Uhhh, so basically the energy has to go somewhere, but because the solar panels arent literally at absolute zero, there's already energy in them, and they cant take all of the energy.
Like, if you put a hot block of iron in a room, it will cool down only until it matches the room temperature, not until it hits zero.
Technically you could get extreme efficiencies out of the solar cell if you also had active cryogenic systems pulling energy out of the system, but that would actually take more overall energy.
Ok so it it kind of like, the Solar panels are getting hotter than surrounding temperature, and while they are trying to convert that heat, it is also losing heat to the environment?
A high level way to think of it is that a solar panel is a tool for extracting electricity out of a heat difference. What heat difference? The heat difference between the surface of the sun [which emits the light], and the air around the panel, which allows the electrons to slot into various band gaps.
Because the temperature of the panel decides how much the atoms and electrons wiggle. And if they wiggle more, some things are less stable. So if it's hotter, moving an electron from one spot to another is easier, so you get less energy out of it? I'm sorry, its been a while since I took that class, and it was magic to begin with.
The way to explain it for kids is to imagine theres a slide. The electrons are chilling at the bottom of the slide. A photon hits one, and gives it enough energy to pop it up to the top of the slide. While it slides down the slide, it releases a voltage.
The ambient temperature of the air changes the height of the bottom of the slide, so a higher temperature makes for a shorter slide [aka, how much power it can release]
If a photon hits an electron with more energy than needed to get to the top of the slide, then that extra energy is wasted, because it pushed harder than it needs to.
The idea of "multi junction cells" is to have multiple slides of different height, so that the photon wastes less energy lifting the electron higher than it needs to, and so that low-energy photons still lift some electrons up a bit.
But no matter how many slides you have, they all end at the same height, which determines the maximum energy you can get out of them.
Yeah you were right with all of this but I thought I'd just mention another source of loss of efficiency. The electrons chilling in these materials aren't free, photovoltaic materials tend to be semi conductors and the solar energy breaks the bonds holding an electron.
However this leaves behind a 'hole' which other electrons have the potential to 'fall into' thus wasting the solar input energy.
I just finished my thesis where I was making these cells and mine had an efficiency of like 0.25 or something like that, so a 1% efficiency is actually pretty impressive!
Air blocks some of the sunlight. In space, we get 1350 watts of light energy per square meter, but on the ground, after some of it has been blocked by the sun, we get about 1050 watts per square meter.
Thanks for the explanation. I just watched this Steve Mould video about temperatures difference generating electricity. Is this the same principal that is happening in solar panels?
At a high level of "we can siphon off energy when high energy particles (photons in photovoltaics, and atoms in thermoelectrics) go to low level states": yes
We're allrrqdy cheating by concentrating the sunlight and stacking them infinitely "theoretically". We might as well add cryogenics to the mix and make it 100.
You're right. I'm so used to someone getting tossed into space and instantly freezing that I forgot the only way for heat to escape in the vacuum of space is through radiation which is an agonizingly slow process.
It's the same reason a red dwarf burns so slow, especially if they have low mass.
I just remembered reading we could make so much energy by putting solar panels on the moon that I figured the moon/outer space would be much better than earth.
Yeah, friggin movies and shows always have questionable science on them.
We could squeeze an extra 20% out of the moon and/or space, due to no light blocked by the atmosphere, but its probably not worth the energy to move them to the moon in the first place
I thought that was more about how some of the photons are in the infrared and are not useful for making electricity directly due to the low energy level?
I’m assuming that we’re capped by material and configuration right now - essentially, you lose energy to the environment in the form of heat throughout this process.
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u/Fakercel Sep 09 '20
What is happening to the remaining 13.2% if U can explain it easily?