SunEdison will purchase up to 1,000 flow batteries from Imergy Power Systems as part of its commitment to bring power to 20 million people by 2020.

The vanadium flow batteries will be paired with SunEdison solar panels, which are being deployed in partnership with Omnigrid Micropower Company (OMC) in India. SunEdison will also increase its equity investment in Imergy.

Vanadium flow batteries are a logical choice for rural applications because they can provide many hours of storage, require little maintenance and can operate for decades.

“In our partnership with Imergy, there is breakthrough potential for long-duration storage for a lot of applications, but particularly rural electrification,” said Tim Derrick, general manager of advanced solutions and energy storage at SunEdison. “We see incredible promise from a cost perspective.”

SunEdison is purchasing Imergy’s ESP 30 systems, a 30-kilowatt battery that can provide about 24 hours, or 120 kilowatt-hours, of storage, according to Bill Watkins, CEO of Imergy.

Although Imergy introduced its third-generation battery for large-scale applications last month, the partnership with SunEdison is more in line with its original business model. Imergy started out as Deeya Energy, making batteries for backup power at telecom towers in India. The partnership with SunEdison will also involve power backup for telecom towers.

To bring power to rural villages, OMC and SunEdison are supplying energy systems to Indian telecom towers, which in turn provide excess power to surrounding villages. Indian telecom towers are increasingly switching to renewable power sources to comply with government mandates.

Because the telecom tower is the anchor for the project, the companies can bank the project using a hybrid power-purchase agreement, even though villagers may have little or no credit. Imergy has also used prepay models in other off-grid applications.

The deployment of the systems has already begun, but the full rollout will take many years. OMC and SunEdison have a goal of 5,000 systems over the next five years to bring power to 10 million people.

Even with the new partnership Imergy inked with SunEdison in India, the battery company expects to be moving away from providing backup power to telecom towers as the basis of its business in the near future. This year, about 80 percent of its business might come from energy storage for telecoms, but Imergy’s president and COO Tim Hennessy said that is likely to drop to about half next year and be reduced further after that.

As for Imergy’s cost target of $300 per kilowatt-hour, “we’re committed to that sooner than later,” said Watkins, adding that the company just needs a bit more volume.

But “cost per kilowatt is a bit of a misnomer,” said Watkins, especially in applications such as off-grid where batteries will be cycled down to zero on a regular basis and last for 20 years.

SunEdison is in developing countries both to make money and provide affordable power to those who live in energy poverty, but it has microgrid ambitions beyond emerging economies, as does Imergy.

GTM Research anticipates the solar-plus-storage market to grow from $42 million in 2014 to more than $1 billion by 2018. SunEdison is already working with Imergy on some requests for proposals in the U.S.

“The applications in developed nations,” said Derrick, “that’s ultimately where we want to be.”