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Calculating how many kWh/day electricity a heat pump will consume (worst case)
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ed110220
Posts: 1,606 Forumite


in Heat pumps
Hi all, apologies for asking this here as well as in the Green and Ethical section but it's buried away in a thread mainly about something else.
I'm trying to work out what battery capacity I'll need to run an ASHP on off peak electricity on a cold winter day. At the moment I have gas central heating. I have a 15 kWh battery which I charge up on Octopus Go at 8.55p/kWh overnight so we hardly import any peak rate electricity. I'm thinking of switching to ASHP and adding more battery storage to run it.
I've looked through our daily gas consumption for the past two winters and the highest was 50 kWh. With a COP of 3 that would be equivalent to 16.7 kWh of electricity (I'll ignore the fact that the boiler has a COP of less than 1 to be conservative). Does that sound right or are my assumptions off?
I'm trying to work out what battery capacity I'll need to run an ASHP on off peak electricity on a cold winter day. At the moment I have gas central heating. I have a 15 kWh battery which I charge up on Octopus Go at 8.55p/kWh overnight so we hardly import any peak rate electricity. I'm thinking of switching to ASHP and adding more battery storage to run it.
I've looked through our daily gas consumption for the past two winters and the highest was 50 kWh. With a COP of 3 that would be equivalent to 16.7 kWh of electricity (I'll ignore the fact that the boiler has a COP of less than 1 to be conservative). Does that sound right or are my assumptions off?
Solar install June 2022, Bath
4.8 kW array, Growatt SPH5000 inverter, 1x Seplos Mason 280L V3 battery 15.2 kWh.
SSW roof. ~22° pitch, BISF house. 12 x 400W Hyundai panels
4.8 kW array, Growatt SPH5000 inverter, 1x Seplos Mason 280L V3 battery 15.2 kWh.
SSW roof. ~22° pitch, BISF house. 12 x 400W Hyundai panels
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Comments
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I think you're about right.My highest daily gas consumption last winter was almost 100kWh ...N. Hampshire, he/him. Octopus Intelligent Go elec & Tracker gas / Vodafone BB / iD mobile. Ripple Kirk Hill member.
2.72kWp PV facing SSW installed Jan 2012. 11 x 247w panels, 3.6kw inverter. 34 MWh generated, long-term average 2.6 Os.Not exactly back from my break, but dipping in and out of the forum.Ofgem cap table, Ofgem cap explainer. Economy 7 cap explainer. Gas vs E7 vs peak elec heating costs, Best kettle!1 -
QrizB said:I think you're about right.My highest daily gas consumption last winter was almost 100kWh ...Solar install June 2022, Bath
4.8 kW array, Growatt SPH5000 inverter, 1x Seplos Mason 280L V3 battery 15.2 kWh.
SSW roof. ~22° pitch, BISF house. 12 x 400W Hyundai panels0 -
I've just done my first winter with a 5kW heat pump. Highest daily consumption was about 30kWh, when temperature was sub-zero and the dunkelflaute meany there was virtually no solar input.
I initially bought a 15kWh Fogstar battery but then they had a Black Friday 20%-off deal, which I couldn't resist, so now I have 30kWh. I will be including islanding in my installation, because I live in a remote area with frequent power cuts.30kWh will cover me for a 24 hour outage, with heating from the ASHP. If the notification indicates it would be longer, then I'd fire up the woodburner, and I'd be OK for a week, even without solar input.
I agree with QrizB that 15kWh would probably be enough if you have a reliable supply, except in the few very coldest weeks.0 -
Netexporter said:I've just done my first winter with a 5kW heat pump. Highest daily consumption was about 30kWh, when temperature was sub-zero and the dunkelflaute meany there was virtually no solar input.
I initially bought a 15kWh Fogstar battery but then they had a Black Friday 20%-off deal, which I couldn't resist, so now I have 30kWh. I will be including islanding in my installation, because I live in a remote area with frequent power cuts.30kWh will cover me for a 24 hour outage, with heating from the ASHP. If the notification indicates it would be longer, then I'd fire up the woodburner, and I'd be OK for a week, even without solar input.
