Most Duke Energy customers who look into time-of-use billing assume there’s one program to consider. There are two, and they work differently enough that picking the wrong one can cost more than staying on the standard flat rate.
The Flex Savings Option (FSO) and the Residential Time-of-Use (RT) rate both reward shifting energy use away from peak hours. But the RT rate includes a demand charge that FSO doesn’t have, and that changes the math for anyone with an EV charger, solar system, or battery.
The Flex Savings Option
The FSO is the simpler program. It charges only for kilowatt-hours at three price tiers:
| Period | When | Duke Energy Carolinas (Charlotte) | Duke Energy Progress (Raleigh) |
|---|---|---|---|
| Discount | 1–6 am (summer); 1–3 am and 11 am–4 pm (winter) | 7.05¢/kWh | 6.88¢/kWh |
| Off-peak | All other hours | 9.74¢/kWh | 9.50¢/kWh |
| On-peak | 6–9 pm weekdays (summer); 6–9 am weekdays (winter) | 21.34¢/kWh | 20.80¢/kWh |
| Critical peak | Up to 20 designated days per year | 44.26¢/kWh | 43.18¢/kWh |
There is no demand charge. You pay more per kWh during three hours of weekdays and less the other 21 hours. Weekends and designated holidays are always off-peak.
Duke Energy can call up to 20 critical peak days per year. You’re notified a day in advance by text or email. These days occur during extreme heat or cold when grid demand is highest.
There is no minimum enrollment commitment. You can leave FSO at any time.
Rates verified April 2026. Verify current figures at duke-energy.com before making enrollment decisions.
The Residential Time-of-Use (RT) Rate
The RT rate uses the same seasonal peak-hour structure as FSO (6–9 pm in summer, 6–9 am in winter). Weekends and holidays are always off-peak. It also includes a discount period for even lower rates during specific hours.
The key difference is the demand charge. Your monthly bill includes two components beyond energy charges:
- On-Peak Billing Demand: the highest 30-minute power draw during on-peak hours in the billing month
- Max Billing Demand: the highest 30-minute power draw during any hour in the billing month
That peak reading, even from a single half-hour window, sets your demand charge for the entire billing period.
The RT rate also has a one-year minimum commitment. Once you leave, you can’t re-enroll in any TOU rate for 12 months.
Why the demand charge matters for EV owners
A Level 2 EV charger draws 7 to 10 kW. Your central air conditioner draws 2 to 5 kW. An electric water heater draws 4 to 5 kW. Run all three at the same time for 30 minutes and your peak demand can hit 15 to 20 kW. Under the RT rate, that one overlap sets your billing demand for the month.
The FSO doesn’t have this exposure. You pay 21.34¢/kWh if you charge during the three on-peak hours, but there’s no separate charge for how many kilowatts you drew at once.
For an EV owner who charges overnight, FSO is almost always the better choice. Discount hours (1–6 am in summer) run 7.05¢/kWh with no risk of a demand charge spike.
How battery storage changes the calculus
A home battery paired with solar performs well under FSO. The battery charges during discount hours when electricity is cheapest (or directly from solar during the day) and discharges during the on-peak window when grid power costs most. The spread between 7.05¢ and 21.34¢ is large enough to make the arbitrage meaningful.
Under the RT rate, the demand charge complicates battery strategy. Depending on how Duke Energy measures demand relative to battery discharge, you’d need to ensure the battery doesn’t cause a demand spike during charging.
For most battery owners, FSO is the cleaner fit. Duke Energy’s Power Manager Battery Control program lets Duke remotely manage your battery’s charge and discharge schedule within the FSO framework, optimizing around peak and discount windows automatically.
Which program to choose
Choose FSO if:
- You have an EV and charge at home
- You have a battery or are adding one
- You have solar and want to maximize the rate spread
- You’re not sure which program fits your household (FSO has no commitment, so you can leave without penalty)
RT might work if:
- You have very predictable, separable high-draw loads
- You use a smart charger or home energy management system that prevents demand spikes
- You’re confident you won’t run multiple large appliances simultaneously
When in doubt, start with FSO. The rate spread is meaningful, the commitment is zero, and the demand charge risk doesn’t exist.