A leading US private equity group is turning up the heat on Congress to extend a tax incentive for solar energy that spurred its plans to invest in the sector last year.

Starwood Energy, a unit of Starwood Capital, which is run by Barry Sternlicht, the real-estate and buy-out investor, said last November that it would team up with Lockheed Martin, the defence company, to develop solar energy fields in the southwestern US.