MARLBORO, Mass. – Solar panel maker Evergreen Solar Inc. said Tuesday it has signed a sales contract with Germany's IBC Solar AG worth $1.2 billion – the biggest deal in the company's history.

Evergreen will make the solar panels at a recently opened plant in Devens, Mass., and at another factory expected to open in 2010. The deal runs through 2013.

Evergreen said the contract with German-based IBC brings its backlog to almost $3 billion, spread among five customers.

“This contract represents the single largest contract in the history of our company and is one of the largest contracts ever between a panel manufacturer and a distributor,” said Richard M. Feldt, Evergreen Solar's chairman, president and chief executive.