Investing.com - Tough times lay ahead for the solar industry amid slumping demand and surging supplies, according to Goldman Sachs (NYSE:GS).In a note to clients, the Wall Street firm says it sees zero upside for solar power equipment companies in the near to medium term, and slashed stock price targets for major players in the industry,Goldman says its outlook is based on China's recent decision to end subsidies for large solar farms and require providers to sell power at competitive prices.The firm is forecasting a 40% drop in equipment sales in China, the world's largest solar market, and a 24% decline in solar installations around the world this year.Among the casualties of the downturn is First Solar (NASDAQ:FSLR). Goldman gave it a sell rating and slashed its stock price forecast from $75 to $48.