• Electricity and solar energy—cleaner heating fuel sources than utility gas, bottled, tank or liquid propane gas, or kerosene fuel—saw the fastest increase (+25.1%) since 2008. From 2008 to 2019, California added just under one million occupied housing units; homes where electricity is the primary heating fuel accounted for a majority of the new units—63.4 percent. Homes where solar energy is the primary heating fuel have also seen an increase, jumping an impressive 17.1 percent year-over-year, with 2019 marking the first year where more than 100,000 homes are fueled by solar energy.