Daylight Saving - TonyM1958/HA-FoxESS-Modbus GitHub Wiki

Daylight saving is when the clocks go forward in Spring and back in Autumn. In the UK, this happens on the last Sunday in March (1 hour forward at 1am) and October (1 hour back at 2am). This changes the time zone we use and, in the UK, we switch to Greenwich Mean Time (GMT) in Autumn and to British Summer Time (BST) in Spring.

Here's what you see in the inverter data time stamps when the clocks go forward:



Data uploaded from the inverter shows the local time and time zone. At midnight, the time zone is GMT and this changes at 1am to BST.

The times are based on UTC (co-ordinated universal time, this the way computers keep track of time). UTC is the same time as GMT, so GMT has an offset of 00:00. When the time zone changes to BST, the offset is +01:00 and your devices add 1 hour to UTC to show you the current local time. Although this is quite technical, it's useful to understand how offsets work to keep track of what is happening when your time zone changes.

The inverter clock doesn't use time zones. It runs in 'local' time. So, when you configure Grid Charge Times and Schedules, the times you set are independent of your time zone and run at your inverter 'local' time.

For example, a charge time of 02:00-05:00 runs at 02:00-05:00 GMT in Winter and at 02:00-05:00 BST in Summer. The upshot of this is that there is normally no need to amend your charge times or schedules when the clocks go forward or backwards because your peak and cheap rate hours stay the same if you are on a Smart tariff.

The exception that you may need to check is if you are on an Economy 7 tariff. For some suppliers, cheap rates for Economy 7 are always GMT so you may need to alter your charge times so they are an hour earlier in the Summer.

When the clocks change, the days are either 23 or 25 hours long so you may see some data that doesn't look right in the app or web site (there are usually a number of FB posts about this). For example, this chart overlays two sets of data between 1am (when the battery was charging) and 2am (when the battery wasn't charging) and alternates the data points producing a block pattern:



You may also see some unusual numbers for battery charge and discharge, going from kWh to MWh that only affect the day when the clocks changed. The Energy Stats app is not affected in the same way, if you need to check any of these values:



The values shown for the day appear to be the Total Charged and Discharged Energy since the system was installed.

If you have a schedule period or charge time that starts before the clocks changes and ends after the clocks change, the duration of the time period is normally preserved. For example, if you set a charge time for 00:30-05:30:

• When the clocks go forward, the charge time will start at 00:30 GMT and end at 06:30 BST (05:30 GMT). It may look like the charge time over-ran by 1 hour but the duration is 5 hours so it charges the battery for the time you set.

• When the clocks go back, the charge time will start at 00:30 BST and end at 04:30 GMT (05:30 BST). It may look like the charge time under-ran by 1 hour but the duration is 5 hours so it charges the battery for the time you set.

After the clocks changed, your time periods will run normally at local time (once the inverter clock has updated).

The inverter clock does not change immediately when the clocks change but does usually update a few hours later (possibly related to what schedule or time periods it is processing?). Some people look at the inverter early in the morning after the clocks change and conclude that the time is wrong so they manually change it. However, if you do nothing, the clock generally does update itself sometime between 2am and 11am.

The recent addition of the remaining time period covering 00:00-23:59 in the app may throw a spanner in the works as it covers the whole day. We will only know what affect this has after the day light saving change happens.