Construction is slated to begin next year on a “bio-refinery” in California that will convert thousands of tons of orchard prunings, rice straw, and other agricultural wastes into ethanol, which could be used as a gasoline additive in place of MTBE. In other clean energy news, sales of geothermal heat pumps jumped 20 percent in 1997, and the Energy Department expects the total number of geothermal systems to keep increasing at a rate of about 6 percent per year. Some renewable energy companies are targeting rural residents, pointing out that it can be cheaper to install solar and other systems than extend electric lines from the grid. Researchers are hard at work trying to figure out how to mass produce a new generation of efficient thin-film solar cells. And a new report by the President’s Committee of Advisors on Science and Technology warns of drastic environmental and political risks if the U.S. does not invest billions in clean energy technology.