You can usually find the wattage of most appliances stamped on the bottom or back of the
appliance, or on its nameplate. The wattage listed is the maximum power drawn by the appliance.
Many appliances have a range of settings (for example, the volume on a radio), the actual
amount of power consumed depends on the setting used at any one time.
Using the information provided on this page, you will be able to estimate your energy usage and figure out the number of batteries and the number of PV panels you'll need.
| Appliance | Typical Wattage |
|---|---|
| Clock radio | 10 |
| VCR/DVD | 17–21 |
| Laptop | 50 |
| Aquarium | 50–1,210 |
| Window Fan | 55–250 |
| Ceiling Fan | 65–175 |
| Radio (stereo | 70–400 |
| Computer CPU | 120 |
| Monitor | 150 |
| Water pump (deep well) | 250–1,100 |
| Clothes washer | 350–500 |
| Refrigerator 16 cu ft | 725 |
| Furnace Fan | 750 |
| Heater (portable) | 750–1,500 |
| Microwave oven | 750–1,100 |
| Dehumidifier | 785 |
| Toaster | 800–1,400 |
| Coffee maker | 900–1,200 |
| Clothes iron | 1,000–1,800 |
| Vacuum cleaner | 1,000–1,440 |
| Dishwasher | 1,200–2,400 |
| Hair dryer | 1,200–1,875 |
| Toaster oven | 1,225 |
| Clothes dryer | 1,800–5,000 |
| Water heater (40 gal) | 4,500–5,500 |
| Flat screen TV | 133 |
| Projection TV | 170 |
(Wattage × Hours Used Per Day) ÷ 1,000 = Daily Kilowatt-hours (kwh)
where 1 kilowatt (kw) = 1,000 Watts
Note: To estimate the number of hours that a refrigerator actually operates at its maximum wattage, divide the total time the refrigerator is plugged in by three. Refrigerators, although turned "on" all the time, actually cycle on and off as needed to maintain interior temperatures. One third of the time is a usable ballpark estimate of daily load.
| Flat Screen TV: | 120 Watts × 4 hours/day | = 480 watt hours daily |
| Personal Computer and Monitor: | 120 Watts x 2 hours/day | = 240 watt hours daily |
| 5 - 60 watt light bulbs: | (5 x 60 = 300) 300 Watts x 4 hours/day | = 1,200 watt hours daily |
| Deep well pump: | 1,000 Watts x 30 Min/day | = 500 watt hours daily |
| Total | = 2,420 watt hours a day |
In this example we will be using a Trojan T-105 6 Volt battery having a total capacity of 1,100 watts. We do NOT want to run the battery down more that 25% to get the longest life time from the battery, so that gives us 275 watt hours from one battery.
2,420 watts used daily ÷ 275 = 8.8. So you would need a battery
bank of 8.8 batteries to maintain your usage without a re-charge. Because most inverter systems are 24 Volts, your battery bank should
be made up of multiples of four 6 volt batteries which equals 24
volts and 275 watt hours. Three strings of four batteries are needed to meet the
requirement in this example.
If you want to recoup your usage from solar PV modules using
a typical 185 watt solar module you would need:
185 x 5(average
# of sun hours) = 925 watts hours available
2,420 ÷ 925 = 2.6 modules
Round up to three panels.
