US transmission company Clean Line Energy has received regulatory approval to start signing customer deals for a 800-km overhead line that will connect wind farms in Iowa with Illinois.

The $1.7bn high voltage direct current Rock Island Clean Line is expected to be operational by 2017 and transfer 3.5 GW of renewable power to eastern states.

Houston-based Clean Line said the approval from the Federal Energy Regulatory Commission would allow it to subscribe up to 75 per cent of the Rock Island line’s capacity with anchor customers. The remaining capacity would be sold through an open season process, the company said in a statement.

“This approval marks an important step forward in the steady progress of our Rock Island Clean Line project,” said Michael Skelly, president of Clean Line.