Adding more panels

Hi
I have an 3.6 Givenergy Gen 3.0 inverter + battery my home Slightly north of East West with 10 solar panels on the East facing roof
Over the summer solar generation starts to drop around 16:00 and virtually stops around 18:00 even on a Sunny evening meaning I'm drawing from the battery from 6pm until 6am ish.

I asked my installer what it would cost to install additional panels to the West roof My plan was to use the afternoon solar energy for longer not so interested in the additional export benefits, i realise at midday both roofs would would get the sun

This is the reply I'm hopping someone might be able to explain why a second inverter is needed and if true it would seem a poor design without an upgrade path,

I can add more panels on the West roof of the property however it would need another inverter. The original system also wouldn’t be able to see this generating power either, what would happen is the load would be reduced. You would however have a separate app to monitor the new inverter.

I have east/west and only one inverter. Why do you need two?

Did your installer split the panels into 2 strings so that both inputs to the inverter are now used?

CW I don't know TBH on the East roof there's two rows of 5 panels I checked the GE web app page string1 is showing generation, string2 isn't generating anything.

You should be able to connect a second string of panels to the string 2 input. You will be limited to the maximum throughput of the inverter though.

The 3.6 kW gen3 hybrid inverter can have a much higher DC input from the panels than the a/c output of 3.6 kW would suggest as it can simultaneously also charge the battery assuming it is not already full. Also having East and West panels on separate string inputs allows them to have their natural peak output at different times of the day.

Assuming your existing East panels are say 10 x 410 W = 4.1 kWpeak (which would only be achieved if they were South facing), you could add just over 3 kW of panels on the West roof without exceeding the data-sheet ratings of the inverter and have them wired in to the 2nd string input.
You may end up with some clipping of the potential generation during the best days of Summer, but will be glad of the extra gen during the Winter when the inverter will not be the limiting factor.

I have East/West facing panels and the gen during Summer in the East Midlands starts around 0530 and continues until around 2030 on bright days. With a total of 16 x 410 W = 6.56 kWpeak panels the peak gen on a blue sky day at 13:15 is around 4.5 kW. There are higher short term peaks for about 5 minutes when there are some clouds around to provide some reflective boosting. I have 10 West panels and 6 East panels so the peak gen is in the afternoon and early evening to suit typical household consumption.

SolarNewbee Well assuming that the web app page is looking at the inverter, then that would suggest to me that you have all the panels into the one string input. If that is the case then the second string input would be available I would have thought. If your inverter is as Simon_C has shown then it looks like you have a second string available with its MPPT tracker. So I am not sure why you would need a second inverter (as long as the second set of panels will satisfy the inverter string constraints)

Only thing you might want to consider is moving to a newer 5kW hybrid inverter.

No idea what the max charge rate is of a 5.2 gen1 battery, but the g1 inverter is capped at 2.6 from battery with newer ones being higher. A 5kW would be able to deal with mid day peak mind.

We have 8 per side on an east/west and have hit 5kW for about 2 hours a day on sunny days. Ours is not GE mind.

kram No idea what the max charge rate is of a 5.2 gen1 battery

I think it might be 2.6kW (0.5C).

My original install was 10 x 415w panels (2 strings) on a ESE roof, 3.6kW Hybrid Gen 2 Inverter & one 9.5 kW Gen 2 batt. Nice early morning generation but it dropped off to little or nothing by 3pm. Depending on use (home all day) the winter battery life was also struggling to last beyond 1-2pm.
Earlier this year I added an extra 9.5kW battery & 5 more 420w panels to a NW roof. The original ESE panels were rewired into 1 string & the new panels on the other string. Same 3.6kW Hy inverter.
Batteries easily last the whole day now & I get extra afternoon / evening generation. All still using the original 3.gkW Hybrid Gen 2 inverter.
My only regret is not having a a bigger capacity inverter that can supply more than a 3.6kW house load. At the time of the original install the AIO was not available & the 5kW Hy couldn't (& still can't) do more than a 3.6kW house load so no better than the 3.6kW Inverter in that respect.

DD

At which point a newer inverter will obviously make zero difference on that front.

Edit : have crossed wire, OP has a gen3

We have a 5kW gen 3 hybrid and it can provide 5kW to the house load. We only have a 5.2kWh battery so that can only discharge or charge at 0.5C, i.e. 2.6kW but solar can add to that.

I've had a reply from installer bellow
It makes sense in it's self but on the GIV-HY3.6 data sheet suggest Max. DC Input Power (per string) 7.5kWp but it also says Max. PV Voltage 580V. Not certain where the 3600w rating comes from.

I don't have the budget for a second inverter, there's also the amount of shading from SW to West to consider extra panels would pay for themselves

_The inverter installed already has 10 x 420W panels on at the moment which equates to 4200W and the inverter is rated at 3600w. the maximum panels we can add to this inverter is 1 more and this would then not produce enough voltage on its own to start the second input generating.

