Add solar to the system you already have — without losing NEM 1.0 or 2.0.
If your usage has grown since your panels went up, expanding the ordinary way can cost you the export rate that made them worth having. There is a route around that, and it is the one we file.
Your array was sized for the house you had then.
An EV, a heat pump, a pool pump, a converted garage — any one of them can add more load than the system on your roof was ever designed to cover. The obvious fix is more panels.
The obvious fix is also the trap. Expand an existing NEM 1.0 or NEM 2.0 system beyond a threshold set by the utility and the whole account moves to the Solar Billing Plan, where exported power is worth a fraction of what your current agreement pays. You would add panels and end up worse off.
This is the single most expensive mistake we see on older systems, and it is usually made by someone trying to do the right thing.
The greater of 1 kW or 10%. Then the rules change.
A NEM 1.0 or NEM 2.0 customer can increase generating capacity by the greater of 1 kW or 10% of the originally approved system size and stay on their existing agreement. Go past that and a new application has to be submitted under the Solar Billing Plan — for the whole property, not just the new panels.
On a 6 kW system that allowance is 1 kW. Two modern panels can use most of it. Which is why so many expansions quietly cost people their legacy rate.
The part worth reading twice is what the utility says about undoing it.
Failure to do so will result in the account being moved to the Solar Billing Plan; SCE cannot guarantee a reversal back to NEM.
Southern California Edison, Net Energy Metering FAQ
A second system that never sends anything to the grid.
Electric Rule 21 is the tariff governing how solar, batteries and smart inverters connect to California's investor-owned utilities. It allows a system to be interconnected in non-export mode: the equipment is required to put zero surplus onto the grid, and it is built to make that physically true rather than merely promised.
- It watches the meterA certified power control system reads current at your main service panel through CT sensors, continuously, so it always knows how much the house is drawing right now.
- It throttles before it exportsIf the house stops consuming what the new array is producing, the inverters ramp output down in milliseconds. Nothing backfeeds, because nothing is allowed to.
- A battery catches the restWithout storage, throttled production is simply lost. A battery takes that surplus during the day and gives it back in the expensive evening hours, which is what makes the expansion worth building.
Two ways to add capacity
| Standard expansion past the limit | Rule 21 non-export expansion | |
|---|---|---|
| Your NEM agreement | Lost — the account moves to the Solar Billing Plan | Kept — NEM 1.0 or 2.0 continues unchanged |
| What exports are worth | Avoided-cost rates, a fraction of retail | Your existing legacy credit, untouched |
| What sets the size | The 1 kW / 10% allowance | What your home actually uses and stores |
| Export from the new array | Yes | None — that is the condition of the approval |
| Battery | Optional | Effectively required to get value from it |
| Paperwork | A new Solar Billing Plan application | A non-export interconnection application under Rule 21 |
Three things this does not do.
Usually one of four reasons.
- An electric vehicle arrived and your annual usage jumped by thousands of kilowatt-hours.
- You went from gas to a heat pump and your winter electricity bill went up rather than down.
- A pool, a shop or a converted garage is now drawing load the original system was never sized for.
- Your original equipment is a different brand to anything sold today, and you were told an expansion was impossible. It usually is not — the new array does not have to match the old one.
The questions we actually get
Nothing. That is the condition of the interconnection, and it is enforced by hardware rather than by good intentions — the power control system measures what the house is drawing and holds production at or below it. If the house is not using it and the battery is full, the inverters simply ramp down.
It is the route designed for it, and it is what we file. What we will not do is promise you the utility's answer in advance. Nothing gets energised before permission to operate arrives, so you are not exposed while the application is pending — and SCE is explicit that if an account does move to the Solar Billing Plan, it cannot guarantee moving it back.
NEM 1.0 and 2.0 customers keep their terms for twenty years from the original permission to operate. Adding capacity correctly does not restart or shorten that clock. It is worth knowing your own date before spending anything, and we will look it up with you.
Practically, on most homes, yes. Without one, any production your house is not using at that moment is throttled away. With one, it is stored and spent in the expensive part of the evening. We will show you both sets of numbers rather than assuming.
Yes, and most of the ones we expand are. The new array and its inverters do not need to match the original equipment, because the two systems operate independently behind your meter.
Adding storage alone is a different and usually simpler conversation, and it does not carry the same expansion question. Ask us about that directly and we will not steer you into panels you do not need.
Bring us your bill and your PTO date.
We will pull your interval data, work out how much of an expansion your house could actually use, and tell you whether a non-export system earns its keep on your roof. If it does not, we will say that too.
Option One Solar has been interconnecting systems in Southern California since 1970. C-10 and C-46 licensed, Lic. #985340. Rules described here reflect the CPUC and utility requirements in force at the time of writing; your own agreement and utility govern.