Solar and storage: Articles 690, 705 and 706, rapid shutdown, Rule 21 interconnection, the Net Billing Tariff, and where the batteries can go
In one paragraph
Solar work for a C-10 is three jobs in one: the code job (Articles 690, 705 and 706: rapid shutdown, the disconnects and labels, the point of connection and the 120 percent busbar rule, and the energy storage rules), the utility job (a Rule 21 interconnection application to the investor-owned utility, and permission to operate before the system exports), and the customer conversation, which since April 15, 2023 is about the Net Billing Tariff: exports are credited at their value to the grid, not at retail, which is why nearly every new system is sold with a battery. Storage brings its own rules for where the batteries may sit. The permit is nondiscretionary by state law and most jurisdictions run a checklist process; the interconnection is what takes the time, and the case in this phase is a system that sat finished for four months waiting for it.
The rule
PV systems on buildings need rapid shutdown so that conductors outside the array boundary are brought to a safe voltage within 30 seconds of initiation, with the initiation device and labeling the code specifies (2025 CEC 690.12, 690.56(C)); a load-side connection to a busbar must satisfy 705.12, most commonly by keeping the sum of the supply breaker and the PV breaker at or below 120 percent of the busbar rating with the PV breaker at the opposite end; the source disconnecting means must meet 705.20 as printed in the California amendments; and energy storage systems are installed under Article 706 and located as Title 24's residential and fire codes allow. Interconnection to an investor-owned utility is under Electric Rule 21, and since April 15, 2023 new customers take service on the Net Billing Tariff (CPUC D.22-12-056). A city or county must approve a solar energy system administratively through a nondiscretionary permit (Gov. Code 65850.5(b)).
Why it matters
The electrical work on a residential solar job is a day or two; the paperwork and the utility are weeks, and the customer blames whoever they signed with. Knowing the 120 percent rule keeps you from selling a system the panel cannot take, knowing rapid shutdown keeps the fire department from failing your roof, and knowing what Net Billing did to the economics lets you sell the storage honestly instead of apologizing for the bill later.