Last Wednesday, the California Energy Commission (CEC) voted unanimously to require solar panels on nearly all new homes built in the state starting January 1, 2020. The 5–0 decision makes California the first state in the country to mandate photovoltaic (PV) systems as a standard feature of residential construction—and it shifts the burden of proof from early adopters to the building industry itself.

What the CEC voted on

On May 9, 2018, the five-member CEC approved the 2019 Building Energy Efficiency Standards—commonly known as Title 24, Part 6—after a public hearing in Sacramento. The vote was not close. Chairman Robert Weisenmiller and Commissioners David Hochschild, Karen Douglas, Janea A. Scott, and J. Andrew McAllister each voted in favor, with no dissent. [Source: KQED, May 9, 2018]

"This is just a milestone. There's a hell of a lot of work to do between now and 2020," Weisenmiller said after the vote. "The bottom line is we're going to stay focused on making this happen, and happen smoothly." [Source: KQED]

Commissioner David Hochschild framed the mandate in blunter terms: "We cannot let Californians be in homes that are essentially the residential equivalent of gas guzzlers." [Source: The Independent, May 10, 2018]

The new rules apply to all new single-family homes, duplexes, garden apartments, and other low-rise residential buildings with three or fewer habitable stories. The requirement does not apply retroactively; homes permitted before January 1, 2020 are exempt.

What builders must install

The standards do not dictate a one-size-fits-all system. Instead, the CEC established a prescriptive formula that ties system size to conditioned floor area and California's 16 building climate zones:

Where CFA is the conditioned floor area in square feet, NDwell is the number of dwelling units, and A and B are climate-zone adjustment factors drawn from Table 7-1 of the draft Residential Compliance Manual. [Source: Aurora Solar / CEC 2019 Draft Compliance Manual]

In practice, the CEC estimates most new homes will need a minimum system of 2 to 3 kilowatts, depending on size and location. For perspective, a 2,000-square-foot home in Sacramento (Climate Zone 12) would need roughly a 2.6 kW system; the same footprint in Fresno (Zone 13) would require about 3.3 kW. [Source: Namaste Solar]

Builders have two compliance paths. The prescriptive method uses the formula above and is simpler but less flexible. The performance method—also called the computer compliance method—lets builders model alternative configurations using the CEC's free CBECC-Res software, trading off PV size against efficiency upgrades, battery storage, or demand-responsive technology.

Exceptions and alternatives

The CEC built in several carve-outs. A home with insufficient unshaded roof space can receive a reduced system size or exemption. Multistory buildings with limited roof area can also qualify for smaller systems. Homes that incorporate battery storage can offset part of the PV requirement. And developers may opt for a shared community solar system serving a group of homes, provided it delivers equivalent benefit to rooftop installation.

Financing flexibility is also preserved. Systems can be homeowner-owned and rolled into the mortgage, or third-party-owned through leases or power purchase agreements—an important concession for builders who worry about sticker shock.

Cost impact: the numbers

The CEC estimates the solar mandate will add approximately $9,500 to the construction cost of an average single-family home. On a 30-year mortgage, that translates to roughly $40 per month. The commission projects homeowners will save about $80 per month on energy bills, yielding roughly $19,000 in savings over three decades. [Source: Holland & Knight, May 11, 2018]

The commission also projects the mandate will reduce greenhouse gas emissions by an amount equivalent to removing 115,000 fossil fuel cars from the road.

Those figures assume current technology and pricing. As of mid-2018, the national average quoted price for residential solar sits around $3.12 per watt according to EnergySage marketplace data, though California premiums and the recent Section 201 tariffs—enacted in February at 30% on imported cells and modules—are keeping some upward pressure on module costs. [Source: EnergySage Solar Marketplace Intel Report, Sept 2018] Standard residential modules today run 270–320 watts with efficiencies in the 16–19% range, while premium panels from SunPower, LG, and Panasonic can push past 20%.

