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Battery max discharge rate

 
Energy Storage
Last Post by pauldavies83 2 years ago
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 pauldavies83
(@pauldavies83)
Eminent Member Member
30 kWhs
Joined: 3 years ago
Posts: 11
Topic starter 04/03/2022 12:55 pm  

Currently looking at home storage batteries to reduce the incoming electricity unit rate shock, and had a (perhaps silly) question

If the max discharge rate of a battery is (for example) 3kWh, and my house is requiring more than the battery can supply (e.g. using the electric oven + hob), does the grid supply the remaining demand and the battery supply as much as it can, or does the battery supply nothing and the grid everything in this instance?

Our usage pattern shows most of our daily demand is when we cook dinner for the kids, which obviously we can't realistically time-shift, so the battery would hopefully do this for us (to a certain extent).

Cheers


   
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Majordennisbloodnok
 Majordennisbloodnok
(@majordennisbloodnok)
Noble Member Member
3791 kWhs
Joined: 2 years ago
Posts: 341
04/03/2022 1:54 pm  

I can only speak for my situation, but I'd hope it's fairly typical.

My array and battery have been configured with a kind of hierarchy.

  1. If the sun is shining, the PV array will generate.
  2. If there is an electrical load, the electricity generated will try to meeting that demand.
  3. If we're generating more than we're consuming, it'll pile the rest into the battery.
  4. If we're generating more than we're consuming and the battery is full, it'll export the excess to the grid and we'll be paid as a result of our outgoing tariff.
  5. If we're consuming more than we're generating, the battery will try to meet that demand until it gets down to 10% (in order to protect the battery).
  6. If we're consuming more than we're generating and the battery is down to 10%, the excess load will be met by energy from the grid.
  7. Over night, during the cheap rate period, the battery will be trickle charged back to about 75% from the grid ready for the big hit from the air source heat pump in the early morning before we're generating again.

My understanding, although I haven't tried tinkering, is that all these scenarios can be configured, so the heirarchy isn't set in stone.

Does that help?

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 inverter
Raised beds for home-grown veg and chickens for eggs

"Semper in excretia; suus solum profundum variat"


   
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 batalto
(@batalto)
Famed Member Member
3655 kWhs
Joined: 3 years ago
Posts: 1091
04/03/2022 3:12 pm  

@pauldavies83 the battery will supply whatever it can, then the grid picks up the rest. for example,

4kw demand = 1kw from grid and 3kw from the battery (until the battery runs out)

12kW Midea ASHP - 8.4kw solar - 29kWh batteries
262m2 house in Hampshire
Current weather compensation: 47@-2 and 31@17
My current performance can be found - HERE
Heat pump calculator spreadsheet - HERE


   
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 pauldavies83
(@pauldavies83)
Eminent Member Member
30 kWhs
Joined: 3 years ago
Posts: 11
Topic starter 04/03/2022 3:17 pm  

Thanks both for confirming what I'd hoped!

Our day usage is actually quite small, so I think we could get most of our usage covered by the battery and shift as much other usage as possible to off-peak. There would just be the odd time when we used too many things at once where we would need to import during the peak.


   
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