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Understanding Loads

Welcome to Electricity 101!

In doing a load analysis, we are primarily interested in POWER and TIME. This means:

Watts x Hours

If we are dealing with more power and/or time, we may use:

KiloWatts x Hours

3000 WattHours = 3 kWHours (3kWh)


Note that this is exactly the unit your electric bill is in (if you get one.) Also, it can be helpful to distinguish between POWER and ENERGY. This means:

Power x Time = Energy

For example, an engine can be very powerful but doesn't use much energy if it only runs for a minute. We capitalize the W for Watts because it is an abbreviation for James Watt, who developed the concept of horsepower. One horsepower equals approximately 746 Watts, by the way.

A quick and easy load analysis for a home on the grid can be done by looking at an electric bill. Usually you are billed for kWh per month. We suggest dividing that number by 30 and working with kWh per day. You may find energy usage from 5 kWh to 60 kWh per day, depending on the type of electrical appliances used. If you are interested in lowering your electric bill, it will pay to look into more efficient lights, insulation and appliances. After you have updated your home, you can size a solar system to offset any or all of your electrical consumption.

If you are looking to meet all of your needs with a solar electric system for an *off-grid* application, you will almost certainly have to eliminate huge loads like electric water heaters, ovens, air conditioners, electric clothes dryer, and space heaters. Tools and pumps are not generally a problem because they are not on for long periods of time. An average off-grid solar-powered home with "all the modern conveniences" is designed for about 4-10 kWh/ Day to keep system costs within budget.

Getting back to specific loads, it is possible to examine all your appliances and multiply the Amps on the nameplate times 120 (or 240 if a large appliance) Volts to get the Watts for each appliance. A saw rated at 12 Amps, for example, will draw 1440 Watts. Some items are rated in Watts already, like light bulbs, hair dryers or microwave ovens.

Volts x Amps = Watts

It is not necessary to tear apart the house to do this, but doing a few calculations like this will give you a better feel for what's going on as you use your system later. You can also buy meters, like the Kill-A-Watt meter, to plug loads into, which measure Watts and Watt-hours very accurately. Or, a good analysis can be done using values in the tables below.


Appliance Watts (V x A) Appliance Watts (V x A)
Alarm/Security System* 3 Humidifier 300-1,000
Central Air Conditioner 1000-1500 (running)

2200-5000 (starting)
Iron 1,500
Blender 350 Microwave* 500-1,500
Cable Box* 20 Mixer 120
CB Radio 10 Laptop Computer 60-120
CD Player* 35 LCD TV* 213
Ceiling Fan 100 LCD Monitor* 80-150
Clock Radio* 7 Oven* 3,000
Clothes Washer 1,450 Plasma TV* 350
Coffee Grinder 100 Printer* 100
Coffee Machine 1,500 Portable Fan 100
Curling Iron 90 Popcorn Popper 250
Dehumidifier 350 Satellite Dish 20
Desktop Computer (Standard) 80-120 Sewing Machine 100
Desktop Computer (Gaming) 400-1,500 Sink Disposal 450
Dishwaser 1,200-1,500 Shaver 15
Dryer (gas) 300-400 Slow Cooker 200
DVD Player* 150 Standard TV* 190
Electric Clothes Dryer 3,400 Stereo* 10-30
Electric Blanket 200 Stock Tank Heater 100
Electric Clock* 4 Table Fan 10-25
Electric Piano* 30 Toaster 1,100
Engine Block Heater 150-1,000 Toaster Oven 1,500
Espresso Machine* 360 Trash Compactor 1,500
Exhaust Fans (3) 144 Vacuum Cleaner 500
Fish Tank 5 Video Game Player* 195
Food Dehydrator 600 VCR* 40
Food Processor 400 Waterbed Heater 400
Furnace Blower 300-1,000 Water Heater 479
Garage Door Opener 350 Waterpik 100
Heater (portable) 1,500 Waffle Iron 1,200
Hot Plate 1,200 Well Pump (1/3-1 HP) 480-1,200



Tools Watts (V x A)
Band Saw (14”) 1,100
Chain Saw (12”) 1,100
Circular Saw (7 ¼”) 900
Disc Sander (9”) 900
Drill (1/4”) 250
Drill (1/2”) 750
Drill (1/2”) 1,000
Electric Mower 1,500
Hedge Trimmer 450
Weed Eater 500



Lighting Watts (V x A)
Incandescent (100W) 100
Compact Fluorescent (60W equivalent) 16
Compact Fluorescent (40W equivalent) 16
25 W. Compact Fluorescent Bulb 22



Refrigeration/ Freezing Watt-Hours/ Day
20 cu. Ft. (AC) 1,411
16 cu. Ft. (AC) 1,200
15 cu. Ft Freezer 1,240
Energy Star 600

 

*Phantom Loads: Many electrical devices draw power even when “off”. These are most often loads that constantly draw power. Some examples include: Television sets, appliances with digital clocks - microwave ovens, DVD players, or any item with a remote control. These loads may seem trivial though they are drawing power 24 hours a day, 7 days a week. That can add up to quite a lot! A simple method to avoid this power drain is to unplug these devices whenever possible or connect them to a power strip that can easily be switched on and off.

Incidentally the volts x amps = Watts works exactly the same for DC and AC. So we can use the same math for looking at loads, solar arrays, generators, or batteries. Although it’s possible to use DC loads for more efficiency, normally we use inverters to convert from DC solar panels and DC batteries to AC power, to run AC loads.

For off-grid, in addition to the kWh per day, we also need to consider the peak load, so the inverter will be big enough. To do that, add up the total loads (in Watts) that might be on at one time. Also, it is imperative to factor in the additional surge required to start large motors. The starting surge of a motor is usually about 4 times as much power as the running load. So for large motors, multiply the running Watts times 4. For Grid-Tie systems, the peak load is not usually a concern because the inverter is only producing energy (kWh) that is synchronized with the utility, and used or sold, but not powering the loads directly.