California now requires new houses and low-rise apartment buildings to include solar power.
The state is the first in the US to list solar requirements in its building code.
The requirements will apply to any building permits issued after Jan. 1, 2020.
The goal is expected to boost the state's solar industry.
"[The rules will] save Californians more than $1.7 billion in net energy savings over the next 30 years and reduce carbon pollution statewide by 1.4 million metric tons." Pierre Delforge, senior scientist for the Natural Resources Defense Council (NRDC)
The solar panel installation will raise prices of homes by an estimated $8,000 to $12,000.