Battery Backup

tamste

I am thinking of putting a backup system in place to power the house when we have power cuts, of which there have been a few recently, some lasting several hours. 

Planning battery installation soon, and only to feed one of the three phases (i.e., not heaters) when in backup mode, but not sure if to go with automated backup, or a manual switch solution.

Whilst the automated backup boxes seem to work well on paper, switching power over quite quickly when the grid goes down, what happens when the grid supply is restored? The information sheets from all the manufacturers I have reviewed are relatively silent on this aspect.
So generally, do they:

1. Switch back to grid supply automatically, or require user input?
2. Notify you of grid failure and restoration?

I am concerned that if I have an automated system installed and it switches to battery (island) mode when I am away for a week or so, the batteries won't last to keep everything working till I get back unless it automatically switches back to the grid.

QrizB

tamste said:

Whilst the automated backup boxes seem to work well on paper, switching power over quite quickly when the grid goes down, what happens when the grid supply is restored? The information sheets from all the manufacturers I have reviewed are relatively silent on this aspect.

It'll be easier to answer this question if you can give some details of the "automatic backup box" systems you are considering.

Things like the Powerwall Gateway will switch to battery when the mains supply goes off then switch back to utility power when the grid comes back up.

Alternatively you might be looking at something like a UPS, which does the same.

What exactly do you have in mind?

tamste

I have a Growatt MOD hybrid 3ph inverter and am thinking of adding ~15kW of APX batteries to it, and at the same time either having the Growatt SYN 50-XH-30 backup, or a manual switch. Note that I only want to run one of the three phases in Island mode as the other two are for storage heating only, and too thirsty for a backup if the failure is during their charge period.

Looking for battery (15-20kW) and backup on one phase of a 3ph system for <£5k installed. This is a moneysaving issue rather than green for me. My base load is ~ 6-8 kW/day without heating.

QrizB

Looking at the datasheet for the SYN 50-XH-30:

https://midsummerwholesale.co.uk/pdfs/syn-50-xh-30-datasheet-en-202310.pdf

... it quotes a 500ms (0.5 second) switchover time, which doesn't guarantee that appliances won't shut off. For that you need 50ms or faster. 20ms (one 50hz cycle) is often quoted.

Is that going to be a problem? Lighting probably won't care, but you might find that some other things shut down and then power-up again (or don't power up, if they need a manual button-press)?

There are videos on YouTube of these boxes changing over and LED lighting loads go dark for a short period before the battery backup cuts in, for example.

If 500ms is OK, then yes I'd expect it to switch back to mains power in about the same time. Your installer should be able to confirm this, and demonstrate it as part of commissioning.

tamste

500ms is fine with me - I wasn't looking for UPS.

So general feeling is that the backup will switch back to grid once power is back on?
Maybe me, but I can't see this in the info for this backup box, or others I have looked at, and its an important to know.

QrizB

tamste said:

So general feeling is that the backup will switch back to grid once power is back on?

Yes.

tamste said:

Maybe me, but I can't see this in the info for this backup box, or others I have looked at, and its an important to know.

I've not seen it demonstrated either, but (as I mentioned above) your chosen installer should be able to answer the question before you contract them, and to demonstrate it after installation as part of the commissioning and handover process.

It's good practice to exercise these things periodically (at least annually) so you have some reassurance that it's going to work on demand when required.

Heedtheadvice

According to the Growatt web site features it is on/off grid switch over within 0.5 seconds.

https://growattinverters.com/products/syn-50-xh-30.html

Certain not seamless but you say that is not an issue for you.