Charging batteries to dump back to the grid just isn't worth it, even with your massive 27kWh capacity a full charge at 11p and discharge at 15p your making less than 70p (taking into account efficiency loses)

@irmartini Yes, I realise that the actual amount gained is not very significant as you can’t even buy a ‘99 ice cream’ for about 97 pence but one needs a little fun in one’s life! 😉 (Seriously though) Obviously it is not the prime aim, once we return to winter and the saving sessions return, then matters may be a little better!. Last winter’s sessions provided over £300 of credit which did bite a hole in the winter energy bill. Regards, Toodles.

Ah yes I can see if you can get a premium export rate with agile or the saving sessions then it could be worth it with a large bank like yours.

But for most of us with much smaller batteries it doesn't seem to worth it unless I just happen to have a small one 😆 

@irmartini Nevertheless, a smaller buffer will help to smooth out the demands and assist in not using the grid at the most expensive times. (As a certain supermarket might tell you - every little helps!😉

I think the best rate offered during last winters’ saving sessions was £4.50 per kW/h; unfortunately, I didn’t have Tesla battery export permission set up then so had to make do with a little solar and ‘abstaining’ from using power during the interval. Later, once permission was set up, I was able to export approx. 8 -15 kWh’s a time for the saving sessions. (Apparently, I was in the top 1% of contributors according to OE. 😊) I must say, it is a fun way to ‘save the grid’! Regards, Toodles.

Posted by: @toodles

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@irmartini Nevertheless, a smaller buffer will help to smooth out the demands and assist in not using the grid at the most expensive times. (As a certain supermarket might tell you - every little helps!😉

Agreed, even a 5kW battery would allow one to charge at 11p and avoid importing at 34p during the peak period, plus it gives added comfort and convenience if one is no longer concerned with minimising usage between 4-7pm (a major gripe with the misses who wants to turn the electric oven on at 6pm just when it is most expensive!)

I would love a battery but just don't see us staying at this property long enough to see payback on it.

I've seen one calculation for a Tesla powerwall that worked out that the capital cost of the battery spread over its life equates to about 25p per kWh of electricity it discharges. So, if you can use it during peak periods, when it would cost 34p to import from the grid, you would need to have paid 9p to charge it, just to make enough 'profit' to cover the capital cost over the life of the battery.

But is 25p realistic?

Posted by: @old_scientist

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as we have a 50L volumiser that will already be at RWT and will not need heating from cold.

Is your volumiser a 2 pipe tank and is it really located in the circuit to the DHW cylinder as well as the circuit to the emitters? A lot of Samsung installs include a 4 pipe buffer tank in the emitter circuit. Depending on its shape, a 4 pipe buffer tank can paradoxically increase the chances of short cycling, due to mixing of flow and return with a resulting fall in the flow temperature to the emitters and therefore reduced emitter output.

Posted by: @mike-h

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Posted by: @old_scientist

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as we have a 50L volumiser that will already be at RWT and will not need heating from cold.

Is your volumiser a 2 pipe tank and is it really located in the circuit to the DHW cylinder as well as the circuit to the emitters? A lot of Samsung installs include a 4 pipe buffer tank in the emitter circuit. Depending on its shape, a 4 pipe buffer tank can paradoxically increase the chances of short cycling, due to mixing of flow and return with a resulting fall in the flow temperature to the emitters and therefore reduced emitter output.

Yes, it really is a volumiser (2 pipe tank), and it is located on the primary 28mm return to the ASHP as shown here:

so is on the return for both heating and DHW circuits (not ideal in summer, but not so bad in winter when (a) it will already be at ~35C from the heating and (b) the house will benefit from a slug of 50C water into the radiators after the DHW cycle finishes).

@old_scientist  Thanks - I have never seen that done before.

@mike-h Yes, I was aware it's not ideal, as discussed in this article:

https://www.linkedin.com/pulse/how-your-heat-pump-system-designer-can-cost-save-you-money-hendra/

The installers insist on a volumiser (a) to ensure the minimum volume is achieved in all installations (without having to actually think about it), and (b) to aid defrost cycles and help prevent short cycling, but they evidently do not give overly much consideration regarding where to install the volumiser.

@old_scientist just looking at the photo you posted. Can't believe they installed a radiator next to all the uninsulated pipework, must be roasting in that room?

Looks like it was boxed in initially, might be boxed again?