Advantages and disadvantages

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Design: Solar Heating of Buildings and Domestic Hot Water

MIL-HDBK-1003/13A

Some deviations from these tilt and orientation angles are allowable without

significantly affecting performance. As shown in Figures 1-3 and 1-4, the

tilt angle may vary +/- 10 degrees and the orientation angle up to 20 degrees

either side of true south (National Solar Heating and Cooling Info Center,

1979). For these deviations the solar collectors would still collect 95%-

100% of their rated capacity in most locations of the U.S. Additional

deviations would require more collector area to capture the same amount of

energy. As a very approximate rule of thumb, for each deviation of 10

degrees beyond that shown in Figures 1-3 and 1-4 add 10% more collector area.

If you must choose between an east roof and a west roof, use the west roof in

the western coastal area. Other areas will require local weather

considerations.

As important as collector location, is keeping the collectors out of the

shade, especially between 9 a.m. and 3 p.m., when most of the useful energy

collection occurs. The designer should try to anticipate any future struc-

tures or vegetation (trees) that could block future solar access. In

summary, although many buildings will not have a "perfect" solar orientation,

there can still be many places with good solar energy potential.

1.3.4 Advantages and disadvantages. Solar energy is inherently

nonpolluting, provides substantial freedom from the effects of fuel price

increases, and saves valuable fossil fuels. Disadvantages are that

collectors perform poorly in cold cloudy weather, when most needed; and room

heat exchangers and industrial unit heaters must be larger than in

conventional systems due to the relatively low temperature of heating fluid.

The disadvantages may be circumvented by good design; where fuel costs are

high enough (as discussed in the examples, Section 4), a solar system will

prove cost effective. Solar systems designed for combined heating and

cooling will utilize the collector all year and thus are potentially more

cost effective.