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
$1,663.33
Holding surplus back beats exporting it, because the credit an export earns is below the evening price by more than the round-trip loss.
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.
Your own figure: the credit your bill shows for an exported kilowatt-hour. Under net billing that is the export rate; on legacy net metering with a time-of-use rate it is the credit for the hours your array exports. The starting value is an assumption we could not source. Used only with the option that takes your credit; the other two fix the credit by assumption or 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 ways an export can be credited, and what each does to a battery
Equal-price netting (an assumption, not a tariff)
Assumes every exported kilowatt-hour is credited at the same price as the evening kilowatt-hour it would otherwise offset. Under that assumption the meter does the battery’s job with no loss, so storing surplus can only subtract the round-trip loss. It matches legacy net metering only where the hour of export and the evening hour carry the same price; on a time-of-use rate, use the next option with your own credit.
Exports credited at a rate you enter
Exports earn the credit you enter. Under net billing that is the export rate on your bill, set at what the energy is worth to the grid in that hour; under legacy net metering on a time-of-use rate it is the credit your bill shows for the hours your array exports. Either can sit well below the evening price, which is what gives storage a job.
No compensation for exports
Surplus generation is given away. Every kilowatt-hour a battery keeps out of the export meter is worth the retail price of the hour it is later used in, less the round-trip loss.
Notice what the first option does to the arithmetic. If an exported kilowatt-hour were credited at the same price as the evening kilowatt-hour it offsets, the meter would act as a lossless, zero-cost battery, and installing a physical one would mean paying capital to lose about a tenth of the energy in transit; the calculator above returns a negative number for that case. Legacy net metering is that case only where the hour of export and the evening hour carry the same price, and then only for exports the bill credits that way. The regulator’s description of the legacy tariffs applies the credits at the retail rates the customer pays under their own rate structure [2], and on a time-of-use rate those rates differ by hour, so a kilowatt-hour exported at midday is not automatically credited at the evening price a stored one would later displace. That household should use the second option with the credit its own bill shows.
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.”
Two parts of that sentence decide a battery. The bracket says the credit covers the delivery and transmission components as well as the energy price; the closing words say it is applied at the rates of the customer's own rate structure, so on a time-of-use rate a midday export is not automatically worth the evening price a stored kilowatt-hour would later displace. The last sentence is why your neighbour's answer is not yours: the arrangement is closed rather than repriced.
What the net billing tariff changed
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 tariff. How long either arrangement lasts is not something that sentence states, so check it on your own interconnection agreement.
Under net billing, then, an exported kilowatt-hour earns what the grid values it at, and the same energy imported in the evening costs the retail price of that hour. When the export credit sits below that evening price by more than the round-trip loss, holding the energy back is worth something; how far below it sits for your household is on your own bill, which is why the worksheet above takes your credit rather than assuming one.
The legacy arrangements were not repriced; they were closed to new enrollments. That is why two neighbours on different arrangements 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 positionThe closed federal credit, and how it treated an export credit and a rebate.
- 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 retail price you pay to import in that same hour, or at a separate published export rate. That distinction sets the charging cost the worksheet above uses for solar surplus.
If I am on legacy net metering, is a battery pointless?
Not necessarily; it depends on your rate. The regulator describes legacy net metering as applying bill credits for exports at the retail rates of your own rate plan. On a rate with the same price at every hour, that puts an export credit at the evening price a battery would displace, so for exports credited that way storing surplus adds the round-trip loss and nothing else; the passage does not say how exports beyond what your bill can absorb are paid, and this site has not sourced that. On a time-of-use rate, a midday export can be credited at less than the evening price, and holding it back can be worth something; enter the credit your bill shows for your export hours in the worksheet above to see how much. For riding out an outage a battery can be worthwhile either way. 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?
Ask before you sign. Whether adding storage to an existing array changes your export arrangement is set by your utility’s interconnection rules, which this site has not sourced, and a change of export terms would change the result of the worksheet above. Get the answer in writing.
Did export credits reduce the federal tax credit?
This matters only for a system placed in service on or before December 31, 2025, because the federal Residential Clean Energy Credit is closed for property placed in service after that date. For such a system, the IRS page says utility payments for energy you sell back to the grid, such as net metering credits, do not affect qualified expenses, while subsidies and rebates for buying or installing the property may need to be subtracted as a purchase-price adjustment, under conditions it lists. The two 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)