Is Solar for You
Now that you have some idea of what kinds of solar systems are available and how they work, perhaps you find yourself squinting calculatingly into the sun, with an eye to using its energy to heat your water and /or living space. But before you rush out and purchase a flat-plate collector, storage tank, and pumps, and before you store your Bo khara rug in the attic in favor of masonry floor-tiles—indeed, before you even decide which solar system to use, you need to find out whether solar is really for you.
It makes no sense even to think about heating your living space with solar energy until you have thoroughly weatherized your house according to the steps already outlined in this guide. Why go to the trouble of producing solar heat if it will only drift up through an uninsulated attic or out through the cracks around the windows? Thermo statically-controlled heaters will not turn on until they are warmer than the space they are designed to heat. Therefore, inadequate insulation is likely to require an increased collection area. and since collectors cost about $20 to $45 per square foot plus installation, it pays to minimize the square-footage requirements of your collector by properly insulating your house.
Once you’re satisfied that your house can retain the solar heat you’re thinking about tapping, then it’s time to take a look at: your geography; your climate; financial considerations; and how you feel about solar energy.
Geography and Climate
Since your use of solar energy depends on how well you can exploit the sun’s heat, the first task is to determine the relationship between the sun and your house. You need to find out how much you can take advantage of the sun and its movements.
• The sun’s orbit: The earth travels an elliptical orbit around the sun that brings the two bodies closest together (less than 90 million miles apart) on December 21, and carries them farthest apart (almost 96 million miles) on June 21. However, the earth is tilted on its axis at an angle of 23½0 with the north pole toward the sun in summer and away from the sun in winter. This tilt makes the sun appear to be 470 higher in the sky in June than in December. Even though the earth is farther from the sun in summer, this angular shift causes the sun’s rays to penetrate the earth’s atmosphere more directly than they do in winter. As a result, our summers are warmer than our winters.
At the same time, the earth’s daily rotation on its axis makes it appear that the sun rises in the east, passes overhead, and sets in the west. (Actually, it appears to rise and set slightly south of east and west in winter, and slightly north of east and west in summer; and it never passes directly over head in the United States.)
Sun’s path: The sun’s angle from the horizon at noon on June 22
is about 85° at the US northern border and 65° at the southern border;
The sun’s angle from the horizon at noon E on Dec. 22 is about 40° at the
U.S. northern border and 20° at the southern border. The sun rises and sets farther north in summer. (bottom) Solar Bands: While sunlight
useful for active or passive solar heating falls on all parts of the United
States, more useful sunlight falls in some places than in others. The map
above divides the continental United States into six principal sunfall
regions, or zones. More useful sunlight falls in zone 1, where it is feasible
that solar heating can accommodate practically all a home’s annual heating
needs, than falls in zone 6, where it is optimistic to think that solar
heating can accomplish more than about 35 to 40 percent of the task. Useful
sunfall does not bear a direct relationship to average daily temperatures.
• The orientation of your house to the sun: More than any other factor, the position of your house relative to the sun will determine whether you can make use of solar energy.
In North America, most of the usable solar energy comes from the south. This means that you need to find out what kind(s) of southern exposure your house has or can have. Look for every place where you might collect and store solar energy, and ways to move the stored heat into your home.
Note everything that seems relevant to receiving (or not receiving) direct sunlight; also observe areas that do or could receive reflected sunlight.
Now get out a notebook and pen for making notes and drawings, and look at your house in terms of the following:
1. Does anything obstruct the sun’s rays from falling on your house? (Look at the roof, the walls, and the southern face of the building.)
2. What is the general orientation of your house? (Note where the south! north axis falls in relation to your building.)
3. What openings are there on the south-facing surface?
4. What is the south-facing roof like?
Is it flat? pitched? Does it have vents, skylights, or anything else would make mounting a collector difficult?
The next most important factor to determine is whether anything pre vents the sun from reaching your potential collection area. In short, look for shading.
1. Are there trees to the south of your site that shade a potential collection point? Are you willing to prune them back or cut them down?.
2. Does a neighbor’s house tower above yours, shading your south- facing windows?
Remember—you need access to the sun in order to use its energy.
You need a good idea of your particular solar microclimate as well as your regional solar climate. In general, every place in the United States receives enough direct and diffuse sun light to make use of a solar energy system. Some parts of the country (for example, Miami Beach, Florida) get more sunlight on more days of the year than other places (for example, Seattle, Washington) and therefore the sun’s heat is available for collection more often. But every part of the country receives sunlight. and the availability of sunlight—not the temperature—is what counts here. Any surface that can be exposed to sunlight can absorb the sun’s radiant heat. As long as the surface’s ability to collect heat, store the collected heat, and direct its flow is enhanced, even an extremely cold location will allow a solar energy system to provide home water and space heating.
In considering the potential effectiveness of a solar energy system, you have to look at your local weather and solar radiation patterns. How much solar energy is available on a clear day differs from one part of the United States to another, just as it differs from season to season, from day to day, and even from hour to hour. In general, the map to the left indicates areas of greater and lesser insolation (solar radiation received by the earth’s surface). This will give you some idea of what your expectations can be for solar energy in your region. But if you find that your interest in solar heating is increasing, and you are seriously considering the possibility of installing some sort of solar system, you will want to locate more specific in formation for your area. There are many books which have elaborate tables and methods of calculation to help you determine the quantity of solar energy available in your particular region. Further, if you are new to the field of solar, you will want to seek out experts in your area who can help you determine the specific details relative to every aspect of a prospective solar system, including these initial calculations. Solar can be a real adventure, but you will want to be realistic.
Next: The Financial Picture; Now That You’ve Decided