Page 149 - Solar Power in Building Design The Engineer's Complete Design Resource

EXAMPLE OF TYPICAL SOLAR POWER SYSTEM DESIGN 119

At a 240-V entrance service this represents about 100 A of load. However, consid-
ering the average power usage, the realistic mean operating energy required discounts
full-time power requirements by the air conditioning, laundry equipment, and kitchen
appliances; hence, the norm used for sizing the power requirement for a residential
unit boils down to a fraction of the previously calculated power. As a rule of thumb,
an average power demand for a residential unit is established by equating 1000 to
2
1500 W per 1000 ft of living space. Of course this figure must be augmented by con-
sidering the geographic location of the residence, number of habitants, occupancy
time of the population within the dwelling unit, and so forth. As a rule, residential
dwellings in hot climates and desert locations must take the air-conditioning load into
consideration.
As a side note when calculating power demand for large residential areas, major
power distribution companies only estimate 1000 to 1500 W of power per household,
and this is how they determine their mean bulk electric power purchase blocks.
When using a battery backup, a 30 percent derating must be applied to the overall
solar power generation output efficiency, which will augment the solar power system
requirement by 2500 W.
In order to size the battery bank, one must decide how many hours the overall power
demand must be sustained during the absence of sun or insolation. To figure out the
ampere-hour (Ah) capacity of the battery storage system, the aggregate wattage
worked out earlier must be divided by the voltage and then multiplied by the backup
supply hours. For example, at 120 V ac, the amperes produced by the solar power sys-
tem, which is stored in the battery bank, will be approximately 20 A. To maintain
power backup for 6 hours, the battery system must be sized at about 160 Ah.

Example of Typical Solar Power

System Design and Installation Plans
for a Single Residential Unit

The following project represents a complete design and estimating procedure for
a small single-family residential solar power system. In order to establish the require-
ments of a solar power system, the design engineer must establish the residential power
demand calculations based on NEC design guidelines, as shown in the following.

REED RESIDENCE, PALM SPRINGS, CALIFORNIA
Electrical engineer consultant Vector Delta Design Group, Inc., 2325 Bonita
Dr., Glendale, CA 91208

Solar power contractor Grant Electric, 16461 Sherman Way,Van Nuys, CA 91406