Why now? The road to zero net energy

The mandate did not appear out of thin air. California has been stair-stepping toward this point for more than a decade. In 2007, the CEC set a goal that all new residential buildings would achieve zero net energy (ZNE) by 2020—meaning they would produce as much energy as they consume. New commercial buildings face the same target by 2030.

In 2013, the state required all new homes to be "solar-ready"—reserving adequate unshaded roof space and pre-wiring for future PV installation. The 2019 standards simply remove the "future" part. As CEC spokeswoman Amber Beck noted, "We update energy codes every three years and in 2013 we required that all new homes be solar-ready. Homes had to have a certain amount of space on the roof so a homeowner could add a solar panel later on if he chooses." [Source: KQED]

The mandate also aligns with Senate Bill 32, passed in 2016, which requires California to cut greenhouse gas emissions 40% below 1990 levels by 2030. Residential and commercial buildings account for roughly 14% of the state's greenhouse gas emissions, per the California Public Utilities Commission.

The housing-affordability tension

Not everyone is celebrating. California is in the grip of a severe housing affordability crisis, and critics argue the mandate will push new-home prices even higher. In San Francisco, only 12% of households can afford a median-priced home, according to a recent Paragon Real Estate Group report. Statewide, half as many Californians can afford median-priced housing as the national average.

"It absolutely will increase the cost of homes," said Lisa Vorderbrueggen, director of governmental affairs for the Bay Area Building Industry Association. "But on the other hand, increasing the energy efficiency of homes has long been a state priority, so there's no free lunch." [Source: KQED]

State Senator Scott Wiener (D-San Francisco), who authored San Francisco's own solar mandate for new construction in 2016, counters that homeowners will have the option to lease panels through third-party providers. "You can have a third party come in and install and maintain those solar panels, so they end up paying for themselves over time," Wiener said. [Source: KQED]

What still needs to happen

The CEC vote is a major step, but it is not the final one. The California Building Standards Commission (CBSC) must still formally adopt the Title 24 amendments, a process expected to conclude in December 2018 when the commission updates the state building code. The CBSC historically follows CEC recommendations, and given the 5–0 vote, observers expect smooth passage.

Between now and January 1, 2020, the CEC will finalize compliance manuals, release the CBECC-Res modeling software updates, and conduct training through its EnergyCodeAce platform. Builders and solar contractors who serve the new-construction market should begin familiarizing themselves with the climate-zone tables and the prescriptive formula now.

What this means for installers and buyers

For solar contractors, the mandate opens a substantial new channel. The CEC projects that roughly 74,000–80,000 new single-family homes will be built under the code each year once it takes effect. That is a captive market that did not exist before—home buyers who will receive solar as a default feature rather than an elective upgrade.

For equipment distributors, the implications are straightforward. Builders will need reliable supply chains for standard residential modules (270–320W), string inverters and power optimizers, and racking systems sized for typical California roof pitches. With the Section 201 tariff now in effect, domestic-assembled modules and tariff-exempt product lines carry additional appeal for cost-sensitive builders.

For homeowners buying new construction after 2020, the mandate effectively bundles solar into the home price. The CEC's math suggests positive cash flow from month one ($40 mortgage add vs. $80 energy savings), but actual returns will depend on utility rate structures, storage attach rates, and how NEM 2.0 credits evolve over the life of the system.

FAQ: California's New Solar Mandate

Where it stands today

This article was originally published on May 16, 2018. The following update reflects the current status of California's solar mandate as of 2026.

The Title 24 solar mandate took effect on schedule January 1, 2020, after the California Building Standards Commission gave its final approval in December 2018. The policy has since been expanded: the 2022 Title 24 update (effective January 1, 2023) extended solar requirements to new commercial buildings and multifamily structures over three stories, and added battery storage readiness as a standard feature.

California remains the only state with a comprehensive solar building code, though Massachusetts, New Jersey, and Washington, D.C. have all considered similar legislation. For builders, installers, and homeowners navigating these requirements, Portlandia Electric Supply stocks a full range of residential solar kits, panels, inverters, and battery storage systems to meet Title 24 compliance.