The Bare Cell

Whats the difference between 'Monocrystalline' and 'Polycrystalline' Solar Cells?

Monocrystalline cells are made by growing a single silicon crystalline structure into a large round (hence the chopped square look) ingot often 10m long and typcially 5 or 6 inches in diameter. These are then sliced very thinly to create the cells. These cells are the most efficient typically achieving 17.5% efficiency in converting the suns energy into electricity. You can often spot them by their almost black colour, and distinctive 'squares with the corners chopped off'

Polycrystalline cells are formed from growing multiple silicon crystals into a square silicon ingot (so no chopped corners) and often achieve 14% efficiency. This makes them cheaper to buy. You can spot them as they tend to be blue in colour with a flaked pattern that shimmers in the sun.

What voltage do solar cells put out?

All solar cells put out about 0.5V in good sun. Large mono cell showing 0.4v As the 'top' of the cells is negative, and the bottom is positive you can use a voltmeter or 'Digital Multi Meter' as I have here to verify the voltage by simply setting it to measure voltage and touching each side of the panel with the probes. Pop it in the sun or in this case under my desk lamp and voila! 0.431V Not bad.

what may seem odd, is that a much smaller polycrystalline cell also puts out the same voltage - about 0.5V in good sun. So here is a nice small solette doing its job nicely putting out 0.408v small poly cell showing 0.4v

Amazingly I can even tke this small poly cell and break it into smaller shards and as you can see each of the small shards still puts the same voltage - in this case 0.412v woohoo! So as you can see the size and shape really don't affect the voltage that solar cells put out - they all generate around 0.5v in good sun and as you can see around 0.4v under a desklamp. shard of poly cell still putting out 0.4v

So why is that? - Well basically thats the voltage that this technology generates. Most people don't question that a car battery is 12v. They aren't surprised to see small medium and large car batteries in the garage and most people would expect them to be 12v. Its a bit like that. The voltage of solar is about 0.5v -always- The larger cells just put out more current. A bit like that wopping car battery that claims it can put out 900 amps while the little one only says it can put out 200amps.

So if all cells put out 0.5v how do you get a higher voltage from a panel?

The clue is in the word Panel, rather than Cell. You link cells to make panels! - Just like batteries you can effectively connect them end to end to increase the voltage. a toy car might need 6v, so you pop 4 AA batteries into it, and as you can see by the springs they connect those four batteries end to end to make up the 6V the car meeds. Solar panels are just like that. They link individual cells to get the voltage they want. Need 1V? just link 2 cells. Need 50V? link 100 or them! So when you see one of those large solar panels on a roof with big black squares, just count the squares to see what the voltage is most will have 36 black mono cells - so they are putting out about 18v when they are working.


Twitter: @cottonpickers

Have an idea, or something to offer and want to work with me? -I'm listening ..