $3.5 million from the Department of Energy's SunShot Initiative to advance solar technology, and $850,000 from industrial partner SolarThermoChemical LLC, which hopes to commercialize the technology.