Understanding Energy

This page consists of a variety of energy data and unit conversion information such as the energy content of different fuels, the conversion of the BTU, Wh, etc into other units, and also how to determine power consumption.

  1. What Energy is and the Different Types
  2. Understanding Power Consumption
  3. Energy Unit Conversion
  4. Other Energy Units
  5. Which Source of Energy is the Future?
  6. Energy Content of Fuels
  7. How much gasoline can come from a barrel of oil?
  8. Difference Between Temperature and Heat Quantity
  9. How to Use Power Monitors
  10. How Much Power Your Appliances Use

What Is Energy?

Energy is defined as the capacity of a physical system to do work. Think of energy as what can be done, and work as what is actually being done.

There are different types of energy that can be converted to each other using a variety of methods and it can also be ‘produced’ by processing matter, such as combustion.

Thermal Energy: Also called heat. Thermal energy is another term for heat. It is the byproduct or waste product of a very large number of processes as well as a precious commodity, which is required to sustain life on earth. Heat exists everywhere and in everything and everyone. Nothing can contain no heat, no matter how cold it seems to be.

Examples of generators and that utilize thermal energy:

  • Steam Turbines.
  • Stirling Engines.
  • Thermoelectric Modules.

Electrical Energy: Also called electricity, and frequently referred to as ‘power’ (but power is not specifically electricity), electricity is another form of energy that is often converted into other types of energy using a variety of methods such as electromagnetic induction for the provision of mechanical energy to move items. Electrical energy is in the form of electrons that are moved by a voltage.

Mechanical Energy: Mechanical energy is the energy possessed by something due to it’s movement. This movement can be the movement of your feet, arms, a rotating wheel, a sliding window, or anything else that moves. Mechanical energy is often converted into electrical energy by two types of generators such: as alternators and dynamos.

Kinetic Energy: Kinetic energy is the energy that an object possesses due to it’s motion. This means that the fact that a car which is moving possesses kinetic energy because it is moving. Hybrid-electric and electric vehicles take advantage of this kinetic energy using regenerative braking. Another example is the wind, as well as the movement of your hand.

Potential Energy: Potential energy is what the name implies. It is not literally energy in the conventional context, but can be used to generate energy, such as compressed air or pumped hydroelectric storage visit the energy storage page for more information. Potential means having capability.

Understanding Power Consumption

Refer to the list of units below this section whenever you are unsure about a unit. The most relevant units are in bold text.

Example 1: If a flashlight bulb is rated at 1 watt, then that means that it consumes 1 watt-hour for every hour that it is on. This means that if the flashlight bulb was on for 1 hour, then it consumed 1 Watt-hour of energy (which is normally abbreviated to Wh). This means that the wattage of the flashlight bulb is 1 Watt. All you need to do is multiply wattage by number of hours left on.

A Watt-hour is not the same as a watt, try not to confuse them with each other. The Watt is the rate of power consumption, and Wh is a quantity of energy. 

Example 2: If an apparatus such as a toaster is rated at 1 kW, then it would have used 1 kWh (kilowatt-hour) of energy after being on for 1 hour.

Example 3: If an apparatus is rated at 2 kW maximum 2,000 watts), and is operated at the 2 kW maximum wattage I mentioned, then it would have used two kWh of energy after being on for 1 hour. Maximum wattage is the amount of power an electrical device uses when it is set to a setting at which it needs to consume that much power. For example, turning up the brightness of a light bulb to the maximum causes it to consume its maximum wattage.

I will tell you how to calculate the amount of energy a heater will use after 5 hours at two settings and then ask you to try calculating it yourself, then check your answer a little further down the page to determine if you did it correctly.

A heater is rated at 1,000 watts or 1 kW when set to high, and 500 watts (which is 0.5 kw or half of a kW) when set to medium. Calculate how much energy it would have consumed after 5 hours on the high setting alone, and afterwards calculate how much it would calculate after operating for 5 hours on the medium setting.

Remember: All you need to do is multiply wattage by number of hours left on.

Also keep in mind that the time that an appliance is on is equally important to the wattage of the appliance. They are exactly of equal importance simply because overall electricity consumption = wattage x time used (in hours).


High: 1 kW * 5 hours = 5 kWh.

Medium: 0.5 kW * 5 hours = 2.5 kWh.

One way to check the rated wattage of an apparatus is by looking at the label on the back of it. You should see either the rated wattage, or the voltage and amperage. The wattage is the voltage x amperage. So if the appliance is rated at 120 volts ( the label might say 120V), and 2 amps (the label might say 2A), then it is a 240-watt appliance (maximum, it may not necessarily use this much energy).

1 Amp (A) = 1000 milliamps (or mA). So 200 mA = 0.2 A, 20 mA = 0.020 amps, and 2 mA = 0.002 amps.

Amp =Ampere.

Wattage = Voltage * Amperage.

