Volume Notification on ‘Long’ Clock Change Day: Sunday 31 October

There will be 50 Settlement Periods instead of the standard 48 on the ‘long’ clock day change. This page explains the impact of the clock change on contract notifications and reports.

UK time changes on Sunday 31 October 2021 from British Summer Time (BST) to Greenwich Mean Time (GMT)/ Coordinated Universal Time (UTC) at 02:00 (BST). This will result in a ‘long’ day as the clocks go back an hour.

Settlement periods during clock change

Settlement Periods one to four inclusive on 31 October 2021 will begin as normal at 00:00 (BST), 00:30 (BST), 01:00 (BST) and 01:30 (BST) respectively.

At 02:00 (BST), the clocks will change to GMT so instead of Settlement Period five beginning at 02:00 (BST), Settlement Period five will begin at 01:00 (GMT). Settlement Period six will begin at 01:30 (GMT) and so on until Settlement Period 50 begins at 23:30 (GMT).

Submitting contract notifications 

Both the clock change day and normal days

If you submit a contract notification which includes the clock change day and normal, non-clock change days, Energy Contract Volume Aggregation Agent (ECVAA) default rules apply.

The notified volumes corresponding to Settlement Periods three and four will also be applied to Settlement Periods five and six on the clock change day.

Notified volumes for the remaining Settlement Periods on the clock change day will all be used for the Settlement Period, two Settlement Periods later than the one they were originally notified for.

The clock change day alone

If you submit a contract notification for the clock change day alone, the Settlement Periods in the contract notification should be numbered from 1 to 50. Please note that contract notifications for the clock change day alone must contain the correct number of Settlement Periods as no defaulting rules will be applied to these notifications.

Will the content of any of the reports I receive be different?

Yes, the ECVAA Notification Report (ECVAA-I014) report for 31 October 2021 will contain 50 Settlement Periods and will include the effect of any defaulting rules applied to multi-day notifications.

The ECVAA Forward Contract Report (ECVAA-I022) for 31 October 2021 will show a representation of the original notifications submitted.


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