Energy
Your flat rate against a time-of-use tariff, with the peak share at which the switch stops paying.
Annual difference
Computed
Your tariffs
From your current bill: supply plus delivery, divided by kWh.
Your load
Excluding the car.
Includes wall-connector losses.
Share of your household electricity used between four and nine in the evening.
Laundry, dishwasher, pre-cooling. Not the oven at dinner.
Set to zero if the tariff has no demand component.
Where the kilowatt-hours land
The three shares always sum to one: moving load out of the peak window cannot create energy, and an engine that lets it do so will understate the saving.
The year, both ways
Saving at each peak share
| Peak share | Annual difference | Verdict |
|---|---|---|
| 20% | $821 | ahead |
| 30% | $622 | ahead |
| 40% | $422 | ahead |
| 50% | $223 | ahead |
| 60% | $23 | ahead |
| 70% | -$176 | behind |
| 80% | -$458 | behind |
A ladder rather than a single number: the answer depends on how much of your evening load is immovable, and only you know that.
Rates are yours to enter: there is no national tariff table that stays true, and a default that ages silently is worse than a blank field.
Time-of-use makes overnight charging cheap and the dinner hour expensive. Whether it pays depends on how much of your load sits in that window and how much of it can move — not on the headline off-peak rate in the utility’s marketing.
The engine solves for the ceiling: the share of household electricity that can land between four and nine in the evening before the tariff costs more. Above that ceiling, the overnight discount is subsidising load you cannot move.
The energy shares always sum to one, so shifting load cannot invent kilowatt-hours. And the published break-even is the inverse of the same cost function the table uses, solved numerically — a closed-form ceiling that drifts from its own model is worse than no ceiling at all.
peak + off-peak + super off-peak = 1
cost = home × (peak·R_p + off·R_o + super·R_s) + EV × (γ·R_s + (1−γ)·R_o)
ceiling = solve savings(peak share) = 0 by bisection
demand charge = peak kW × $/kW × 12
No utility tariffs are bundled. Rates come off your own bill, with a demand-charge field for the riders that add one — several 2026 schedules do, and a model that cannot see it overstates the saving.