Reuters: Retail giant Wal-Mart Stores Inc plans to expand the use of renewable energy in its stores by installing thin-film solar panels in up to 30 of its locations. This would be first time that Wal-Mart, which already has solar installations in 31 other sites in California and Hawaii, would use thin-film solar technology to generate power. “Until now, all of our solar projects have been with traditional crystalline panels,” a Wal-Mart spokeswoman said in an email …