Solar not doing as well as you hoped?

Your expectations are too high?

Let's say you have a 5kW inverter and 17 x 300W panels (5.1kW).
When you look at your solar output reports it never gets over 4kW.
Are the panels faulty, or the inverter a dud?

No, it's perfectly normal.

A solar panel is rated in the factory unrealistically compared to the real World.

In the real World, your 300W panels will rarely produce more than 225W each.
If you have 400W panels the same 25% reduction applies, so 400W panels make 300W.

Heat, angle of the sun, intensity of the solar irradiation, cable resistance losses, dust on the panels. All of these things conspire against you to reduce your solar panel output and apart from a bit of panel cleaning in Summer there's nothing that you can do about it.

Your solar inverter works very hard drawing every drop of power it possibly can from your panels. If available it allows them to produce a little bit more, to cover the typical conversion 2% loss that happens when the inverter converts the DC panel power to the AC power your home uses.

This is why solar companies recommend 'over-sizing the inverter' and the Government agrees. The Government gives you a discount on your panels of about $200 per panel as long as you don't oversize the inverter by more than 33.33%. Oversizing it any more than that produces such a minimal additional gain that they won't give you the discount on your panels at all if you do it.

So a 5kW inverter can have 6.66kW of panels.
As we now know that the output of 6.66kW of panels at peak time will be 25% less...that's 5kW of output going into your 5kW inverter. Perfect !!

Under really ideal conditions (very rare) your panels might be producing more than 5kW and you'll see your solar output chart flatline at 5kW, because that is all the inverter can draw from the panels for conversion to AC.

However, as most panels are virtually free due to the Government discount, adding extra panels to 'oversize' your inverter didn't cost you much more than a bit more roof space.

Other reasons why your solar output goes down.
Shade on one or more of your panels.
Direction the panels are facing. North best, East 2nd, West third, South last.
Time of day.
Time of year. Solar irradiation is weaker and shorter in Winter.
Age of panels. Most panel's output drops by 0.7% a year as they age.
Roof pitch. Flatter the roof, the lower the output.
Inverter over-heating. Inverters derate their output if they get too hot.
Inverter derating or shutting down to over high grid voltages.