In the typical US household, lights and small appliances run on 120 VAC, while appliances and motors that require high power use 240 VAC. Examples of large power-consuming items might be an electric tank water heater (5000 watts), or an electric dryer (which uses both voltages, 120 VAC for the motor that turns the drum and 240 Volts for the heating element) that can draw 4000 watts or more. Large workshop equipment like a cabinet saw can have a 3 HorsePower motor, which uses 2250 watts or so.
Terminology:
Initially, the terminology can be confusing because there are so many terms that are often considered interchangeable, though technically they may not mean the same thing. You currently buy your power from your local power company as KiloWatt Hours (KWH). A kWh is the equivalent of one thousand watts (kilowatt) of power consumed for a total of one hour. Electricity Energy Consumption The rate you pay per kWh varies tremendously depending on where you live, and your real cost of power is the amount of your bill divided by the number of kWh you used in that month. In some areas of the US, the rate may be as low as 7 or 8 cents per KWH, while in others, like Hawaii, as high as 42 cents. Thus, where you live can have a great impact on whether you can afford to go green with the solar electric generation, not just because of your solar gain, but due to how long it would take to amortize (payback) the cost of the installation. But, I digress, back to the terms: Power is the product of voltage and current. Thus, because a KWH is 1000 watts over an hour, and the voltage applied to an ordinary light bulb is 120 volts, dividing 120 into 1000 is about 8.3, which is the number of amps you can draw for 1 kWh. If you have a 100 watt light bulb, which coincidentally does use (or draw) 100 watts, you could run it for 10 hours for 1 kWh. Working the math, 100 watts divided by 120 volts is 0.83 amps, and because there are 8.3 amps in a KWH at 120 volts, the math all works, as you can see the light bulb burns for 10 hours, no matter which way you do the math. Though somewhat confusing, understanding this will be helpful later.
How much do we use
Most of us in the US don't pay enough attention to our energy consumption habits, primarily because we either don't understand it or don't see the effect until we get the bill each month. Though big things take a lot of energy, even the little things add up. For example, I could run the cabinet saw in my workshop for a bit less than 27 minutes and use 1 kWh. A 100-watt bulb would take 10 hours to use the same amount of power. However, if I buy an energy-efficient fluorescent bulb that replaces that 100-watt bulb, it only draws 23 watts, so now I could burn it over 43 hours for the same cost.
One way to get a handle on how much we consume is to make a chart, and jot down the uses as we go. While this works, it breaks down in a couple of days once you get tired of updating the chart. For plug-in devices, you can purchase a meter that measures all of the power used by whatever is plugged into it. One of these is a unit called a Kill-A-Watt Electricity monitor, and it costs about $20, depending on where you buy it. Having a couple of these around will give you a lot of information and cause you to change your habits in no time. You just plug the unit into the outlet and plug the appliance into it. When power is applied (when you plug it in) it starts a timer at zero and begins counting all the electricity used by whatever is plugged into it. When I did the electrical energy audit of my home, I started with the big consumers of power, monitored each for a week, then moved on to others. Boy was I surprised at what I found. By the way, when you unplug the Electricity Energy Consumption Kill-A-Watt from the wall, it loses its data, so make sure you write it down before you move it to another appliance or lamp. The monitor provides a bunch of information that is useful. While something is running, you can see how much current is being used. At any time, you can see the actual voltage of the outlet, the number of hours it has been monitoring, and the total KWH consumed. If the appliance load isn't purely resistive, the monitor can provide a power factor, which can be important if you are contemplating an inverter-based solar electric system, which is the most common. Based on the running current and the total KWH used, I found my old refrigerator was running at least 11 hours a day, and costing me a pretty penny.
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