Posted by: @chandykris

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but with a big push towards EVs it would be surprising if they are dropped completely.

I doubt that matters, ToU tariffs are for the benefit of the grid and electricity suppliers not to aid the transition to EVs.  They have been around for decades as a means of load shifting (and thus balancing).  With increased electrification they should, in principle, become more important still but apparently (according to @transparent) the government is being pushed by the industry for 'upgrade max' (my words) to deal with electrification rather than sensible load management.

Posted by: @jamespa

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more important still but apparently (according to @transparent) the government is being pushed by the industry for 'upgrade max' (my words) to deal with electrification rather than sensible load management.

Indeed.

Present ToU tariffs are based on national supply and demand statistics.

But most of the new renewable sources of generation are connected at the EHV (33kV and 132kV) levels of the grid.
The electricity passes down from there to reach consumers across the 11kV level.
It doesn't go upwards to the 400kV National Transmission Grid.

There is a need for ToU tariffs which better reflect the available capacity on the 11kV level,
which accounts for 90% of grid cable routes.

Posted by: @wally

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We have neither solar nor batteries but we are thinking of installing the latter. This would primarily be to benefit from the TOU tariff. Furthermore we are also considering replacing our electric shower with one run from our massive 250l DHW tank which for two people I think is OTT.

This would help, electric showers are very power hungry. Luckily for us the installer could only fit a slimline cylinder in our house so we only have a 180l one which heats up in 30 mins and when there is just the two of us only really needs to do that once a day. Even if you keep the electric showers for emergencies sticking a shower adapter on your bath taps will help. 

@grantmethestrength MCS requirements for DHW capacity have a lot to answer for! For us, ‘Standard’ designs are too rotund and ‘Slimline’ are too tall for any space we have. My installer informed me just this week that ours was the first Sunamp Thermino that they installed in 2023 - they have installed many more since!

My installer had attended as our MyEnergi Eddi has failed, and this may be another story in due course as we wait for a detailed response about a replacement under warranty… Regards, Toodles.

@wally

Hi

Posted by: @wally

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We have neither solar nor batteries but we are thinking of installing the latter. This would primarily be to benefit from the TOU tariff. Furthermore we are also considering replacing our electric shower with one run from our massive 250l DHW tank which for two people I think is OTT.

I am not sure how large your house is but from what I gather DHW tank sizing is based on house size not occupants. For example our 5 bed house has a 200L DHW tank which is OTT for just the two of us but for a 5 bedroom house is actually undersized. However 200L was the largest we could fit in the installation space, it should be nearer 300L in size. The advantage at the moment is it only needs heating up once a day on cheap overnight electric on average. The old tank that was replaced was only 180L so a small step up for us.

I recently installed solar / batteries to take advantage of TOU tariffs and was able to size the correct battery only because I now have my heat pump system running optimally and have a clear picture of my consumption at different points in the year. 

For your information, I have a 12Kw Samsung (I know its not an Aira 🙂 ) and my power consumption for December was 511 Kwh and so far for January 362 Kwh. That is for a 1970 5 bed house in Cambridgeshire with a heat loss of 10.2 Kw @ -2C.

Our motivation for batteries was mainly because we also have an EV which made running the HP during the day more expensive than oil. If you do not have an EV, a tariff dedicated to heat pumps may prove to be a less expensive option than batteries but until you have a clear consumption figure (after system tuning) for the year you are flying blind a little.

Regards

@wally How did your heat pump perform across  the whole month? After the big freeze in the first week of the month in our county, rest of January was relatively mild and we ended up with a lower than anticipated usage overall. On average, we used 20 kWh every day (including DWH) and a CoP of 4.1 for heating. We started the month with approximately 35 kWh per day in the first week and a CoP of 3.

Hope your changes have helped with a better performance.

ChandyKris,

Thank you for your continued interest. I envy your usage for January! On average for the month of January 2026 our daily usage was 42.2 kWh, including DHW and a CoP of 3.3 for heating. The average outdoor temperature was 3.0. Our overall electricity bill for January was in excess of £400.00. Although I note with interest that Aira reckon I saved £52 in the month of January had I been using gas!

I have escalated this with Aira and am optimistic we will get things sorted out. We cannot continue with this kind of performance.

Interesting January stats @chandykris and @wally 

For comparison I have an 8kW Aira plus 250L tank for a 4 1/2 bed semi-detached house built in 1933, installed Sep 2024. Thermostat is in the hall and is set at 19C, reducing by 3C at night through the app. In January Energy consumption was 1,185.6, Average temp 4C, Average Heating Energy Efficiency 3.8, Average Hot Water Energy Efficiency 2.8.