Annual growth in solar generation often lags annual capacity additions because generating capacity tends to be added late in the year. For example, in 2016, 29% of total utility-scale solar generating capacity additions occurred in December, leaving few days for an installed project to contribute to total annual generation despite being counted in annual generating capacity additions. In 2017, December solar additions accounted for 21% of the annual total. Overall, solar technologies operate at lower annual capacity factors and experience more seasonal variation than biomass technologies.
Biomass electricity generation comes from multiple fuel sources, such as wood solids (68% of total biomass electricity generation in 2017), landfill gas (17%), municipal solid waste (11%), and other biogenic and nonbiogenic materials (4%).These shares of biomass generation have remained relatively constant in recent years.
Solar can be divided into three types: solar thermal, which converts sunlight to steam to produce power; large-scale solar photovoltaic (PV), which uses PV cells to directly produce electricity from sunlight; and small-scale solar, which are PV installations of 1 megawatt or smaller. Generation from solar thermal sources has remained relatively flat in recent years, at about 3 million MWh. The most recent addition of solar thermal capacity was the Crescent Dunes Solar Energy plant installed in Nevada in 2015, and currently no solar thermal generators are under construction in the United States.
Solar photovoltaic systems, however, have consistently grown in recent years. In 2014, large-scale solar PV systems generated 15 million MWh, and small-scale PV systems generated 11 million MWh. By 2017, annual electricity from those sources had increased to 50 million MWh and 24 million MWh, respectively. By the end of 2018, EIA expects an additional 5,067 MW of large-scale PV to come online, according to EIA’s Preliminary Monthly Electric Generator Inventory. Information about planned small-scale PV systems (one megawatt and below) is not collected in that survey.