Solar power holds the promise of clean, limitless energy, but it currently suffers from high costs and an inherent disadvantage of not working when the sun isn't shining. The Department of Energy's Pacific Northwest National Laboratory is taking a best-of-both-worlds approach by developing a hybrid solar/gas system that increases the efficiency and reduces the carbon footprint of natural gas power plants.
The PNNL system uses a parabolic mirror to focus sunlight on a four by two-foot (1.2 x 0.6-m) chemical reactor lined with narrow channels 8.1 mm (0.318 in) wide. The sunlight heats natural gas in the channels next to a catalyst that breaks down the gas molecules into a mixture of hydrogen and carbon dioxide called synthesis gas or syngas. Connected to the reactor is a heat exchanger that collects waste heat from the reaction and recycles it back to the reactor to boost the process until 60 percent of the sunlight is converted to chemical energy. Tests indicate that the system allows a natural gas plant to operate at about 20 percent greater efficiency.
"Our system will enable power plants to use less natural gas to produce the same amount of electricity they already make," says PNNL engineer Bob Wegeng, who is leading the project. "At the same time, the system lowers a power plant's greenhouse gas emissions at a cost that's competitive with traditional fossil fuel power."
It's no surprise that the system works best in areas with lots of sunshine and according to PNNL, it's adaptable to different sizes of natural gas power plant sizes with a 500 MW plant needing about 3,000 solar dishes. In addition, the syngas can also be used to produce synthetic fuels for vehicles.
PNNL plans to test the system at its campus in Richland, Washington as part of a program to increase the system’s efficiency and bring down the cost to a projected six US cents per kilowatt-hour by 2020 to make it competitive with conventional fossil-fuel plants. Also, methods aimed at mass producing the system will be developed at the Microproducts Breakthrough Institute, a research and development facility in Corvallis, Oregon, while industrial partner SolarThermoChemical LLC plans to manufacture and sell the system after development.
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