Reuters: Growth of a nascent U.S. industry to build and install clean energy sources, like windmills and solar cells, could be stunted if Congress doesn’t extend tax incentives set to expire next year, industry officials and lawmakers said on Wednesday. Democrats last week dropped a $21.5 billion package of tax incentives from a broad energy bill after Republicans and the White House threatened to block it. Without the tax credits set to expire at the end of 2008, homeowners and …