SAN JOSE As demand for clean energy rises around the world, the nation's high tech hub is finding new ways to squeeze money from silicon. Silicon Valley, named for the material used to make computer chips, is applying its expertise to design and manufacture silicon solar cells that convert sunlight into electricity. Advocates hope the region's engineers and entrepreneurs will help make solar competitive with traditional energy sources such as coal and natural gas. "We're in the very early stages of a long build-out in solar technology," predicted Erik Straser, who heads the "cleantech" practice at the Menlo Park venture...