What 3 string inverter to use?

Hi,
Having installation issues with my current Solis 1p8k-5g which is suppose to have 3 string inputs. E.ON have replaced as they thought the inverter was broken, 2nd unit still doesn’t work.
What inverter does anyone have that works with 3 strings?
Would having a GE hybrid inverter for 2 strings and an additional smaller inverter for 3rd work? Ideally want just GE system, but that doesn't seem to be possible.

My current system:
GE AC Coupled 3.0
GE 9.5 Bat (x2)
Solis 1p8k-5g Inverter

I've just seen that its possible to buy a Combiner Box 3 way, which would take the 3 strings into 1 DC output. Would you use these?
I could have then had a GE Hybrid Inverter...
Combiner Box 3 Way

I’d look at 3 small inverters for the three strings, but 3 string inverters are obviously easier to run.

I wouldn’t use a combiner as you’re not going to get maximum benefit from the MPPT.

Or 2 inverters, 2 strings on 1, 1 string on the other. I know that inverter listed will take 3 strings but checking the manual you have to be careful about load on each mppt

"Please note this inverter has two MPP trackers, each with different maximum allowed DC Current! MPP Tracker A is limited to 12.5A and should only have single string connected to it, MPP tracker B can have two strings connected to it with maximum current up to 25A."

THALL Would have thought that the installers know this!!

Cpt Darling

That device sounds like it has 2mppt and three strings rather than 3 strings with independent mppt.

Is that supported by the documentation? if so you’re likely better off with an alternative:

• 3 inverters
• 1 dual string + 1 single string inverters
• optimisers or microinverters
• 3 string inverter with 3 independent mppt

I think E.ON need to give me the right solution, they decided on the Solis Inverter, but I had always asked for complete GE system.
If the solution is to have either 2+1 or 3 individual inverters, could I have 2x GE HI5.0 gen2/3??
(Would I need the AC3.0 to join the inverters to the batteries...?)

Cpt Darling If your EON install was like mine then the installers are not actually EON but are sub contracted.

Not sure EON will go for dual hybrids as it is a not supported by GE. But that would be nice, would give you double the battery throughput etc.

THALL Cheers. Just wondering then what GE would suggest for 3 MPPT setup?

Cpt Darling technically I have 5 strings with a single AC3 and dual batteries. 3 pv inverters all Solis, a 8kw, 5kw and a 2.5. The AC coupled will grab power from any sources, the only issue is monitoring if you want the givenergy system to monitor your solar production etc. You can run data from multiple pv inverters back to 1 meter/monitor point on the AC3. So for me my 8kw is on its own and my 5kw and 2.5kw will be linked to the same monitor on the AC3.

Though just to throw a wild idea out there, how about a AIO instead of the AC3 and dual batteries ;-)

THALL Cheers for this. No idea if E.ON would swap this all out now... but worth asking
Can you couple an addition battery, giving 23kWh :-) (13.5 + 9.5)

Thanks

Cpt Darling Well I think @TheDragon (GivEnergy) has a AIO and AC3 at home. But you can not hang the current batteries off the AIO. I would assume EON will order in 2 smaller inverters to match however many panels you have. I assume 3 strings means 3 different facing roofs?

THALL Yeah, my house is L shaped, so have 3 roofs with panels (10, 5, 4)

AIO can have as many PV inverters as you like, the PV MCB is C32, so 8kw would be a safe Max

Off grid, would be 5kw max, else risking the PV output being greater than the charge capacity and tripping the AIO failsafe mechanisms.

I have AC3 and AIO in a test environment
3 solar inverters all mixed types

TheDragon (GivEnergy) Going to hijack this now..... So that AIO PV MCB so the AIO does more than just monitor like the AC3? I have 13.5kw of pv now but when I saw you had a AIO and AC3 together that did get me thinking about 1 more possible home upgrade!!

Cpt Darling

EON supply solaredge and optimisers (local panel level MPPT)

I’d be asking for a SE + AC3 inverter solution or another inverter that supports 3 strings fully. (At no extra cost)

Out of interest are the panels pointing in three different orientations with one string per direction?

THALL

Interested also as we now have 7.5kWp of SolarEdge PV on two orientations and an AIO plus gateway coming.

kram I understand that the AIO like the AC3 will only suck upto a certain amount of power, but in the event of a powercut it can keep PV systems running, so for me with 13.5kw of pv I am wondering what happens to unwanted power, the pv inverters have no limits set anymore.....

@TheDragon (GivEnergy) any chance you can share how the magic works? Take my house for example 3pv's totalling just over 13.5kw peak generation is about 10.5kw. What would happen if the system went off grid?

THALL If the system went off grid and PV power > Charge+Load the microgrid voltage would skyrocket and the AIO & PV would go offline immediately.
Off grid the AIO can turn PV on and off using grid frequency, so if you have a normal PV amount, and the SOC gets to 90% the microgrid frequency would move from 50Hz towards 54hz, PV would see a grid fault and stop output, preventing charge.
SOC < 80% and Fgrid returns to normal and PV wakes up.

TheDragon (GivEnergy) Oh very cool 😃 Not sure the wife would be very happy if I drop another £8k on ANOTHER battery however 👎️

TheDragon (GivEnergy)

So can I just check if PV > load + charge rate the AIO and the PV would go offline when off grid?

