Store it, or sell it?
Every kilowatt-hour your array makes and your house does not immediately use has exactly two destinations. The rules governing which one pays better are set by a regulator, not by your installer, and they can flip the answer for identical hardware on identical roofs a hundred metres apart.
A year of holding surplus back instead of exporting it
$1,603.33
Holding surplus back beats exporting it, because the credit an export earns is well below the price the same energy avoids later in the day.
a projection from published rate and hardware data, not a quote and not financial advice2.9 kWh a day goes to the grid regardless because the pack is already full. That portion earns the export credit whatever you buy, so it is not part of the case for a bigger battery.
Which regime you are on, and how much surplus you make
Your interconnection agreement names this. It is the single most important line in it.
A placeholder we could not source: avoided-cost export rates move by utility, by hour and by season. Used only under net billing — the other two regimes fix the credit by definition, so this box does nothing there.
Generation left over after the house has taken what it needs during daylight.
Fewer in a cloudy winter month; this is your own count, not a national figure.
Three regimes, and only one of them makes a battery pay
Full retail netting (legacy net metering)
An exported kilowatt-hour earns the same retail price an imported one costs, so the grid is already acting as a lossless battery with no capital cost.
Net billing at the value of the export
Exports earn what the grid says the energy is worth in that hour, which in the middle of a sunny afternoon is a small fraction of the retail import price.
No compensation for exports
Surplus generation is given away. Every kilowatt-hour a battery keeps out of the export meter is worth the full retail price of the hour it is later used in.
Notice what the first one does to the arithmetic. If an exported kilowatt-hour is credited at the same retail price an imported one costs [2], then the meter is a perfectly efficient, infinitely large, zero-cost battery that the utility maintains for you. Installing a physical one to duplicate that service means paying capital for the privilege of losing about a tenth of the energy in transit. The calculator above returns a negative number for that case, and it should.
Quoted from the source document, retrieved 2026-08-06
“These bill credits are applied to customers' monthly bills at the retail rates (including generation, distribution, and transmission components) that the customers pay for energy consumption according to their otherwise applicable rate structures. These tariffs are closed to new enrollments.”
The clause in brackets is the one that decides a battery: the credit matches not just the energy price but the delivery and transmission components too, so under this arrangement the meter returns the whole retail rate and a physical pack can only subtract its own losses from that — and the last sentence is why your neighbour's answer is not yours, because the arrangement is closed rather than repriced.
What changed, and why storage suddenly appeared in every quote
The largest state solar market in the country moved new customers onto a net billing tariff in 2023 [1]. The structural change was narrow and enormous: exports stopped being credited at retail and started being credited at what the energy is worth to the grid in the hour it arrives.
Quoted from the source document, retrieved 2026-08-06
“Since April 15, 2023, customers applying for interconnection have taken service on the new net billing tariff (NBT) pursuant to D.22-12-056.”
The trigger in that sentence is the interconnection application, not the purchase, the installation or the move-in — so the question to answer about your own house is when its application was filed, and a household that applied a week either side of that date is on a different economic footing for the life of the system.
Midday is precisely when that value is lowest, because every other solar roof in the region is exporting at the same moment. So the credit for a sunny afternoon collapsed, while the price of importing at seven in the evening did not. That gap is the entire reason batteries started appearing on residential quotes — not a breakthrough in cells, not a change in installation cost, but a rewritten tariff.
The legacy arrangements were not repriced; they were closed to newcomers. Anyone already on retail-rate netting keeps it for their remaining term, which is why two neighbours can get opposite answers from the same calculator and both be right. D.22-12-056 is the decision that made the change, and it is worth checking whether an equivalent proceeding is open in your own state before assuming today’s export credit is the one you will live with.
The number to write down before you go any further
One figure carries this whole page: the ratio of your export credit to your evening import price. Above about ninety percent, storage is a resilience purchase and should be judged as one. Between roughly a third and ninety percent, it is marginal and the round-trip loss is doing real damage. Below a third, holding energy back is straightforwardly worth more than selling it and the rest of the arithmetic becomes worth doing.
Those bands are our own reading of the arithmetic on this page rather than anyone else’s published thresholds, and we would rather say so than dress them up. The underlying calculation is not ours though — it is two prices, a division, and the efficiency figure the manufacturer prints.
- The cycle-level tradeBreak-even peak price, and what a day of dispatch actually returns.
- The tax positionWhy an export credit and a rebate behave in opposite directions.
- When it does not workThe three failure modes, told apart properly.
Questions this page gets asked
How do I find out which regime I am on?
Your interconnection agreement names it, and so does the generation section of your bill. Look for whether exported energy is credited at the same price you pay to import, or at a separate published export rate. That single distinction decides more about a battery than any hardware specification.
If I am on legacy net metering, is a battery pointless?
For bill savings, essentially yes — the meter already does the job at no capital cost and with no losses, so a battery adds the round-trip loss and nothing else. For riding out an outage it can still be entirely worthwhile. Those are different purchases and it is worth being honest with yourself about which one you are making.
Does adding a battery move me off my current arrangement?
It can, and this is the trap. Adding storage to an existing array is often treated as a system modification, which in some places means losing legacy terms and landing on the current export rules. That change alone can swamp the savings the battery was bought to produce. Ask before you sign, in writing.
Do export credits reduce my federal tax credit?
No. Ongoing payments for energy you sell back are not treated as a purchase-price adjustment, so they do not reduce the expense the credit is computed on. An up-front rebate from a utility is a different matter and does reduce it. The two get conflated constantly and they behave in opposite ways.
Provenance for every figure printed above
s2.nbt_start_year— California Public Utilities Commission, Net Energy Metering — https://www.cpuc.ca.gov/industries-and-topics/electrical-energy/demand-side-management/net-energy-metering (retrieved 2026-08-06)s2.retail_credit_fraction— California Public Utilities Commission, Net Energy Metering — https://www.cpuc.ca.gov/industries-and-topics/electrical-energy/demand-side-management/net-energy-metering (retrieved 2026-08-06)