Inverter Sizing

[Javanerd]

Hello all,

I am new on here and sorry for the lengthy message below, but I am desperate for advice as in a battle with eON over sizing.


Not only did they install less panels than would fit on my roof, after telling me that 10 panels either side was the maximum, they also fitted a very small (in my opinion) inverter.

I have a E/W configuration with 10 panels each side and Trina 325w panels. This gives a total of 6.5kW, although I am aware that due to the orientation they will not give 100%. I am finding however that the 4kW Solis inverter is hitting its maximum if 4.34kW at about 10:20 and then still able to generate this at 15:20 in the afternoon and it is not even Summer yet.

I have graphs I can share and I have had loads of info form eON, stating that under specifying the inverter is common practice, but by 47% seems excessive. I asked for a 4.6kW inverter at the install time, which could peak to 5kW, but I was told due to the configuration I would never generate this.

Does anyone know for the G99 application whether the reason for the 4kW rather than 4.6kW was a pricing issue with the distribution company. If I has been able to choose, I would have had the extra 4 panels (12 each side) and a 5kW hybrid inverter so I could have added the battery later.

Many thanks for your replies

Clipping.png

[solarix]

Your installer is being cheap. First going with a Chinese made brand and then undersizing it. There is not much difference in price between inverter sizes these days. You should put the biggest inverter your electric service can handle to future proof your system. Down the road, you are most probably going to want "more power" and will have to change up to a 6 or 7kW inverter to accommodate it. Would have been just a few dollars more to put that inverter in now.

[SunEagle]

Your installer is being cheap. First going with a Chinese made brand and then undersizing it. There is not much difference in price between inverter sizes these days. You should put the biggest inverter your electric service can handle to future proof your system. Down the road, you are most probably going to want "more power" and will have to change up to a 6 or 7kW inverter to accommodate it. Would have been just a few dollars more to put that inverter in now.

Remember the kw rating of the inverter will determine the circuit breaker size in the panel which may also be limited due to the buss amp rating. So going with a bigger inverter may be an issue.

I also am not concerned with the clipping as much as the dips in the chart. Is that due to clouds or the grid causing the inverter to shut down?

[bcroe]

I agree a larger inverter would have been a good investment. Net Metering agreements
here change their rules with larger sizes, I am in the second group of over 10KW inverters.

From experience here, I just assumed the graph showed clouds and gaps
between clouds, is that right?
Bruce Roe

[oregon_phil]

Javanerd , I believe you have a two MPPT inverter. You could graph each MPPT output vs time of day (bcroe does on analog graph paper), to see the power contribution of the East and West arrays. Maybe you already have that.

I also looked up some of the specs for Solis. Any inverter larger than 3.5kw starts up at the same 120 VDC so the argument of a smaller inverter starting up faster to give you power sooner doesn't hold any water (the 2.5kw inverter does start up at 60VDC, but that doesn't apply to you).

[Javanerd]

Remember the kw rating of the inverter will determine the circuit breaker size in the panel which may also be limited due to the buss amp rating. So going with a bigger inverter may be an issue.

I also am not concerned with the clipping as much as the dips in the chart. Is that due to clouds or the grid causing the inverter to shut down?

Not sure what they are. They could be clouds, but interesting question as the other day it was quite cloudy and the system was still generating 2.6kw.

The electic panel should be able to hole more than 4kW. The have stuck the inverter on a 16A fuse, but there was not reason it should have been lower and I am pushing for 4 more panels and a bigger inverter. They used a dedicated 4mm feed from the inverter to the panel

[Javanerd]

Javanerd , I believe you have a two MPPT inverter. You could graph each MPPT output vs time of day (bcroe does on analog graph paper), to see the power contribution of the East and West arrays. Maybe you already have that.

I also looked up some of the specs for Solis. Any inverter larger than 3.5kw starts up at the same 120 VDC so the argument of a smaller inverter starting up faster to give you power sooner doesn't hold any water (the 2.5kw inverter does start up at 60VDC, but that doesn't apply to you).

Many thanks. I also noted that from the stats, but didn't have any validation that my assumption was right. Many thanks The peak of the E and the peak of the W are not at the same time and this does mean that there is a little dip at high noon but this is not massive. The more I here, I am thinking that they didn't fit more panels, because they didn't do a proper survey and the inverter was spec'd off the original quote of 16 panels.

[oregon_phil]

Are you in the UK? Do you know the applicable regulations for solar installations & electrical panels?

[Javanerd]

Here are the E/W images and the total power for the 11th April.

On certain days just one panel is generating 3000w and I wonder whether the inverter is limiting the input too. I reached out to SOGEN, but they said to take it up with my supplier. You can imagine how well that went.

total pwer 11.jpgsame day East and West.jpg

[Javanerd]

Are you in the UK? Do you know the applicable regulations for solar installations & electrical panels?

Yes I am in the UK, and as a customer, I am afraid I don't really even understand the question. In relation to what? I know they have said they need to leave 300mm at the edge of the roof, but even with the extra 4 panels I think it would be 400mm easy

[Javanerd]

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

[SunEagle]

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

An inverter software is set up to make it stop working for a number of reasons. If the input voltage from the panels drops below Xdc then it can go into standby mode. If the grid frequency, voltage or phase angle go outside the limits programmed the inverter also goes into standby mode for X minutes and then will check those values before going back on line.

With that many dips in the graph it could be clouds but it may be the grid. Can you check to see if you get those dips when the sun is not blocked by clouds?

[Javanerd]

An inverter software is set up to make it stop working for a number of reasons. If the input voltage from the panels drops below Xdc then it can go into standby mode. If the grid frequency, voltage or phase angle go outside the limits programmed the inverter also goes into standby mode for X minutes and then will check those values before going back on line.

With that many dips in the graph it could be clouds but it may be the grid. Can you check to see if you get those dips when the sun is not blocked by clouds?

I might setup an Arduino to monitor the brightness. I have checked and there are no alerts on the Inverter and I would expect any issues like that to be logged

[SunEagle]

I might setup an Arduino to monitor the brightness. I have checked and there are no alerts on the Inverter and I would expect any issues like that to be logged

Sounds like a plan with the Arduino. Not sure why the inverter wouldn't log issues as to why it stopped working but it may just be because of how the manufacturer cut corners.

[oregon_phil]

Yes I am in the UK, and as a customer, I am afraid I don't really even understand the question. In relation to what? I know they have said they need to leave 300mm at the edge of the roof, but even with the extra 4 panels I think it would be 400mm easy

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?