We will have 7.5kW E/W so that would potentially cause some problems if that’s the case. I thought there was a way to signal an inverter to throttle back?

Do you mean it would go offline if you lost grid whilst that was true? If so wouldn’t that be a pain for it being an emergency EPS?

It's called frequency shifting - a few others do it (Tesla, Victron) - there's a couple of bits about it. One somewhat weird consequence is that if you have devices that derive say time from the grid frequency then they will start to run fast.
Likewise some devices (although probably not many these days as they are 'worldwide' market 50/60Hz) may get upset. I suspect many EV chargers & EVs would get annoyed and trip out - although the likelihood of wanting to support those in a powercut is probably a bit of a stretch.

Here's someone who's boiler gets upset when their Tesla Powerwall does its shifting:
https://www.conferencesthatwork.com/index.php/technology/2022/01/solving-tesla-powerwall-power-frequency-problem/

hoggy

I knew about messing with the frequency, but surprised the AIO would just go offline if you’re producing and the grid goes.

It makes sense, but how does a Powerwall deal with this situation differently?

I guess I was hoping battery power would be available and the PV would be ramped down quickly so that the house remains powered.

kram it doesn't go offline though?
Providing your PV output is below the capability of either the AIO and the house to absorb it when the gateway drops into island mode everything will keep running. Frequency response will modulate the PV inverter as per G98/G99 (over frequency) on a sliding power output scale up until >52Hz where its output will be 0.
Once the battery empties a bit itll drop frequency down again and PV will come back up.

I think Paul is getting at the very rare occasion that people with huge amounts of PV on grid loss which would cause an insta voltage spike and shut everything down because it had nowhere to go. Even then though once the PV inverter is shutdown the AIO is free to restart and carry on doing its thing.
(I know the Victron units keep a little bit of battery buffer in the tank to deal with that spike, not sure on Tesla or GE)

@kram the AIO with gateway will keep running if the grid goes down. It will keep your pv inverters running and will basically throttle them for the AIO's max PV support. So even for my setup 13.5kw wont hurt it or cause a problem. It is very cool.

If anyone wants to offer me a decent price for my AC3, 9.5 and 8.2 batteries I would get the AIO!

TheDragon (GivEnergy)

hoggy THALL

That makes it sound like it would go off line rather than immediately shutting PV off. I’m hoping I am reading that incorrectly, but want to understand.

The document I posted?
It’s 100+ pages and I’m cherry picking. There’s a graph someplace near the end with the droop/derate curve example.

kram it allows generation to a point, a safe limit. Then upps the frequency which will cause the pv inverters to stop. But even then the AIO will remain online to run things from battery power. I expect PV generation can start and top as the AIO lowers the frequency. Someone correct me here but it sounds like it will work like a tap filling a glass, you turn it on to to fill it and off once full. Drink it, empty it turn the tap back on?

So AIO always on, PV on/off controlled by the AIO (this is only when the grid is down)

hoggy THALL

I get the it will charge and slow PV as required, but the post by Paul makes it sound like if PV> load plus charge rate the would both cut out.

I’m trying to understand if that is a short term battery exports only or if it’s all off until manual intervention.

kram If it turned anything off to the point of manual intervention that would be disappointing. I doubt that is the case though, the aio is meant to be a whole home auto switch over in the event of a power cut.

THALL Yes but does have safety cutouts

TheDragon (GivEnergy) expected, but I expect those trip rarely. Happy to trial an AIO with my triple PV and regular powercuts ;-)

TheDragon (GivEnergy) THALL

Right, so let’s say it’s a cool sunny day and you have 7-8kWp of solar. The battery is quite full and you’re away so low load. The grid goes and the system islands.

1) Would the AIO immediately ramp up the frequency to tell the PV system to throttle or stop?

2) How long have you got before it’s going to shut off and require manual intervention?

3) is it not possible to electronically open a “virtual isolator” which disconnects the PV inverter?It would see it has lost grid and shut down as required and only when the battery is say 70/80% would it reconnect the PV to the now generated Grid?

If it was 1 and/or 3 with a 2 if it gets it wrong or something goes wrong I get it.

If it’s 2 first, surely that means you don’t have backup when you’re away on a summer holiday as low load and full batteries = increased risk of the condition being met to trip.

If 2 happens is it a time out then automatic check/turn on again or is it really a manual reset job?

kram Hi Kram. Not been online all weekend so did not see your reply So answer from me are how I believe it would work, but I do not own one to be sure.

1) yes, it should push up the frequency which would make the pv inverters stop

2) you should not need to manually intervene. There are safety cut outs but unless there is some kind of serge etc these should not trip.

3) no idea, I expect controlling the local frequency is enough. All of these change overs happen in 20ms I believe.

I think for confirmation you could post on a tesla powerwall forum and ask how they get on with these kind of issues. But the couple of people I know of with powerwalls have never commented about having to turn things back on in the event of a power cut. To be honest with you at least one of them would have no clue what to do and would be straight on the phone to an electrician but as far as I know that's never happened. He's not someone that would ever touch anything electrical, he just wants it all to work without issue.

TheDragon (GivEnergy)

I don’t suppose you can confirm or otherwise what @THALL has suggested could you please?