The world's largest rooftop solar power system is being built on General Motors' assembly plant in Zaragoza, Spain.

Energy Conversion Devices said on Tuesday that its supplying the thin-film flexible solar laminates for the system through wholly owned subsidiary, United Solar Ovonic.

The Zaragoza installation will cover about 2m sq ft of roof at the plant and comprises about 85,000 solar panels.

When fully operational this autumn, the photovoltaic system will have a peak capacity of 12 megawatts, producing as much as 15m kilowatt hours of energy annually, enough to power approximately 4,500 homes.

GM currently has two of the largest solar power installations in the United States on the roofs of its Rancho Cucamonga and Fontana, California parts warehouses.

Rancho Cucamonga was the first public solar project in the US over 1 mega watt, when it began operating in autumn 2006. The solar panels provide about half of the facility's electricity.

Fontana, also 1 megawatt, became operational in December 2007 and generates about 1.3m kilowatt hours of electricity a year, about the amount needed to power 200 homes yearly.

GM with Veolia Environnement, Clairvoyant Energy and the government of Aragon to develop the Zaragoza renewable energy project.

GM is leasing its roof space to Clairvoyant and Veolia, who will build, own and operate the rooftop installation.

The Zaragoza plant builds the Opel/Vauxhall Corsa, Meriva and Combo models for Europe.