"The strong response to our request for proposals reflects on the healthy solar market in North Carolina," said Rob Caldwell, vice president, renewable generation development.

He says Duke hopes to be able to select the winning projects – all greater than 5MW - and complete negotiations by 1 October. All selected projects should be online by 31 December 2015.

Utility spokesman Randy Wheeless says that federal law requires Duke to buy solar power from projects under that amount at a pre-established tariff.