Most solar savings estimates multiply your production by one average price per kilowatt-hour. That shortcut fails on a time-of-use (TOU) plan, where the price changes by the hour. Panels make most of their power at noon, while the most expensive hours land between 4 and 9 p.m. In California, SCE states that Solar Billing Plan customers must be on its TOU-D-PRIME rate, so this matters for nearly every new system. This guide explains time-of-use optimization, shows what it does to your savings, and gives you a checklist to act on, so you can compare solar quotes with confidence.
Key Takeaways
- Time-of-use optimization means matching when you use, store, and export power to the hours when the price is lowest and highest.
- Peak pricing usually runs 4 to 9 p.m., right when solar output fades.
- A flat-rate estimate can overstate monthly savings by roughly 30 percent in an evening-heavy home.
- A battery, load shifting, and the right rate plan recover most of that gap.
What Time of Use Optimization Means for Solar Homes
A time-of-use plan charges different prices depending on when you use electricity. Time-of-use optimization is the practice of arranging your solar, battery, and daily habits around those prices so every kilowatt-hour is used where it is worth the most.
Peak, mid-peak, and off-peak windows
Most California plans split the day into a few pricing windows. Exact hours vary by utility and plan, so check yours.
| Window | Typical hours | Solar output | Price pressure |
|---|---|---|---|
| Super off-peak (some plans, winter and spring) | 8 a.m. to 4 p.m. | High | Lowest |
| Off-peak | Overnight and some midday hours | None to high | Low |
| Mid-peak or partial-peak | Weekends, or shoulder hours | Low | Medium |
| On-peak | 4 to 9 p.m. (some plans 5 to 8 p.m) | Fading to zero | Highest |
Why 4 to 9 p.m. is the problem for solar
Your array peaks near noon and goes quiet at sunset. Your household cooks, cools the house, and charges devices in the evening. The power you buy at 6 p.m. is the priciest on the schedule, while the surplus you made at noon is worth the least. Under a flat rate, this timing did not matter. Under TOU, it decides your bill.
Time of Use Rate Plans by Utility
Rates change often. The figures below were published on each utility’s site in October 2026. Confirm the current schedule for your address before making decisions.
SCE time-of-use plans
| Plan | Peak hours | Summer weekday (June to September) | Winter (October to May) |
|---|---|---|---|
| TOU-D 4 to 9 p.m. | 4 to 9 p.m. summer weekdays | Off-peak 33 cents, on-peak 59 cents | Off-peak 36 cents, super off-peak 32 cents, mid-peak 50 cents |
| TOU-D 5 to 8 p.m. | 5 to 8 p.m. summer weekdays | Off-peak 34 cents, on-peak 72 cents | Off-peak 37 cents, super off-peak 32 cents, mid-peak 55 cents |
| TOU-D-PRIME | 4 to 9 p.m. | Off-peak 26 cents, on-peak 61 cents | Off-peak 30 cents, super off-peak 24 cents, mid-peak 45 cents |
- TOU-D-PRIME is for customers with an EV, a home battery, or an electric heat pump, and has no baseline credit.
- After switching to a TOU plan, SCE customers cannot switch again for 12 months.
PG&E time-of-use plans
| Plan | Peak hours | Best for |
|---|---|---|
| E-TOU-C | 4 to 9 p.m. every day | Homes that stay near their baseline allowance and can cut evening use |
| E-TOU-D | 5 to 8 p.m. weekdays; weekends and most holidays are off-peak | Homes that can shift weekday evening loads |
PG&E summer runs June 1 to September 30, and winter covers the other eight months at lower prices. PG&E allows a plan change up to once a year.
How Time of Use Changes Your Solar Savings Estimate
Flat-rate estimate versus time-aware estimate
Here is an illustrative California home using about 700 kWh a month with a 6 kW array. It uses only 45 percent of its solar output while the sun is up.
| Scenario | Assumption | Monthly savings |
|---|---|---|
| Timing-blind estimate | 700 kWh offset at a blended 40 cents | About $280 |
| Real TOU bill, no battery | Evening use at 60+ cents, midday surplus exported at low credits | About $170 to $200 |
| TOU with battery shifting 6 to 8 kWh into peak | Self-consumption rises toward 80 percent | Recovers most of the gap |
The fix is not a bigger array. More panels only create more cheap midday surplus. The fix is moving usage or stored energy into the expensive window. Figures are illustrative, and your result depends on your plan and usage pattern.
