Solar Cells: Wavelength and Magnification
Solar panels. Your environmentalist friend has them on top of her house, the preppy school in your city has them lining their roofs, and I’m sure when you were younger you wanted a build-your-own solar panel toy. We’ve all seen em. We all know they help the environment and lower your electricity bills. But do we all know how inefficient solar panels really are?
Solar panels actually have a maximum efficiency rate of 33.7%. That really sucks. And honestly, current methods to solve this inefficiency are barely changing that percentage but are still drastically changing the price on these advancements.
What’s a cheap way to increase efficiency? Well, what adds the least things onto a solar cell, and what can be done to already existing solar panels? Here is where I got the idea of changing wavelengths and concentration.
Experiment Basics
Lab Ideas
First, changing wavelength. The easiest way to do this is to filter out undesired wavelengths. This can be done by using colored gels to filter out certain colors (or wavelengths) of light, and using only useful wavelengths could improve efficiency.
Second, concentrating light. I got this idea as sort of a byproduct of watching my sister burn ants while I was working on that first part. If I could use a magnifying glass to change how much light hits what part of the solar panels, that could potentially change how much energy a solar panel can convert.
Tools You Should Know
Here are the materials I used throughout the lab and what they do, just so you know what the heck I’m doing here.
- Digital Multimeter — I turned it on to a setting that measures the direct current voltage(DCV) in volts to the hundredths place (block thing at the forefront of the picture)
- Gel color sheets — thin sheets of colored PVC plastic film to filter out light-colored anything but the color of the gel (the colorful rectangles in the back of the picture)
- Magnifying glass — you know this one (not pictured)
- mini solar panels — just a super small solar panel (black rectangle), the wires on the end were wrapped around the wires of the digital multimeter so I could measure the voltage
Wavelengths
Solar panels mostly absorb visible light which is between 400 and 700 nanometers. Anything longer (infrared) is too big and too weak to knock out an electron, while anything shorter (ultraviolet) is too small and too strong to actually be absorbed.
Hypothesizing Based on Light Facts
For clarity, light facts are simply a light’s frequency, wavelength, and photon energy. (Yes I definitely made that term up.)
Here is a close up of the visible light spectrum. On the left, you have the fastest, most energetic waves of light in the color violet (think like a puppy dog). I hypothesized that these waves would not be as efficient as other colors because it is moving too fast and not every photon will be able to knock out an electron. On the right, you have the slower and less powerful red waves of light (like an old fish). I hypothesized these lights would not knock out enough electrons and therefore could not be as efficient as other wavelengths.
After reasoning these sides out, did I even have a hypothesis? Actually, yes! I believed that coming to the middle and refining the light to be only green (middle of the road frequency, wavelength, and energy) would be the right option. It would make sure that there are enough photons approaching the cell while also making sure it is not too crowded. Basically, every photon would be able to make it to the cell and be able to knock an electron out of place.
Process and Results
Here’s the procedure: I hooked a solar panel up to a cell, measured the voltage of the cell by itself, put a gel on and measured its voltage, and repeated with every color. And it was that simple. At the end, there will be a video linked that shows me actually doing it, if you need a stronger visualization.
Note: These measurements were taken at about 11:00 pm in Nevada, so it was somewhat sunny and consistently sunny. These measurements are the modes of the data gathered from the video.
As you can tell, the solar panel by itself worked much better than its gelled counterparts. I believe this can be accounted for by the fact that because I was limiting how much light could reach the solar panel, I was not giving enough electrons enough attempts to get in.
For example, the pink gel lets only pink light touch the cell, not any other color. And because it was such a small amount of light hitting the cell, there were simply not enough electrons moving to create the voltage that a solar cell with all the light hitting it could get moving.
Concentration and Magnification
So if changing small things within the solar panel doesn’t work, why can’t we add external factors? How about putting as much light onto the solar panel to give it as many chances to convert photons as possible…
Process and Procedure
Basically, I took the magnifying glass and made it so that the solar panel had either a really small and concentrated dot, a big but concentrated area, and then just the magnifying glass covering the solar panel (top to bottom).
Applications?
Although magnifying glasses do not have a good track record of helping solar cell efficiency, could there be a way to use them in favor of solar cells? Maybe.
I will be looking into ways to make the protective glass on top of the solar panel a magnifying glass itself, and hopefully a cooling method alongside it so the solar panel does not overheat. Be on the lookout for another article!
IV. More About the Process
Want to see more about the processes I explained? Or do you just need a stronger visual? Here is a short clip with the details needed to know exactly how the methods I used worked in real life. (And some extra cool details on the solar cells themselves!)
V. What’s Next?
Even though this lab was simple in concept, and part of it was completely off the top of my head, there are some serious future applications. Although (unfortunately) we won’t be seeing any neon green or purple solar panels in the future, maybe we will be seeing some warped ones…
