How Heat Affects Solar Panel Efficiency

Excessive heat can significantly reduce the output of a PV system. This article gives some pointers on avoiding unexpected energy loss in an array.

It may seem counter-intuitive, but solar panel efficiency is affected negatively by temperature increases.  Photovoltaic modules are tested at a temperature of 25 degrees C (STC) – about 77 degrees F., and depending on their installed location, heat can reduce output efficiency by 10-25%.  As the temperature of the solar panel increases, its output current increases exponentially, while the voltage output is reduced linearly. In fact, the voltage reduction is so predictable, that it can be used to accurately measure temperature.

 As a result, heat can severely reduce the solar panel’s production of power. In the built environment, there are a number of ways to deal with this phenomenon.

 Different module designs and different semiconductor compounds all react to temperature – here’s a brief intro into what to expect.

Determining Your Efficiency

The best way to determine your panel’s tolerance to heat is by looking at the manufacturer’s data sheet. There, you’ll see a term called the “temperature coefficient (Pmax.)”  This is the maximum power temperature coefficient.  It tells you how much power the panel will lose when the temperature rises by 1°C above 25°C. @ STC (STC is the Standard Test Condition temperature where the module’s nameplate power is determined).

 For example, the temperature coefficient of a Sharp Solar Panel NU-U230F3 is -.485% per 1 degree Celsius.  So, for every degree above 25°C, the maximum power of the Sharp solar panel falls by .485%, for every degree above, it increases by .485%.

 What This Means

No matter where you are, your panel may be affected by seasonal variations. However, the temperature coefficient also tells you that efficiency increases in temperatures lower than 25°C.  So, in most climates, the efficiency will balance out over the long run.

 For a geographic region where temperatures higher than 25 degrees C. are the norm, one can consider alternatives to Mono or Polycrystalline modules, which have the highest efficiency (At 1:1 concentration), but also the highest temperature coefficient at PMAX. Project designers may want to consider a thin film or CdTe module – or in the case of a very large project, High Concentration PV, which is designed for hot climates, but not applicable for small projects.

How to Reduce the Effects of Heat

After the module technology is selected for an installation, there are several ways to minimize the negative effects of high temperatures: 

  • Install panels a few inches above the roof to allow convective air flow to cool the panels down.
  • Ensure that panels are constructed with light-colored materials, to reduce heat absorption.
  • Move components like inverters and combiners into the shaded area behind the array.

Further information about temperature coefficients can be found in this research paper, produced by Sandia National Laboratories: "Temperature Coefficients for PV Modules and Arrays" David L. King, Jay A. Kratochvil, and William E. Boyson" (PDF)

Comments

Really great article, thanks.   It is amazing how much high ambient temperature reduces the efficiency of Mono and Polycrystalline solar panels.   It further explains why panels in high altitude locations perform so well.  


Use the "view lifetime" of my array.
Look at how heat debilitates the 10 panels that are mounted above asphalt shingles by ~ 10% beginning in mid-May thru August (temp about 49C 120F---space clearance for cooling is important!  We know there is much more sun in July than the highest output time in the merry, cool month of May.  What a waste.  

10 panels, 1 year, $750 saved

I live in Mexico and because of the higher average temperature spent the money and got Sanyo Hip panels, they actually are the only ones we found in our research that perform better in high temperatures. We are Loving our pannels and so far are not seeing any loss at all due to heat.
Ojo Del Agua

I believe in the future of renewable energy. Our house has solar panels to save money on our bills (which are extremely high). I suggest anyone with a bit of property, a business or a roof to see if you can put solar, it's really worth it. Quick tip: we used www.mysolarinstaller.com to get tailored quotes for our home. They got us the top solar installers in our area to send free quotes...it took us less than a minute with their process and we got to compare apples with apples.

Hi Rob. Do you have an actual install or are you just promoting MSI? We allow postings with outside links if the information is related to the article / question. Please post details of your project and how they relate to heat and solar arrays.