The transition to and from British Summer Time makes life a bit awkward in some scenarios, like travel times and energy calculations. Because the UK energy industry operates on UTC (Coordinated Universal Time, the current official name for Greenwich Mean Time) all year round, there are several pitfalls to be aware of when working out our energy usage and bills when suddenly a 23-hour day comes along. Here are some of them:
- Time of Use electricity tariffs
Some customers will be on plans with different unit rates for different times of day. The simple example of this is Economy 7, which in much of the country charges a lower rate from midnight to 7AM. These timings change from region to region, but it's usual for them to be UTC times. This means that the cheap rate runs from 01:00 to 08:00 BST. Most modern equipment, including smart meters, will allow for this. Things that don't (clockwork timers on immersion heaters, for example) will have to be adjusted twice a year if they're to be sure of only operating at cheap rate.
- Smart meter readings are I think always taken at midnight UTC, so during BST this means 01:00AM.
- OVO's Usage charts reflect the change, but their presentation of the results on the Day page is fudged to make the figures fit. Numbers are shown for each half-hour from midnight to midnight BST, but the underlying data are for the period from midnight to midnight UTC. To 'correct' for this, the data for the first hour on the page - labelled 12:00am and 12:30am - in fact belong at the bottom of the table and to the following day. The figures that ought to be shown for 12:00am and 12:30am belong to the previous day.
This won't normally have much significance, because usage at that time of night doesn't vary much from day to day for ordinary people, and it's usually a lot less than during daytime anyway. It will matter, though, on occasion, as some customers have discovered and asked about in these forums. A couple of examples:
- A tenant arrived one evening at his flat that had been empty for some weeks. He was alarmed to discover when checking the electricity account later that there had apparently been a lot of usage in the middle of the night before he arrived. There hadn't, but the heating he turned on when he arrived was still on after midnight, and the electricity it used between midnight and 01:00 was displayed as if it had been used 24 hours previously.
- An EV user set his car to charge at midnight one day, then later checked his usage charts to see how much he'd used. He was surprised to note a spike in his chart at midnight the previous day, when there had not been any major energy-consuming equipment in operation.
OVO are aware of this problem, but have clearly chosen not to do anything about it.
- Those attempting the Power Move challenge should be wary of the change. I'm not sure whether the weekday consumption is measured from midnight BST or UTC, even though the peak timings are obviously BST. Again, this won't make much difference for ordinary users, but for those of us who like to get precise results, it could make the difference between earning and not earning the reward if we're on the borderline.
- Most of those who retrieve smart meter data with 3-figure precision will know that they have to take care when manipulating the data, to be sure that the numbers are in the right time slot. It can be quite confusing and I'm sure we've all got it wrong at some stage. Clock-change day itself is particularly challenging.
- OVO’s system retrieves the current time zone from the device operating system. If this isn’t set properly (e.g. to UTC + 00:00 with daylight savings time applied automatically), then the usage pages won’t necessarily show the correct local timings.
[Thanks to@deanphillips2005 for leading me to this revelation 😊]
There may be other consequences of summertime that I can't think of just now, but please point out any omissions, additions or corrections in a reply here.
