SOLAR TODAY - April 2010

CLICK For data and worksheets: solartoday.org/consumptionchart

If your home is energy efficient, you can get by with a smaller photovoltaic array.

will it fit?

Atop-quality silicon PV module can produce roughly 140 watts per square meter, or about 12 watts per square foot. As an example, a 20-by- 22 foot garage with a pitched roof might offer about 230 square feet ( 21 square meters) of usable south-facing roof surface — enough to accommodate two rows of modules that are each 20 feet ( 6 meters) long. That ought to accommodate a 2.6-k W PV array, depending on how the modules are tilted up from the roof surface. The rack needs to be designed to prevent the lower tier of modules from shading the bottom of the upper tier when the sun is low in the sky. If your roof won’t accommodate a south-facing array, consider a ground-mount system in the yard.

dAn Bihn

Copyright © 2010 by the American Solar Energy Society Inc. All rights reserved.
entation to the sun and wind. When building a
new home, it’s customary to improve efficiency
by installing more energy-efficient appliances
and lighting. You may choose passive solar heat-
ing and cooling designs. If you follow these strat-
egies, electrical consumption could easily be 50
or 75 percent lower. You can adjust electrical
demand to reflect efficiency upgrades.
Another way to estimate electrical con-
sumption is to perform a load analysis. Begin
by listing all the appliances, lights and electronic
devices in the new home or office. Rather than
try to list each light bulb separately, just lump
them together room by room. Work from room
to room, using a worksheet like the one you can
download at solartoday.org/consumptionchart.

The power consumed by any device can be estimated from the chart shown at left. For more accurate data, check out the nameplate on the appliance or on its power supply. The sticker or engraved plate lists the unit’s rated voltage (typically 120) and power draw in either amps or watts. If it’s given in watts, simply enter that number in the watts column. If it’s in amps, enter the number in the amps column, and the

Air conditioner (1 ton) ............................................1500 Alarm system .............................................................. 3 Blow dryer..............................................................1000 Ceiling fan ............................................................ 10-50 CFL (60- watt equiv.) ................................................... 16 Clock radio................................................................... 5 Clothes washer .......................................................1450 Computer (desktop) ............................................ 80-150 Computer (laptop) ................................................ 20-50 Computer printer..................................................... 100 Dishwasher.............................................................1500 Dryer (gas) ...............................................................300 Furnace fan ..............................................................500 Garage door opener..................................................350 Heater (portable) ....................................................1500 Iron.........................................................................1500 Microwave ...................................................... 750-1500 Range (electric, large burner) ..................................2100 Refrigerator ( 22 cubic feet) (runs 14 hours per day) ...540 TV (19-inch color) ....................................................... 60 VCR............................................................................. 40

Average Electrical Consumption of Common Appliances in Watts

spreadsheet will calculate watts. If you’re doing this manually, on a hand calculator, the formula is: Volts x Amps = Watts.

For appliances with large induction motors — fans, washing machines, dryers, dishwashers, pumps and furnace blowers — the rated wattage is called the apparent power. To calculate the real power drawn by these devices, multiply the rated wattage by the power factor 0.6.

Be sure, when determining the run wattage of laptop computers, cordless drills, cordless phones and other rechargeable devices, to use the wattage listed on the charger, not the device.

A more accurate way to determine the wattage of any electrical device is to measure it directly with a watt-hour meter. Plug the meter into an electrical outlet and then plug the appliance into the outlet on the face of the meter. A digital readout indicates the instantaneous power in watts. When measuring a device that cycles on and off, such as a refrigerator, leave the watt-hour meter connected for a day or two. The meter will record the total energy used during this period as watt-hours. Divide by the number of hours to get the average wattage for the period.