Three published tariffs, read the way a battery reads them
A household reads a rate plan looking for the lowest average price. A battery reads it looking for the widest gap. Those two readings pick different plans, and the second one is what decides whether storage earns anything at all.
What a published rate rail looks like before anyone tidies it
This is how the utility publishes the periods and prices of the first plan below. Each number is a price in cents and the time immediately after it is the hour that block begins; the ellipsis marks material we skipped between the summer rail and the winter one.
Quoted from the source document, retrieved 2026-08-06
“Summer Rates June - September Weekdays Off-Peak 34 12am On-Peak 58 4pm Off-Peak 34 9pm 12am ... October - May Weekdays & Weekend Off-Peak 37 12am Super-Off-Peak 33 8am Mid-Peak 51 4pm Off-Peak 37 9pm 12am”
The thing a summary of this loses is the shape: the expensive block is bounded on both sides by the same cheap price, so the plan is not a high rate with a discount attached but a flat rate with a five-hour spike, and a battery only ever earns inside that spike.
Reading it that way also settles a question that comes up constantly. The winter rail opens a block in the middle of the day that is cheaper than the one running overnight, so the cheapest hour to charge in winter falls in daylight rather than at three in the morning. A dispatch schedule set once in summer and never revisited spends the whole winter paying more to charge than it needed to.
TOU-D 4 PM to 9 PM
4 p.m. to 9 p.m., the only hours worth discharging into
| Season | Peak | Off-peak | Cheapest daytime block | Spread | Expensive hours |
|---|---|---|---|---|---|
| Summer | 58¢/kWh | 34¢/kWh | none published | 24¢/kWh | 4 p.m. to 9 p.m. |
| Winter | 51¢/kWh | 37¢/kWh | 33¢/kWh | 14¢/kWh | 4 p.m. to 9 p.m. |
Summer runs 58¢/kWh [1] against 34¢/kWh [2]; winter runs 51¢/kWh [3] against 37¢/kWh [4]. A fixed $0.79 a day [5] is levied regardless and no battery touches it.
A baseline credit of ten cents per kilowatt-hour applies up to the monthly baseline allocation and is not modelled here, because it lands on consumption rather than on the spread.
TOU-D 5 PM to 8 PM
5 p.m. to 8 p.m., the only hours worth discharging into
| Season | Peak | Off-peak | Cheapest daytime block | Spread | Expensive hours |
|---|---|---|---|---|---|
| Summer | 74¢/kWh | 34¢/kWh | none published | 40¢/kWh | 5 p.m. to 8 p.m. |
| Winter | 60¢/kWh | 38¢/kWh | 32¢/kWh | 22¢/kWh | 5 p.m. to 8 p.m. |
TOU-D-PRIME
4 p.m. to 9 p.m., the only hours worth discharging into
| Season | Peak | Off-peak | Cheapest daytime block | Spread | Expensive hours |
|---|---|---|---|---|---|
| Summer | 59¢/kWh | 26¢/kWh | none published | 33¢/kWh | 4 p.m. to 9 p.m. |
| Winter | 56¢/kWh | 24¢/kWh | 24¢/kWh | 32¢/kWh | 4 p.m. to 9 p.m. |
Choosing is a twelve-month decision
Quoted from the source document, retrieved 2026-08-06
“If you switch to a Time-of-Use rate, you will not be able to make another switch for a full 12 months.”
A rule written to stop customers gaming seasonal prices lands on a battery owner as something else entirely: it means a tariff chosen on a savings estimate cannot be corrected when the estimate turns out to be wrong, so the modelling has to happen before the enrolment rather than after the first bill.
Moving onto a time-of-use plan starts a lock of 12 months [16] before another change is permitted. That turns plan selection from something you can iterate on into something worth modelling first — particularly when the difference between two of these plans is a third of the arbitrage income.
There is a second constraint worth knowing before you compare anything: households on the current solar billing arrangement are required to take a particular plan rather than choosing among these. If that is you, the useful question is not which plan to pick but whether the plan you are obliged to take supports a battery at all.
One caution on scope. These are the delivered prices published for a bundled customer of one utility, before any baseline credit, transcribed on a single date. Prices change with regulatory filings, and a household buying generation from a community aggregator pays a different total. Use these as a worked example of how to read a tariff, then run the same arithmetic on your own.
- Turn a spread into moneyBreak-even peak price and annual arbitrage from these prices.
- The other half of the tariffWhat exports earn decides as much as what imports cost.
- Size to the windowA three-hour peak and a five-hour peak want different packs.
Questions this page gets asked
Which of these three is best for a battery?
