By definition, residential solar is small and utility-scale is very large. But recently, the annual output of the most prolific rooftop solar installers is starting to rival utility-scale plants.

Sunrun leads the pack; it is on track to install more than 400 megawatts this year through its in-house crews and installer partners. That puts it on par with, for instance, the 400-megawatt Eland project 8minute Solar Energy is developing for the Los Angeles Department of Water & Power. That project’s scale helped it nab the lowest price for combined solar-storage in the country.

But Eland got final approval this fall and will take three to four years to fully complete. Rooftop solar costs more than massive plants in the desert, but it can move much more quickly through the contracting and installation processes. The actions of the biggest installers are validating the argument that small-scale solar can add up to big capacity, a key test as California in January begins implementation of its mandate that all new homes install solar.

And Sunrun’s annual installations keep growing, expected to rise about 10 percent this year; the company reported that labor constraints will prevent a higher rate of deployment, but sales track with 15 percent growth year-over-year.

The problem, as far as rapid grid decarbonization is concerned, is that there’s only one Sunrun. Runner-up Vivint installed about two-thirds of what Sunrun did last quarter, 65 megawatts. No. 3 installer Tesla did even less, 43 megawatts, and that was a surprise improvement from the previous quarter’s paltry 29 megawatts.

It’s clear that national rooftop installers can contribute serious scale. The next question is whether there’s a market for several companies pumping out a decentralized 400-megawatt power plant every year. Will residential leaders eventually dwarf even that level of achievement?

Give me a P, give me an S…

About 150,000 Californians braced for another round of preemptive power shutoffs Wednesday, as utility Pacific Gas & Electric warned of exceedingly dry and windy conditions in 18 counties.

The threat of days without power has become business as usual in particular parts of the state this fall, with PG&E initiating rounds of blackouts to deter wildfires (it’s unclear whether it’s worked; the state is still investigating the cause of Sonoma’s Kincade fire, but the utility reported a malfunction in the area).

The situation has created dangerous conditions for vulnerable residents, riled up policymakers and caused a headache for PG&E. But home solar-and-storage companies say they’re seeing the upside.

Vivint Solar CEO David Bywater said in November that the shutoffs provided a “reset” in California, offering the company a renewed entrance into a market where lots of early adopters have already gone solar.

Residential solar executives including Sunnova’s John Berger and SunPower’s Tom Werner have also noted increased interest coming from customers in the state, though they’ve so far demurred on offering specific figures on any increase in sales.

SunPower cited residential storage attach rates averaging 20+ percent in Q3 — fortuitously, it unveiled its in-house residential storage product in September — but said that percentage is higher in California. Sunnova reported Q3 battery attachment rates at 15 percent, up from 11 percent in Q2, citing a “large growth opportunity surrounding storage.”

“With the devastation in California caused by wildfires and the resulting blackouts and deliberate power shutdowns across the state, it is clear we are witnessing a critical moment across the energy landscape,” said Berger. “As a result, we are seeing stronger demand for our storage products as customers look for alternatives that provide energy resiliency and reliability in the face of the effects of climate change.”

In a particularly stark snapshot of changing customer attitudes, Sunrun CEO Lynn Jurich told GTM that the percentage of Bay Area customers choosing storage alongside solar doubled in October, from 30 percent to 60 percent. That was the month PG&E initiated its biggest power shutoffs so far. Sunrun’s rate of storage adoption was 30 percent for California overall in the third quarter.

The demand for backup power is also compelling companies to shift their offerings. Vivint, a bit of a laggard in the residential storage space, expanded its financing options in California to include storage in solar power-purchase agreements (more on that below). And in September, Sunnova added a 10-year finance agreement to its existing stable of options, which includes leases and loans.

Vivint is behind on storage, but doesn’t seem to care

Vivint doesn’t seem to be in a hurry when it comes to solar-plus-storage.

The No. 2 rooftop solar installer initially staked its storage success on a partnership with Mercedes-Benz Energy back in 2017. What the latter lacked in market-ready products, it made up for with great brand recognition. A year later, the German carmaker gave up on residential storage, and Vivint never followed up with a similarly high-profile replacement (but it did start stocking LG Chem’s Resu battery).

That quiet touch is surprising, given that competitors Sunrun and Tesla talk up their energy storage achievements on each quarterly earnings call, and companies like SunPower increasingly frame the solar value proposition as inseparable from storage.

Vivint, instead, only sells solar-plus-storage in California and Hawaii, making it easily the most geographically limited of the major rooftop solar companies. And Vivint declined to launch a no-money-down offering in California, the largest market by far, until this month. It’s possible to convince customers to buy batteries outright, but no money down sweetens the deal by lowering upfront sticker price.

Leadership launched the service after conducting a survey of several hundred California homeowners in August, in which the company noted increasing interest in the product. That result shouldn’t come as much of a surprise to Vivint — for the last few months, the news has been awash with coverage of California’s fires and Pacific Gas & Electric’s deliberate grid outages.

Adding batteries gives solar installers a chance to upsell. In places where time-of-use rates hurt standalone solar returns, it may even be vital to the economics. Given the upside, it’s hard to see the strategic value of trailing the competition on this growing sector of the market.

Then again, home storage sales are small enough that Vivint hasn’t missed out on much in terms of revenue. It’s more the opportunity to get the hang of a product that will play an increasingly central role in the industry.