The next step is to look at your climate. Are you in the sunbelt, or are you in a fog-bound sea port? If you are in fog it does not mean that you cannot use solar, it just means that you will need a lot more solar modules than a sunny location and the system will likely not be cost-effective. For a map of the solar resource (called insolation) across the United States, see http://www.nrel.gov/gis/solar.html(See Figure 1) Zoom in on your location and then compare that color to the scale to find your insolation. For instance, for Phoenix, Arizona, the average annual insolation is about 6.5 W/m2/d (Watts per square meter per day). If the insolation is low in your area, the financial assistance will have to be high to make your system cost-effective.
Notice that the insolation values on Figure 1 are for “Fixed Plate Tilted at Latitude.” This brings up the topic of orientation. In general, the most output for stationary solar modules are when they are tilted approximately equal to your latitude. Most residential solar systems are mounted on the roof. Look at your roof. Do you have a large roof surface that is pointed south (in the northern hemisphere) and tilted about equal to your local latitude? If you do, great. If the roof is oriented towards the north, your system will not produce very much electricity. East and west orientations are not as good as south orientation, but not as bad as north orientation. To accurately determine the effect of orientation, you will need a computer program. Such programs are available on the internet. Search for “Solar Calculator” or similar (one is at http://www.nrel.gov/gis/solar.html/, click on “PVWATTS Version 2”). Solar contractors also have such calculators. In general, roof orientation may be a determining factor, with south-facing roofs the best, and north-facing roofs the worst.
You can build a mounting frame on your roof to re orient the solar modules. This adds concentrated stress to your house and may not meet the aesthetics factor. You will need a structural engineer to help with the design. Of course, if you have room to mount the solar system on the ground, you can orient and tilt the solar modules to produce the most power.
Shadowing is an often overlooked factor in solar installations. Is your house surrounded by a forest, located in a canyon, or surrounded by tall buildings. If only one cell on a solar module is shadowed, the entire module will produce very little power. Ideally, your roof should have full sun all day long. If not, the more sun the better. If the shadows do not leave until mid morning and return early in the afternoon, you will need a great deal of financial assistance to offset the poor performance. You can see what the shadowing will be like throughout the year by using an instrument like the Solar Pathfinder, see http://www.solarpathfinder.com/. Sometimes you can eliminate the shadows, such as cutting down or trimming a tree, or moving a TV satellite dish. Other times you can move the solar array. If you have shadows throughout the day, a solar system may not be for you.
The beauty of solar is in the eye of the beholder. Most solar modules are mounted a few inches above the roof to provide air circulation underneath. Some people consider this a visual nuisance. Others want the world to know that they have a solar system and consider this a badge of honor. If you are one who doesn’t want modules to ruin your roof line, you can do one of several things. You may be able to mount the solar modules on a portion of the roof that is not visible. You can also buy special modules that are designed to blend into the roof (usually not as efficient, so you will need more). If none of the available solutions suits your situation, solar may not be for you.
The bottom line is something called the payback period, in years. This is the time at which the savings equal the cost. The payback period is fairly straight forward to calculate. First add up all the initial cost, such as materials and labor, subtracting any rebates. Then, for each year, add in any recurring cost, such as maintenance (usually minuscule), insurance and interest payments. Then subtract anything like tax breaks. Now calculate the savings by multiplying the actual annual electricity generated in KWh by the cost you would normally have to pay for the KWh of electricity. Subtract the savings. Continue to do this for subsequent years until the number becomes negative. This is the payback period. If you have a payback period of 8 years, great. The solar system should last for 30, so you will have 22 years of saving money on your electricity bill.
You may be committed to renewable energy even if the solar system is not profitable. If this is the case, you still want to be efficient with your solar system, because it makes the best use of the resources.
If you are serious about installing a solar system on your house, start by reading. There are lots of good books on the market. Also subscribe to a good solar magazine. Then, when you are ready, start to work with a solar professional: an installer or solar contractor. Do yourself and the planet a favor, check it out.
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