Understanding module anatomy and the semiconductor process.
By: Adam Baker
I wanted to do a brief review of how a solar module works. I’m not sure if you’ve ever sat down and analyzed how a module is put together, and how the semiconductor’s interaction with light conducts electricity, but I can talk you through it pretty quick.
If you don’t want to read about it, check out the video instead:
The solar module anatomy
A standard utility-scale solar module is 72 cell module. It’s 6 cells wide by 12 cells long. Each cell makes about 2 volts of potential, and the amount of current will vary based on the irradiance (light) that interacts with it.
Each of these cells is wired in series in a loop that goes up one row and back up the next row in a solar module. This creates a circuit.
There are 3 circuits in a normal module, and each circuit has 24 cells. As I said before, each cell makes 2 volts, so, about 48 volts go across a module. (This is why most modules come in at just under 50 volts.)
How the semiconductor works
How the semiconductor works is an absolutely fascinating process.
If you imagine the solar cell’s profile, the semiconductor is doped such that it has N-Type material on top and P-Type material on the bottom. When a photon of light comes in to interact with the solar module, if it has the right amount of energy, an electron from the N-Type material will get kicked loose, and move over to the P-type material.
So now there’s an electron on the bottom, and the place where the electron used to be (called a hole) on top. This is an unsustainable condition, because the electron wants to get back to where it belongs.
Because N-Type material is on the top and P-Type material is on the bottom, and the electron is negatively charged, it can’t easily move from the bottom of the semiconductor back up to the top. The current can flow in one direction through the cell, but can’t easily move the other way. (This is called a transistor junction.)
What we do in the real world, is attach a piece of wire to the bottom, and piece of wire to the top of the cell. These are connected through a resister, and end up making a circuit where there is a negative contact and positive contact. Again, this makes about 2 volts.
How a photon ultimately produces energy
The whole process goes like this:
- The photon kicks an electron loose
- Now the electron is on the bottom
- It flows through the circuit into the resister (commonly an inverter, but can be any type of electrical load)
- Does a little work inside the resister
- Flows through the wire attached to the top of the cell and through the N-Type material
- Gets back home.
This one little photon wanting to make its way back around the electrical circuit is only doing a little bit of work, but if it happens often enough in an electrical circuit, you can generate a lot of power.
In a normal module, how frequently does this process happen?
1,000,000,000,000,000,000,000 (that’s 1 sextillion) times per second, per cell, over the 72 cells in the module!
That’s a whole lot of electrons interacting with little pieces of silicon over a utility-scale solar farm.
Just thought you might find that interesting.
Adam Baker is Senior Sales Executive at Affinity Energy with responsibility for providing subject matter expertise in utility-scale solar plant controls, instrumentation, and data acquisition. With 23 years of experience in automation and control, Adam’s previous companies include Rockwell Automation (Allen-Bradley), First Solar, DEPCOM Power, and GE Fanuc Automation.
Adam was instrumental in the development and deployment of three of the largest PV solar power plants in the United States, including 550 MW Topaz Solar in California, 290 MW Agua Caliente Solar in Arizona, and 550 MW Desert Sunlight in the Mojave Desert.
After a 6-year stint in controls design and architecture for the PV solar market, Adam joined Affinity Energy in 2016 and returned to sales leadership, where he has spent most of his career. Adam has a B.S. in Electrical Engineering from the University of Massachusetts, and has been active in environmental and good food movements for several years.