The US Federal Bureau of Investigation (FBI) has raided the offices of California-based solar energy firm Solyndra.

The FBI executed a search warrant at the firm’s Fremont headquarters just a few days after Solyndra announced that it was planning to file for bankruptcy protection.

Solyndra manufactures photovoltaic solar energy systems for installation on commercial rooftops, and has received more than $500 million in federal loan guarantees.

According to local press reports, the FBI’s investigation is being conducted in conjunction with the US Department of Energy’s Office of Inspector General.

The FBI has not revealed further details of the case.

Solyndra announced at the end of August that it had suspended manufacturing operations and laid off approximately 1100 staff. It said that the move was because of poor market conditions in the solar industry market.

In an August statement, Solyndra said that it could not compete “with the resources of larger foreign manufacturers” and that the competitive challenge was exacerbated by “a global oversupply of solar panels and a severe compression of prices that in part resulted from uncertainty in governmental incentive programs in Europe and the decline in credit markets that finance solar systems”.

“Regulatory and policy uncertainties in recent months created significant near-term excess supply and price erosion,” said Solyndra’s president and CEO, Brian Harrison. “Raising incremental capital in this environment was not possible.”

Prices for solar PV panels have fallen by around 42 per cent in 2011, largely due to an oversupply in the market and competition from Chinese manufacturers.