Reading electricity interval data without confusing kW and kWh
An interval chart shows when electricity was used, but first check what its bars mean. Energy per interval and average power can look similar while requiring different arithmetic.
Keep the export definitions
Find the unit, interval duration, time zone and whether timestamps mark the start or end. Imported, exported and net energy are different quantities for a home with generation. Check how missing intervals and clock changes are represented. A blank cell should not silently become zero consumption.
Convert a bar into a useful scale
A fictional half-hour interval containing 0.6 kWh has average power 0.6 ÷ 0.5 = 1.2 kW. Two intervals containing 0.6 and 0.4 kWh total 1.0 kWh over the hour. If the file instead lists half-hour average powers of 1.2 and 0.8 kW, multiply each by 0.5 hours before adding. The result is again 1.0 kWh. Summing kW alone does not give energy.
Patterns suggest questions
An overnight plateau can include refrigeration, networking and heating controls. A short large interval may combine several appliances. Compare timing with household notes, then measure a suspected appliance separately where appropriate. A plateau change after switching off a device is informative only when other loads and conditions are comparable.
Sum valid energy intervals across the exact billed dates. Investigate missing or estimated readings, rounding and import/export definitions before assuming an error. Apply time-of-use prices to energy in each window. Demand charges, where present, use a tariff-defined measure and need separate treatment. The Appliance Energy Cost Calculator prices an average load over a known duration; it does not import interval files or identify appliances.
Appliance Energy Cost Calculator
Worked example: Separate a summer usage spike from a price change
Related reading: How time-of-use electricity pricing changes your costs
Reference: EIA: measuring electricity.