by Julian Spector
August 13, 2020

It's been a strange earnings season, all about the extent to which companies avoided the kind of losses they could have sustained from a shut-down economy.

The distributed solar sector, at least the large national players, largely weathered the turbulence without falling apart. Despite the coronavirus disruption, and possibly because of it, the solar companies pushed further into pairing batteries with home solar. Now the value proposition includes keeping the lights and AC on while you’re stuck at home during quarantine.

The ecosystem of home storage providers has grown considerably compared to a few years ago, and now we have real competitive dynamics to examine. This week on Storage Plus, I’m breaking down the latest numbers on where the competitors stand.

It’s hard to make apples-to-apples comparisons because the publicly traded companies don’t report the same metrics on their storage business, and some individual companies vary their disclosures from quarter to quarter.

Some companies say total megawatt-hours deployed; some talk about total customers or deal count. The most popular metric seems to be the attachment rate, which is the percentage of solar deals that include battery storage. But companies disclose attachment rate in different ways, referring to specific regions, states or the whole U.S. Sometimes they also share the attachment rate of installed customers, which is more of a hard measurement but says less about where the market is headed.

Here’s what we can glean from the information that did come out of Q2.


The dominant home backup generator company, based in Waukesha, Wisconsin, is making headway in its bid to shake up the residential battery competition.

Reaching customers through TV ad buys, a network of generator dealers and a partnership with Sunnova, Generac hopes to achieve an ambitious 125 to 150 megawatt-hours of battery sales this year. As of Q2 earnings, the company was trending toward the low end of that range, based on slowdowns in the solar market.

Just this week, Generac sweetened its battery offering with hardware upgrades for whole-home backup. The PWRcell will come with inverters capable of 9-kilowatt continuous discharge and 50-amp current. That’s more powerful than the competition and vital for powering up equipment like air-conditioning units and well pumps after an outage.

Generac is even jumping into grid services by partnering with software startup Virtual Peaker to aggregate its batteries. The companies are active in the utility territories of Green Mountain Power and Portland General Electric.


The residential solar company, which works through a network of installers, hit 34 percent storage attachment nationwide in the second quarter. This is wild — it’s the largest national attachment rate any of the solar companies revealed this quarter. A year ago, Sunnova’s attachment rate was 11 percent.

That’s a shift from packaging storage with one-tenth of solar deals to one-third of deals in the course of a single year. And it’s not banking entirely on the California market, with its Self-Generation Incentive Program subsidies and high power prices. Sunnova is bringing batteries to Puerto Rico to keep the lights on after hurricanes.

What’s not clear is just how widespread the battery demand is. It’s possible that a few really bustling markets lift the national average even with minimal activity in most states. Sunnova does not give a state-by-state breakdown.

Some of the island markets are already at 100 percent battery attachment, Chief of Staff Kelsey Hultberg said in an email (the company's island markets include Hawaii, Guam and the Northern Mariana Islands). CEO John Berger has said the attach rate could hit 80 percent in the coming years.  

Batteries still account for just 5.6 percent of Sunnova’s installed base, translating to around 5,128 units in the field.


The leading rooftop solar installer did not report its attachment rate this quarter. That’s a notable omission given that Sunrun still talked up the storage business as a key value-add and long-term growth vehicle for the company.

Then again, Sunrun had a lot of other developments to highlight, including a deal to acquire its next-largest competitor and new wins in the grid services market. CEO Lynn Jurich added some extra color when asked about storage on the call with investors.

She said the attachment rate is 100 percent in Hawaii and in the high 30s in California; other markets are at 0 percent. “But certainly, it’s steadily growing,” she noted. “It continues to grow much faster than the solar-only product is.”

Those market-specific numbers track with what Sunrun has said previously. The last time we got comprehensive battery reporting from Sunrun was the Q4 2019 earnings, when the company said attachment rates were 35 percent for California and 20 percent nationwide — for the direct installation business, rather than the long-tail installers that use Sunrun as a financing partner.

In Q1 earnings, Jurich said that in April 60 percent of Bay Area residential solar customers chose to add batteries. That’s a very specific framing, calling out the most favorable market (generally well-off, climate-conscious customers with a grid that regularly shuts down to prevent killing people with wildfires).

Sunrun’s offering could gain steam in the second half due to an imminent decline in price.

“The price improvements for the battery that we’re selling [in the] back half of this year [are] 15 percent lower than in the first half,” Jurich said. “And again, we’re going to be passing through some of that to our customers to just make the value proposition stronger.”

A spokesperson attributed that significant decline to improvement in installation and hardware components. Sunrun has long offered the LG Chem Resu and recently added the Tesla Powerwall to cover whole-home backup.

Finally, I got some detail on how Sunrun hopes to leverage the Vivint Solar acquisition for battery expansion. Vivint leadership has admitted to being “behind on storage,” raising a real question of what value the acquisition could add in that department. But Jurich told me she hopes to use Vivint’s direct-to-home sales team to cluster storage installations in particular neighborhoods.

Concentrating battery capacity on specific, high-value feeders of the distribution grid makes it more attractive to utilities than if the same capacity were scattered across an entire territory.


The distributed solar company rolled out its branded home storage product to Californians in June, and said it’s pairing batteries with 30 percent of rooftop solar deals in the state. SunPower markets its SunVault storage package as “the only home solar-plus-storage solution designed by one company.”


Tesla gave no reporting on its storage attachment rate this time, which is a surprising choice for a company that almost single-handedly popularized home batteries. But the oversight may have more to do with the car manufacturer’s habit of giving its energy business short shrift during quarterly earnings calls. In Q1, the company said that more than 40 percent of residential solar customers opted to add storage and that it had installed its 100,000th Powerwall.

Tesla deployed 27 megawatts of solar in Q2 (an all-time low) and 419 megawatt-hours of storage (up 1 percent year-over-year). But the storage number is skewed by Tesla’s massive grid storage shipments; Tesla doesn’t break down how much of the total number goes to residential sales.