How TOU and NEM 3.0 work together
Time of use sets the price of what you import. Net billing sets the value of what you export, and midday exports are worth far less than retail. Together, they reward using your own power at peak. For the export side, see how NEM 3.0 values an exported kilowatt-hour. For the bigger picture, read whether solar is still worth it in California after NEM 3.0. Peak prices have also been climbing, which is part of why rising utility rates push solar ROI higher.
5 Ways to Optimize Time-of-Use Solar Savings
| Lever | What to do | Upfront cost | Impact |
|---|---|---|---|
| Battery schedule | Charge from solar at midday, discharge 4 to 9 p.m. | High | Highest |
| Load shifting | Run dishwasher, laundry, pool pump outside peak | None | Medium |
| Pre-cooling | Cool the home before 4 p.m., let it coast through peak | None to low | Medium |
| EV timing | Charge at midday or overnight, not at 6 p.m. | None | Medium to high |
| Rate plan choice | Compare plans once a year against real usage | None | Varies |
Add a battery and set a peak discharge schedule
Storage lets you bank cheap midday solar and use it at peak instead of exporting it for pennies. The wider your plan’s peak-to-off-peak spread, the faster this pays back. For costs and payback, see our guide on whether a solar battery is worth it.
Shift flexible loads out of the evening
- Run the dishwasher and laundry at midday or after peak ends.
- Set pool pumps for late morning.
- Load appliances during peak and start them later with a delay timer.
Pre-cool and use a smart thermostat
Cool the house before 4 p.m., then raise the setpoint during peak. PG&E suggests 78 degrees or higher during peak, health permitting.
Schedule EV charging off-peak
The car is often the biggest movable load. Charging at midday on solar or overnight can change a monthly bill by $50 or more. See how to charge an EV on solar.
Pick and review the right rate plan
The best plan depends on when you draw power. Compare each plan’s peak window and prices against your hourly usage before choosing, and recheck annually.
How to Check That an Estimate Is Time-of-Use Aware
- It names your utility and rate plan.
- It separates self-consumed power from exported power.
- It values midday and evening kilowatt-hours separately.
- It states whether storage is included.
Run your numbers through our California solar savings calculator and learn what the calculator numbers actually mean. A solar design built on your roof and shading keeps the inputs honest.
The Bottom Line on Time of Use Optimization
Panels still cut bills substantially, but the size of the cut depends on self-consumption at peak, the value of your midday surplus, and whether storage or scheduling moves energy into the expensive window. Treat any single blended-rate number with suspicion. When you are ready to see what your roof and rate plan would really earn, get a free, no-pressure solar estimate built around your actual bills.
Frequently Asked Questions
What is time of use optimization?
It is the practice of shifting when you use, store, and export electricity so more of it falls in cheap windows and less in the 4 to 9 p.m. peak. For solar homes, that usually means a battery schedule, load shifting, pre-cooling, EV timing, and a well-chosen rate plan.
Do solar panels still save money on a time-of-use plan?
Yes, but savings depend on timing. Panels offset daytime use at full value, while evening peak prices and low midday export credits make the real figure lower than a flat-rate estimate. A battery or shifted loads recover most of the gap.
What are peak hours on a time-of-use plan in California?
Peak is commonly 4 to 9 p.m., and some plans use 5 to 8 p.m. on weekdays. PG&E’s E-TOU-C peaks daily from 4 to 9 p.m., while E-TOU-D peaks from 5 to 8 p.m. on weekdays.
Why is my real bill higher than my solar savings estimate?
The estimate likely used one average rate. If you export cheap midday power and buy expensive evening power, real savings land below a timing-blind projection.
What is the best time-of-use plan for solar with a battery?
Often the plan with the widest peak-to-off-peak spread, because a battery profits from that gap. For SCE customers with a battery, TOU-D-PRIME is built for that case. Compare plans against your usage before choosing.
Can I lower peak charges without a battery?
Yes. Move laundry, dishwashing, pool pumps, and EV charging out of peak, and pre-cool the home before 4 p.m. These changes cost nothing, though a battery captures more savings.