Amperage = Wattage / Voltage.

Voltage = Wattage / Amperage.

The ampere is the unit of electric current. The volt is the unit of electromotive force (EMF) or potential difference (pd).Voltage is the force that motivates current to move from one place to another (for example: from a battery to a light bulb).

Sadly, some devices do not have their power consumption printed on them, therefore you will have to measure it yourself, and you can do so with a devices such as power consumption meters. One example of such devices is the Kill A Watt line of energy use meters.

Energy Unit Conversion

  • 1 TW (Terawatt) = 1,000 GW or 1 trillion watts.
  • 1 GWe = 1 Gigawatt electrical power.
  • 1 GW (Gigawatt) = 1,000 MW or 1 billion watts.
  • 1 MWe = 1 MW electrical power.
  • 1 MW (Megawatt) = 1,000 kW or 1 million watts.
  • 1 kWe = 1 kW electrical power.
  • 1 kW (Kilowatt) = 1,000 watts.
  • 1 W (Watt) = 1,000 mW (Milliwatts).
  • 1 mW (Milliwatt) = 1,000 microwatts.
  • 1 µW (Microwatt) = 1,000 nanowatts.
  • 1 nW (Nanowatt) = 1,000 picowatts.
  • 1 A (Ampere or Amp) = 1000 milliamps.
  • 1 mA = 0.001 Amperes.
  • 1 µA = 0.000001 Amperes or 0.001 mA.
  • µWh: Microwatt-hour.
  • mWh: Milliwatt-hour.
  • Wh: Watt-hour.
  • kWh: Kilowatt-hour.
  • MWh: Megawatt-hour.
  • GWh: Gigawatt-hour.
  • TWh: Terawatt-hour.
  • Ah: Ampere-Hour or Amp-hour. Amp is an abbreviation of ampere.
  • mAh: Milliampere-hour.
  • µAh: Microampere-hour


  • 1 Wh = 3.6 kJ or 3600 Joules.
  • 1 kWh = 3,600 Kilojoules.
  • 1 MWh = 3,600,000 kJ, 3600 MJ, or 3.6 Gigajoules.
  • kJ: Kilojoule.
  • MJ: Megajoule.
  • GJ: Gigajoule.


  • 1 kV: Kilovolt = 1,000 volts.
  • 1 V: 1 Volt (1/1000 of a kV).
  • 1 mV: 1 Millivolt (1/1000 of a volt).
  • 1 µV: 1 Microvolt (1/1,000,000 of a volt).

Other Energy Units

This section is meant to help you to understand other energy units better and their relationship with the watt unit.

1 watt = 3.41 BTU.

1 Wh = 3.41 BTUh.

1 Wh = This means that energy is being consumed or supplied at a rate of 1 watt and for one hour.

1 BTUh = 1 BTU for one hour.

Just like there is the watt and the watt-hour, there is the BTU and the BTU-hour. BTU means British Thermal Unit and is usually used to measure heat energy and also the cooling or heating capacity of air conditioners. A 12,000 BTU air conditioner is capable of removing 12,000 BTU of heat from the room(s) it is cooling every hour that it is operated. This assumes that the air conditioner is operating at its maximum performance setting. Keep in mind that cooling is the process of removing heat from an area or an object, and “cold” is  actually a lack of heat.

You can convert the BTU rating of the 12,000 BTU air conditioner above to watts if you want to. If 1 watt = 3.41 BTU, then 1 BTU = 0.293 W. So 0.293 * 3,516 watts.

Source of Unit Conversion Information – Read more.

Which Source Of Energy Is The Future?

The answer to that question is: No single source of energy. It is not wise to rely on one source of energy, especially in the case of fossil fuels because demand for the fuel would be very high. For example: The more you rely on gasoline, the greater gasoline demand will be. If the world currently received half of its electricity from coal power plants (not quite accurate, but I did this for the sake of simplicity) and relied on those plants for 100% of it instead, that would double coal demand for electricity generation, causing coal prices to surge in accordance with the laws of demand and supply. The same applies to natural gas.

If you were to obtain the other half of that power from solar power plants instead of coal, then you would not only prevent the enormous coal price surge I mentioned above, but you would also slow down the rate at which the price of coal increases due to its dwindling reserves.

The drawback of relying on solar power entirely is considerably different from what I mentioned above. Less sunny and overcast locations such as Germany require more solar panels to generate the same amount of electricity as sunnier locations, such as Florida or Jamaica, and this means that solar power plants and other solar systems, including solar water heaters cost more in Germany because they need to be bigger in order to harvest the same amount of sunlight that a smaller system could in Jamaica or Florida. This is due to the fact that there Florida and Jamaica receive more sunlight per square metre.

Energy Content of Fossil Fuels (Based on U.S. consumption in 2009)

The BTU is a unit of thermal (heat) energy.

