PV/Batteries for Back-up Power

Coltrane · 05-04-2020 9:10pm #1

Anyone else out there giving more thought over the past weeks to the back-up power potential of PV/batteries, in case C-19 causes grid outages?

I think the crisis has highlighted a certain lack of redundancy and allowance for the unexpected in supply chains and government. We may have developed an over-reliance on just-in-time delivery and forgotten to put something aside for black swans.

Batteries as has often been discussed here most often provide negative returns on investment. Some on here have bought them for emergency power, but generally in locations with frequent outages. Could they have a more widespread emergency power benefit that hasn’t been discussed as often on here.

PV generally doesn’t function when the grid is down but there are mainstream EPS type products that claim to work around that.

I bought a 7kWh battery, a very large PV array and an EPS with this kind of scenario somewhere not too far at the back of my mind. Haven’t put it to use yet but wonder whether there are others out there with similar ideas...

quentingargan · 06-04-2020 9:02am

Coltrane wrote: »

PV generally doesn’t function when the grid is down but there are mainstream EPS type products that claim to work around that.

I wouldn't be quite so alarmist - utility workers are working as normal. But this is an issue in rural areas during winter storms. Grant aided systems must have a firefighter safety switch that disconnects the panels when firefighters cut the grid. Personally, I think this is nonsense if the inverter is in the loft, and if the inverter is elsewhere, a latching relay device should be acceptable as an alternative, provided labelling is very clear on its location. After all, your inverter will continue to provide backup when the grid is cut if there is power in the batteries.

You can set most inverters to only discharge batteries to 80%, 50% or whatever you like to ensure you have some supply in battery storage. If you get the sort of rotating power cuts which you see during a crisis, this would work fine.

Personally, if there are storms causing long power cuts for people with a freezer full of food defrosting and no water to flush toilets, or home heating working, I can see folks googling how to bypass a firefighter safety switch...

It would be better and safer to allow a latching relay.

Coltrane · 06-04-2020 4:16pm

quentingargan wrote: »

I wouldn't be quite so alarmist - utility workers are working as normal.

Thanks.

I was talking about planning for the unlikely and the value that PV/batteries might offer in the unlikely case of outages caused by COVID (or other crises). I don’t consider a discussion of that to be in any way alarmist.

My own installer stated that my panels (and battery) would continue to function while the inverter was in EPS mode. I’ll run some tests and post the results! It has a fireman’s switch.

Does anyone else have PV that keeps running while the grid is out?

quentingargan · 06-04-2020 4:44pm

Coltrane wrote: »

Thanks.

I was talking about planning for the unlikely and the value that PV/batteries might offer in the unlikely case of outages caused by COVID (or other crises). I don’t consider a discussion of that to be in any way alarmist.

My own installer stated that my panels (and battery) would continue to function while the inverter was in EPS mode. I’ll run some tests and post the results! It has a fireman’s switch.

Does anyone else have PV that keeps running while the grid is out?

You're quite right to plan. Alarmist isn't the right word. Most EPS systems can provide power during the outages caused during an overall fuel crisis. It is when you lose power for 2 or 3 days in a row that you need solar top-up each day.

You generally need special wiring of an EPS system to supply your consumer unit circuits, and solar installers don't normally do this as part of the install. In some cases, a single RCBO and wall socket might be fitted to provide a power source during an outage. If the unexpected happens, a spaghetti of extension leads will be the least of our problems...

I happen to have a system that runs my house off-grid during power cuts, but it is rare.

unkel · 07-04-2020 6:29pm

My car has an 85kWh battery. I can safely connect a low power inverter to it with an extension lead into my house that I can plug in essentials like fridge, tv, internet router, led lights and phone chargers. If fully charged it would power my house like that for about a fortnight if the grid was down.

Coltrane · 10-04-2020 1:32pm

quentingargan wrote: »

You generally need special wiring of an EPS system to supply your consumer unit circuits, and solar installers don't normally do this as part of the install. In some cases, a single RCBO and wall socket might be fitted to provide a power source during an outage. If the unexpected happens, a spaghetti of extension leads will be the least of our problems...

Mine was intended (specified) to run all of the circuits in the house, subject to a max of 2kW; so that for example the A2W and EV were to be switched off while in EPS-mode.

Have run some tests over the past days and...it doesn't work at all! Not even for the contents of the battery. Whether the panels will keep running with the grid down an unknown. Both were promised. Should have stood behind the installer as he commissioned it!

V2H would be great but in case of my own EV seems really hard to operate - max something like 400W, etc.

unkel · 10-04-2020 4:49pm

400W is still enough for the base load, fridge, internet router, led lights, phone chargers, tv. Could run my house on my car like that for over a week.

If you run the A2W on your home battery, it'll be empty within the hour

20-04-2020 1:36am

I AC coupled this to my grid tied solar last "power cut".

It's a secret feature.

unkel · 28-04-2020 12:49pm

Here's my system taken just now. I have my mining rig running, my Tesla charging (at just 5A), the rest of the house powered, and it is still charging the battery. Not buying any electricity from the grid during the day any more. Battery is a 20kWh AGM lead acid, recycled used data centre batteries

mun1 · 28-04-2020 9:11pm

unkel wrote: »

Here's my system taken just now. I have my mining rig running, my Tesla charging (at just 5A), the rest of the house powered, and it is still charging the battery. Not buying any electricity from the grid during the day any more. Battery is a 20kWh AGM lead acid, recycled used data centre batteries

How do i get my app display to show my setup like in your picture ?
I seem to have the daily revenue screen in place of it . Any ideas?

championc · 10-05-2020 7:59pm

mun1 wrote: »

How do i get my app display to show my setup like in your picture ?
I seem to have the daily revenue screen in place of it . Any ideas?

Click on "Intro" and go to "Other Info" and change your On-Grid Type to "Storage System"

mun1 · 10-05-2020 8:09pm

Thanks very much , it was driving me mad.

PV/Batteries for Back-up Power

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