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.
