Energy Use and Measurement

Power vs. Energy: There is a Difference
Differentiating between power and energy is critically important for informed decisions. Power and energy are frequently used interchangeably, but they are not – and you should have an accurate understanding of the difference.

Power is the instantaneous rate of energy production or consumption. It has no units of time in it.  Think of a Corvette with 500 horsepower or a wind turbine that is rated at 10 kilowatts.  Examples of power measurements are horsepower, watts, kilowatts or megawatts.

Energy is power production or consumption over time.  Examples are horsepower-hour, watt-hour and kilowatt-hour.  Electricity is typically sold this way.  Think of your electric bill, which is usually in terms of kilowatt-hours.

Electrical power is usually stated in watts. This is convention – it could be stated in terms of any other measure of power, but watts are almost universally used.  A 100 watt light bulb in use for one hour consumes 100 watt-hours of electricity.  The same 100 watt light bulb in use for 10 hours, or a 50 watt bulb in use for 20 hours, will use 1,000 watt-hours or 1 kilowatt-hour (kWh) of electricity.

Appliance Power & Energy Demands
Different types of appliances or equipment have different power requirements but, remember, power and energy are different.  An appliance might have a large power requirement but small energy consumption, if it is used infrequently or for short periods of time.  A 1,200-watt hair dryer used for just 10 minutes per day will consume 200 watt-hours of energy a day.  Conversely, an appliance might have a small power requirement but large energy consumption, if it is used frequently or for long periods of time. A 75-watt light bulb used for eight hours per day will consume 600 watt-hours of energy a day.  An appliance could also have a large power requirement and large energy consumption, if it is used frequently or for long periods of time.  An air conditioner that uses 1.5 kW (1,500 watts) and runs for 10 hours on a hot day will use 15 kWh (15,000 watt-hours) during that day.

Not all of the energy delivered to your house is necessarily electrical, but your primary energy source is probably electricity.  Your consumption of electricity depends on numerous factors: the size and construction of your house, geographic location of your house, life style, time of year, number of people living in the house, type of appliances in the house, etc.

The 2,000,000 Watt Month
The cost of the electricity that you use can also vary widely, depending on the source. You can find out each month about your current rates and consumption from your electric company. Your electric company can also provide you with historical data.

The average American uses about 1,000 kWh per month in electricity and the equivalent of a little over 2,000 kWh per month in total energy consumption, from all sources, in their homes.  So an average monthly consumption of 2,000 kWh will be used for the following analysis.  Now 2,000 kWh may not seem like much energy, but that is 2,000,000 watts per month (and 24,000,000 watts per year). Using 2,000 kWh in a 30 day month averages out to about a constant 2.778 kilowatts, or 2,778 watts.

The $95,000 Electric Bill
You can relate your home energy consumption to the output of human physical efforts.  A fit and capable young male can generate about 200 watts on a stationary bicycle, but 150 watts is more reasonable and sustainable (That would just be enough to keep a couple of 75-watt light bulbs on, but not even enough to keep three 60-watt light bulbs on).  So, in theory, you could generate the energy required for your house with about 19 people.  But better plan on 3 – eight hour shifts every day. That’s 57 people.  This is not light work, either.  They are not going to live on 2,600 calories per day.  Better double that food budget. The energy requirements are peaky, too.  This is not going to increase the number of riders, but you need more equipment in place.

How much do you suppose you’d have to pay the bicyclists to work seven days a week?  $20,000 per bicyclist per year?  That’s $95,000 a month for the 57 people.  How much do you think food for the 57 bicyclists would cost?  That $500 per month electric bill is looking pretty good by now.  So is the industrial revolution.  And so is a $180 monthly payment for the purchase of a wind turbine or solar panels.

As Bad as it is Now
Those figures show just how difficult it will be to convert to a non-fossil fuel based electric generation system, and why houses used to be dark, damp, hot in the summer and cold in the winter before electrification.  They also demonstrate the consequences of depleting fossil fuels before we convert to generating electricity with renewable energy systems.

Electricity demand is projected to steadily increase even as fossil fuels dwindle.

So what do we do when the fossil fuels begin to run out, or become prohibitively expensive?

If you now think it might be a good idea to try and reduce your home energy consumption, and you’d like to learn some great ways to do it, please go to Save Energy & Save Money on this website.

Your Car vs. Your House
The energy consumption of your car can also be related to the energy consumption of your house, and your car may be using more energy than your house.  One gallon of gasoline contains about 115,000 BTU’s of energy, which is equal to about 34 kilowatt-hours of electricity.  If you drive your car enough every day to use 2 or more gallons of gas, your car could be consuming more energy than your entire house.  This basic comparison shows just how inefficient and wasteful cars are.  It also points out how difficult it’s going to be to produce electric cars with any reasonable mileage range.

About the Author

Mark H. Witte is a strong proponent for energy efficiency and renewable energy, and believes individuals should have more control over how the energy for their homes is produced.