AC coupled battery system

[Stinsy]

Let's hope the fuses are up to scratch! That lot will give a fair few kWhr in an instant if there is a short...

I just followed the instructions and fitted a 100A double fuse switch in the DC cables from the battery to the inverter. The batteries seem to have some sort of solid state switch as they turn on and off with no surge that I've been able to measure.

My plan for using the backup connection is to get new consumer units installed, splitting the house circuits into two parts, with a changeover contactor wired as shown in the SoFar manual. I've had a look at our downstairs ring main (from lots of photos I took before the house was plasterboarded inside) and the downstairs ring main looks as if it can be split into two halves, the kitchen and the rest of the house. We can manage without the kitchen being on the backup supply and that is where most of the big loads are.

I haven't yet discussed this with the electrician, but I think that it should be OK to have both the lighting circuits and the downstairs circuit (without the kitchen) connected to the backup power switched consumer unit, with the rest of the circuits contained within another consumer unit that is only ever power by the grid.

Splitting the downstairs ring (it is a "ring final" not a "ring main") into two 20A radials was my first thought. However it isn't good practice to have a kitchen on a 20A circuit because there are too many high-power appliances in a typical kitchen. A 32A radial (wired in 4mm²) is acceptable but you already stated you don't want to rewire your kitchen!

The best solution is probably to have two CUs first everything that runs only when mains power is available and the other that is "UPS". Have your lights on the UPS CU and run a new circuit to your Fridge/Freezer, TV, WiFi router, and a socket behind your bed for charging devices.

[Ken]

Lots of people around here think I'm already a bit of a nutter for building a passive house, that has no foundations and just sits on 300mm of polystyrene foam laid on the ground!

House with no foundations!
How does that work/pass building regs.
Is the house timber frame?

Ken

[Oldgreybeard]

Lots of people around here think I'm already a bit of a nutter for building a passive house, that has no foundations and just sits on 300mm of polystyrene foam laid on the ground!

House with no foundations!
How does that work/pass building regs.
Is the house timber frame?

Ken

I used this foam insulation foundation system: https://www.isoquick.co.uk/

The walls are single skin concrete block on side with external insulation that buts tightly to the wing insulation around the concrete slab.

I had some fun with building control, but they were pretty supportive once they had got their heads around something non-standard.

[Stinsy]

Lots of people around here think I'm already a bit of a nutter for building a passive house, that has no foundations and just sits on 300mm of polystyrene foam laid on the ground!

House with no foundations!
How does that work/pass building regs.
Is the house timber frame?

Ken

I used this foam insulation foundation system: https://www.isoquick.co.uk/

The walls are single skin concrete block on side with external insulation that buts tightly to the wing insulation around the concrete slab.

I had some fun with building control, but they were pretty supportive once they had got their heads around something non-standard.

It is the mortgage companies who have the biggest problem with “non-standard”!