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One of the greatest advantages of a grid-tied system is that you can avoid buying a large battery bank. Batteries in a grid-tied system only provide backup power during utility outages. This may seem like a good idea in theory, but the batteries make the system unnecessarily complex, less efficient and substantially more expensive. Batteries also contain hazardous heavy metals and last only for a limited time (they will need replacement about every five years). What’s more, battery-based grid-tied systems take up more space and require more equipment.

A much better tool exists for backup power — a gas or diesel generator. If you expect long power outages in your area, you would want a generator just to avoid having to maintain a large battery bank. And once you have a generator, why have batteries at all?

Photovoltaic Options

Photovoltaic (PV) modules (the panels that collect the sun’s energy) come in two main types: crystalline and amorphous (also called “thin-film”). Both cost about the same for quality modules ($8 to $12 per installed watt), but they differ in the way they look and work.

Crystalline modules come in two types: mono and poly. Monocrystalline PV has blue or gray-black cells that don’t completely cover the module face. A white backing usually shows at each cell’s rounded corner, producing a visible pattern that some homeowners find unappealing. Polycrystalline cells are cut into rectangles that completely cover the white background, providing a more uniform appearance. They usually are a sparkly blue color. Both mono and polycrystalline modules are covered with tempered glass in an aluminum frame. Mono and polycrystalline PV perform similarly — your choice likely will be decided on availability, price and personal aesthetics.

Amorphous PV has not been on the market as long as crystalline PV, and the first generation or two did not prove to be durable. Even now, most amorphous modules only carry a five-year warranty, although United Solar Systems’ UniSolar amorphous PV carries at least a 20-year warranty and has maintained good performance after decades of operation. UniSolar’s standing-seam thin-film laminates can be bonded directly onto a metal roof, creating a durable, uniformly dark surface that also is pleasing to the eye. Usually, the thin-film PV can be connected invisibly to its wiring under the roof’s ridge cap.

Amorphous PV requires more space per generated watt than crystalline PV, but it has two significant advantages: High temperatures and partial shading do not affect amorphous PV as much as crystalline. For crystalline PV, electricity production is more affected by shadows; when just one cell is shaded, it blocks the flow of all electricity in that series. UniSolar amorphous PV transfers electricity using a weblike series of connections that bypasses shaded areas.

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