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Does heat affect your solar panels?

RVwithTito has recently added a new video to his YouTube channel where he looks at the power production from his flexible solar panels and if temperature has an affect on their performance. It's a great comparison between his ground mounted non-SunPower 115W flex panels and his roof mounted SunPower 110W flex panels.

No spoiler alert here! Have a watch of the video below to see the results.

Without spoiling the video it is worth sharing some more info on temperatures, how that does affect solar panel performance and the SunPower advantages that help them handle it.

Nearly all solar panels are rated (ie given a wattage of say 110W) under Standard Test Conditions (STC). To go into full details on the STC is another news post in itself, but it helps to compare differnt solar panels. What we are looking at here is to do with temperature. STC for panels is done in the lab at 25'C (77'F). In general solar panels will perform better if the panel temperature is lower than 25'C and will perform worse if the panel is warmer than 25'C.

This is called the temperature coefficient and SunPower has a very low rating, meaning that it handles the temperatures well. This data you can find on the spec sheet or the sticker (nameplate) on the back of each solar panel. Here's the one for the SunPower 110W and 100W panels.

As you can see there is a lot of data that these nameplates provide, rated Watts, Amps and Voltage, but today we're looking at the Power Temp Coefficient.

The SunPower 110W has a Power Temperature Coefficient of -0.30%/'C, so for every 1'C above 25'C you lose 0.3% or it's easier to say for every 10'C above 25'C you lose 3%. So for example at 35'C (95'F) you have lost 3% or 3.3Watts. The main reason why SunPower has this low temperature coefficient is that each cell has a solid copper backing which helps to dissipate heat across the whole cell.

A quick search of typical solar panel temperatures shows that an average can be around 49'C (120'F). In Brian's video he records panel temperatures on the roof of his RV in Arizona of between 50'C and 56'C (122'F and 132'F)

So with panel temps at 56'C that's 31'C over the STC of 25'C, that means 0.3% x 31 = a loss of 9.3% or 10.23 Watts. This in fact ties in pretty close with RVwithTito's video as his 2x110W panels wired in series (220W total) producing 192W, a difference of -28W from their rated output. There are of course more variables to consider; what was the state of charge of the battery bank, this video was filmed in March with lower sun angles, what time of day was it etc but it does give a good indication of panel performance v. panel temperature.

Don't forget we tend to think of the temp coefficient as only applying when the panels get warmer than 25'C but this works the opposite way too, so when it gets cooler than 25'C (77'F) your panels will start to produce more power, bonus!

In summary SunPower E-flex panels hold up really well to higher temperatures and will provide you with clean & quiet solar power so you can enjoy the great outdoors even more!

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