Can New ADU Solar Panels Be Added to the Main House System?
Yes. The Energy Commission says new PV modules added to the main house's system can meet a new detached ADU's solar requirement. They must sit on the same residential lot, the utility must allow the expansion, and they must be part of the ADU permit application, sized under the Energy Code. The Code does not say which meter they serve.
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How big the added array must be
The size comes from Equation 150.1-C applied to the ADU alone: floor area times factor A, divided by 1,000, plus factor B for one dwelling unit. An 800 square foot ADU in climate zone 12 works out to 0.613 times 800, divided by 1,000, plus 1.40, or 1.89 kWdc of new modules. The existing array's size does not enter the calculation. The roof-area cap is on the solar system size page.
What the new modules must meet
They must satisfy Joint Appendix JA11, as any new array does. For prescriptive compliance the compliance manual asks for an azimuth of 90 to 300 degrees from true north on roofs steeper than 10 degrees, any orientation on low slopes, and annual solar access of at least 98 percent by panel count, shown with an approved assessment tool. JA11 also calls for CPUC Rule 21 inverters and remote monitoring; how those apply to modules joining an older system is a question for the designer and the building department.
Paperwork
The installer certifies JA11 on form CF2R-PVB-01-E with a solar assessment image dated after installation, or site photos showing the array matches the model. The building department checks that the certificate is in an approved registry.
Meter and utility
The Code leaves the meter open, so the utility's rules decide. HCD notes that an ADU not created from existing space may be required to take a separate utility connection, and that HCD has no authority over electric service disputes. Ask the utility before the design is final.
What does not count
The existing modules themselves: a new detached ADU needs newly installed PV. A voluntary array on an existing house is a different case, on adding solar to an existing home. If the ADU may calculate under 1.8 kWdc, check the ADU solar exceptions first. See also the ADU solar overview and the detached ADU report; orders start on the ADU page.
Common Title 24 Questions
- Do ADUs need Title 24 in California?
- What plans are needed for an ADU Title 24 report?
- How much does an ADU Title 24 report cost?
- How long does an ADU Title 24 report take?
- Does a garage conversion ADU need Title 24?
- Does a JADU need a Title 24 report?
Frequently Asked Questions
No. The Energy Code does not specify whether added modules serve the ADU meter or the main house meter, only that they are on the same lot and the utility allows the expansion.
No. The existing modules do not count. Only newly installed modules, sized for the ADU and listed in its permit application, satisfy Section 150.1(c)14.
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View all ADU and JADU guides → · Permits and Compliance · Title 24 guide