Batteries
Battery Payback on Ontario's Ultra-Low Overnight Plan: The Real Math
October 15, 2026
VerifiedOctober 15, 2026
Next reviewNovember 2, 2026 (after the OEB's November 1 price reset)
AuthorGriffEnergy Research Team
The short answer
On Ontario's Ultra-Low Overnight plan, a battery that covers about 8 kWh of weekday evening use saves roughly $700 to $800 a year. That puts payback at about 15 years with new solar and the rebate, and about 23 years for a grid-charged battery with no rebate, longer than most 10 to 15 year warranties. The savings are real; backup is still the main reason to buy.
Ontario's ULO plan has the widest price spread in Canada, so it is where a home battery has the best financial case. Some quotes promise a 5 to 9 year battery payback on ULO alone. Here is the math with the assumptions shown, so you can check any quote against it.
The prices that matter
| ULO period | Hours | Price |
|---|---|---|
| Ultra-low overnight | Every day, 11 p.m. – 7 a.m. | 3.9¢/kWh |
| Weekend off-peak | Weekends and holidays, 7 a.m. – 11 p.m. | 9.8¢/kWh |
| Mid-peak | Weekdays, 7 a.m. – 4 p.m. and 9 – 11 p.m. | 15.7¢/kWh |
| On-peak | Weekdays, 4 – 9 p.m. | 39.1¢/kWh |
These prices run through October 31, 2026. The Ontario Energy Board resets them every November 1, and we will update this page when the new prices are announced.
Two worked examples
Both use a 13.5 kWh battery, about 8 kWh of household use between 4 and 9 p.m. on weekdays (about 250 weekdays a year), and 89% round-trip efficiency, the figure on a common battery's datasheet.
| Line | A: Battery only, charged overnight | B: Battery with new solar (rebate path) |
|---|---|---|
| Installed cost | $16,000 | $16,000 |
| Ontario battery rebate | $0 (battery-only is not eligible) | −$4,050 (13.5 kWh × $300) |
| Net battery cost | $16,000 | $11,950 |
| How it charges | Grid at 3.9¢; 9 kWh in to deliver 8 kWh | Surplus solar on about 160 weekdays; overnight grid on the rest |
| Saving per weekday | About $2.78 (8 × 39.1¢ minus 9 × 3.9¢) | About $3.13 on solar days; $2.78 on grid days |
| Weekend use | Little value (9.8¢ vs 3.9¢) | About $55 a year from stored solar at 9.8¢ |
| Yearly saving | About $695 | About $805 |
| Simple payback | About 23 years | About 15 years |
Savings are before the Ontario Electricity Rebate, which is a percentage of your bill and so shrinks a little as your bill falls. Variable delivery charges are avoided too when stored solar replaces grid power, which adds a few cents per kWh to example B.
What would change the answer
- Bigger evening loads. Electric heat, a heat pump or cooking in the peak window can let the battery discharge 12 to 13 kWh a day. At 13 kWh, example A saves about $1,130 a year, a payback near 14 years.
- New prices on November 1. A wider gap between 3.9¢ and the on-peak price shortens payback; a narrower one lengthens it.
- Battery price. Each $1,000 off the installed cost cuts example B's payback by over a year.
- Degradation. Usable capacity falls slowly over time, which trims late-life savings.
- Net metering instead of the rebate. With net metering, daytime surplus already earns a credit, so a battery adds less. You cannot combine the rebate and net metering.
How to read a battery quote
Ask for the yearly savings figure and the assumptions behind it: kWh discharged per day, how many days a year, the price spread, efficiency and rate increases. A quote that assumes a full 13.5 kWh discharge every single day at 39.1¢ is assuming you use that much power between 4 and 9 p.m. on weekends too, when on-peak prices do not apply.
See what a home battery costs and the Ontario solar and battery rebate.
Does a home battery pay for itself in Ontario?
On ULO savings alone, usually not within the warranty period. In our examples payback is about 15 to 23 years. Large evening loads or a lower battery price shorten it.
Should I switch to the ULO plan if I get a battery?
Usually yes: the 3.9¢ overnight price and 39.1¢ weekday peak create the spread a battery earns from. Check your usage with the OEB bill calculator first.
Can I charge the battery from the grid overnight?
Yes, on ULO that is how a battery without solar earns money. Rebate-funded batteries should mainly store solar, per program rules.
Verified October 15, 2026. Examples are illustrative; your savings depend on your evening usage, prices after November 1, 2026, and equipment. General information, not financial advice.
