Using new information, EIA combines data on utility-scale solar photovoltaic (PV) capacity with customer-sited PV capacity, as reported in the graphic. EIA’s utility-scale electric generator survey has a threshold of 1 MW for reporting and, thus, does not capture most customer-sited installations. However, in 2010, electric utilities started reporting to EIA the capacity of their customers’ behind-the-meter generation, which is larger than utility-scale capacity.
National solar PV capacity is growing rapidly. Tracking this rapid growth is a challenge, however, because PV solar is more often used at a consumer’s location—e.g., rooftop solar panels—and less often in large, centralized generating stations like other technologies.
An estimate of total PV capacity must therefore account for many small installations (often referred to as distributed solar capacity). However, while EIA maintains an inventory of all power plants of 1 megawatt capacity and greater, there is no census—either from government or industry—of the thousands of small rooftop commercial and residential solar PV installations across the United States.
EIA is improving its data collection to address this issue. Meanwhile, EIA presents this lower bound based on existing electric power industry survey data: at the end of 2011, EIA data show U.S. solar PV capacity was at least 3,536 megawatts (MWAC). The chart above summarizes the calculation (also, see below).