More sunlight hits the Earth in one day than every person on Earth could use in 27 years!
Today’s lesson is on Photovoltaic cell. Or for us normal people, solar cells.
I’m sure you’ve all seen them. Or at least a picture of them. Like these…
They provide electricity at no cost. No fuel required. There are zero emissions, zero pollution, zero noise. So how do they work?
First, you already know electricity is the movement of electrons – those negatively charged particles of an atom. When they move, we get zapped.
Second, silicon is a metalloid which means it’s sort of a metal. So it can sort of conduct electricity.
A solar panel is basically a silicon sandwich- negative and positive silicon (like peanut butter and jelly). Where they meet is where the action is. The trading of electrons could be described as some peanut butter getting in the jelly and some jelly getting in the peanut butter.
There’s a whole lot of science involved and I’m trying not to get too technical. But, to simplify it as much as I can; the negatively charged electrons join with the positively electrons in the middle of the sandwich. Sunlight then causes them split up again. When the panel is connected to a circuit the divided electrons flow through the circuit and meet up again in the “sandwich” and start the process all over.
When many panels are joined, you get an array, like the one shown in the first picture. These arrays can be used to power everything electrical in houses. If this house creates more electricity than it uses, that electricity is sent back to the power company. In many areas, power companies are required by law to pay the user for any electricity that is returned to them.
Most solar panels are only 11-15% efficient. This means that only 11-15% of the sunlight that hits the panel is converted into electricity. While this may sound low, it’s more than efficient for a few rooftop panels to create enough electricity for the house to be self sufficient.
Now let me entertain you. The reason for this science lesson is because Crash already got one, sort of. I haven’t really explained this all to him because I, myself, just learned it as I was typing this. Hence, I’m no expert.
Anyway, Crash received a solar power kit for Christmas. This thing can be built into 14 different robots and they all move of their own accord under the power of direct sunlight.
The first thing he wanted built was a car. But first we had to assemble the motor box (that’s the box under the solar panel “head”). It wasn’t easy because those parts were small. After we completed the motor we were supposed to test it. Unfortunately, it snowed for five days, so it sat for a while. We played in the snow in the meantime.
Anyway, when we had a sunny morning we opened the front door and direct sunlight beamed in. We grabbed the car and set it up and IT WENT BACKWARDS!
Crash and Bang laughed at that. I did too. I thought I put gears or the motor or something in backwards. Confused, I switched the positive and negative wires. Guess what? That made it run forwards. I seriously had no idea switching the wires would cause it run in the opposite direction. But now that I know how solar panels work, it makes sense. Those electrons are going to flow, unlike a battery, in the same direction (hence it’s called direct current). Switching the wires simply changes the direction of the flow.
Anyway, Crash and Bang played with it until the sun didn’t shine through the door anymore. And Bang was getting a kick out of cast a shadow on the panel to make the car stop.
We’re certainly not setting any land speed records here, but we are learning!