methodology ยท time-of-use
Why time-of-use windows are so hard to read
Why electricity tariffs make simple off-peak questions difficult, and how Cheapest Hours turns schedules into direct answers.
Published
The basic question sounds simple: when is electricity cheapest? The source material rarely is.
Utility tariffs are legal and operational documents. A residential plan may spread its energy prices, seasonal definitions, weekday hours, weekend rules, holidays, riders, and eligibility requirements across several pages. The same utility may publish several plans with nearly identical names. A chart might use period numbers without showing the price next to each hour.
The OpenEI U.S. Utility Rate Database helps by turning many tariffs into structured records. Its schedules use twelve monthly arrays, each containing 24 period numbers. Those period numbers point to price structures that may contain adjustments and usage tiers. This is excellent machine-readable material, but it still requires careful interpretation before a household can act on it.
Cheapest Hours converts that structure into a direct answer. For each month and day type, it calculates the effective tier-one energy price, finds the minimum and maximum hours, joins consecutive hours into windows, and groups months with matching schedules into seasons. The page keeps the original source link and effective date close to the answer.
The calculation also stays deliberately narrow. Energy prices are only one part of a bill. Fixed charges, minimum bills, taxes, baseline allowances, demand charges, export credits, and eligibility rules can change the result. That is why every rate page carries a reminder to confirm the current tariff with the utility.
The goal is not to replace the tariff. It is to make the first useful answer easy to find, then make the source and limitations easy to inspect.