The 2019 Energy Code PV system prescriptive requirements under Section 150.1(c)14 apply only to newly constructed detached accessory dwelling units (ADU's) for which the permit application was submitted on or after January 1, 2020. Smaller ADU's will require smaller PV systems, or may be exempt from the PV system requirements if they meet Exception 1 to Section 150.1(c)14:
Exception 1: No PV is required if the effective annual solar access is restricted to less than 80 contiguous square feet by shading from existing permanent natural or man-made barriers external to the dwelling, including but not limited to trees, hills, and adjacent structures. The ,effective annual solar access shall be 70 percent or greater of the output of an unshaded PV array on an annual basis.
The PV system can be installed on the ADU, or on the main house. In the event that panels are added to an existing PV system to satisfy the PV system requirements for the ADU, those additional panels must be part of the ADU’s permit application.
The PV system requirements do not apply to alterations or additions to existing homes, including detached additions where an existing detached building is converted from unconditioned to conditioned space (this is an addition per the Energy Code definitions).
Note: Energy Code requirements, including the PV requirements, do not apply to mobile home ADUs, which are subject to Title 25, not Title 24.