Backup Power Mode configuration problem

I had a new Battery system installed a couple of weeks ago to supplement an existing PV system. Everything works in in normal mode brilliantly.

As my house already had a manual supply changeover switch, so that a petrol generator could be connected to the house system during a power cut, the installer and I thought it would be useful to take a cable from the backup output of the inverter to the changeover switch, thus making the petrol generator redundant if there is a power cut.

Tested the back-up function for the first time today - I isolated all the high load items first so the inverter would not be overloaded, but the inverter just kept tripping in and out when the changeover switch was moved to the 'generator' position. Lots of 'clicking' from the inverter. Put it back to normal mains supply and everything still worked thankfully.

It occurred to me that there might be a need to isolate the normal connection to the inverter before switching to backup mode so it does not see itself as an 'essential' load and get confused. Could this be the cause of the symptoms? - I don't want to use trial and error to solve the problem in case I break something!

Thanks

Yeah it really won't like trying to feed itself in a loop. You will need to isolate the "normal" AC input to the inverter.
Obviously I assume the changeover switch disconnects you from the grid itself otherwise the inverter will try to power the whole street.

Hope you didn't leave it ticking too long, they can be a bit fragile on the EPS side these things.

Gliderman isolate the normal connection to the inverter before switching

It'd be easier if there was a schematic diagram but you've mentioned that you're connecting the inverter EPS circuit to the consumer unit without isolating the normal ac to the inverter. Your installer should have been able to advise on how this should be commissioned and tested. The EPS has to work in "island" mode, so no other sources of power including your existing (FIT?) PV system or standby generator.

Gliderman

Coincidentally, just had my EPS connected today by the original installation electrician. I have been told to isolate the inverter (there is an isolator switch to do this) and then switch the manual changeover switch.

He explained that the inverter effectively is trying to power itself if you don't isolate it .

Martyn correct.
Very soon Boom, or pop.

The changeover should include an inverter feed interlock isolater too.
As per the option 3 and 4 EPS diagram. Where the inverter can only be fed from Grid

KB Id12 refers

https://kb.givenergy.cloud/article.php?id=12

Thanks everybody.

I thought that might be the problem. There is an installed switch to isolate the normal ac connection to the inverter so its easy to do. Unfortunately I did not get any guidance from the installer on how to use the back up mode! Hopefully I have not done any permanent damage.

Yes, the changeover switch isolates the grid supply from the house systems. I will try the test again when I get a moment. I definitely need to prepare a checklist for the few times this might be needed 'in anger'. Or perhaps more often given what they're saying about next winter.

Gliderman
The Inverter needs to be powered from the Grid side of the changeover switch. Just isolating the grid and then connecting the EPS to the consumer unit, that also powered the inverter gives you this loop.
The diagram for option 4 is quite clearly explained for your installer to work from.

Hopefully nobody minds me tagging onto this thread as my question is kind of similar/related to the backup mode.

If you lose the grid connection and put the inverter into an Island mode, can the solar panels charge the battery whilst in Island mode (Assuming correct wiring, earthing isolation etc) or is this not possible?

We were supposed to get a Tesla battery system, but long story short, I think the installer lied a number of months ago about it being physically in their stock. Those quoting now are all offering Giv, which was going to be our choice except it was on a long lead time and the Tesla aledgedly wasn't.

Thanks in advance 🙂

TheDragon (GivEnergy) Yes - it's very clear. Just a shame that my installer did not follow it. Anyway, it's easy to effect a manual isolation of the inverter. I will also manually isolate the ac supply to the PV system as Tim suggests. Hopefully the backup mode is only needed for short periods, probably when its dark anyway, so no big deal. Thanks

kram only with a hybrid givEnergy inverter e.g. the solar DC is connected to the GE.

If your solar has its own inverter, they'll be grid tied and will shut down when the grid is gone.

You can't have multiple "generators" on the same consumer unit as they'd all be out of sync and that's not good!

TX200 I have a separate PV inverter also. When this boots up under normal circumstances it must be clever enough to synchronise itself with the grid supply. So if it boots up with the battery back-up supply already present, how would it know what it was seeing was not the grid supply and just synchronise with the battery inverter? I'm not an electrical engineer, just interested in what is possible.

Gliderman The answer will be in the detail of the tech specs for the devices. From a power engineering point of view, you may be able to synchronise your existing PV to the EPS supply and supply the house from PV, reducing input from EPS. However, the system is likely to be unstable, even with small load swings. You might be lucky, or not, if you attempted this configuration but as the EPS is designed to operate in island mode, you might get short shrift if damage did occur.

If you want to continue supply during grid disconnection, I would blend your backup generator and EPS as you see fit, but use them separately, unless you can get an engineering assessment to underpin an operating mode that complies with the separate device tech specs.

Gliderman the issue becomes what happens to the excess power from your second PV inverter when the Givenergy can’t take any more into the battery. Normally it would export it out to the grid (which has negligible impact on network voltage as it’s spread over numerous consumers)
When your running in island it has nowhere to go so then you’ll get all sorts of voltage swings as it tries to lift its voltage output more and more to try and export to a dead end.

