According to the U.S. Energy Information Administration (EIA), the nation’s solar photovoltaic (PV) capacity now exceeds 3.5 GW. This figure is the result of a new system at the EIA for estimating the lower bound on total installed PV capacity. The figure includes both utility and customer-scale installations. The latter was not captured in previous estimates.
Of this 3.5 GW of installed solar PV, about 30% of it is considered utility-scale solar. The remaining 70% is found in consumer-sited installations, including commercial/industrial (42%) and residential (28%).
These customer-scale installation data were gathered starting in 2010, when electric utilities were first asked to report the capacity of PV installations for any net-metered customers. These data will give researchers the ability to more accurately track small-scale solar grown in the United States. Though, these data will still not capture off-grid PV systems.
For more details on the calculations behind this estimate, you can go to EIA's website (here).