A hunter attempting to kill their prey could throw an arrow at it, transforming the chemical potential energy stored in their tissues into kinetic energy of the arrow. This hunter would not likely be very successful though, since their muscles can only contract so fast, and they would not get the arrow moving quickly enough to strike the prey with any significant effect.

A better approach is to use an energy transformation technology, such as a bow. This technology will involve two energy transformations:

First, the chemical potential energy stored in the hunter’s tissues is used to contract muscles resulting in a force that stretches the bow.

Once the string is released, the elastic potential energy stored in the bow is transformed into kinetic energy of the arrow. The use of this energy transformation technology allows the hunter to use what their body is good at – generating a strong force on the bow over a slow movement – combined with what the bow is good at – releasing its stored energy rapidly – to accelerate the arrow to a high velocity resulting in a successful hunt.

You probably do not need to look very far to find an example of an energy transformation technology. A light bulb, a kitchen range, an air conditioner, an automobile, a water sprinkler; all are examples of devices that transform energy from one form into another. In this activity, you will learn about energy transformation technologies and factors that affect their impact on society and the environment, with a focus on electricity production.

Efficiency

The efficiency of an energy transformation technology is the ratio of the useful output energy to the total input energy. Mathematically this can be expressed using the following equation:

Where  is the useful output energy and  is the total input energy. But wait, doesn’t the principle of conservation of energy tell us that energy cannot be created or destroyed? Where did the “missing” energy go? In any real world energy transformation device, some energy is always converted into forms that are not useful (you can think of this as “waste” energy). We can model this, while still adhering to the principle of conservation of energy, using the following equation:

Where  is energy that is converted into forms that are not useful.

Consider an electric motor. The friction of components inside an electric motor will convert some of the total input energy into thermal energy. Also, the electromagnetic coils inside the motor will convert some of the input electrical energy into thermal energy as they heat up due to the electric current flowing through them. Even the power cord that supplies power to the motor will convert some of the electrical energy flowing through it into thermal energy.

Consider an electric toaster. Surely there cannot be any wasted thermal energy, since the purpose of a toaster is to heat up, right? The answer is “No.” Even a toaster will not be 100% efficient since the useful output energy is that which is used to heat up the toast, but the parts of the toaster will heat up as well, and this is not useful. In addition, some thermal energy will escape the toaster, heating its surroundings. This energy is also not used to heat the toast, so it is not useful, either.

Consider a bicycle tire pump. The work done by the force of the person pushing down on the piston is used to compress air and force it into the tire. The mechanical energy used to push on the piston is therefore converted into the potential energy stored in the air as a result of its higher pressure. This system will let some of the compressed air escape, through leaks between the piston and the wall of the pump cylinder, as well as air that escapes when connecting/disconnecting the hose from the valve stem of the tire.

As you can see, there are many ways that a single energy transformation device like an electric motor or toaster can convert the input electrical energy into less useful forms, and the less useful form is not always thermal energy.

Example

An interesting example of recovering energy that would otherwise be lost, in order to increase the efficiency of a system, is regenerative braking. Regenerative braking is used in hybrid and electric cars and is used to transform the kinetic energy of the car into electric potential energy stored in a battery, rather than dissipating the energy as heat through a conventional friction-based braking system. Regenerative braking turns the motor(s) used to propel the car into generator(s), which charge the car’s batteries as they reduce the car’s speed. Regenerative braking gives hybrid and electric cars a significant benefit for city driving, where there are many stops and starts. Regenerative brakes cannot be used on conventional gasoline-powered cars – although the kinetic energy can be transformed into electrical energy, in a gasoline-powered car the battery is not designed to store this electrical energy, and even if it could store it, a gasoline-powered car lacks the electric motors that are needed to put that energy to use once the driver decides to start moving again.

Example

Electricity Production – Renewable and Non-Renewable Sources

Today’s society would not function as it does without a reliable supply of electricity. There are many jobs in the electricity supply sector from the power plant, where energy is converted from some other form into electrical energy, to the transmission lines that carry it to the consumer, to the electrician who ensures that the wiring in your home and business is safe to use. People working in all of these areas do so in order that you will be able to light up a room with the flick of a switch anytime of the day or night. There are many different means of “generating electricity” or, as a physicist would say, converting some form of energy into electrical energy at the power plant.

Hydroelectric power plants operate by converting the gravitational potential energy of water in a reservoir first into mechanical energy as it moves down the penstock, turning a turbine, which then turns a generator which converts the mechanical energy into electrical energy.

Coal-fired, gas-fired, and nuclear power plants all work on the same principle: using thermal energy to boil water producing steam which is transformed into mechanical energy by a turbine, which then turns a generator which converts the mechanical energy into electrical energy.

There are two main types of solar power plants: those based on solar cells and those that concentrate the Sun’s energy to boil water and operate a turbine. With a solar cell plant, arrays of solar cells are used to directly convert the radiant light energy from the Sun into electricity. With a concentrator plant, arrays of mirrors focus the Sun’s energy on a boiler at the top of a tower, heating it up so much that it changes state to form steam. This steam is then used to turn a turbine which in turn is connected to a generator to convert the mechanical energy from the turbine into electrical energy.

Wind turbines are becoming more and more popular. They operate, usually in arrays known as “wind farms,” by harnessing the energy of the wind blowing through the turbine blades, and then transforming that energy into electrical energy through a generator.

Pumped Hydroelectric Storage

One solution to the problem that solar and wind power plants are highly weather dependent is to store the energy that they produce when it is sunny/windy so that it can be used when needed. Pumped hydroelectric storage is one way to accomplish this. A pumped hydroelectric storage plant usually incorporates two reservoirs at different heights, upper and lower. When surplus electricity is available from another plant, the pumped hydroelectric storage plant uses this electricity to pump water from the lower reservoir into the upper reservoir, storing the electrical energy used in the form of increased gravitational potential energy in the upper reservoir. If the grid needs additional electricity later, the water in the upper reservoir is allowed to flow through a turbine to the lower reservoir, generating electricity in much the same way as a standard hydroelectric power plant.

Summary

The efficiency of an energy transformation technology is the ratio of the useful output energy to the total input energy:

Energy that is transformed into non-useful forms is usually, but not always, transformed into thermal energy.

Electricity is produced using a variety of technologies that employ non-renewable sources such as coal, gas, and nuclear fuel, as well as renewable sources such as hydroelectric dams, solar, and wind energy. Each of these technologies have strengths and weaknesses and no one technology is well suited to all applications.

Pumped hydroelectric storage is one technology that makes weather-dependent electric production technologies, such as solar and wind, more viable.