Capturing more heat from low-temp resources to aid geothermal power
By Darren Quick
July 20, 2009
Geothermal power is cost effective, reliable, and environmentally friendly, but it has previously been limited to geographic areas near tectonic plate boundaries. New technologies, such as that employed in the Raser low-temperature binary geothermal plant, promise to expand the opportunities for geothermal plants. Now scientists at the Department of Energy's Pacific Northwest National Laboratory (PNNL) have devised a method for capturing significantly more heat from low-temperature geothermal resources to further boost the possibility of virtually pollution-free electricity.
PNNL's conversion system will take advantage of the rapid expansion and contraction capabilities of a new liquid, developed by PNNL researchers, called biphasic fluid. When exposed to heat brought to the surface from water circulating in moderately hot, underground rock, the thermal-cycling of the biphasic fluid will power a turbine to generate electricity.
To aid in efficiency, scientists have added nanostructured metal-organic heat carriers (MOHCs), which boost the power generation capacity to near that of a conventional steam cycle. It was actually research on nanomaterials used to capture carbon dioxide from burning fossil fuels that led to the team's discovery of these properties.
The goal is to enable power generation from low-temperature geothermal resources at an economical cost. To this end they aim to have a functioning bench-top prototype generating electricity by the end of the year.
According to US Department of Energy, electricity from geothermal resources accounted for just 0.13 percent of overall energy production in the US in 2006. But the PNNL research team expects that figure to rise significantly with a technical and economic analysis conducted by the Massachusetts Institute of Technology estimating that enhanced geothermal systems could provide 10 percent of the nation's overall electrical generating capacity by 2050.