Putting one a different directional roof would then drag the existing string down when shaded if we added it to the existing string._

SolarNewbee Not certain where the 3600w rating comes from.

That's the maximum AC generation power. I think gen-2 also allows 3.6kW DC to the battery, so a total of 7.2kW as long as there's space in the battery to accept that charge.

SolarNewbee, I do not understand why you are saying only 1 more panel can be added to your inverter.

With 6 x 420W on the West roof, connected to the currently unused string, there would be sufficient Voltage to start that inverter string input, and the total would not exceed the stated 7500 W DC input.

With 8 x 420 W on the West instead the theoretical peak output is 18 x 420 W = 7560 W, but the peak output of the 2 strings occurs at different times of day so at any one instant in time the 7560 W peak will not be reached.

I have an East string of 6 x 410 W, and a West string of 10 x 410 W connected to a 5 kW Gen2 hybrid inverter. The peak total is 4784 W in this example of a sunny day, not 1875 W + 3449 W (= 5324 W) which is the peak output of each string but at different times of day.

I set the battery charge rate during the morning so that the battery does not reach full charge until around 15:30 or 16:00 after the peak PV gen has passed. This means the peak PV gen is able to go above the a/c output rating of the inverter whilst simultaneously charging the battery.

SolarNewbee Over the summer solar generation starts to drop around 16:00 and virtually stops around 18:00 even on a Sunny evening meaning I'm drawing from the battery from 6pm until 6am ish.

At what time does the power peak from your existing system? While the nominal max is 4.2kW, I'm wondering how much it's still producing around noon, when presumably the W panels might be starting to ramp up.

Simon_C With 8 x 420 W on the West instead the theoretical peak output is 18 x 420 W = 7560 W, but the peak output of the 2 strings occurs at different times of day so at any one instant in time the 7560 W peak will not be reached.

But my understanding looking at the spec is that the max is 7.5kWp per string - am I mis-understanding what the spec sheet is saying?

CW the max output is 3.6kW AC + 3.6kW DC + overheads. So even if you could feed in 7.5kW per string, there's nowhere for excess power to go.
The 5kW unit can output a bit more.

Losses amount to 100's of watts when running at full power, so the excess power becomes heat. For example our panels produce about 5kW peak but we only get about 4.6kW AC from that.

DD Over this summer it's starts generating around 6am and the battery is fully charged by about 9am when it's sunny bellow is a typical day sunny morning around 12 noon PV power is 3.239w so nearing the inverters 3,600w capacity
All times are BST the sun is in line with the ridge around 13:30 - 14:00

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Are you guys suggesting I'm being advised wrong? If so how might I resolve this?
The installer isn't going to install more panels on my say so not without a second inverter.

SolarNewbee yes, advice does seem to be wrong. You'd want to change strategy a little so that battery charges during the peak period on, at least on days when peak solar exceeds 3.8kW or so (allowing for losses).

SolarNewbee. If you set the battery charge power to say 800 W rather than the maximum of 3600 W, then the solar charge period is potentially extended in time until ideally just after the PV gen peak. It still gets to 100% battery charge, but will have done more export in the morning of the excess PV gen over the battery charge rate plus your house load.

If you have fairly regular house loads and starting battery % first thing in the morning then a bit of experimentation will help you find the optimum value. Note - On my Gen2 hybrid, the battery charge rate from solar is approx 200 W higher than the value you set either via the App or on the web portal.

In this example you can see multiple peaks in the PV gen of around 5800 W with a 5000 W inverter between 1230 and 1330 because the battery was still charging at 600 W at the time.

SolarNewbee I have an 3.6 Givenergy Gen 3.0 inverter + battery

What's the size of your battery ?

DD What's the size of your battery ?

Battery Capacity
153 Ah | 7.83 kWh | (2 Packs)
Initially I was advised to get 5.2 kWh battery this wasn't enough to go through the night so added a 2.6
On a normal day I use 7-8 kWh mostly in the evenings with a base load about 250w

I hadn't thought about reducing the battery charge I can see that working on a clear day but what about when it's murky and cloudy surly I'm better off charging the battery ASAP in case it gets overcast latter on.

SolarNewbee I was thinking about the max charge rate. I think a 5.2 battery is limited to 2.6kW, but if you also have a 2.6 it's presumably a bit higher - perhaps the full 3.6 of the inverter?

Yes, it's tricky to balance leaving space in the battery to avoid clipping, vs running out in the evening on a dull day.

SolarNewbee, it depends on how much you are exporting anyway and whether that is spread over a longer time period of the day. The reduced battery charge rate does not have to be that accurate as much of the daily fluctuation in PV gen just affects the level of export, especially once more panels are added.

You seem to get decent PV gen between around 0800 and 1500 which is 7 hours, to put up to 7 kWh in to the batteries then requires a 1000 W charge rate. You could try say 1500 W as an experiment for the charge rate which would also put less stress on the batteries. Not such an issue with your current relative PV and inverter size, but useful if more PV panels are added.