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Make a list of the appliances and/or loads you are going to run from your PV system. Find out how much power each item consumes while operating. Most appliances have a label on the back, which lists the wattage. The following chart lists typical power consumption of some common devices that you can use as a guide.

Appliance Watts appliance watts APPLIANCE Watts
Coffee Pot 200 Computer   60W equivalent 16
Coffee Maker 800 Laptop 20-50 75W equivalent 20
Toaster 800-1500 PC 80x86 150 100W equivalent 30
Popcorn air 300-1000 Printer 100 ¼" Drill 250
Blender 300 Typewriter 80-200 ½" Drill 750
Microwave 600-1500 TV 25" Color 150 1" Drill 1000
Hot Plate 1200 19" Color 70 9" Disc Sander 1200
Washing Machine   12" B&W 20 3" Belt Sander 1000
Automatic 500 VCR 40 12" Chain Saw 1100
Manual 300 CD Player 25 14" Band Saw 1100
Vacuum Cleaner   Stereo 10-30 7¼" Circ. Saw 900
Upright 200-700 Clock Radio 1 8¼" Circular 1400
Hand 100 Satellite Dish 30 Refrig/Freezer  
Sewing Machine 100 CB Radio 5 20cf (15 hrs) 540
Iron 1000 Electric Clock 3 16cf (13 hrs) 475
Clothes Dryer   Lights:   Sunfrost  
Electric 400 100W Incandescent 100 16cf DC (7 hrs) 112
Gas Heated 300-400 25W Compact Fluor. 28 12cf DC (7 hrs) 70
Water Pump 250-500 50W DC Incandesce 50 Freezer  
Ceiling Fan 10-50 40W DC Halogen 40 14cf (15 hrs) 440
Table Fan 10-25 20W Compact Fluor. 22 14cf (14 hrs) 350
Electric Blanket 200 Compact Fluorescent   Sunfrost Freezer  
Blow Dryer 1000 Incandescent Equivalent   19cf (10 hrs) 112
Shaver 15 40W equivalent 11    

Calculate your AC loads. Determine how many hours each week that each load will be used. Watts X hours per week = WH/Wk. Add all of your watt-hours per week to find your total AC watt-hours per week needed.

Calculate your DC loads. It is more practical to use DC directly from the batteries for small appliances i.e. cell phone, small lights, CD's and stereos that you can use a cigarette lighter adapter for. If an appliance is rated in amps, remember that P=E x I. Where P is power or watts, E is volts or Electro-motive force, and I is current or amps.

12, 24, or 48 volt system?
Many people begin with a 12-volt system because of its simplicity and low cost. Higher voltage will travel longer distances with less loss. Since watts = volts x amps, your power is increased proportional to your volts, given the same current. Generally, 12 volt is adequate for small to medium systems.

You may be able to save 50% or more of your present usage simply by conserving. Do not use electricity for heating, air or water. Propane is much more efficient. Power companies in NE Arizona will give people free hot water heaters and some people are stupid enough to go get one. Air conditioning is not practical, but there are some very efficient swamp coolers, some use DC. You probably do not need lights on in a room if no one is in it. If you use heat tape to keep pipes from freezing, use tape with a thermostat. Propane heaters in each room allow you to heat only those rooms in use.

To calculate your battery requirements, first decide how long you will want your system to run without being recharged. For a weekend cabin, you may want a lot of batteries to power you for the weekend and they can recharge after you leave. If you have a backup generator, you may not need so many batteries as you can always start the generator (hopefully). If you have enough solar panels or wind generator to fully charge your batteries every day, you may want to get more batteries to allow for days when the wind does not blow and the sun does not shine. In any case, double what you think you need because you will lose up to 20% through your inverter and another 20% if you live in a cold climate.

Use the following table to calculate wire size. On the left, locate the current you will be dealing with. Move across to locate the distance traveled. Move up to find wire size.

AWG< ampsV 14 12 10 8 6 4 2 1 0 00 000
1 106 169 269 427 679 1080 1717 2166 2730 3444 4342
2 53 85 134 214 340 540 859 1083 1365 1722 2171
4 27 42 67 107 170 270 429 542 682 861 1086
6 18 28 45 71 113 180 286 361 455 574 724
8 13 21 34 53 85 135 215 271 341 430 543
10 11 17 27 43 68 108 172 217 273 344 434
15 7 11 18 28 45 72 114 144 182 230 289
20   8 13 21 34 54 86 108 136 172 217
25     11 17 27 43 69 87 109 138 174
30     9 14 23 36 57 72 91 115 145
35       12 19 31 49 62 78 98 124
40         17 27 43 54 68 86 109
45         15 24 38 48 61 77 96
50         14 22 34 43 55 69 87