R.I. Keeping Up with Rest of U.S. in Residential Solar Installation

Rooftop solar's popularity increases 

By Rob Smith / ecoRI News staff

Photo by Will Collette

Rhode Island’s residential rooftop solar systems are getting bigger and cheaper to install, but the state still lags when it comes to energy battery storage.

That’s the main takeaway from a new report from California’s Lawrence Berkeley National Laboratory’s Energy Markets & Policy Department. The report, called Tracking the Sun, is an annual publication studying the average size of residential solar panels, installation prices, and module efficiency.

Data from the report shows that, when it comes to residential system size, Rhode Island is keeping up with the Joneses. The median system size in Rhode Island for rooftop residential is 7.4 kilowatts (kW) a system, pretty on par with the national average. The state’s solar arrays are drawing more power from the sun, but it’s still lower than neighboring states’ averages; Massachusetts boasts a median system size of 9.3 kW, and Connecticut’s median isn’t far behind at 8.9 kW.

The increase is likely from efficiency in the specific solar modules installed on homes, according to the 46-page report. Solar installed on rooftops covers anywhere from 15% to 40% of any given residential home, with the national median landing at 26% for last year.

“Increases in module efficiencies since 2019 closely track the rise in residential system sizes,” according to an executive summary of the data, “suggesting that module efficiency gains have been a primary driver for growth in residential system sizing.”

Solar arrays for residential homes have grown popular in Rhode Island as the cost of installation has decreased. According to data from the Solar Energy Industries Association (SEIA), the state has 1,029 megawatts (MW) of solar, over a fourth of which (276) was installed last year, including utility-scale, commercial, and residential.

Decarbonizing the electrical grid and lessening the stranglehold fossil fuels such as natural gas have to power businesses and homes is a key action item in Rhode Island’s emission reduction, goals laid out in the Act on Climate law. Electricity consumption accounts for 18.4% of all greenhouse gas (GHG) emissions in the state, with residential and commercial heating from fossil fuel sources like natural gas or heating oil accounting for a combined 29.3% of all GHG emissions.

The state still has a long way to go before it reaches net-zero emissions by 2050, or even its next benchmark goal of a 40% reduction by the end of this decade. A 2020 study, commissioned by the state and authored by Cambridge, Mass.-based Synapse Energy Economics Inc., showed which areas in the state had the biggest potential capacity for solar.

The third-largest area, after parking lots and commercial and industrial properties, was rooftops, which could provide up to 850 MW of solar power and reduce GHG emissions by 0.74 million metric tons of CO2 equivalent. The total rooftop potential for single-family residential solar alone was around 2,100 MW.

One area of residential solar in which the state is failing is battery storage installation, according to the report. Data from the Berkeley Lab shows that battery storage virtually plateaued in the years following the pandemic and nosedived last year. Only 2.1% of residential solar systems installed last year have battery storage and the resulting ability to store excess solar power for later use, according to the report.

Nationwide, 9.4% of systems have battery storage installed on-site, with Massachusetts far exceeding both the national and Rhode Island averages with a median of 14.8%. Connecticut had no data available on battery storage.

Data from the Rhode Island Office of Energy Resources (OER) shows 1,048 solar systems in Rhode Island have energy batteries interconnected with the electrical grid, and the overwhelming majority are found in residential homes. Only nine are connected to commercial business’ solar systems.

Every municipality has at least one solar system with a battery except for two: New Shoreham and Little Compton have no reported battery system, according to OER’s dashboard data. The largest capacity batteries are clustered in Westerly, Providence, Warwick, Cranston, and East Greenwich.