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As the thermometer rises , solar produces less electricity

Solar panels produce their highest voltages when it's pretty cold outside, just a few degrees above zero is perfect.

If the sun is shining very strongly AND it's cold, think Swiss Mountain top, then that's a lot of voltage and a lot of current, making a lot of power.

The reality is that if you were to buy a 400W solar panel, you can expect that most of the time it won't achieve much more than 300W.

Typically if 100W is 'lost' then in Perth, 40W would be due to temperature increases, 15W due to dirt on the panels (soiling), 5W due to electrical resistance losses in cables, and the remaining 40W due to the angle of the sun and 'irradiance' on the panels not achieving the 1000W of sunlight per square metre that the panel was tested under in the factory.

So, if your 400W panel really averages 300W and you have 15 of them making a 6kW system then instead of 6kW output, you are really going to get 4.5kW much of the time.

And that is why you always see inverters 'over-sized'..5kW inverter with 6.6kW of panels typically. In the old days, when we all knew less about solar we would sell 5kW inverters and 5kW of panels.

What about inverter losses in the heat?

As the temperature rises, an inverter will 'de-rate' meaning that it will be able to convert less of the DC panel power into AC power used in your home.

The big question though is "How much will it de-rate?" and the answer is 'Very little indeed if it's a quality inverter".

There's been an almost endless "battle" over the past few years as to whether Fronius inverters with fans are superior at keeping cool and de-rating less than 'fanless' inverters. Fortunately, we have the real World answer to that because we have installed both Fronius and Huawei (fanless) inverters in large enough numbers to have meaningful statistics.

To make things even easier to compare, I have both on my garage wall at home.

All of the Fronius and Huawei 5kW single and three phase inverters are rated almost exactly the same with 98% efficiency (Euro standard).

That means that under the 'Euro' testing conditions they convert 98% of the panel power to AC. Anything less than that once the inverter is up and running would be 'de-rating'.

I have both a 5kW Fronius Symo and a Huawei 5kW M0 inverter in my garage.
My garage is typically 5°C hotter than in the shade temperature outside meaning that if it's 40 degrees under my red flowering Gum tree then it's usually 45°C in my garage where the inverter is.

On 8th December 2020 at 3.15pm it was exactly 40°C under the gum tree, and 46°C inside my garage.

The internal cabinet temperature of the Huawei was 65.7°C and the efficiency 98.33%.
The internal cabinet temperature of the Fronius was 63.6°C and the efficiency 97.4%.

I've done similar tests on very hot days in the past with very similar results and this Summer I'll post more results here on scorcher days, but to me the result of the 'battle' is a draw.

Quality inverters, one with fans, one without, almost identical results.