Can my ADU's required solar go on the main house roof or the ground?

Yes. The California Energy Commission's 2025 FAQs say the Energy Code does not specify where new solar modules must be installed, so a newly constructed detached ADU can meet its solar requirement with new modules on the main house, on a carport or ground-mounted on the same lot. What won't work is counting panels that are already there: the ADU needs newly installed PV.

Which ADUs need solar

• New detached ADUs are newly constructed buildings and fall under Section 150.1(c)14, which calls for a newly installed PV system or newly installed PV modules.
• Attached ADUs are treated as additions, and the Commission says solar PV is not required for them. Garage conversions are also classified as additions.
• Solar-ready rules in Section 110.10 apply to subdivisions of ten or more homes, not to an ADU on an existing lot.

Exceptions that can shrink or remove the requirement

• No PV is required if the solar access roof area (SARA) is less than 80 contiguous square feet.
• No PV is required if the calculated minimum system size is less than 1.8 kWdc.
• The calculated size may be reduced by 25 percent when paired with a qualifying battery with at least 7.5 kWh of capacity.
• Roof areas with less than 70 percent annual solar access, and certain north-facing steep roof areas, are left out of SARA.

Adding modules to the main house system

The Commission says new modules may be added to an existing PV system to meet the requirement, as long as they are on the same lot, the load-serving entity (your utility) allows the expansion, and the work is part of the ADU permit application. If your ADU has its own meter, the Energy Code doesn't regulate which meter the added modules serve, but your utility's interconnection rules do, so confirm with the utility first.

Ground mounts, carports and community solar

The Commission's PV FAQs say a system can be ground-mounted on the property or mounted atop a carport on the lot. Section 150.1(b)1 also allows an approved community shared solar program in place of on-site panels where one is available.

What this means for your electrical plan

The electrical plan should show where the new modules go, the conduit route, the point of interconnection and its effect on the panel, and the required labels, while your Title 24 report documents the required system size. Read how solar is shown on ADU electrical plans, battery-ready requirements and our ADU Title 24 guide.

Sources: energy.ca.gov, energy.ca.gov, energy.ca.gov.