Adding batteries or panels to existing NEM 1.0 or NEM 2.0 solar on PG&E

Homeowners who interconnected solar under PG&E Net Energy Metering 1.0 (NEM 1.0) or 2.0 (NEM 2.0) received a 20-year grandfathering window from their original Permission to Operate (PTO) date. Under those legacy tariffs, daytime solar exported to the grid earns nearly full retail credit.

Under PG&E’s tariff rules, adding exporting solar capacity beyond the greater of 1 kW or 10% of your original system size moves the entire meter onto the current Solar Billing Plan (NEM 3.0). However, adding battery storage—or adding a separate non-exporting solar and battery system—does not forfeit your legacy NEM 1.0 or NEM 2.0 status.

If your existing solar array still covers most of your annual kilowatt-hours, or if you mainly want outage backup and peak time-of-use (4–9 PM) bill protection, adding a standalone battery bank is the simplest upgrade.

Under PG&E rules, adding a battery to an existing NEM 1.0 or NEM 2.0 solar system leaves your 20-year grandfathering date untouched. The new hybrid inverter AC-couples with your existing microinverters or string inverter, stores your midday solar or cheap off-peak energy, and powers your home during the expensive 4–9 PM evening peak and during PG&E outages.

What if you added electric vehicles, heat pumps, or an ADU and your legacy solar array is now far too small? PG&E allows you to install a second, independent solar-plus-battery system configured in Certified Non-Export (Zero-Export) mode.

Because the new system uses current transformers (CTs) at your meter to ensure its power only serves your home loads and charges your batteries—never exporting past the utility meter—PG&E allows your original solar array to stay on grandfathered NEM 1.0 or NEM 2.0 while your new panels and batteries wipe out your added daytime and evening consumption.

Sometimes keeping a tiny 2–3 kW legacy NEM 2.0 array is not worth the constraint—especially if you only have a few years left on your 20-year NEM 1.0 clock or you are tripling your solar capacity alongside 28.6 kWh or more of battery storage.

When you pair a larger solar array with two or more EG4 batteries and the Potrero Energy Management Service (EMS), the battery captures your daytime solar and can discharge stored energy during late-summer evening windows (particularly August and September from 6–8 PM) when PG&E’s Avoided Cost Calculator export credits spike to $1.00–$3.00 per kWh. We model both the Non-Export path and the full NEM 3.0 transition side by side in your proposal so you can see which delivers higher annual savings.

Because Potrero builds on the open-protocol EG4 FlexBOSS21 hybrid inverter, we can integrate with your existing solar in whichever way fits your roof hardware best:

• AC coupling (working Enphase microinverters or newer string inverters): Your existing solar inverter stays in place with its original manufacturer warranty untouched, feeding AC power into a dedicated port on the new system.
• Direct DC replacement (failed or 10–15 year old string inverters): If your old string inverter has failed or is near the end of its life, we can remove the old box and land your existing rooftop DC solar strings directly into the new EG4 hybrid inverter alongside any new panels—eliminating the cost of buying a separate replacement string inverter.