Lawrence Berkeley National Laboratory has released the latest iteration of its “Tracking the Sun” report, which looks into the 3.7 million distributed solar systems installed through the end of 2023. 

The size and efficiency of installed residential solar systems has been growing over the past two decades, with the median size rising from 2.4 kW in 2000 to 7.4 kW in 2023, and the average efficiency from 12.7% in 2002 to 20.8% last year. 

“Increases in module efficiencies since 2010 closely track the rise in residential system sizes, suggesting that module efficiency gains have been a primary driver for growth in residential system sizing,” the report said. 

The roof-coverage ratio for residential systems has been relatively stable, ranging from 15 to 40%, with a median of 26% in 2023. Nonresidential rooftop systems have a lower median, but a much broader range. 

The report found that solar panels increasingly are being paired with storage systems over time, rising from nothing in the middle of the past decade to 12% of new residential systems in 2022 and 8% of new nonresidential. Hawaii has the highest storage attachment rate, at 95%, while new policies that went into effect in April 2023 in California have driven its rate to 14% — and most other states have attachment rates of 4 to 10%. 

The new net billing tariffs going into effect are driving more storage pairing in California, with the report noting 60% of systems paid under them are linked with storage. 

Third-party ownership for residential solar systems has been declining in general, falling from 60% in 2012 to 27% in 2023. There was a slight uptick in third-party ownership last year, which the report said could be from higher interest rates for solar loans. 

Residential systems overwhelmingly are deployed on single-family homes, but the nonresidential sector sees much more variety in customer type, with half on commercial businesses, one-third on agricultural sites and 15% on tax-exempt customers (government, schools, churches, etc.). 

Berkeley developed inflation-adjusted prices for standalone residential customers, which fell by 10 cents/W in 2023 — the same rate of price decline for the past decade. Median prices for nonresidential systems actually went up by 10 to 20 cents/W, which the report blamed on inflation.

Between 2021 and 2023, nominal installed prices were up 2 to 3 cents/kW across customer segments, but when controlled for inflation, they were down 50 cents/W for residential systems and 10 cents/W for others. 

“The fact that real prices fell suggests that PV pricing has thus far been less impacted by inflation compared to other consumer goods (as measured by the CPI), though the effects on installed prices for large nonresidential systems may have not yet entirely materialized,” the report said. 

Prices vary depending on a range of factors, from system size to state policy. The report said residential prices vary by about $1/W between the largest and smallest systems, while commercial generation varies $2.20/W between sizes.