Simple primer on PVs and electricity

Ask the solarman

Let’s look at how a PV module makes electricity.

The simple version is this: A solar PV module is made up from several solar cells.

Sunlight strikes the module and excites electrons in the solar cells. This causes the electrons to move from one side of the solar cell to the other. When electrons move, you have electrical current.

A single PV cell consists of two very thin wafers generally made of pure silicon. These two wafers are doped with elements that produce a surplus of electrons in one layer (called the n-layer) and a deficit of electrons in the other layer (called the p-layer).

When exposed to the sunlight the cells are bombarded with photons, which liberate some of the electrons and causes them to flow. When electrons flow, you have electrical current.

A single silicon cell produces just under half a volt. A module consists of many individual cells wired in series and in parallel to produce the required voltage and amperage output.

Solar modules are sold by the watts they produce. You can buy modules rated from 10 watts to over 200 watts.

The face of the module is covered with a low iron, high tempered glass. The sides and back of the module are generally framed in aluminum. A reputable solar module will be warranted by the manufacture for 20 years. You can expect them to last far longer.

There are currently three types of commercial technologies for PV cells.

Single Crystal: This is the oldest and most expensive technique, but is still the most efficient sunlight conversion technology available. Loafs of pure single-crystal silicon are grown in an oven, then sliced into wafers, doped, and assembled. This is the same process used in manufacturing transistors and integrated circuits, and therefore is very well-developed, efficient, and clean.

Multicrystalline: In this technique, which is also called polycrystalline, loafs are grown or cast, then sliced off a large block of multicrystalline silicone. These types of solar cells are slightly less efficient than the single crystalline cells but cost less.

Amorphous: In this technology silicon material is vaporized and then deposited on glass or stainless steel. One manufacture of amorphous cells produces a module on a flexible matt. These types of solar cells are less efficient than the other two types mentioned above but are also less expensive. They are very durable and are often seen on sailboats. They can be purchased in many lengths and sizes.

A big benefit of amorphous cells installed in this part of the world is that their efficiency does not decrease in high temperatures. In fact they slightly increase. The efficiency of single and multicrystalline cells decreases when their temperatures exceed 80 degrees Fahrenheit. It is necessary for air to circulate above and below these modules.

The question now is which technology is best for you. A good solar designer can help you decide. Things that should be considered are: what space is available (with limited space the more efficient modules may be preferred); your budget (Can you afford the more expensive modules?); availability of the product; where will the modules be mounted (Is temperature going to be a factor?).

All these variables should be addressed before making your decision.

Note: If you have any questions about what has been discussed in this article, please email me at [email protected].