Sun Power

Making photovoltaics cost-effective



Two big reasons for this growth are the electric-utility deregulation of the late 1990s and recently enacted state-government incentives.
Deregulation has enabled homeowners in most states to connect their PV systems to the power grid and sell their excess production to a utility.
This sale is reflected as a credit on their electric bills, a process called net-metering. In addition, many states offer tax incentives and/or rebates to homeowners who install PV systems.

So why doesn't everyone have solar panels sprouting from their roofs? Because the sun doesn't shine equally in all areas of the country; because the technology isn't widely recognized yet; because financial support from state and federal governments is uneven; and because it's expensive -- in effect, a PV system can be like buying 20 years of electricity in one fell swoop.

Still, many of the major international oil and electronics companies are convinced that PV is a big potential market, and they're investing considerable resources toward its development.

So are major industrial countries such as Germany and Japan. For anyone who wants to live off-grid or who just likes the idea of making cleaner energy, photovoltaics are becoming a truly viable alternative.

There are three types of PV silicon cells

Single crystalline cells are most efficient at solar conversion (12% to 15% conversion to electricity) and carry the longest warranty (usually 25 years) for tested technology.

Multicrystallinecells are easier to manufacture, but also slightly less efficient (11% to 14%) due to a lower-grade silicon. The warranty is similar to that of single crystalline. Prices for both single- and multi-crystalline cells are around $5.50 per watt generated; generally, multicrystalline costs slightly less.

Amorphous (noncrystalline) cells are made from a thin film deposited on various (even flexible) substrates. These cells have a higher cost, lower efficiency (5.5% to 7.5%) and shorter warranty than the others. The thin-film technology does allow the cells to be used in building-integrated PV products, such as roof shingles made by Uni-Solar (www.unisolar.com).

Pre-engineered systems take out some of the guesswork.

Recently, manufacturers have begun marketing pre-engineered systems to make hardware selection easier.

With a pre-engineered system, you choose the system size you want, typically between eight and 32 100w or 120w modules, and whether you want battery backup.

The packager then adds the appropriate mounting hardware and inverter. Buying components as a kit or package can save money (5% or more), plus many companies offer technical support.