When one of Japan's leading carmakers decides to start making solar cells, is it any surprise that the result is twice as efficient as current methods? Honda's entry into the market will hit full stride this fall, when its 39,000-square-foot facility in Kumamoto, Japan, goes on line, producing enough solar cells each year to power 8,000 homes. By making thin-film cells from a compound of copper, indium, gallium, and selenium, Honda will use only 50% of the energy and carbon dioxide needed to make traditional silicon cells. Designed by Honda Engineering, they will be used mainly for homes and small businesses in Japan. While the $70 million in expected annual sales is a drop in the bucket for Honda, it hopes to expand production and start selling the cells in the United States and Europe as well.