When you think of a solar panel, maybe you envision a sunny day with a panel angled towards the sun baking in its rays.
You might think that these sun-soaked conditions are ideal for the panel to work at its most efficient level.
The more sun the better! Right?
In reality, temperature, both hot and cold, are vital parts of determining how well a solar panel will operate and has to be accounted for when designing a solution.
Today we will walk through how temperature can affect solar panel’s substrates, encapsulations and also if the color of a panel plays a role in overall performance.
Additionally, we’ll talk about ideal solar panel operating temperatures, temperature coefficients, how long you should test your solution and the importance of testing in the same environment as the solution will operate.
While there are many different solar technologies on the market, today’s post will focus on amorphous silicon solar panels as well as crystalline silicon solar panels.
What effect do different substrates have on the performance of amorphous silicon & crystalline silicon solar panels?
Substrates are an essential part of designing a solution that operates in your specific conditions and for your particular use case.
The most important thermal thing a substrate can do is to remove heat from cells. Thermally conductive material will convey heat away from the semiconductor and a highly emissive back surface like a polymer or paint will radiate the accumulated heat through infrared radiation while a metal surface will not.
In general, a white substrate is preferable over a black or darker color due to heat absorption, but this difference is minimal compared to selecting the materials themselves (aluminum, fabric, fiberglass, etc.).
Conversely, in a cold environment, you may wish to insulate cells to reduce the effects of light-induced degradation.
The best material for removing heat from cells is aluminum with a thin polymer (paint) surface. CDTE fiberglass is ideal for colder temperatures because there is less expansion and contraction due to the temperature, which leads to a more stable product that’s less prone to mechanical issues.
What effect do different encapsulations have on amorphous silicon & crystalline silicon solar panels?
When designing a solution, it’s vital to select the proper encapsulation to protect the panel from UV as well as temperature fluctuation.
Many panels on the market use an inexpensive polyester polyethylene encapsulation. While this option is low cost initially, it will lead to issues down the road as this material is far less resistant to heat degradation and the performance of your panel will be negatively affected.
With this in mind PowerFilm panels (both thin-film amorphous and crystalline silicon) use a TPU or EVA with ETFE as the top film if the panels will be used outdoors. This encapsulation provides significantly higher protection to the solar panel and allows operation in extreme temperatures without issue. A glass front surface will trap heat, which is generally not good (Learn more about the importance of encapsulation).
Is color a factor when designing a solar solution?
You’ve selected the proper substrate for your application and isolated the best encapsulation, now what?
You might think that a panel’s border or non-active area color could play a role. While these portions can become hotter if they were black vs. white, a minimal amount of this heat would be transferred laterally to the cells themselves. While there is a little effect, color is more an aesthetic choice.
A crucial part of designing a solution is understanding how to mitigate heat absorption. This is less important on the solar panels themselves but becomes vital when electronics are introduced.
For example, Soltronix Solar Panels feature custom-designed integrated charge controllers. These controllers contain complex circuitry. The general rule for electronics is colder is better. In order to mitigate these issues, a white charge controller housing was selected to reduce heat absorption.
Additionally, a white polymer paint was selected that allows for infrared emissivity, meaning that heat from the non-visible spectrum can radiate from the device easily and reduce the risk of heat build-up issues.
What are the temperature coefficients of amorphous silicon & crystalline silicon solar panels?
Before comparing amorphous and crystalline, it’s important to understand what temperature coefficient is.
At its most basic level, temperature coefficient, in this case, can be described as a solar technologies change in performance (whether positive or negative) due to a change in temperature (both increase and decrease).
Crystalline is greatly affected by heat and degrades 0.40% per degree C over 25C.
Amorphous is less affected by heat and degrades 0.16% per degree C over 25C.
What are the ideal operating temperatures of amorphous silicon & crystalline silicon solar panels?
PowerFilm amorphous silicon solar panels are guaranteed to perform in normal atmospheric conditions (50C surface temperature). The optimal operating temperature is between 25-50C.
Crystalline solar panels perform better at colder temperatures and don’t handle heat as well as amorphous.
What is the importance of testing your solution during the design/prototyping phase?
You’ve completed your design accounting for substrate, encapsulation and the effect color can have on performance. What’s next?
Now, it’s time to test your solution.
While it might seem obvious, it’s incredibly important to test your solar panel in the conditions it will be operating in. If for whatever reason this isn’t possible, calculations can be done, but real-world results will always be the best source of data as you try to prove your concept.
Not only is it important to test in the same environment, but it’s also important to test for a similar amount of time or to calculate accordingly.
For example, depending on the time of year a solar panels performance changes. An amorphous panel is going to have a different output initially due to the Staebler-Wronski Effect, but in the summer an annealing heat process caused by rising temperatures helps cancel out the Staebler-Wronski Effect. (Learn more about the Staebler-Wronski Effect)
In the winter the amorphous panel is technically more efficient but unable to heal the effects of Staebler-Wronski as quickly.
Conversely, crystalline solar panels perform worse in the summer and better in the winter.
If you planned to deploy a solution for years, spanning multiple different seasons, your testing needs to account for this.
If you only test during the summer, but the panel will be deployed in the colder seasons as well your data isn’t going to be nearly as valuable when thinking about the total scope of your solution.
Planning and designing for the effect temperature has on solar solutions takes time, analysis and being able to anticipate issues you might run into under real-world conditions.
If you think critically about the materials you select, the environments you test in and the timeframes in which you test, you will be off to a great start.
Are you designing or looking to develop a solution and need more information?
We would be happy to walk through some of these points with you or answer any other questions you might have to ensure that your design accounts for temperature variables.
We look forward to helping you design a solution that will perform no matter the temperature for years to come.