Types Of PV systems

Those systems that are designed to generate electricity are called photovoltaic systems or simply PV systems. There are several types of PV systems to choose from, though most of them are currently made of purified silicon, similar to that used to make computer chips. However, new technologies are coming on line that are sure to make the choice a lot harder in the coming years.

Generally there are four kinds of silicon-based systems available, differing in the silicon manufacture process. These are:

• Single crystal
• Multi-crystal
• Ribbon
• Amorphous

Single and multi-crystal silicon both use purified wafers of silicon that are attached to a substrate. A slight charge differential exists between layers of the cells, and as photons excite the silicon from one layer to another, a “hole” is created in the positive layer. This causes a slow migration of excited silicon to “flow” from one layer to the other.

These PV cells are recognizable as the familiar blue or black glassy surface with thin silver lines that many people are familiar with from the 1970s and 80s. The only difference is in the purity of the silicon used. While the single (or more perfect) crystal design is used with very high quality silicon, multi-crystal PV cells are made with a less refined type of silicon. While this results in lower efficiencies, the cost is kept down.

The next technology to come online is ribbon silicon. Here, the only difference between the single and multi-crystal designs is the method in which the silicon is produced. Instead of slicing off wafers of silicon from a purified ingot, the material is grown as a single “ribbon” of material that requires no slicing or dicing.

These are often used in space technologies and are the basis for the newer holographic silicon systems that reflect wasted solar energy (photons) back into the cell for greater efficiency. As such, they often have a rainbow-coloured appearance.

Lastly, the amorphous or so-called “thin film” silicon deposits the material in such thin layers that photons not captured by one layer may pass through and be caught one of what can be many layers below. This material does not have a crystalline struture as the other types do, but can be “tuned” to most readily collect at different wavelengths (or colours) of light, though not infra-red just yet.

Amorphous PV arrays have the potential to be far more efficient than the older technologies, but so far, they have proven to be about half as efficient, though less expensive to produce. Such systems also have the disadvantage of loosing about 20% of their efficiency after being exposed to sunlight for a few weeks.

No matter which you choose, it will be quite an investment, with current technology running several thousands of dollars, though even high cost investments have been shown to pay off in less than a decade for most.