The last couple of weeks have brought a dizzying array of partnerships between solar and storage companies, most of them with Tesla.

Add SunPower and Stem to the list.

For the last five months, SunPower has been reselling Stem's behind-the-meter battery systems to commercial customers across the U.S. The companies are not revealing the number of systems they've installed through the partnership, but SunPower's Ivo Steklac said he expects storage to help increase commercial-sector business "rather dramatically" based on early activity.

"It's a market pull. Our customers are asking for these solutions," said Steklac, SunPower's GM of residential and commercial energy solutions.

SunPower's reseller agreement with Stem was signed just weeks after it entered into a similar partnership with Sunverge, which gave SunPower access to a battery and software solution for residential applications in the U.S. and Australia. 

SunPower has been talking about integrating storage with solar for the last couple of years, but it has yet to scale beyond pilots. Steklac said the move into commercial batteries was a sign of SunPower's confidence in the long-term potential for storage services.

"We're going to be touching a much larger number of customers by offering storage," said Steklac. For now, SunPower is going after customers in markets like California and New York, where high demand charges for commercial and industrial customers make batteries much more competitive.

Adding storage to its suite of services allows SunPower to reach customers who may not have suitable roof space or a lease arrangement that will allow them to install solar. It also gives existing solar customers more options for managing their energy use.

In March, SunPower inked an exclusive agreement with EnerNOC to provide energy management software to its commercial and industrial solar customers -- adding a third pillar for SunPower's strategy to build energy services around its commercial solar PV business.

"You’re seeing us expand our portfolio of what we can do so we can aggregate and dispatch these resources into the market and become a better participant on the grid," said Steklac.

The partnership also gives Stem another deep channel to sell systems, both for new and existing customers. 

Stem CEO John Carrington said that his company is set to install 10 megawatts of batteries in 2015. The company is currently working on projects at 140 sites across the U.S. "The growth rate is remarkable," he said.

According to GTM Research, distributed projects could make up 45 percent of the U.S. storage market by 2019.

As the cost of capital for batteries continues to drop and companies build strong pipelines of projects across the country with consistent cash flows, Carrington believes that storage will get sold into YieldCos. 

Because of a pending YieldCo with First Solar, Steklac wouldn't comment specifically on the subject. But he did say that battery projects like the ones Stem is developing are "consistent" with the type of projects that would go into a YieldCo.

For more on SunPower's plans for storage and energy management, watch our recent fireside chat with CEO Tom Werner:

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