California took a major step Wednesday toward becoming the first U.S. state to require solar panels on nearly all new homes. The California Energy Commission voted 5-0 to approve a requirement that residential buildings up to three stories high, including single-family homes and condos, be built with solar installations starting in 2020. The commission estimates that the mandate, along with other energy-efficiency measures being incorporated, would add $9,500 to the average cost of building a home in California. The state is already one of the most expensive housing markets in the country, with a median price of nearly $565,000 for a single-family home, according the California Association of Realtors. Still, the change appears to have broad support from home builders as well as state leaders and solar advocates. Part of an update of the state’s energy efficiency building codes, it needs final approval from the California Building Standards Commission. […]