Storage is "a problem" for yieldcos, says Tom Leyden, because such companies are designed to aggregate assets with firm and predictable revenue streams – something hardly any storage projects are currently able to secure.

"Yieldcos are very conservative vehicles by nature," says Leyden, SunEdison's VP for storage deployment.

"They want to see long-term contracted revenues. Most of the revenues you get from storage are market based, not contracted revenues," he said, speaking this week at the Solar Power International conference.