The one with the cheapest charging block relative to its peak, which is not the same as the one with the highest peak price. A battery buys and sells; a plan with a tall peak and an equally tall off-peak is worse for storage than a plan with a modest peak and a genuinely cheap overnight rate.
What is the daily charge doing in the comparison?
Nothing a battery can affect, which is exactly why it is listed. A fixed daily charge is levied regardless of how much energy you move or when, so it cannot be reduced by storage and should never appear in a savings claim.
Can I switch plans if the one I picked turns out to be wrong?
Not immediately. Switching onto a time-of-use plan starts a 12-month lock before another change is allowed, which makes the choice a commitment rather than an experiment. Model the plan before you enrol, not after.
Do solar customers get to choose freely?
Not always. Customers on the current solar billing arrangement are required to take a specific plan, so for a new solar-plus-storage household the tariff may already be settled. Confirm that before comparing spreads, or the comparison is academic.
Provenance for every figure printed above
s3.sce_tou_d_4_9.summer_peak— Southern California Edison, Time-Of-Use Residential Rate Plans — https://www.sce.com/residential/rates/Time-Of-Use-Residential-Rate-Plans (retrieved 2026-08-06)s3.sce_tou_d_4_9.summer_offpeak— Southern California Edison, Time-Of-Use Residential Rate Plans — https://www.sce.com/residential/rates/Time-Of-Use-Residential-Rate-Plans (retrieved 2026-08-06)s3.sce_tou_d_4_9.winter_peak— Southern California Edison, Time-Of-Use Residential Rate Plans — https://www.sce.com/residential/rates/Time-Of-Use-Residential-Rate-Plans (retrieved 2026-08-06)s3.sce_tou_d_4_9.winter_offpeak— Southern California Edison, Time-Of-Use Residential Rate Plans — https://www.sce.com/residential/rates/Time-Of-Use-Residential-Rate-Plans (retrieved 2026-08-06)s3.sce_tou_d_4_9.daily_fixed— Southern California Edison, Time-Of-Use Residential Rate Plans — https://www.sce.com/residential/rates/Time-Of-Use-Residential-Rate-Plans (retrieved 2026-08-06)s3.sce_tou_d_5_8.summer_peak— Southern California Edison, Time-Of-Use Residential Rate Plans — https://www.sce.com/residential/rates/Time-Of-Use-Residential-Rate-Plans (retrieved 2026-08-06)s3.sce_tou_d_5_8.summer_offpeak— Southern California Edison, Time-Of-Use Residential Rate Plans — https://www.sce.com/residential/rates/Time-Of-Use-Residential-Rate-Plans (retrieved 2026-08-06)s3.sce_tou_d_5_8.winter_peak— Southern California Edison, Time-Of-Use Residential Rate Plans — https://www.sce.com/residential/rates/Time-Of-Use-Residential-Rate-Plans (retrieved 2026-08-06)s3.sce_tou_d_5_8.winter_offpeak— Southern California Edison, Time-Of-Use Residential Rate Plans — https://www.sce.com/residential/rates/Time-Of-Use-Residential-Rate-Plans (retrieved 2026-08-06)s3.sce_tou_d_5_8.daily_fixed— Southern California Edison, Time-Of-Use Residential Rate Plans — https://www.sce.com/residential/rates/Time-Of-Use-Residential-Rate-Plans (retrieved 2026-08-06)s3.sce_tou_d_prime.summer_peak— Southern California Edison, Time-Of-Use Residential Rate Plans — https://www.sce.com/residential/rates/Time-Of-Use-Residential-Rate-Plans (retrieved 2026-08-06)s3.sce_tou_d_prime.summer_offpeak— Southern California Edison, Time-Of-Use Residential Rate Plans — https://www.sce.com/residential/rates/Time-Of-Use-Residential-Rate-Plans (retrieved 2026-08-06)s3.sce_tou_d_prime.winter_peak— Southern California Edison, Time-Of-Use Residential Rate Plans — https://www.sce.com/residential/rates/Time-Of-Use-Residential-Rate-Plans (retrieved 2026-08-06)s3.sce_tou_d_prime.winter_offpeak— Southern California Edison, Time-Of-Use Residential Rate Plans — https://www.sce.com/residential/rates/Time-Of-Use-Residential-Rate-Plans (retrieved 2026-08-06)s3.sce_tou_d_prime.daily_fixed— Southern California Edison, Time-Of-Use Residential Rate Plans — https://www.sce.com/residential/rates/Time-Of-Use-Residential-Rate-Plans (retrieved 2026-08-06)s3.switch_lockout_months— Southern California Edison, Time-Of-Use Residential Rate Plans — https://www.sce.com/residential/rates/Time-Of-Use-Residential-Rate-Plans (retrieved 2026-08-06)