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What is Energy?

Let’s not put the cart before the horse. To harness and control energy we first need to understand “what is energy” and understand how it behaves. I’m not going to give you a long-winded technical definition of energy because that isn’t the purpose of this website. When you’re doing an energy project, what you really need to know is how energy flows so you can think your way through how to save or channel the energy.  You’ll be the neighborhood expert in no time!

Definition of Energy

So what is this thing called Energy?

Webster defines it as “a fundamental entity of nature that is transferred between parts of a system in the production of physical change within the system and usually regarded as the capacity for doing work”.

Oh – you forgot to mention you wanted it in English! Ok – so again I ask: What is energy?

Many of the good things in life come from energy, like heat for our homes, a car to drive, electricity for lights and for running appliances. Catastrophic things like meteors crashing to earth, solar flares, nuclear bombs, volcanoes, and earthquakes are destructive forces all resulting from the unleashing of energy.

I think we can agree that when energy does its thing, work gets done, be it good or bad. So let’s keep it simple and just use the end of Webster’s definition. We’ll define energy as “the capacity to do work” or the ability to do work. Work results from a force acting over a distance, and it takes energy for that to happen.

Saving is as simple as 1-2-3

So now that we have a definition of energy let’s see how it behaves. And since our goal is to save money by saving energy, let’s bring the almighty dollar back into the picture. Lucky for us, there are only 3 ideas we need to keep in mind when it comes to saving money through saving energy.

  1. Efficiency
  2. Cost per unit
  3. Flow from high to low energy

I’ll explain these in a minute, but just remember – if you keep these 3 simple ideas in mind you’ll be able to logically approach any energy saving project and understand why it works.


Efficiency is simply Output Energy divided by Input Energy. High efficiency means getting more out for less in. So if we use energy efficiently, it’s like buying it on sale. That’s what we want!

Now let’s look at how to calculate efficiency.

Energy is constantly converted from one form to another, for example, an electric motor converts electrical energy into mechanical energy to turn the shaft and has a by-product of heat energy. There are many types of energy including heat, light, mechanical, electrical, chemical, nuclear, sound, gravitational, etc. The cool thing is that there are ways to transform each of these to any other, and we do this every day – our car burns gasoline and converts it into mechanical energy, power plants convert the burning of coal or gas into electrical energy, and a curling iron converts electrical energy into heat energy.

Each type of energy has its own units of measure, and one unit can be mathematically converted into another unit. For example, we can show that 1 kilowatt of electrical energy is equivalent to 1.341 horsepower of mechanical energy. The reason this is important is that it allows us to calculate efficiency even when energy undergoes conversion from one form to another. By the way, did you know that the origin of “horsepower” dates back to the late 18th century when people needed a way of comparing the power of the newly developed steam engine to the power of a horse – so a horsepower really is the amount of work that people determined an average horse can accomplish.

Suppose we measure an electric motor to have an output of 1 horsepower and we measure the electricity required to run it at 829 watts. To calculate the motor’s efficiency we have to convert both output and input to the same units before dividing. We can do this by converting horsepower to watts (1 hp = 746 watts) and dividing output by input (746 watts / 829 watts) to find that the motor has an efficiency of .9 which is 90%.

We can talk about the efficiency of air conditioning equipment, heating equipment, appliances, solar collectors, wind generators, and the list goes on and on. But the take-away is that we always want to get the most output for our input – and that will give us the most bang for the buck – and that will put a smile on our face.

Now you can define efficiency (output divided by input), and by definition, you can calculate efficiency given the right conversion factors.


  • Energy Conversions.
  • Energy Star. This important international standard does much of the heavy lifting for us by setting energy consumption standards for appliances and many other energy consuming devices – even new homes.

Cost Per Unit

This one is simple. We always want to buy energy at the lowest possible cost – electricity at the lowest cost per kilowatt-hour, and natural gas at the lowest cost per hundred cubic feet, and water at the lowest cost per thousand gallons. Done. Next subject.

Flow From High to Low energy

This is a subject that could get into some deep thermodynamics, but we don’t need to do that to save energy and money. All we need to know is that energy moves from “high” to “low”. By that I mean it moves from high heat to low heat, from high voltage to low voltage, from high pressure to low pressure, from high altitude to low altitude.

This principle becomes important when we look at insulation and radiant barriers. Here’s a question for you: In the summer when running air conditioning, do you improve the insulation in your home to keep the cool air inside from escaping, or to keep the heat outside from entering? Remember, high to low, so we insulate to keep the heat from entering. Hot air has more energy than cold air so the energy flow is from hot to cold.

If you put a radiant barrier on the outer part of a wall, it keeps the radiant heat from penetrating most of the wall, but in the winter it allows the radiant heat inside to penetrate most of the wall before being stopped. So, in cold climates it is ideal to have a radiant barrier installed closer to the inside wall, and in hot climates it is better to have it closer to the outside of the wall. Keep in mind that other variables such as moisture control often overrule optimum energy design.

Create a picture of one-way energy flow in your thought. When you’re thinking about energy saving, visualize energy flowing from hot to cold, air flowing from high pressure to low pressure, etc. That’s what the experts do, and after a while it becomes second nature.

March forward and save!

Now you have a feel for what energy is and how it behaves, at least with respect to the topics we’ll examine to save on your utility bills. Buy energy at the lowest cost, use it efficiently, and visualize its flow so you can put up barriers (like insulation) and direct it where you need it. That’s how you minimize energy waste and keep dollars in your pocket.


P.S. – A friend of mine uses the quote “the least expensive watt is the one not used”. Great point. The most efficient light in the world uses 100% more energy than the one that is turned off! So, keep in mind that not using energy is always the first line of defense against high energy bills – and turn the lights off when you’re not using them!