Excessive heat can significantly reduce the output of a PV system. This article gives some pointers on avoiding unexpected energy loss in an array.
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.
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.
module designs and different semiconductor compounds all react to temperature –
here’s a brief intro into what to expect.
Determining Your Efficiency
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).
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
What This Means
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.
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
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.
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)