How we turn a tariff into a dollar figure: the three households, hour by hour

Why not just multiply by an average rate

Because the rate is not a number; it is a rule. A time-of-use plan has no single price until you know what hour each kilowatt-hour was used. A tiered plan has no single price until you know the monthly total. A seasonal plan changes in June. Multiplying a monthly total by a headline rate gets all three wrong, and gets them wrong differently for different plans, so the comparison between plans is wrong too. The only way to price a tariff honestly is to give it a load — a use for every hour — and let the tariff price it.

The three households

The totals were chosen to sit below, near, and above the national average. But the totals are the least important part. Each household has a shape:

• A base load spread across the day the way household use actually is — low overnight, a bump at breakfast, a larger one in the evening.
• Central air conditioning, for the two houses, that rises through the afternoon and peaks around 3pm, scaled month by month from nothing in winter to full load in July and August.
• An electric car, for the third, charging 10 kWh a night from midnight for six hours — the pattern a scheduled charger produces, and the one time-of-use plans are designed to reward.
• Weekends follow a different daily shape from weekdays, since the tariff often prices them differently.

The shape is what makes the three answers differ. A plan with a 4pm-to-9pm peak charges the air-conditioned house heavily and the apartment lightly; a plan with a cheap overnight rate rewards the car and does nothing for the other two. Three households with the same totals and no shape would produce three identical rankings, which would tell you nothing.

What the engine does with the tariff

1. Reads the tariff’s weekday and weekend schedules — a 12-month by 24-hour table saying which pricing period applies in each hour.
2. For each hour of the year, looks up the period, then prices the household’s use in that hour at the period’s rate, including any adjustment riders the tariff lists.
3. Where the period is tiered, accumulates the month’s use and moves to the next tier when the threshold is crossed, at the tariff’s tier boundary.
4. Adds the fixed charge, converting daily or monthly amounts to the period.
5. Sums twelve months. Divides by the year’s kilowatt-hours for the effective rate.

Worked example: Evergy Metro’s Residential High Differential Time of Use (Schedule RTOU-3) has the widest hourly gap in our index — 36.2¢ at peak against 2.6¢ off-peak. Run the three households through it and the apartment comes to $780, the family home $1,435, and the home with a car $1,538 — effective rates of 16.0¢, 15.2¢ and 11.7¢. The car house uses the most electricity and pays the lowest rate per unit, because most of what it added was overnight.

What it deliberately does not do

• Demand charges. 45 household plans bill on the single highest hour of the month. We do not model that peak, because it depends on coincidence — the oven, the dryer and the air conditioner all running at 5:15pm — more than on habit. Those plans are flagged, and their annual figures shown as a floor.
• Solar exports. None of the households generate. Plans written for solar customers are shown but not ranked; here is why.
• Holidays. Tariffs that bill holidays as weekends are modelled as if they did not, which makes summer peaks very slightly high.
• Monthly supply changes. In retail-choice states the supply half of the bill moves monthly. We price the tariff as filed; a bundled tariff’s supply rate is the one on file at the snapshot date.
• Your house. The model is not you. What holds up is the gapbetween plans, since every plan is priced off the same assumptions. The calculator on each utility page lets you adjust the household — more use, electric heat, a car, a water heater on a timer — and reprices every plan against that.

Checking it

Every rate page links to the filed tariff document it was read from, and the whole index — with the three annual figures for every plan — is a downloadable, public-domain CSV. The engine’s test suite runs real tariffs with known answers on every build. If a number looks wrong to you, it might be, and we want to hear about it.