Ups and power cut backup / off grid

NoobSolar

Can anyone advise on a good household battery that could be added to my solaredge system (6.4 kW) that would have an islanding switch and also retain the capacity to charge from the panels during an outage? I basically mean the capacity to charge and use power during an outage or in fact off grid. Such things are discussed bere:

https://www.solarguide.co.uk/solar-back-batteries-power-cuts#/

I was just wondering where the tech has got to so far. Two examples are given at this link - but time has passed since it was created.

I think I would need at least 9kwh.

QrizB

What yuo're asking for is quite difficult. Your existing inverter has been carefully designed to cut out if the grid goes down. Convincing it to keep working in a grid-down situation isn't trivial.

A hybrid inverter with EPS output would do it (and @Reed_Richards has one) but that would mean replacing some/all of your Solaredge kit. Or a DC-coupled battery might work?

Do SolarEdge offer a battery upgrade?

Reed_Richards

Yes, my system can do this, it's a feature  built-in to the inverter.  Only the lighting and a few sockets (including those for the fridge, freezer and router) are on the back-up circuits.  We lost power for 24 hours during Storm Arwen and we still had lights and internet connectivity although I had to switch the fridge and freezer off overnight as the battery was already quite low.  If I had completely discharged the battery then I don't think I would have been able to recharge it again because the inverter would have lost power and therefore capability.  

ggmf

Reed_Richards said:

If I had completely discharged the battery then I don't think I would have been able to recharge it again because the inverter would have lost power and therefore capability.  

Hmm, I'll have to do a test with mine at some stage, I'd like to hope that with the power shut down then the inverter might still provide charge to the battery, so the EPS output may still be available for light loads, just not feed any excess back to the grid?

NoobSolar

But what about this: https://www.solaredge.com/us/products/the-solaredge-energy-hub-solution/battery

"When paired with a battery and our new backup interface, this DC-coupled solution can keep the whole home on even when the grid is off."

Magnitio

Both solutions from Huawei and Givenergy provide the option for power during an outage, though it's recommended that this is for low current circuits (e.g. lighting) and selected sockets. There's also Tesla, but that's quite expensive.

Reed_Richards

I agree.  Before I got my ASHP my house would typically use about 8 kWh per day.  On average the battery will not be fully charged when the power goes off and you need to have enough power to keep you going until the sun shines.  I concluded that my 6.4 kWh battery would not have enough capacity for the whole house so I backed-up the lighting and a selected set of sockets. 

As it happened, when the power went out at the end of November my battery had 35 % charge left, and that was because we were getting so little sun that I wasn't letting it discharge any less than that (except on back-up).     

Verdigris

The larger Lux inverters have that facility, too.

NoobSolar

Thanks very much for the comments. I recognise now that such a facility is intended to sustain emergency items like fridges and freezers. In a typical semi, I wonder what the likely battery size I might need might be?

Verdigris

Just work out how much your fridges and lighting are likely to use in a day, multiply by the number of days protection you want, and then add on a bit more. I'd add in a microwave, too, but remember you could switch the cooling off whilst you're using it.

Reed_Richards

If you have a gas or oil boiler for do add that to the back-up circuits!  These boilers consume very little electrical power (mostly the consumption is down to the pump).  But if you can keep your boiler going when the power is out that is a huge benefit!  I had my old oil boiler backed-up but then I switched to a heat pump.