  • Petroleum/Oil: 1 barrel of oil (used in the United States, oil quality varies) contains 42 U.S gallons of oil, which is equal to 5,800,000 BTU, 1,700 kWh, 1.7 MWh, or 1.7 million Wh of energy.
  • Gasoline: 1 gallon of gasoline contains 124,238 BTU or 36.41 kWh of energy. This equals 13 kWh/kg of gasoline.
  • Diesel: 1 gallon of diesel contains 138,690 BTU or 40.64 kWh of energy.
  • Coal: 1 short ton of coal contains 19,953,000 BTU, 5,847.89 kWh, or 5.84 MWh of energy.
  • Natural Gas: 1 cubic foot of natural gas contains 1,027 BTU or 300.9 Wh of energy (0.300 kWh).

Source: U.S Department of Energy

Gasoline Content of Crude Oil

The amount of gasoline obtainable from a barrel of petroleum is dependent on the quality of the barrel (this depends on where the barrel came from). 1 barrel normally contains 42 U.S gallons of oil. Typically, 19.5 gallons of gasoline are obtained from each barrel of oil, in addition to other products such as heating oil.

Read more.

Difference Between Temperature and Heat Quantity

Heat quantity is the amount of heat energy something contains. Temperature is how hot it is. Just because one object is hotter than another, does not mean that it contains more heat (which is heat energy) than the other. Smaller objects of the same type heat up to higher temperatures with less energy than larger objects.

If you have two pieces of iron, one piece is 1 gram, and the other piece is 3 grams, and you want to heat them both to 100 °C then you would have to supply them both with heat using a device such as a flame at whatever rate you please, as long as it exceeds the rate at which they cool.

If both of them are supplied with the same amount of heat per hour, then the 3 gram piece will take 3 times as long to heat up as the 1 gram piece because it requires 3 times as much heat overall, or, you could supply the 3 gram piece with 3 times as much heat per hour to heat it to 100 °C just as fast as the 1 gram piece.

Please bear in mind that the temperature of the flame being used to heat the iron has to be greater than 100 °C. A rule to keep in mind is that heat travels to colder places. If one object is 100 °C and the second object is 70 °C, then heat will travel from the first object to the second until they are both the same temperature. The first object heats the second one, and the second object cools the first one.

How To Use Power Monitors

To use a power monitor such as the Kill A Watt, for example, you would simply plug the apparatus into it, and then plug the monitor into an outlet. Please read the manual carefully before doing anything. It should tell you the amperage, voltage, and power draw (in Watts/kW) of the appliance. It will also help you to determine the amount of money that your appliances cost you because of their power consumption.

Average Wattage of Common Appliances

Please note that I listed only the rated wattage of the appliances below, some of them contain inverters and utilize energy efficiency improvement methods, so they do not all consume that much electricity, all the time, and some items have a peak wattage, which is not the actual wattage. Always check the back of your appliances for the power consumption. If a personal stereo system says ‘520 Watts Peak’ on the front, then check the back, because that is not likely to be the actual wattage.

You really should visit the appliance power consumption page before or after this section, it is much more relevant and helpful for residential matters. It explains how to determine appliances’ actual power consumption.

Please note that the length of time and how frequently the appliances are used is one of the most significant factors determining their power consumption.

  • Air conditioner window or split unit: 515-1,500 watts (not necessarily the maximum power, but average).
  • Single room heater: 500-1,500 watts.
  • Water heater: 2,000-6,000 watts (It could be less depending on the setting).
  • Clothes dryer: 1,000-6,000 watts.
  • Dishwasher: 1,200 watts.
  • Standing fan: 30-60 watts.
  • Ventilation fan: 50 watts.
  • Hair dryer: 600-3,000 watts.
  • Personal computer system unit: 200-1,000 watts.
  • 17 inch Personal computer CRT monitor: 80-140 watts.
  • 17 inch Personal computer LCD monitor: 20-60 watts.
  • 32 inch CRT television set: 180 watts.
  • Fluorescent light bulb for typical room: 7-23 watts.
  • Incandescent light bulb for typical room: 25-100 watts.
  • Home stereo: 50-350 watts.
  • Computer speaker system: 10-200 watts.

Upgrading Appliances

It does not make sense to upgrade all appliances. Some extremely old appliances dating back to the 1980s are worth upgrading, such as air conditioners, refrigerators (as well as refrigerators from the 90s),

Other upgrades include:

  • Incandescent light bulbs: I would recommend upgrading these to CFLs/fluorescent bulbs (except in rooms where lighting is rarely used). Some LEDs are great candidates that can pay for themselves quickly too.
  • TVs: Generally, you won’t see an ROI by upgrading your TV, unless you are upgrading to a small LCD (less than 27″).

Further Reading

University of Pennsylvania: Understanding Electrical Ground.

GSU.edu (An excellent source of information, please visit).

BBC GCSE Bite Size: U.K. Mains Electricity.

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