A Solar Panel Primer – Part 2

Text of the 7 minute podcast

Welcome to the 7minutesolar podcast.

Hi. I’m Jeff Butler with the second episode in our solar panel primer series. In our first we found out how solar cells turn light into electricity, why they’re black and blue and criss crossed all over, and now we’re going to find out what needs to be done to get that solar power out of the panel and into your house…and beyond. But we’ve only got 7 minutes, so let’s get started.

First an episode 1 recap: When sunlight hits the silicon in a solar cell, some of the energy in the light knocks electrons off some of the atoms, like a cue ball at the begnning of a game of pool. The solar cell gets those electrons organized – sort of marching from one atom to another, and they march along the solar cell through printed wires called bus bars that connect 60 or 70 cells to make up a solar panel. Five or six panels are wired together to make a string of panels – remember that – then those strings are connected to make up the big flat solar array that goes on your roof.

The more sun hitting a cell, the more electrons joining the marching. The parade is called an electric current, and this current moves from the solar cells to the end of the panel towards your house in one direction…a direct current. Commonly called DC

Now about a hundred and thirty years ago Thomas Edison and Nikola Tesla – yes, Tesla – had a big debate about the best way to distribute electricity. Tesla won and since then almost all of the things that use electricity – from lightbulbs to subway trains – have been built using his idea, where the flow doesn’t move in just one direction, it alternates, going back and forth 50 or 60 times a second. It’s called Alternating Current. AC

Yep, AC/DC

Your solar panel puts out DC, but everything works on AC, so you need something to change that direct current to alternating current. That thing is a called a power inverter, and there are two kinds of inverters for home solar systems. Well, two and a half.

The old school and most common one is called a string inverter, because it inverts the electricity from those strings of 5 or 6 solar panels that have been wired together.

String inverters work great if the conditions are great, when the panels get lots of direct sunlight and there aren’t any oak trees or other things casting shade through the day …but there is a drawback.

When an oak tree or something else does throw shade on one of the panels it lowers the power from the whole string. It’s not exactly like this but if you think of that parade idea, even if only a few slow marchers join in a parade, they slow down the entire thing.

So to avoid that, another kind of inverter was developed – a microinverter – micro meaning small. They attach to each individual solar panel, so if panel A is under the oak tree it doesn’t effect the amount of power being inverted from panel B.

The two and a half solution is something in between called an optimizer. It attaches to each panel in the string, but it doesn’t invert the current. It does something called conditioning the DC current from each panel before sending it to a central inverter.

Microinverters are the most efficient – and expensive…string inverters are the least expensive – and efficient – and optimizers are somewhere in between.

But however it gets done, now that the power is inverted to AC you can connect it to the electrical panel in your house.

One problem. Night time. It’s dark, you want to turn on a light. But… no sun, no electrons getting knocked off atoms…no electricity.

The electrons WERE getting knocked off when the sun was shining, but of course you didn’t need your lights on then.

What to do. Well, Before we go further, there’s something to understand about electricity and the marching. Electricity is not PUSHED anywhere, it is PULLED somewhere. Think of the lightbulb or refrigerator or subway train needing some marching electrons and saying – ‘Hey, march over here, we could use a hand.’

And if electrons don’t get invited anywhere, they just stand around. In the solar cell, when the sun is shining but electricity isn’t needed, they still get knocked off the atoms, but then rejoin those same atoms and twiddle their atomic thumbs with nowhere to go.

Well, that’s a waste of sunlght – and your investment, so what you could do is have a battery and have them march in there. A battery is kind of like a holding pen where special chemicals allow the electrons to march in and keep building up – we call that charging the battery.

And at night, when you turn on a light, the call goes out: ‘help needed at lightbulb A, marchers needed at lightbulb A’. The door of the pen opens…and off they go.

You might also be able to get those electrons marching into this mysterious thing you may have heard of called THE GRID. People say they want to be off THE GRID. Or they want to sell power to THE GRID.

The grid is nothing more than the wires that connect everything electrical. And I mean everything. Your house, your neighbour’s house, your street, the streetlights, offices, factories – everything that has a wire connected to it is connected to everything else with a wire. And all of those wires, that whole grid, is filled with electrons marching.

We’ve been taught to think over the years that the starting point for electricity is a large power station and that the electricity is made there and then goes to all these places that need it.

But really, the electricity can start anywhere. And go anywhere. The thing that needs electricity just uses the electrons closest to it. It doesn’t care where they started marching from.

All those big power stations do is exactly what your little solar cell does – get electrons marching. Now, they get a lot more electrons marching, but that’s all do – the electrons march out of the power station and join the big parade in the grid to replace the marchers being used in lightbulbs and factories or whatever is saying ‘Hey, give a guy a hand!’.

For a long time, the replacements have been supplied by those big stations because that’s all we had but there’s no reason they can’t come from your solar panels. Or your battery.

Let’s say the sun is shining and you’re not home, your solar panel can put electrons into your battery. If that gets full, you can allow the new marchers to get called into the grid to replace marching electrons there. Some utilities will pay you for those workers – that’s selling back to the grid.

If it’s night and you turn on a bunch of stuff and your battery runs out of marchers, then YOU can send out the message – Hey, a little help over here! and something you’re connected to out there on THE GRID, maybe one of those big power stations, maybe a really big battery somewhere, maybe someone else’s small battery, sends over some help. Because when it comes to electricity, we’re all connected to each other, and we’re all in this together.

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.

Keep on shining!

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