Text of the 7 minute podcast
Welcome to the 7minutesolar podcast.
Hi, I’m Jeff Butler. and this is part 1 of our Solar Panel Primers, in which we keep solar power simple and take it in 7 minute chunks. Today you’ll learn about how solar cells and panels turn sunlight into electricity, the two most popular kinds of panels that perform that electromagnetic trick, how they’re made and why that effects the look, efficiency and price of different panels. But we’ve only got 7minutes, so let’s get started.
75 words MAXIMUM
A solar panel? It’s just a collection of solar cells, those are the things that actually turn light energy into electrical energy.
But one solar cell doesn’t generate much power, you need a bunch of them to do anything useful and since it wouldn’t be practical to put them on a building individually we wire the cells together to collect all the electricity – put a back on it all to keep it rigid, add a front for protection from the weather and TADA! a solar panel. Some people in some places call a solar panel a solar module. But whatever you call it you still can’t do much with one solar panel, so we wire a bunch of THEM together and put them on a roof or the ground and THAT is called a solar array. Cells make solar panels, pnaels make solar arrays.
Let’s get back to the cells because that is where the story begins – well, it actually begins with the sun…
Light is made up of energy packets called photons and when sunshine hits the material in a solar cell those packets transfer their energy by knocking electrons off some of the material’s atoms – like a cue ball hitting other balls in the beginning of a game of pool. The solar cell directs those moving electrons toward other atoms in the material that are looking for electrons, and it gets them to kind of march from atom to atom in an organized way. And when electrons march from atom to atom in an organized way, we call that electricity.
The material that is used in the solar cell is important, because it needs to be something with atoms that can have electrons knocked off easily, but not TOO easily. That kind of material is called a semi-conductor, and it turns out that one of the BEST semi conductors on the planet is actually the second most common element in the earth’s crust and can easily be found…at the beach.
Yep, sand is largely made up of silicon, which in addition to being a great semi conductor, is almost literally dirt cheap and partly why it is used in over 90% of today’s solar cells and panels.
And silicon is one of the reasons for that distinctive solar panel look – those black squares with white dots in between and thin white lines crisscrossing the whole thing. Each of those squares is a solar cell – and here’s why the panels look that way when you put the cells together.
Obviously you can’t use just beach sand for a solar cell, the silicon needs to be purified, so it’s melted in a furnace and then distilled, kind of like making whiskey.
Then it can go to make two different kinds of solar cells. Monocrystalline – mono meaning one – and polycrystalline – poly meaning many crystals.
For mono cells the silicon is melted again, and a tiny seed crystal on a rod is dipped in to the molten silicon, which looks like the stuff the cyborg is made out of in Terminator II.
The rod is slowly turned as it pulled out and the seed crystal literally grows bigger and bigger, making a cylinder – an ingot – about 6 feet – two meters – long and about 6 inches – 15 centimers around. Solid, pure silicon – and all one single crystal.
(Incidentally this is almost exactly the same way computer chips are made out of silicon and why a certain valley in California is named after it.)
You following this, Arnold?
So then the sides are sawn off the cylinder, like taking the crusts off a loaf of bread, and it is sliced into thin wafers only about 5 to 10 times as thick as a human hair.
Then molten silver or another high conductor metal – meaning it has electrons that CAN be easily knocked off – is printed on top of the cells – and those are the white criss crossing lines you see that are called bus bars — they’re the wiring for the electricity to flow from one cell to the next when they are put together on a panel.
The white dots you see are actually diamond shaped up close – that’s where the sides were sawn off the cylinder, and with the corners being rounded, it gives each wafer an eight-sided octagon shape. And the panel is shiny black because all of those wafers are cut from that one perfect flawless crystal.
Now, polycrystalline cells and panels are a bit different. Silicon is melted, then poured into a big square-sided container and cooled down. As it cools, MANY crystals – poly – start to form at the bottom and spread throughout the silicon – kind of like frost spreading on a cold window. And because the ingot started out square, you don’t get those diamonds between the cells when it’s sawn and sliced.
Also poly cells and panels are blue instead of black. The tiny crystals reflect some of the light instead of absorbing all of it, and if you look closely you’ll be able to see little white flecks in them that are the edges of the crystals.
Mono is black, poly is blue. Which solar panel is better for you?
Well, not surprisingly, the mono cells are more efficient at absorbing light and turning it into electricity. About 10-15% more efficient. But also not surprisingly, they’re more expensive, growing an ingot is not a cheap process. Monos generate more electricity per panel. But polys are cheaper per panel. If you have a small roof you might want on, if you have a larger one… a lot of it comes down to how much money and roof area you have.
There are other kinds of solar cells available or being developed, one is called thin-film, which is flexible and can be used on curved surfaces. Even windows.
But as I said, we only have 7 minutes and naming the chemicals they’re made of, like copper indium gallium selenide or gallium arsenide germanium might take up most of that time. Also, many of them are not yet economically feasible for basic home use. But we’ll cover them in another podcast.
For now though, lets review how it all works. Sunlight hits the atoms in the solar cell, knocks off some electrons, the solar cells get them marching and the bus bars connect the solar cells and collect the electricity, a back is put on it to keep it all together add a front for weather protection and now you’re all ready to start powering things in your home and…
Welllll, actually not quite yet. And THAT is the topic of our NEXT 7minutesolar podcast: Part 2 – AC/DC, power inverters, batteries and the big wide grid.
I hope you’ve found this 7minutesolar podcast informative, and maybe even entertaining. You can find out more about solar power and other green energy, electric cars – and more – including all the latest news and updates, by visiting our website, 7minutesolar.com. Thanks for listening. Until next time, I’m Jeff Butler for 7minutesolar.
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