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Advice needed after a successful "leftfield" experiment.....

 
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Air Source Heat Pumps (ASHPs)
Last Post by ChandyKris 4 weeks ago
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 pauli
(@pauli)
Active Member Member
Joined: 1 month ago
Posts: 9
Topic starter 12/03/2026 2:20 pm  

@chandykris 

yup, my error, i was looking at old data 



   
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 pauli
(@pauli)
Active Member Member
Joined: 1 month ago
Posts: 9
Topic starter 12/03/2026 2:26 pm  

@majordennisbloodnok 

just checked, didn't realise this forum has been going on for so long, must be going through a recent surge in popularity seo wise 🙂



   
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Majordennisbloodnok
 Majordennisbloodnok
(@majordennisbloodnok)
Famed Member Moderator
Joined: 4 years ago
Posts: 1724
12/03/2026 2:32 pm  

No problem, @pauli. If you can find something useful, the forum has served its purpose.


105 m2 bungalow in South East England
Mitsubishi Ecodan 8.5 kW air source heat pump
18 x 360W solar panels
1 x 6 kW GroWatt battery and SPH5000 inverter
1 x Myenergi Zappi
1 x VW ID3
Raised beds for home-grown veg and chickens for eggs

"Semper in excretia; sumus solum profundum variat"


   
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 ChandyKris
(@chandykris)
Estimable Member Member
Joined: 2 years ago
Posts: 150
12/03/2026 7:36 pm  

@pauli Depending on whether you can get an EV tariff, I find that Octopus Go is a better option than Cosy for me. We were on Cosy in 2025 when we initially switched to Octopus in February after our heat pump installation. Prior to that we were on British Gas EV tariff  As we only had a 6.5 kWh battery, I preferred Cosy as we needed that 8 hours of off-peak energy and that too spread over the day in three slots. I was averaging 15p as I was able to avoid drawing from the grid during peak times. But, we switched to Go in April and then doubled the battery capacity to 13 kWh in May. So far this winter I am averaging 12p and now in March as there's more PV production, more like 9p.

Given that battery prices have dropped, it might work in the long run to get a bigger battery and be on Octopus Go or Intelligent Octopus Go than on Cosy. This would also reduce battery cycling and lead to longer battery life. Check out the Solar Optimiser tool on Tim and Kat's Green Walk website and model a few scenarios to help making the battery decision.


16 * 435 watts PV
13 kWh Growatt battery
1 EV - Mercedes EQB
6 kW Aira Heat Pump
Bosch Induction Hob


   
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 pauli
(@pauli)
Active Member Member
Joined: 1 month ago
Posts: 9
Topic starter 13/03/2026 7:54 am  

@chandykris 

thanks, good real world info there, can i ask what your yearly kw usage is?

mine (gas plus elec) is low (hence why i waited till my gas boiler died before making the move over to hp)

i think the bigger the house and the higher the energy usage the more monies you can putting the effort into the "maths" with a good short ROI period  



   
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 ChandyKris
(@chandykris)
Estimable Member Member
Joined: 2 years ago
Posts: 150
13/03/2026 10:41 am  

@pauli Approximately we use about 10 kWh daily, then about 1300 kWh for the EV and around 3000 kWh for the heat pump. Before the changes, our electricity baseline was roughly the same about 3500 kWh, but were using around 12K to 15k kWh of gas and petrol for car on top. But, this was after spending loads of time and money on Tado to optimise the gas usage at certain times of the day only. Even then, some parts of the house that we don't use often in the winter were unheated. This is for a circa 200 SQM house in the South East.

We imported about 6000 kWh from the grid at 12p over the last year. We consumed about 2000 kWh from our PV and exported 2200 kWh back to the grid. Though, Outgoing Octopus has dropped from 15p to 12p, we would probably stick to Octopus Go for now. If it falls any further, maybe we could self consume more of that 2200 kWh export.


This post was modified 4 weeks ago by ChandyKris

16 * 435 watts PV
13 kWh Growatt battery
1 EV - Mercedes EQB
6 kW Aira Heat Pump
Bosch Induction Hob


   
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 pauli
(@pauli)
Active Member Member
Joined: 1 month ago
Posts: 9
Topic starter 13/03/2026 12:27 pm  

@chandykris 

thanks, its good to haver some approx baseline figures in the back of your head for different house types

also can you give an approx figure on how much it cost to get to your current HP/Solar/battery setup please (without ev costs)?

An extreme example of the disparity in the industry ..... I was talking to someone today who visited a large well healed house that was being covered by two gas boilers to service it fully, the peoples removed the boilers and installed hp/solar/battery at a cost of over £50k ... they were complaining of cold rooms and bills of over £1000 a month - sounds like a bit of incompetence during the initial surveys and installers who dont cost into their quotes several after site staggered visits, to tune and inform the customer of proper non gas like usage when it comes to heating/hot water (people like us dont need it, but were outliers)



   
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 ChandyKris
(@chandykris)
Estimable Member Member
Joined: 2 years ago
Posts: 150
13/03/2026 2:32 pm  

@pauli I have sent a direct message with the financial numbers.


16 * 435 watts PV
13 kWh Growatt battery
1 EV - Mercedes EQB
6 kW Aira Heat Pump
Bosch Induction Hob


   
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