Solar Panel Temperature Coefficient: The Solar Panel Info You Need
Solar panel temperature coefficient sounds pretty complicated, doesn't it?
We're going to do our best to show you that this solar panel info isn't as mind numbing as it might sound.
We're also going to provide you with some standard solar cell temperature coefficient percentages so you can get an idea of what type of performance you should expect from your solar modules.
First, however, we should probably get a few basic facts out of the way regarding solar panels and temperature.
The first thing to know about solar electric panels and heat is that they do not play well together.
This can seem a little contradictory until we remember that it is actually the light of the sun and not the heat that is used to create electricity through the photovoltaic effect.
As the air temperature rises and a solar panel heats up, the panel has more difficulty doing its job and the power output of the solar module actually decreases.
(It's a different story for a solar hot water heater which loves the heat and doesn't lose any efficiency due to high temperatures.)
When you are choosing a solar panel company for your solar panel installation, you can find out how well the company's panels perform in the heat by looking for the Maximum Power Temperature Coefficient in the solar panel specifications.
This solar panel temperature coefficient is usually expressed as a percentage per degree Celsius (% per degree C). This means that the temperature coefficient indicates what percentage the solar module's output power will decrease for every degree Celsius the temperature of the solar cells rises above 25°C.
Let's look at a specific example using the Sharp NT-175U1 solar module to make this a little more clear:
This means that the 175 Watt NT-175U1 would lose 0.49% of its power output for every degree above 25°C the solar cells heated up. This would equal a loss of 0.86 Watts (0.49% x 175 Watts) of power output for each degree.
That doesn't sound like too much, but it can really add up. Remember that it is not the temperature of the air that is being measured but rather the temperature of the solar cells in the panel. A dark solar panel up on a roof can reach temperatures of 70°C on a hot day!
If our trusty Sharp NT-175U1 reached 70°C its power output would be reduced by 38.7 Watts and instead of a panel producing 175 Watts we would have a panel producing only 136.3 Watts. That is a reduction of over 22%!
Another important fact to remember is that thin film solar panels lose less of their power output as their temperature rises. This helps to make up for the lower overall efficiency levels of thin film panels.
And just to make things a little more complicated, you should know that there are actually some other solar temperature coefficient specifications for panels besides the Maximum Power spec we've discussed here.
These additional solar panel temperature coefficient specs are:
Open-Circuit Voltage Temperature Coefficient
This measures the change in the solar panel's open-circuit voltage due to an increase in temperature.
Short-Circuit Current Temperature Coefficient
This measures the change in the solar module's short-circuit current as solar cell temperature increases.
Getting back to the Maximum Power Temperature Coefficient, let's look at the range you can expect from different solar panel brands.
As mentioned earlier, thin film panels do relatively well under hot conditions. Many of these panels only lose about a quarter of a percent of power output per °C increase in cell temperature. Examples of thin film temperature coefficients include:
Unisolar -0.21 (%/°C)
First Solar -0.25 (%/°C)
Kaneka -0.26 (%/°C)
Examples of temperature coefficient specs for crystalline solar panels include:
Sunpower -0.38 (%/°C)
Mitsubishi -0.45 (%/°C)
Suntech -0.47 (%/°C)
Sharp -0.49 (%/°C)
Keep an eye on the solar panel temperature coefficient numbers if you're thinking about a solar installation. You'll get a better idea of how much power your panels will produce in the real world.