Adding plug-in solar when you already have rooftop solar

The short answer: check with your utility before you plug anything in. The Senate committee analysis of SB 868 says using a plug-in kit alongside rooftop solar on net metering "may be a gray area, as the utility's interconnection agreement required for NEM systems may not allow such a use."^[source]

This page is not legal advice. Where we haven't confirmed something, we say so.

Why it's a gray area

From Jan 1, 2027, SB 868 lets a certified plug-in system skip the usual interconnection process. Your rooftop system is different: it was connected under an interconnection agreement and a net metering (NEM) tariff, and those terms still apply to your home.^[source] The same analysis notes that plug-in kits are marketed to rooftop solar owners as a way to get more out of their net metering credits.^[source]

Not confirmed: we haven't been able to check whether the enacted text of SB 868 says anything about homes with existing solar.

How much you can add under net metering

If you're on NEM 1.0 or NEM 2.0, PG&E's tariffs let you change your system and keep your net metering terms as long as the change adds no more than the greater of 10% of the original system size or 1 kW, and the system doesn't end up producing more than your home uses in a year.^[source] The limit comes from a CPUC decision on net metering system changes.^[source] We have read PG&E's wording; we haven't yet checked SCE's or SDG&E's.

If an addition goes over that limit, PG&E's tariff gives two options: connect the addition separately so it can't send power to the grid, or move the whole system to the Net Billing Tariff, which pays less for exported power.^{[source][source]}

Not confirmed: no source we found says whether a plug-in kit counts as a change to your net-metered system.

Power sent back to the grid

The Assembly committee analysis notes that SB 868 lets qualifying devices send power to the grid during normal conditions.^[source] With rooftop solar on the same meter, that's exactly where your utility's net metering rules come in, so ask before you add anything.

What to do

• Ask your utility in writing whether adding a plug-in kit affects your net metering agreement, and keep the answer.
• Have a licensed electrician look at your setup. Homes with solar already have extra equipment on the electrical panel. See Do I need an electrician?
• Read what SB 868 allows and whether a kit qualifies.