According to the latest report from the Department of Energy’s Energy Information Administration (EIA), the June 2017 (latest data available) estimate for small-scale (less than one megawatt in capacity) solar photovoltaic (PV) output reached a new monthly high of 1,480 gigawatthours (GWh). This represents a year-over-year increase of 34.4 percent compared to the June 2016 level.                  

Total capacity has also been growing year over year. Capacity was 2.68 gigawatts (GW) in June 2014, 4.0 GW in June 2015, 6.35 GW in June 2016 and 8.57 GW in June 2017.

According to the EIA, growth is being driven largely by decreases in the price of solar PV technologies, state policies that encourage solar investment (e.g., net metering, renewable portfolio standards, etc.) and the emergence of third-party operators that facilitate net metering arrangements.

Most residential small-scale solar PV systems are very small, averaging about 5 kilowatts, are usually installed on residential rooftops, and provide electricity directly to the homeowners. In cases when the PV generation exceeds residential use, the surplus electricity flows into the connected utility distribution system, allowing residential customers to get (in some cases) monetary credit, depending on that state's net metering rules.

Where do most of these units reside? According to the EIA, the two main regions are the Southwest, where high solar irradiance is conducive to solar PV; and the Northeast, where a number of state policies encourage residential solar PV and where retail electricity rates/prices are high.

The top ten states are: California (684 GWh in June 2017), Arizona (121 GWh), New York (82 GWh), New Jersey (77 GWh), Maryland (60 GWh), Hawaii (57 GWh), Massachusetts (54 GWh), Texas (43 GWh), Colorado (33 GWh) and Nevada (31 GWh).

These ten states total 1,242 GWh of the nation's 1,460 GWh.

The three states that experienced the greatest percentage increase from June 2016 to June 2017 were Texas (105 percent), Maryland (71) and New Jersey (45). Though, the EIA report says, "Interestingly, in the 'Rest of U.S.' category, all the combined states outside the top ten grew by 54 percent, exceeding the national rate of growth of 34 percent."