4kW of 12-year-old panels with a 2.5kW or 3kW inverter?

[PVReeper]

We have 16 x 250W panels that were installed 12 years ago. The 4kW inverter was dying, so we asked for a 3kW inverter to replace it and were quoted a Growatt MIN3000TL-X. However we've just spotted that a 2.5kW inverter was fitted, the Growatt MIN2500TL-X. Now, should I insist that it be replaced with the 3kW version, or could the smaller size generate more power overall, safely? I.e. the panels won't be generating 4kW due to degradation.

I have figures covering just over 4 years of 10 min interval readings including continuously from 2020 onward. They show that there were 376 readings over 2.5kW and these occurred on 119 days, averaged around 3 a day. There were 11 readings over 3kW and these occurred on 9 days averaging just over one per day).

Total Readings in 1580 days​	Readings over 2.5kW​	Readings over 3kW​
115,160​	376​	11​
	=0.3265%​	=0.0095%​

Assuming after 12 years the panels are operating around 90% of their original 4kW power, that means that they are 3.6kW now. With a 2.5kW inverter that gives a 144% ratio/overclock, which is on the high side atm.

From these figures, is it safe/wise to keep the 2.5kW inverter, with the hope of generating a bit more power overall ( https://www.projectsolaruk.com/blog/how-many-solar-panels-can-i-connect-to-an-inverter/ ). Or, should we play it safer with a 3kW inverter? Thoughts?

 

[kommando]

Considering 250W panels 2nd hand a lot newer than 14 years are £30 ea locally to me due to upgrades I would go for the 3KW and in a few years replace the 250W with newer panels if the degradation continues . That's newer in a relative term as the current panels the same size as an old 250W must be close to 300w or more by now new.

 

[DIYrich]

I don't think a 2.5kW inverter will generate more power than a larger inverter. Especially when you are comparing 2.5kW to 3.0kW, or even 4.0kW. The starting voltage should be fairly close. Also, at starting voltage, the total watts tend to be fairly low.

On the upper end, the 2.5kW will max out at ..... 2.5kW. The 3.0kW and 4.0kW will max out at 3.0kW and 4.0kW, delivering more power at the top.

 

[PVReeper]

I don't think a 2.5kW inverter will generate more power than a larger inverter. Especially when you are comparing 2.5kW to 3.0kW, or even 4.0kW. The starting voltage should be fairly close. Also, at starting voltage, the total watts tend to be fairly low.

On the upper end, the 2.5kW will max out at ..... 2.5kW. The 3.0kW and 4.0kW will max out at 3.0kW and 4.0kW, delivering more power at the top.

Solar Inverter Sizing to Improve Solar Panel Efficiency | Solar Choice

What is the optimal solar inverter size for your solar power system? Read our comprehensive guide on what you need to know!

www.solarchoice.net.au

"Although under perfect conditions the maximum power output of a solar system will be ‘clipped’ back to the inverter’s output through overclocking through the middle of the day, there can also be gains in the overall amount of energy (kilowatt-hours – kWh) generated. The gains come from additional energy being produced in the early morning and late afternoon as a smaller inverter will turn on sooner and off later and operate more efficiently with lower DC inputs."

I can't find a calculator to work out the difference between clipping the top off the power curve, versus widening it at the side.