EV Tariff - 2am to 6am but GMT or BST?

Dear Bulb,

I had a support discussion a day or two ago about whether or not the 2am to 6am cheap rate period was always in GMT, or whether it was in BST during the summer. The response from Bulb Support was quite clear that it was always in GMT.

However, I checked my meter at 06:50 (BST) yesterday, and found it showing Rate 1 as the active rate. This would suggest that it had already switched back to day rate before 7am BST (which is 6am GMT).

This shows that my meter seems to be applying the 2am to 6am times in BST, not GMT.

In any case, please can Bulb clarify this in their tariff description so that it is crystal clear to all EXACTLY when the cheap rate applies in both summer and winter.

If I get this wrong and set my car to charge wrongly by an hour, it will cost me roughly £1 per charge with a 7kW charger.


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My previous thread on this topic was closed by support, and linked to a non-existent thread. This time, please actually answer the question. Thanks.

@holly_at_bulb You put his last post onto the private EV members part of the forum, which is only available for people who are actively on the EV trail. You need to give @MartinR the “ev members” badge if you want him to be able to read you response, or just give ham a response here.

I am now on the EV Tariff, as of last week - so should be able to see that thread anyway? I thought I was invited to join the EV tariff as a ‘beta’ tester.

Oops! @MartinR I thought you were part of the EV forum! I’ve now added you in- let me know if you can now see the thread I merged for you? :relaxed:

Hi, How do I join the EV forum p,ease. We have moved to the Ev tariff and need information on exact timing for off peak, both winter and summer. Thankyou

@holly_at_bulb, like @Rob-Jane I would also like to join the EV forum if that’s OK please. I have not yet switched to the EV tariff because of SMETS 1 meter problems that I am trying to get resolved, but I have an EV and I am interested in the discussion.

By the way, assuming it is not a particularly sensitive industrial secret, the question of whether the EV tariff schedule follows GMT or BST could also be answered here.

We have moved to the EV tariff and because we only have electricity at the house and use off peak to heat storage heaters it is absolutely critical to have these times correct. Bulb has said:
"Hi Rob,

It is set on GMT and unfortunately it doesn’t change to British Summer Time.

During this period your would have to adjust your usage by one hour.

All the best,

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That completely contradicts what Bulb previously told me!

Come on Bulb! Which is it? GMT or BST?

In answer to my question:-

(Can I have) Clarification about the times of the EV tariff concerning GMT and BST.

I received an email reply:-

Vikki (Bulb Help)

Apr 13, 2022, 14:37 GMT+1

Just to confirm the timings of the tariff are always 2am-6am, whether we’re in GMT or BST.

I think one of the elements of confusion is that economy 7 tariff timings are always GMT (I have been told by Bulb) whereas the EV tariff is always 2am to 6am whether it’s GMT or BST (I have been told by Bulb!). As they are both off peak rates metered by the same meter, it seems illogical.

We really need Bulb staff to be singing from the same hymn sheet!

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Am I correct in saying that the EV tariff is only available if you have a smart meter? In which case, the smart meter automatically adjusts the EV period so that it will always fall between 0200 and 0600, regardless of whether we’re in GMT or BST.

Am I correct in saying that the EV tariff is only available if you have a smart meter?


In which case, the smart meter automatically adjusts the EV period so that it will always fall between 0200 and 0600, regardless of whether we’re in GMT or BST.

Well, that would depend on the implementation details. Even if the smart meter itself automatically updated its internal clock to BST (this may or may not be standardised and could vary between different meter models, especially I imagine SMETS 1), billing is under Bulb’s control (backend software) and the meter data would have to be imported for billing computations. The backend code could make an assumption about the meter data timezone and convert the timezone as needed, which could go wrong if the assumption is incorrect. And then there’s the DCC network too, so possibly two or three points of time zone mismatch:

  • The time zone used by the meter itself for its internal clock (which may be model dependent, especially SMETS 1 models).
  • The time zone used by the national SMETS 2 DCC network (smartdcc-co-uk), in case Bulb takes the readings from there rather than from the meters directly (I don’t know!).
  • The time zone used by Bulb’s own billing backend software, which may or may not treat old Economy 7 meters differently to smart meters.

The worst case might be (hypothetically) each step making incorrect assumptions about the previous step, such that billing ends up shifted by 2 hours:

  • The meter automatically adjust from GMT to BST and sends its readings to the DCC network in BST, e.g. 2am BST.
  • The DCC network incorrectly assumes that the meter reading is 2am GMT and adjusts it to BST by adding 1, ending up recording 3am BST.
  • Bulb’s billing software incorrectly assumes that the meter reading provided by the DCC network is GMT and adjusts it to BST by adding 1, ending up recording 4am BST, for what was really 2am BST.

This is just to make the point that there’s more to it than just whether or not a meter adjusts its internal clock to BST, with room for error, misunderstanding and negligence.

And if proof of the last statement was needed, in this thread we seem to have two contradictory answers from Bulb’s staff, one saying GMT, the other saying BST. Perhaps Bulb could share their billing backend source code with us (e.g. in GitHub) and the source code or technical specs of the supported smart meters and the DCC API, so we could do our own analysis and submit pull requests for the bugs and contradictions that we will find.

Or more realistically, Bulb could allow customers to download a spreadsheet (CSV) with hour-by-hour readings in KWh and the tariff rate applied to that hour. This would allow customers to match their EV charger data against Bulb’s billing data and conclude “the meaning of 2am” – BST or GMT.

It is sad that, somehow, even when we manage to get an answer to a straightforward question like “Does your billing use GMT or BST?”, we still cannot trust it.

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