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.

How Heat Affects Solar Panel Efficiency
How Heat Affects Solar Panel Efficiency
How Heat Affects Solar Panel Efficiency
How Heat Affects Solar Panel Efficiency

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.  

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.

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.

A typo..

"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%."

This should read "for every degree below, it increases by .485%."

Great article though! Thanks..