Measuring the temperature coefficient of a PV module
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12 February 2016 

Measuring the temperature coefficient of a PV module

As we all know, the smooth performance of a solar PV module is strongly geared to the factor temperature. Higher than standard conditions temperatures can actually mean losses in maximum output power which is why we would usually aim at optimally cooling the modules and this regard the assembled cells.

This article is a basic introduction to the temperature coefficient of a solar module, its significance and calculation. Before explaining the measurement of temperature coefficients, we will first look at the definition of temperature coefficient.

 

What is the temperature coefficient of a PV module?

Each solar cell technology comes with unique temperature coefficients. These temperature coefficients are important and the temperature of the solar cell has direct influence on the power output of a solar PV module.

Once the temperature a solar module operates in increases, the power output of the solar module will decrease.

Crystalline solar cells are the main cell technology and usually come with a temperature coefficient of the maximum output power of about -0.5% / degree Celsius.

The rated power as generally indicated on the module’s label is measured at 25 degrees Celsius, and with any temperature increase above 25°C you have to take into account power losses of 1% for every 2°C increase.

Most installed solar modules in sunny countries easily reach higher temperatures than 25°C. In fact, temperatures of 50°C and above are easily reached.

 

Temperature coefficients calculation

Temperature coefficients of a solar PV module

 

Calculation of the temperature coefficients

We will take here a solar PV module of Trina Solar as an example, and calculate the power loss when this type of solar module is installed in a region with a hot climate.

We pick their currently highest power polycrystalline silicon 60cell module: the 260W. Temperature coefficient of the maximum output power (Pmax ) at STC is -0.41%/°C.

Now, let’s have a look at an example if the solar cells inside a solar module reach 65°C. With the solar module reaching 65°C, the power loss of this module is:

  1. 65°C – 25°C = 40°C, which is the temperature difference between the module’s Pmax at STC and the hypothetical example temperature of 65°C reached by the cells
  2. 40°C x -0.41% = -16.4%, which means that the module loses 16.4% in power output when the cells reach 65°C

Solar module power loss: -16.4% x 260W = 42.64W. The maximum power this module will operate at 65°C is: 217W.

As you can see in the sample screenshot above, besides the temperature coefficient of Pmax there are also other temperature coefficient ratings for solar PV modules. These are:

  • temperature coefficient of the open circuit voltage (Voc), which measures the changing open circuit voltage values of the PV module when the temperature increases (or decreases)
  • temperature coefficient of the short-circuit current (Isc), which measures the changing short-circuit current values of the PV module when the solar cell temperature increases (or decreases)

Solar module testing and temperature coefficients

Each type of solar cell has its own temperature coefficient. During this measurement, the temperature coefficients of current (α), voltage (β) and peak power (δ) are determined.

For this test, the following equipment setup is needed:

  • a radiant source (usually solar simulator)
  • equipment to vary the temperature of the solar module
  • accurate temperature monitoring
  • equipment to measure the voltage and current of the solar module

The resulting coefficients are applicable at the same irradiance level at which the measurement was made.

For more material on this subject, the international standard IEC 60904-10:2009 Photovoltaic devices – Part 10: methods of linearity measurement provides for measurement methods related to solar PV module temperature coefficients and different irradiance levels.

About the author
Niclas is Quality Director at Sinovoltaics Group. Sinovoltaics Group assists PV developers, EPCs, utilities, financiers and insurance companies worldwide with the execution of ZERO RISK SOLAR projects - implemented by our multinational team of solar PV-specialized quality engineers and auditors on-site in Asia. Niclas has been living and working in Asia for 9 years, including Mainland China, Taiwan, India and Iran. Niclas is PV quality specialist with extensive experience with manufacturers in Asia and has before worked on clean energy projects at UNIDO and Grameen Shakti. Connect with Niclas on LinkedIn

By

leon

on 26 October 2016

Yes, exactly! Cenergy - Leon

By

Muhammad shafiq

on 2 November 2017

good information about solar panels

By

Eric Scherzinger

on 21 January 2018

What about Panels in Cold winter climates with negitive - temperatures? Will there be a power Increase rather than a loss? How would one calculate for - (neg) C winter Temperature Conditions. I'm mainly using this for max voltage produced in very cold conditions to avoid going over my MPPT max incoming voltage specs.

By

Gavin

on 9 March 2018

The most suitable temperature for solar panels is 25°C,which means temperature above or below 25°C will both cause power loss.

By

SolarRat

on 30 October 2018

You are incorrect. PV modules produce more power when cold. The temperature coefficient is negative for increased temperature, not decreased temperature. I have seen my array produce 125% of its rated power when below freezing.

By

Automic

on 15 February 2019

Total rubbish. Don't know where you get this idea, but it is wrong, diddly wrong wrong.

By

Automic

on 15 February 2019

Probably too late now, but the fact that a temperature is considered by us (those using celcius) as negative is of no consequence. All that is important for your calculations is the number of degrees away from STC (25°C) so if you are preparing for a cold winter and are expecting minus fifteen degrees celcius then that would be 25+15=40°C so you'd do your calcs with 40xcoeff etc. Itis useful for avoiding exposing the inverter to voltages outside of their safe range. But don't be confused into trying to stay within an inverter's mppt max power range (unless you are using a three axis tracker) as most likely because the sun is so low in the sky during winter, the actual power generated during this low temperature is likely to be far reduced from the theoretical max power of the modules concerned. Plus of course if the panel is well exposed to the sun at this time perfectly perpendicular then it will only be at this extremely high voltage momentarily as it will quickly heat up (unless you are in an arctic wind). Enjoy.

By

maher al qadhi

on 4 March 2018

Good day Thanks for information, kindly I have question regarding your post if I have PV module with voltage temperature coefficient = -0.31%/K not by C, do I need to change it to C to use it in my calculation? as you know STC used Celsius, and how I can do this? thank is advance Maher

By

Rudy Puister

on 29 August 2018

a temperature difference of 1K (=1 Kelvin) is the same as 1C (1 Celsius) Only the absulute figures are different. 0 degree Celsius is 273.15 Kelvin and 100 degrees Celsius is 373,15 Kelvin. So a degree difference in both scales give exactly the same outcome.

By

Ali

on 22 March 2018

Well done!! very clear explanation,

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