Rooftop solar increasingly comes with batteries, Berkeley Lab study says

Rooftop solar installations are getting bigger, more efficient, cheaper, and are increasingly being paired with batteries as consumers respond to power outages and changes in net metering policy.

This is one finding from the latest edition of Berkeley Lab’s Tracking the Sun, an annual report that tracks pricing and design trends for grid-connected, distributed solar photovoltaic (PV) systems in the United States. The report is based on data from roughly 2.5 million systems installed nationally through year-end 2021, with preliminary data for the first half of 2022. New to the report this year is an expanded coverage of paired PV-plus-storage systems.

The report, published in slide-deck format, is accompanied by a narrative summary briefing, interactive data visualizations, a public data file, and summary data tables, all available through the link above. The authors will host a webinar summarizing key findings from the report on September 22, 2022, at 10:00 AM PT/1:00 PM ET. Please register for the webinar here.

The following are a few key findings from the latest edition of the report.

Residential systems are getting larger.  Residential system sizes have been rising steadily over the past two decades, driven by declining costs and rising module efficiencies (see Figure 1). As of 2021, the median size of new residential installs was 7.0 kW, compared to just 2.4 kW in 2000. Non-residential systems have also gotten progressively larger over time, though typical system sizes have plateaued in recent years, with the median size of non-residential systems in 2021 equal to 33 kW and a much larger average size of 255 kW.

More PV systems are being paired with storage. In 2021, 10% of all new residential PV installations and 5% of all non-residential installations included battery storage. Hawaii has, by far, the highest attachment rate, with more than 90% of new residential installations in 2021 paired with storage, and attachment rates in California are also relatively high (11%), but other pockets of activity emerged in 2021. For example, following Winter Storm Uri in Texas, PV+storage attachment rates rose to 14% in CenterPoint’s service territory in 2021. In addition, storage is increasingly being added to pre-existing PV systems. In 2021, 15% of all new paired PV+storage systems in the U.S. were the result of storage retrofits onto existing PV systems.

Storage sizes are increasing for paired residential systems, while decreasing for non-residential systems. Storage systems in paired residential applications are getting larger, reflecting growing demand for backup power, with 42% of all paired residential installs in 2021 consisting of at least 10 kW of battery storage. In contrast, paired non-residential systems have been trending toward smaller storage sizes, as uptake expands into applications beyond demand charge management for large commercial & industrial customers.

PV system prices have continued to fall, when adjusting for inflation. In real dollar terms, median installed prices for stand-alone PV systems fell by 10-20 cents per watt, from 2020-2021, across residential and non-residential customer classes, consistent with the trajectory seen over most of the past decade (see Figure 2). In the first half of 2022, real prices held flat for residential customers, while falling by 10-30 cents per watt for non-residential customers, depending on project size. These prices represent the up-front price paid by the customer, prior to receipt of any incentives, and can include loan-financing fees bundled into the prices charged by installers.

PV system prices vary widely across individual projects. Among stand-alone PV systems without storage, installed prices vary by almost $2/W between the 20^th and 80^th percentile values for both residential and small non-residential customers, and by roughly $1.5/W for large non-residential customers (see Figure 3). That pricing variability reflects differences in project characteristics as well as features of the local market, policy, and regulatory environment. Adding storage further amplifies pricing variability beyond that shown in the figure below. Among paired residential projects installed in 2021, average storage costs were roughly $1200 per kilowatt-hour of storage capacity (equating to an additional $1.9 per watt of PV).

Tracking the Sun 2022 was funded by the U.S. Department of Energy Solar Energy Technologies Office, with data provided by numerous individuals and organizations.