Converting energy to practical applications is usually a concern that you would encounter in the study of engineering and kinetics. By definition, energy is an amount or quantity that describes how much work a physical force can accomplish. Meanwhile, power is the rate at which energy is converted from one form to another.
Energy comes in two forms—kinetic and potential. Potential energy is usually stored in some form, and it can be converted into another form by chemical or mechanical means. For instance, gasoline fuel has a certain amount of potential energy. This is converted into kinetic energy when the fuel gets inside the cylinders of an automobile’s engine, when the petroleum is ignited. And when the fuel combusts inside the engine’s cylinders, the pistons turn and energy turns into mechanical energy. In this case, the engine generates power that propels the vehicle forward (or backward, as the case may be).
Another example is energy stored inside a battery. These are in the forms of chemicals (which could be based on different chemistries like Lithium, Nickel, Zinc, or others). When a battery is connected to a circuit, the energy is converted into power, that lights up a bulb, turns a motor, or does other activities, like for example power up a laptop computer.
Energy is usually measured in quantities of work done at a given amount of time. For instance, one basic unit of energy is the Joule, which is one Watt second of energy. This is the work that is accomplished by one Newton of force through a distance of one meter. Therefore, since one hour contains 3,600 seconds, one Watt-hour contains 3600 Joules of energy.
Batteries are usually rated on a mAh basis, or milli-Ampere hour. If you know the average voltage at which the battery discharges current, you can determine the energy stored in the battery. For instance, if an AA battery holds 1000 mAh of charge, and has an average voltage of 1.5 Volts, you can multiply the two figures to achieve 1,500 mA-Volt hours, or 1,500 milliwatt-hours. This is equivalent to 1.5 Watt-hours. Multiplying it with 3,600 we get 5,400 Joules of energy.
Converting this energy into power is a different matter altogether. In this case, a factor called efficiency also comes into play. When converting energy from one form to another, sometimes there are efficiency losses, mostly in the form of heat. For instance, when a battery powers up a motor, the transfer of energy sometimes generates heat within the circuitry, which is simply lost into the air. In the same case, while the motor is running, friction can cause the motor to have difficulty in rotating and will also generate heat. This heat is usually considered a loss, because it does not contribute to the end that you would want to achieve from the battery and the motor (unless generating heat is your primary goal).
Converting energy into power without the resulting efficiency losses is what engineers usually want to achieve, especially in fields like automotive engineering. This is where the latest hybrid cars come into the picture. For instance, these feature regenerative braking, in which the kinetic energy caused by the friction from stopping a vehicle is transmitted back by recharging the battery cells. There are other applications that attempt to capture all the energy and reduce wastage. But still, because this is an imperfect world with imperfect scenarios, we still have to contend with losing some energy as efficiency losses.
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