context: so If I google how efficient are solar panels and it says the average is roughly 15 to 20% with the max is can get up to is 45%. my question is how is what does that mean?
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Not all light that hits a solar panel is used to generate electricity. The Sun emits light on a continuous spectrum, from ultraviolet (UV) to infrared (IR), however the solar panel can only convert a portion of that spectrum into electricity. To be specific, it can only use light with a higher energy than a specific cutoff point which depends on the material the panel is made out of. Light with lower energy is basically ignored, and light with much higher energy is partly converted to electricity and partly lost as heat (so again, not a perfect conversion). You measure the total energy of the sunlight hitting the solar panel (let’s call it A) and the energy output of the panel (let’s call it B), and efficiency is defined as (B/A)%. So a panel which converts a fifth of the energy it receives would have an efficiency of 20%. You can expand the usable sunlight range by basically sandwiching together multiple solar cells which work at different wavelengths of light, these are called “tandem solar cells” and can achieve a higher efficiency, but they get much more expensive and the cost is rarely justified. Instead, you focus on solar panels which perform well in the visible region where most of the total energy is.
The sun hits the surface of the Earth with a certain amount of energy, a common daytime reference value is 1000 Watts/m^2. But this energy is spread across the spectrum from radiowaves to microwaves to IR to visible light to UV.
Solar panels can only collect certain wavelengths of light, so if it only grabs the 20% of the spectrum around green light then it’ll produce 200W of power from the 1000 watts of light that fell on it giving you 20% efficiency.
If you make a fancy cell with 3 junctions that can grab a wider swath of light then you can get 30-40% efficiency giving you 300-400W of power from your 1 meter^2 solar panel
It means that 20% of the incoming energy (in this case the light from the sun) is converted into electrical energy by the solar panel. The closer you get to 100% the better. (100% would mean all the energy is being converted)
It refers to how well it works, meaning how it uses the energy that comes in. So the more efficient the better it is at taking the energy coming in and converting it into storable electricity.
There is a certain amount power in terms of light energy falling on the solar panel. Number of photons per square metre per second times photon energy times area of panel. You can measure the electrical power energy output, current times voltage times time and ratio the two.
Solar panels create quite a bit of energy, the storage and usage aspect determines their efficiency. If a solar panel is 50% efficienct that means 1 watt of energy is being used or stored for every 2 watts it’s creating. Say if you work a job during the day, when the sun is the brightest, your solar panels will be creating quite a bit of energy while you’re not at home, you may max out your storage in the first three hours so your solar panels just continue creating energy regardless of your usage, but it all effectively goes no where reducing your total efficiency.
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