(Bloomberg) -- A factory boom in China that’s lowering the cost and boosting demand for solar panels is also squeezing the margins of the companies that make them.Most Read from BloombergUS Health Officials Urge Moving Pot to Lower-Risk CategoryStocks Up Again in ‘Bad News Is Good News’ World: Markets WrapSingapore S$1 Billion Laundering Scandal Embroils Its Banking GiantsFed Ramps Up Demands for Corrective Actions by Regional BanksApple Tests Using 3D Printers to Make Devices in Major Manufactu