Lower-temperature geothermal power generation has been too expensive for practical use before now, however United Technologies Research Center has developed a relatively low-cost system that can convert temperatures as low as 165°F into electricity. According to Technology Review, "The technology is similar to steam engines, except that steam or hot water vaporizes a hydrofluorocarbon refrigerant that drives the turbine. And the refrigerant has a lower boiling point than water." [Link]