temperatures under roof-mounted panels

[nerdralph]

Although I've only used string inverters, I've still been paying attention to micro-inverters in the market. Looking at the specs on the IQ7A, I noticed it's operating ambient temperature range tops out at 60C. Using an infrared thermometer, I've measured PV panel temperatures approaching 60C on clear, calm, sunny days.
I'm looking for data on temperatures under panels when mounted 10-15cm above asphalt-shingled roofs with a pitch of 20-30 degrees. Has anyone come across such data?

[davidcheok]

Screenshot 2023-01-13 at 7.02.50 AM.pngScreenshot 2023-01-13 at 7.01.09 AM.pngScreenshot 2023-01-13 at 6.56.37 AM.pngimage_15349.png The inverter temperatures are dependent on the output/conversion power and the solar intensity. I have 15 APSystem DS3 which run up to a max of 90C at 440w/channel before throttling and then 100C before shutdown (15 mins to restart). According to the manufacturer, its nominal operating temp is up to 95C. From my observation, the panel temperature doesn't really affect the inverter because the inverters are outputting more in the conversion than the accumulated heat from the panels.

My roof pitch is 18C and local irradiation can reach up to 1200 w/m2 with average at around 800 w/m2. The distance from the bottom of the panel frame to the ridge of the roofing shape is roughly 10cm with another 3-4 cm down to the bottom of the roof shape (cliplock roofing). The PV panel in my zone (equatorial) easily hits 50C on the coolest and I am guessing as high as 65-70C on the strongest day.

Micros are designed to work under very hot temperatures with the external casing acting as a heat dissipator. Good airflow would be ideal though so careful placement helps. The inverters throttle back around 20-30% when it hits the threshold.

I think asphalt roofs would perform better because metal roofs conduct the heat from exposed areas across the entire roof over time.

Hope that helps.

PS. I designed my system to use the highest temperatures (based on pmax drop at max operating panel temp) to the inverter output. i.e. at lowest panel output, my inverter produces close to max so my DC/AC ratio is around 1.38.

[nerdralph]

My roof pitch is 18C and local irradiation can reach up to 1200 w/m2 with average at around 800 w/m2.

Interesting data, particularly the pyranometer graphs. Now I want one...

You should be seeing a correlation between the air temperature under the panels and the temperature of the micro-inverters. Perhaps the variation in ambient temperatures where you live is too low to notice it. My guess is under full load, the micro-inverters would be about 25-30C warmer than the air temperature under the panels.

[davidcheok]

Interesting data, particularly the pyranometer graphs. Now I want one...

You should be seeing a correlation between the air temperature under the panels and the temperature of the micro-inverters. Perhaps the variation in ambient temperatures where you live is too low to notice it. My guess is under full load, the micro-inverters would be about 25-30C warmer than the air temperature under the panels.

Ambient here is 30-33c at max.. its way way higher.

[davidcheok]

Screenshot 2023-01-02 at 12.26.07.png

Temps hit 90C easily especially on clear skies. Ultimately, the heat all comes from the micros rather than from the panels. If you have the option to place the micros or design a system that increases the space around the micros so the heat can be dissipated or transferred away more easily I suggest doing so but if you dont have a choice, the micros were designed with these in mind i.e. heat throttling at reduced temperatures. All you lose is some production. Spec the panels around the micros you want to use rather than other way around. Mine were designed with inverter total system output in mind rather than panel output. Especially true if you live in hot sunny areas with high temp and humidity. Calculate the panel output at its hottest operating temperature to just clip the inverter output at peak and you should have an optimised system suited for good collection during cloudy and dark days and some amount of clipping at peak.

[nerdralph]

Ambient here is 30-33c at max.. its way way higher.

The temperature under my panels (connected to a string inverter) on a calm and sunny day is usually 30-35C above ambient. So if your ambient is 30-33, I'd expect close to 70C air temperature under your panels. The temperature reported by your DS3s is not the air temperature, it's the internal temperature.

[davidcheok]

The temperature under my panels (connected to a string inverter) on a calm and sunny day is usually 30-35C above ambient. So if your ambient is 30-33, I'd expect close to 70C air temperature under your panels. The temperature reported by your DS3s is not the air temperature, it's the internal temperature.

I meant the inverter temp is way above ambient or the air temperature below the panels. Frankly if I were to guess, I think the air temp below the panels would be around 50-65C.