PV output: Theory versus Practice

[Marvin]

What percentage of the designed Wattage output have you seen, produced by your inverter, at peak production from your panels?

 

I do not have a continual monitor on mine but the highest I noticed was about 80%. 

 

The difference would be because of the angle and direction of my panels is not at the ultimate position, and I expect the panels are not completely clean.

 

Has any one else any record of the peak production percentage?

 

The reason for the question is because the 6kW inverter permits more than 6kW of panel to be installed, but the output is limited to 6kW and I could squeeze a few more panels in if this would work.

 

[Carrerahill]

3 minutes ago, Marvin said:

What percentage of the designed Wattage output have you seen, produced by your inverter, at peak production from your panels?

 

I do not have a continual monitor on mine but the highest I noticed was about 80%. 

 

The difference would be because of the angle and direction of my panels is not at the ultimate position, and I expect the panels are not completely clean.

 

Has any one else any record of the peak production percentage?

 

The reason for the question is because the 6kW inverter permits more than 6kW of panel to be installed, but the output is limited to 6kW and I could squeeze a few more panels in if this would work.

 

It is actually fairly common to add more panels than the inverter rating, the idea being that say 20% more panel peak capacity than the inverter can handle will mean that when you see 80% peak generation on the panels you sort of end up at the full rated output... 

 

I seem to see about 83% of peak panel power as a norm during this current sunny weather. 

 

 

 

 

[Conor]

In theory, 86% here according to the inverter. Not checked it for real but I've inverter limited for G98 compliance anyway.

[SteamyTea]

We will once fitted 3.5 W_p of modules to a 3 kW SMA inverter.

The instantaneous display showed over 3 kW every now and again.

The cooling fan was at full chat.

 

If under sizing the inverter, fit it where it can draw in lots of air, so not a loft or cupboard.

Edited August 9, 2022 by SteamyTea

[jack]

We have 8.5 kW (peak) installed, but our panel orientation is a long way from ideaI, and I don't recall ever seeing more than 6.6 kW (~78% of nominal peak output).

 

We regularly hit 6.1-6.3 kW during June, and usually exceed 6 kW at least every few days across the whole of summer.

[SteamyTea]

The usual way to measure a PV installation is to divide the output over a time period by the installed capacity i.e. 950 kWh/kW_p.

Suppose you could do something similar with the nominal inverter capacity.

[JohnMo]

NE Scotland, 3.1kW with optimisers,  45 degs and SSW direction.  Have seen a little over 3kW being generated a couple of weeks ago.  But I don't monitor all the time, just happened to at the inverter so took a look 

[Marvin]

I notice that the PV calculator I use indicates a typical 14% loss...

 

https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html

[kommando]

I currently have 2 1500W panel sets feeding 2 SMA SB1200's, all the inverter data is pulled every 10 secs and is held on a Solar-log. This shows on a summer sunny day I get MPPT-peak, eg 1150 to 1200W, messages from 10am to 2pm from both inverters. I get a lot more MPPT-peak messages from the wall mounted array at an adjustable angle and no shading. I can also create a graph laying the daily output by minute by inverter, this confirms what I already knew, ie the first array is set too steep an angle and past 5pm it suffers from shading. In Sept that set of panels will be joining the wall mounted set and should match the better performance, first days figures will tell me. In the last 2 months best days total production was 15KWh, worst was 1.4KWh 2 days ago.

[Dillsue]

22 hours ago, Marvin said:

The reason for the question is because the 6kW inverter permits more than 6kW of panel to be installed, but the output is limited to 6kW and I could squeeze a few more panels in if this would work.

 

So in the summer your inverter will limit generation to circa 6kw. Spring, autumn and winter its likely the array will limit what you generate so I would squeeze in as many panels as you can to maximise generation for the majority of the year outside the summer peak.

 

The maximum DC input figures manufacturers state are when all panels are facing the same way so are all generating at max at the same time. You can massively oversize your array if the panels are orientated differently so not hitting peak generation at the same time. Our SE inverter has a max 5250w DC input but currently has 6.4kwp panels connected with a further 2kwp to be added in the next few weeks. With 2kwp facing SE, 3.2kwp facing SW and 3.2kwp facing NW, PVGIS figures for the last 2 years say max we'll generate is just over 5kw so hopefully no smoke from the inverter!

 

If youve got the space and funds, Id definitely oversize your array up to the manufacturers max rating or beyond if you want to crunch the figures.