Inverter Sizing

[Javanerd]

My question relates to an earlier reference to your electrical panel. Did the electrician say tell you the maximum fuse size you could put in for your solar system? I don't understand UK electric regulations and was trying to understand how your installer determined system size and fuse ratings.

Also, I have attached a screen shot of my string inverter on a day with bright sun and big puffy clouds. Is this the type of day your had for your earlier power output graphs?

Thank for that, it looks similar to mine and also looks like you are clipping too, or is that the max gen of the panels?

[oregon_phil]

I have 10.22kW of panels on a 7.7 kW string inverter or a DC to AC ratio of 1.32. So yes, there is clipping. One thing about bright sunny days with clouds and clipping. In the right circumstances, a bright shot of sun between clouds will cause clipping because the solar panels are cold compared to solar panels that have been exposed to the sun all day.

I am not a solar designer and have no East West solar panel orientation design expertise, but on the Solis datasheet, it says "Max DC Input watts 4600" for the Solis-1P4K-4G. There must be some design justification somewhere in your paperwork.

Also, another website said "UK only: Please note, the SOL-4.0-4G-DT is rated at greater than 16A per phase and therefore must be installed as per G59/3 or G99. Select the SOL-3.6-4G-DT for an inverter limited to 16A"

Your inverter can put out 18.2 amps or 17.4 amps at 220V/230V but whatever the G99 is, it seems to be the limiting factor for this inverter.

[Javanerd]

I have 10.22kW of panels on a 7.7 kW string inverter or a DC to AC ratio of 1.32. So yes, there is clipping. One thing about bright sunny days with clouds and clipping. In the right circumstances, a bright shot of sun between clouds will cause clipping because the solar panels are cold compared to solar panels that have been exposed to the sun all day.

I am not a solar designer and have no East West solar panel orientation design expertise, but on the Solis datasheet, it says "Max DC Input watts 4600" for the Solis-1P4K-4G. There must be some design justification somewhere in your paperwork.

Also, another website said "UK only: Please note, the SOL-4.0-4G-DT is rated at greater than 16A per phase and therefore must be installed as per G59/3 or G99. Select the SOL-3.6-4G-DT for an inverter limited to 16A"

Your inverter can put out 18.2 amps or 17.4 amps at 220V/230V but whatever the G99 is, it seems to be the limiting factor for this inverter.

Many thanks for this. All ammunition against eON. The G99 was 4K and it is installed with a 16a fuse. I am expecting it to trip in summer , but one of my worries is feeding in 5.5/6kw DC into the inverter. Surely this could damage it, but hopefully enough protection to stop it doing damage to my electrics or house.

[oregon_phil]

Also, another website said "UK only: Please note, the SOL-4.0-4G-DT is rated at greater than 16A per phase and therefore must be installed as per G59/3 or G99. Select the SOL-3.6-4G-DT for an inverter limited to 16A"

Your inverter can put out 18.2 amps or 17.4 amps at 220V/230V but whatever the G99 is, it seems to be the limiting factor for this inverter.

I think you have it right but I need to make a clarification on my assumptions because I was in too much of a hurry earlier and didn't know anything about G99.

In your case, G99 type A is for power generation greater than 16 amps and less than 1 MW. In the quote above, Solis is saying the SOL-4.0-4G-DT puts out more than 16amps and should be installed as a G99 type A device. The Solis manual says Current for Protective Device (A) = 25. I gather this means you should have a 25 amp breaker.

If 10 panels are East (10x 40volts= 400 volts) and 10 panels are West and are on different MPPT inputs, then each string would be under 600VDC max, but then there is the total DC power issue.

I didn't answer the clipping/East/West issue because I don't know enough about this.

[J.P.M.]

Now people have mentioned potential problems, I have seen this very jagged graph right from installation. This is today and does seem wierd that clouds could make this much impact. Any thoughts

today.jpg

Doesn't seem weird to me. Looks like a typical partly cloudy with cumulus type clouds kind of day.

There does however seem to be what looks like some clipping going on.

[SunEagle]

Doesn't seem weird to me. Looks like a typical partly cloudy with cumulus type clouds kind of day.

There does however seem to be what looks like some clipping going on.

Wow. You would get that much of the system shutting down due to just clouds passing by. Now I understand why some Floridians have reluctance to installing solar. There seems to be a lot of clouds on most sunny days here.

[J.P.M.]

Wow. You would get that much of the system shutting down due to just clouds passing by. Now I understand why some Floridians have reluctance to installing solar. There seems to be a lot of clouds on most sunny days here.

Well, If it's broken cumulus and a clear atmosphere, I saw less than 1 kW to ~ 4.6 kW about 10 minutes apart on 04/01/2021and that's not at all unusual, particularly under pt. cloudy skies. Under such conditions the GHI will go from maybe 950 W/m^2 to maybe 150 W/m^2 in a matter of seconds and then bounce back in almost as short a period of time. I didn't see Javanerd's output dropping below maybe 0.5 kW so it diddn't shut down . He may well have an undersized inverter, but since he didn't say the shown graph was under clear skies, I assumed the graph was for a partly cloudy day as the pattern looked so familiar. The voltage stayed pretty constant but fluctuated some as would be expected as the varying irradiance heated and cooled the panels some, and the current fluctuated pretty much in sync with what the irradiance might have been.

Maybe Javanerd doesn't know that array output is not supposed to be constant if the irradiance is variable.

Seems to me also that with two arrays 180 degrees apart with maybe different shade regimes that different power outputs would probably be expected.