The first thing to know is that solar cells directly convert the sun's energy into electricity. That may sound easy enough, but what makes solar cells work?
There are a few words we need to know to get started.
- Solar cells are photovolatic cells.
- Modules are a group of photovolaic cells.
Taking apart the word photovoltaic, we see photo meaning light, and voltaic meaning electricity. So, as we now know photovoltaic cells transform the sun's "light" into electricity.
It is a little more complicated than that, but easy enough to understand. Silicon is a semiconductor that is the key component in most photovoltaic cells. Basically, what happens when sunlight hits the solar cell is that the silicon, the semiconductor, absorbs some of the light's rays. When the light hits the silicon it knocks loose some of its electrons. At that point, some of the electrons are free, not longer attached to the atom and are free to move or "flow."
Metal contacts are placed on the top and the bottom of the PV (photovoltaic) cells to draw current for our use. What is important is that the current created and the voltage (the electric fields that are built into the solar cell) tell us how much power we have generated. That power is measured in Watts.
Silicon atom in solar cell
Without getting into too much chemistry, we can see from the diagram to the left that the silicon atom has three shells (the three ellipses around the nucleus). As silicon atoms come close to one another they connect, latching onto the electrons in the outer shell of other atoms to form a silicon crystal. It is the crystalline structure formed by joining the atoms together that is important for PV cells. The crystalline structure is what makes solar cells work.
Now, here's the odd part. These silicon structures have impurities. Ordinarily, we would think this to be a problem, but in this case it is the impurities that make the solar cells work. These impurities are other atoms that get mixed in with the silicon atoms. Without these other atoms the PV cells would not work. We will not go into the specifics of the chemistry but the impurities which are phosporous atoms are necessary.
When energy ---heat from the sun --- is added to these atoms, electrons are set free. These electrons are called free carriers. The free carriers are what carry the electrical current.
The phosporous doped silicon free carriers have a negative charge. There is another set of silicon atoms doped with boron which carries a positive charge. This should start to sound vaguely familiar. We now have a negative and a positive. When the positive charge and the negative charge come together we have an electrical field. The electrical field is what makes solar cells work.
At the point where the negative electrons and the positive electrons meet, the positive side electrons flow to the negative side electrons. A diode is created. It is important to note that only the positive electrons flow to the negative electrons.
With an electric field created and the positive electrons flowing to the negative electrons, when the sunlight (photons) hit the electric field energy is freed in the form of electron pairs. The electron flow is current, and the electric field supplies the voltage. Put together, the two form power --- in this case solar power.
There are a couple more steps to complete the solar cell. One is to apply a coating on the solar cell that reduces reflection. All the photons (sunlight) that is reflected cannot be used to make power. The other step is cover the solar cell with a glass plate to protect it from the elements.
This is a very basic explanation, but it should be sufficient to present a general idea of how a solar cell works, straight from the sun to solar energy.