Smart meter data analyser: methodology

Where your data goes

Nowhere. The page reads your file with your browser’s own file reader and does every calculation in the tab. There is no upload, nothing is stored when you close the page, and the code that reads the file contains no network requests. The privacy policy says the same.

Reading the file

There is no standard export format, so rather than a list of supplier templates the page reads the file the way a person would.

• Layout. Comma, semicolon or tab separated, quoted or not, with or without lines about the meter before the header, and with or without a header at all.
• Columns. The timestamp column is the one where nearly every value is a date and time; a column called “start” beats one called “end”. Separate date and time columns are joined. The energy column is the numeric one whose name suggests consumption, and columns about export, cost or carbon are passed over. Gas data is sent to the gas analyser rather than mislabelled as electricity. If we choose wrongly, you can pick the columns yourself.
• Dates. ISO dates with or without a UTC offset, and UK day-first dates. A timestamp without an offset is taken as UK clock time.
• Interval. Half-hourly, hourly or daily, from the typical gap between readings. Files stamped at the end of each interval are moved to the start.
• Units and quirks. A Wh column is converted to kWh, as are numbers too large to be kWh for a home (over 10 kWh in a half-hour). A column of rising meter readings is turned into usage between readings. Duplicated rows are removed and negative readings, usually export, are ignored. Each of these is reported on the results.

Clock changes

Cheap windows are defined in UK clock time, so every reading is placed on the UK calendar. British Summer Time is worked out from the rule (from 01:00 UTC on the last Sunday of March to 01:00 UTC on the last Sunday of October), not from your computer’s time zone. When clocks go back, 01:00 to 02:00 happens twice; a file without offsets lists those half-hours twice, and both are kept.

Complete days

Averages use complete days only: at least 95% of the expected readings, which allows for the 46 and 50 half-hour days when clocks change. A half-day at either end of a download would otherwise drag every average down.

A year from part of a year

With 12 months of data, the yearly figure is measured: the last 365 days, scaled for any missing days. With less, multiplying the daily average by 365 would overstate a winter download and understate a summer one. Instead each day is weighted by how much a typical home uses on a day in that month, from the Faraday monthly figures: a January day counts as 1.09 of an average day and a June day as 0.91. Homes heated by electricity swing far more between seasons than that, so for them a short download is a rougher guide.

Your day, and always-on use

The average day is the mean of each half-hour across complete days, added up into hours. It is drawn against the typical home: the Faraday average for homes with no heat pump, EV or solar, which uses 9.7 kWh a day.

Always-on use is the lowest reading of each day, turned into watts, with the median taken across days so that one odd night doesn’t decide it. It needs half-hourly or hourly data.

The EV tariff comparison

We add up the share of your electricity that falls in each cheap window, to the half-hour: 23:30 to 05:30, 00:30 to 04:30, 00:30 to 07:30. Hourly data is split where an hour straddles the edge of a window. The comparison uses the first window, 23:30 to 05:30, with Intelligent Octopus Go (12-month fixed) rates averaged across regions (7.6p overnight, 36.7p by day, 54.34p a day standing charge), against the price cap.

standard  = year kWh × cap rate + cap standing charge × 365
EV tariff = year kWh × (share × night rate + (1 − share) × day rate)
          + EV standing charge × 365
break-even share: the share at which the two are equal

It prices your home as it runs today. If you would also add a car, the EV charging calculator does that sum.

What it doesn’t do

• Gas. The gas usage analyser reads gas files.
• Solar or batteries. An import meter isn’t consumption when panels are generating, so a solar home will look smaller than it is.
• Your exact tariff. Comparisons use the price cap and averaged EV tariff rates.

Back to the analyser