Thanks again for the info - very helpful. I won't be trying to use my PV when using the battery backup mode! Just got to remember to isolate the PV before switching to back-up......................

Thanks for the reply, we have finally got the deposit back and looking at a HY5 Gen2 and 1 or 2 9.5kWh batteries.
If we went down the second inverter either 2x HY5/HY3.68 or 1xHY5/1xAC3 is there any way to use these as a single system in the event of a power cut, or would we only get one functioning?

Essentially we're trying to replicate the rated 5kW/7kW output that the tesla would give, albeit with a manual power failover.

My first thoughts are that one inverter would work and the other would do nothing, at which point I guess we just take the single inverter and keep an eye out for GE coming out with something that is maybe 5kW/5kW rated in the future.

kram You could connect EPS of one HY5 to say the lighting and the EPS of the other to say a ring main, each via a changeover switch that isolated the grid supply and connected the EPS. Both circuits would be limited to 2.5kW (gen1) or 3.6kW (gen2) and would have to be earthed. This means that you could run lights from one system and TV, broadband etc from the other. While you could run gas/oil boiler control and pumps from the ring main (if they were on this circuit), you wouldn't be able to boil a standard kettle, immersion heater or power an oven from a gen1. From a gen 2, you could probably do one appliance with other things not drawing power.

The way things stand, you would not be able to feed the EPS of both inverters to the same changeover switch as each has to operate in island mode.

Tim

Thanks for that, I had a feeling that might be the case.
It's a real shame, as that's the big weakness in the GE package and whilst g2 improved it from unacceptable to acceptable but not great, I really wish they'd had the 5kW be able to put the full 5kW into the battery and draw the same from it it needed.

FWIW, we have just purchased a new kettle, which whilst not inexpensive (It has multiple temperatures) has the benifit of only having a 1.85kW element. As such when boiling it, the full power can be taken from battery rather than a mix of battery/grid.

Just in case it is helpful, this is the kettle we got and they do a version with termperature control:

https://www.zwilling.com/uk/zwilling-enfinigy-electric-kettle-black-53005-003-0/53005-003-0.html?

If the link breaks any forum rules I appologise, but I figure finding a decent capacity, quality kettle that's less than the GE invert battery output is probably a useful thing.

90 quid for a kettle.
Why is saving money so damn expensive??? 😵‍💫

There was a 20% discount voucher, but basically yes...
It's rather annoying as maybe 15 years ago most kettles were 2kW ish, then along came fast boil 3kW kettles.
Now if you want a 2kW kettle it's crazy expensive and everything out at a sensible price is boasting it will boil in 3m not 4.

I mean technically you're not saving any energy, as the water requires the same amount to heat it, so you're running 2kW for 50% longer than 3kW.

The reason it's nice is that the GE inverters can only so 2.6/3.6 from a battery, take away .6 for background loads and maybe the heating pump or a TV and you have 2-3kW max you can pull from the battery. At that point a 2kW kettle is more likely to pull all the energy from the battery system, as opposed to a mix of grid/battery.

TBH I just wish GE would do a 5kW inverter that could do 5kW from solar and 5kW to home and to/from battery.

https://amzn.eu/d/i0NxRlb
£14.99, delivered. The same maker has a whole range, glass and metal from 1.5 to 2.2kWh.

kram 5kW to home and to/from battery.

I think the issue is the ability of the battery to discharge at such a high rate. The current 9.6kWh batteries have a maximum discharge current of 80A, so about 4.2kW. We were fortunate enough to install 32 panels with two HY5s and two 8.2kWh batteries. We can meet the 5kW output when the two inverters are going full chuff from battery, or 15.2kW if there is sufficient PV (does happen from time to time), adequate battery charge and a house demand so high (not happened yet). About the highest we've ever had was 7.3kW to EV, and 5kW to batteries, some house load and about 2kW to grid. Inverters were getting warm though!

Zakalwe

Not sure I trust the brand, as you get plenty of garbage for sale on many online marketplaces.....
However the fact that people are doing these thigns for sub £30 is a good thing and hopefully more will come 🙂

Tim

I think 2 x 9.5 + a HY5 should be able to give us more than 3.6 from the batteries, but sadly they can't.
I'd actually pay more for an inverter upgrade to allow the full 4.2 or maybe 3.6 from one battery and 5 from more than 1.

@Zakalwe

This is interesting as it's a known brand in the UK:

https://www.amazon.co.uk/Judge-JEA85-Electrical-Kettle-Steel/dp/B07TXZ87XP/ref=sr_1_22?c=ts&keywords=Electric+Kettles&qid=1662914356&s=kitchen-appliances&sr=1-22&ts_id=3538311031

We bought one of these; 680 Watt Neostar® Perma-Therm Water Boiler and Dispenser. Sold in various places. Cost has increased since we bought ours for about £40, but still less than £90.
It works well with Solar & TOU tariffs as it keeps the water hot and can be set with a timer to be ready for morning hot drinks.