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Battery sizing - How low can you go!

 
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Energy Storage
Last Post by bontwoody 5 days ago
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 s_gatorator
(@s_gatorator)
Active Member Member
137 kWhs
Joined: 3 months ago
Posts: 10
09/01/2025 3:03 pm  

Posted by: @transparent
↑

h, we're both right about how the ASHP would be supported from a Sunsynk inverter, but we've made different initial assumptions

Hi @transparent , that's all good then. Yes, I'm not changing wiring or adding a backup power distribution board (having recently done a major refurbishment) and we're in a city, all power distribution is underground and power cuts rare and short.

This is the diagram approved by the DNO (no surprises where I got the original, thank you 🙂) - I was stymied by not being able to PM you for the OpenDraw file without first posting. 

Highcrown EESS

End 1980's terrace in Southern England
NIBE 12kW air source heat pump
2 solar water panels
1 x Ohme ePod
1 x VW ID Buzz


   
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Transparent
 Transparent
(@transparent)
Illustrious Member Moderator
11847 kWhs
Veteran Expert
Joined: 3 years ago
Posts: 2051
09/01/2025 3:41 pm  

I would happily send you ODT files of my diagrams for you to dissect and amend.

The more graphics we have on this forum, the easier it is for others to understand.

You will note that I keep a graphics library of 200+ PNG/JPEG images from which I can quickly build an appropriate diagram.
It's not as slick as I'd like, but at least the software is free...
... and therefore anyone else can replicate the style.

You will occasionally find my graphics on other 'official' sites and in government leaflets.
Provided that no one is trying to gain an income by their use, then that's fine by me.

Save energy... recycle electrons!


   
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bontwoody
 bontwoody
(@bontwoody)
Noble Member Contributor
4742 kWhs
Joined: 3 years ago
Posts: 703
Topic starter 09/01/2025 4:15 pm  

Posted by: @s_gatorator
↑

@bontwoody , thank you. I'm looking to do a similar off-peak storage (ASHP, but no Solar PV) and was interested to compare your figures with my calculations. Could I just check? - your December off-peak usage is 550kWh, presumably this supports about 150kWh of charging your 5kWh battery once every day (assuming the PV is not charging it) - does that mean your normal off-peak December consumption is 400kWh (i.e. 400/756 = 52%)? 

Yes thats right, although I dont totally use all my battery capacity and its closer to 4.5 kWh charging rather than 5kWh per night

I think what Im seeing is that depending on the cost of the battery and usage, its doesnt aways make financial sense to try and cover 100% of your daily usage for all days of the year. That said extending my current battery pack is quite expensive at £2500 for an extra 5kWh and the calculation will alter with something like the Fogstar 15.5 kWh battery at a similar price.

hope thats helpful

 

House-2 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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