Which way should the array face? The rule of thumb is always face the array true South (in the Northern Hemisphere). Oh, there may be exceptions, such as your immediate neighbor to the east is a thousand foot high mountain, and it keeps the sun away from your place until noon every day. Sure, there are exceptions—but not very many!
Keep trees away, or anything that can possibly shade the system—or grow to shade—during its lifetime. Shade is cool for people, but not for PV!
Another rule of thumb is to elevate the array so it is at an angle of around the latitude of the site. Normally placing the modules on a standard pitched roof is fine—and facing south. If one is tweaking things to get the most energy out of a system, PV purists would have the array on a tracker that constantly points the array at the sun—from sun up to sun set, and changes its elevation angle, too, as the sun changes its seasonal position in the sky. Not too practical for the normal homeowner, however. Placing the array flat on a flat roof is OK, but means your system won’t generate electricity at its best.
A photovoltaic array can either be designed as an integral roofing members (such as the Unisolar amorphous architectural modules) or simply attached to the finished roof, using standoffs of 1 or 2 inches to provide air circulation that the crystalline silicon modules need. Include the array as part of a south-facing roof, if you can, so it will look like it’s part of the structure, esthetically pleasing and doesn’t look like a sore-thumb (oops, another unit of measure for that thumb) afterthought.
Some companies are coming out with PV “shingles” that look and act exactly like roofing shingles—except you can also get electricity from them. Others are aiming at commercial buildings where modules can be integrated with and look just like vertical glass exteriors.
Another company is expanding on the shingle concept by attaching PV modules to large (3 feet x 4 feet) roofing tiles that can be used as the roofing structure on flat, industrial buildings. Might be applied to a homeowner’s large, flat roofed garage, for instance.
But for the single family, non-technical homeowner, who is interested in generating green electrons—but not going overboard in the process, either technically or economically, a 1kW grid intertie system will do the trick. Simple, relatively inexpensive and pollution free generation.
What of the homeowner who wants to become a little more sophisticated? What if the concern is to make certain power—at least in an emergency mode—is available if the power company’s lines are knocked out during a lightning (or wind) storm? The simple grid intertie system will go down, too. The power companies, wisely, have said that “we can’t have independent distributed power producers—meaning your rooftop PV array—pumping power into our lines when our linemen are out there trying to fix damage from lightning—or any other cause.”
Should your homeowner want to be “the only beacon in the darkness” when the power goes out, this can be done, but it’s much more expensive. Using that favorite rule of measure, the thumb, you’ll probably find the cost for such a system to be in the range of $8 to $10 per watt. It does provide a degree of independence. The system automatically will disconnect from the power company grid at the first sign of trouble, then switch to the “independent,” or “stand-alone” mode. Power companies like that, as you’ve disconnected your potentially lethal system from their grid. But it will make you the envy of the neighborhood, as you may be the only house on the block with lights—and computers and TV up and running!
But, “there ain’t no free lunch.” The homeowner must have a degree of sophistication to operate and maintain the system. A battery bank is needed to store the energy needed during your emergency. And batteries need maintenance. Too, after a number of years, they’ll need replacement. If your homeowner is clamoring for an Uninterruptible Power Source that will power the house, then this is the system to consider. Automatic controls will keep the battery system charged, will sense when the grid system goes down, then will disconnect the home from the grid lines and automatically begin operating in the “stand-alone” mode—to the chagrin of the non-UPS owning neighbors! As implied, it comes at a price. Not only dollars (a system size of at least 2 kW may be appropriate) but also being able to maintain the system—or have the system maintained. Another implication by that statement? Not too many technicians are capable of servicing PV systems yet. Therefore, the KISS principle should be employed—Keep It Simple Senor(ita)!