I agree with QrizB that 15kWh would probably be enough if you have a reliable supply, except in the few very coldest weeks.
Solar install June 2022, Bath
4.8 kW array, Growatt SPH5000 inverter, 1x Seplos Mason 280L V3 battery 15.2 kWh.
SSW roof. ~22° pitch, BISF house. 12 x 400W Hyundai panels0 -
I'm hoping to get DNO permission for an 8kW inverter. That will fully charge the batteries withing a 4 hour cheap window and will be more than enough to run the heat pump and at least one "big ticket" item, like cooking, washing machine, dishwasher simultaneously.0
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Netexporter said:I'm hoping to get DNO permission for an 8kW inverter. That will fully charge the batteries withing a 4 hour cheap window and will be more than enough to run the heat pump and at least one "big ticket" item, like cooking, washing machine, dishwasher simultaneously.Solar install June 2022, Bath
4.8 kW array, Growatt SPH5000 inverter, 1x Seplos Mason 280L V3 battery 15.2 kWh.
SSW roof. ~22° pitch, BISF house. 12 x 400W Hyundai panels0 -
On a really cold day our leccy consumption gets up to 55-60 kWh in 24 hours (thats all in lighting, heating TV and possibly washing etc) It peaked at 78kWh on 29th December when the whole family descended , but on average its around 40kWh
We've got a 15year old Daikin heatpumpNever under estimate the power of stupid people in large numbers0 -
I think you would be crazy to buy batteries big enough to cover your worst case. The worst case is a very rare event and, because of the way heat pumps work, the worst case is liable to be a lot worse than all but a tiny minority of other cases.
And a flaw in your reasoning is assuming a COP of 3. Whilst your heat pump should be able to achieve an SCOP of 3 or more, this is a figure averaged over the entire year. On the coldest days of the year it may well not be able to achieve a COP as high as 3.
I've had a heat pump since late 2020. After 4 years, it had used an average of 15.3 kWh per day for heating and hot water (my heat pump has a dedicated electricity meter). The worst consumption I have ever caught it doing was 65.84 kW from 23:30 on 12/12/2022 to 22:30 the following day. It's set back at 22:30 so the result for the full 24 hours should be the same.
I reckon that the battery size that you need should be calculated on the basis of your annual usage, not the worst case. If I took my average figure of 15.3 kW hours and doubled it to say 30 kWh there would be very few days throughout the year when that wasn't sufficient to cover my heat pump usage, 10 to 20 days I estimate. Do you really want a battery that you will only use for 10 to 20 days each year?
My recommendation is that you take your annual gas usage and work out from that what your daily average is. Divide that by 3 (for SCOP of 3) then double that number and see what battery size that gives you. And even then you have probably made an overestimate because if you have some hours of cheap electricity with which to charge your battery you'll want to be running your heat pump as much as possible during those hours, heating your hot water at the very least.
Reed3 -
I'd go with "try before you buy" and see how you go for a few months with with the battery you already have. If it doesn't work out you can add more storage fairly quickly but it's a chunk of money to fork out if you find you don't need it very often.Barnsley, South Yorkshire
Solar PV 5.25kWp SW facing (14 x 375) Lux 3.6kw hybrid inverter installed Mar 22 and 9.6kw Pylontech battery
Daikin 8kW ASHP installed Jan 25
Octopus Cosy/Fixed Outgoing0 -
Alnat1 said:I'd go with "try before you buy" and see how you go for a few months with with the battery you already have. If it doesn't work out you can add more storage fairly quickly but it's a chunk of money to fork out if you find you don't need it very often.Solar install June 2022, Bath
4.8 kW array, Growatt SPH5000 inverter, 1x Seplos Mason 280L V3 battery 15.2 kWh.
SSW roof. ~22° pitch, BISF house. 12 x 400W Hyundai panels0
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