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Running from backup generaor in powercut?

 
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Air Source Heat Pumps (ASHPs)
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 Pipcart
(@pipcart)
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Joined: 3 years ago
Posts: 23
Topic starter 07/01/2026 10:54 am  

Does anyone have experience of running an ASHP from a backup generator, even with only with minimum output to prevent freezing during a power cut? Our system has antifreeze valves, but I really dont want these to be triggered. If you are able to run from an emergency generator, then a brief description of your setup would be much appreciated. We need to install a backup generator anyway, to keep essentials (e.g. sewage system) running during a power cut and we'll ask an electrician to provide the necessary connections - the ASHP has its own distribution board.



   
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bontwoody
 bontwoody
(@bontwoody)
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Joined: 4 years ago
Posts: 1009
07/01/2026 11:12 am  

I think it should be possible. If you are thinking of battery storage at any time, I have looked at these from Sigenergy, which allow charging from a generator or compatible EV 

https://www.sigenergy.com/en/products/gateway


House-3 bed partial stone bungalow, 5kW Samsung Gen 6 ASHP (Self install)
6.9 kWp of PV
5kWh DC coupled battery
Blog: https://thegreeningofrosecottage.weebly.com/
Heatpump Stats: http://heatpumpmonitor.org/system/view?id=60


   
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 Pipcart
(@pipcart)
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Topic starter 07/01/2026 11:16 am  

@bontwoody Thanks, that a very interesting avenue I had not thoght of!



   
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Mars
 Mars
(@editor)
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07/01/2026 2:21 pm  

@pipcart, good topic!


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Abernyte
 Abernyte
(@abernyte)
Reputable Member Member
Joined: 3 years ago
Posts: 259
07/01/2026 2:34 pm  

I do/did. I have a 4KW Hyundai petrol genny which can be plugged into an external socket and feeds the manual change over switch to energise the house circuit.  It covers most of the demand for the ASHP once it is running and the temperature is up but we have to ensure that all other use is severely curtailed, especially the freezers/fridge. The combined load of high heat demand and them craps out the genny. I now usually just leave the heat pump off for power cuts. If it turns into a days long outage, haven't had one of those for a while, then the plumbing was left with manual change over valves to isolate the heat pump and run the old LPG boiler to provide heating, which can be adequately powered by the genny.



   
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Batpred
 Batpred
(@batpred)
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Joined: 1 year ago
Posts: 761
07/01/2026 2:41 pm  

Posted by: @pipcart
↑

@bontwoody Thanks, that a very interesting avenue I had not thoght of!

Having a heatpump on its own distribution board is great, if you have spare space. It may become easier to add to it. 

There are plenty of other options of inverter+battery coupling that would do this. 

You have two type of systems:

1- a battery that includes an inverter (the component that is connected to the electrical supply of the house). This may help if you just want a small 5kw to keep the heat pump from freezing

2- an inverter that charges and discharges one or several batteries. Typically with three 16kw batteries you can run a heatpump for a day. Some of these would sell for £4 or 5k + labour and certification

You may also benefit from option 2 having sufficient storage to run the heatpump on a cheap ASHP tariff. If your heatpump is working more efficiently during the day, your electricity 

I have a Solis inverter and started a thread on this that gives you a better idea of what is involved at https://renewableheatinghub.co.uk/forums/energy-storage/solis-s6-eh1p8k-l-plus-why-i-chose-it-and-what-ive-learned-so-far/paged/1/

My system costed about half+labour (I only have one 16kw battery) and is able to keep the whole house power going for a day and a half of power outage. 

Beware of horror stories about lithium batteries. The ones we are discussing here are safe. This may help https://renewableheatinghub.co.uk/forums/energy-storage/lifepo4-lithium-battery-fires-and-explosions/paged/3/#post-54522

 


8kW Solis S6-EH1P8K-L-PLUS hybrid inverter; G99: 8kw export; 16kWh Seplos Fogstar battery; Ohme Home Pro EV charger; 100Amp head, HA lab on mini PC


   
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 Pipcart
(@pipcart)
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Topic starter 07/01/2026 2:54 pm  

@abernyte Many thanks for taking the time to reply. It's good to know that it is possible.



   
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 Pipcart
(@pipcart)
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Topic starter 07/01/2026 2:55 pm  

@batpred Thanks again. Lots to consider 🙂



   
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Batpred
 Batpred
(@batpred)
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Posts: 761
07/01/2026 3:18 pm  

@abernyte 

Thank you for sharing. 

Just wanted to make sure you are aware that feeding power into an RCD protected circuit may burn the solenoid in the RCD/RCBO. This could mean the circuit is no longer protected as expected. 

There´s a thread here that goes into more detail on a typical solution https://renewableheatinghub.co.uk/forums/energy-storage/buying-large-amp-bidirectional-rcd-and-rcbo/#post-51433


8kW Solis S6-EH1P8K-L-PLUS hybrid inverter; G99: 8kw export; 16kWh Seplos Fogstar battery; Ohme Home Pro EV charger; 100Amp head, HA lab on mini PC


   
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Abernyte
 Abernyte
(@abernyte)
Reputable Member Member
Joined: 3 years ago
Posts: 259
07/01/2026 3:52 pm  

Thanks...the sparky handled all the technical bits and bobs and out here he does lots of off grid and change over stuff. I trust him.  I also have a complete wired 13amp generator only board and circuit in the house, which doesn't touch the change over switch or any of the grid fed circuits, with genny only sockets along side the key appliances. It has an external socket to plug the genny into, near where the genny runs outside and of late we have just been using that. 

It would be fine if I could get a smart meter signal then I might invest in a battery to make all of this redundant!



   
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 Pipcart
(@pipcart)
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Posts: 23
Topic starter 07/01/2026 3:52 pm  

@batpred Thanks for the warning. definately a job for a qualified professional!



   
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Batpred
 Batpred
(@batpred)
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Joined: 1 year ago
Posts: 761
08/01/2026 1:02 am  

Posted by: @pipcart
↑

@batpred Thanks for the warning. definately a job for a qualified professional!

Definitely and professionals sometimes miss it.

I had a similar situation when my EV charger was fit. It is not bi-directional ready, but I remember it being discussed...

 


This post was modified 3 months ago by Batpred

8kW Solis S6-EH1P8K-L-PLUS hybrid inverter; G99: 8kw export; 16kWh Seplos Fogstar battery; Ohme Home Pro EV charger; 100Amp head, HA lab on mini PC


   
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