What is energy besides heat

Basic concepts of energy

This page is intended to explain the scientific fundamentals of energy generation. In the interests of general comprehensibility, physical accuracy is deliberately avoided.



Energy is the ability to do work.

Energy comes in different forms:

  • Kinetic energy
  • Position energy (potential energy)
  • Thermal energy
  • Electrical power
  • Atomic energy, nuclear energy
  • Radiant energy (electromagnetic waves, solar energy)
  • Chemical energy

The different forms of energy can be converted into one another.

With all energy conversions, the amount of energy always remains the same (physical law). In a strictly physical sense, energy cannot be destroyed or generated. Under Power generation one understands thereby the conversion of one form of energy into a rather desired other form. With all energy conversions, however, only part of the specified amount of energy can be converted into the desired final form. When generating electricity in conventional power plants, for example, part of the chemical energy of the fuel (oil, gas, coal) is converted into electrical energy, here 30% -45% depending on the technology of the power plant. This percentage is known as Efficiency. The remaining amount of energy is undesirably converted into heat. This part is called colloquially Loss of energy. Since energy is mostly bound to certain materials, one also speaks of Energy carriers.


Meaning of the individual forms of energy

Kinetic energy

This form of energy is always present when something is moving, e.g. a vehicle, the air (wind energy), water (energy in waves and rivers). The kinetic energy of the air or flowing water is used in wind and water mills. Kinetic energy is often the target of energy conversions. So z. For example, in a car, the chemical energy of the fuel is first converted into heat and then (partially) into the vehicle's kinetic energy.

mechanical positional energy (potential energy)

A stationary object that is at a local level that is higher than another local level has a certain positional energy. This can be converted back into kinetic energy by letting the object fall to a lower level. In storage reservoirs, for example, energy is stored in the form of potential energy. If necessary, you can let the water fall again to a lower level and convert the potential energy back into mechanical kinetic energy and finally back into electrical energy. A hollow body filled with gas under high pressure also contains potential energy that can be recovered after opening the discharge valve. This form of energy storage is used in large salt caverns filled with compressed air.

Thermal energy

The heat that is generated when an energy source is burned is partly transferred to the combustion products, for example to the flue gases. Hot flue gases have a high level of thermal energy. They can be used, for example, in a car engine or a turbine to generate mechanical energy. The value of the thermal energy depends primarily on the temperature level. The higher the temperature (actually: the temperature difference between the heat accumulator and the environment), the greater the proportion of heat that can be converted into kinetic or electrical energy. With temperatures of a few hundred degrees, a variety of technical processes can be carried out, e.g. burning cement or steel production. Low temperatures are only suitable for heating apartments. In almost all energy conversions, thermal energy arises as "waste energy", i.e. it is often counted as a form of energy that cannot be further used as part of energy losses.

Electrical power

Electrical energy is very practical because it can easily be converted into almost all other forms of energy in small devices (electric motor, heater, lamp). It can also be easily transported over long distances using cables. However, it has the disadvantage that it can only be stored in larger quantities with great effort and always has to be produced from other forms of energy at the time of consumption. Large conversion losses often occur here.

Atomic energy, nuclear energy

When using atomic energy, in contrast to all other forms of energy, the atomic nuclei react, which releases very large amounts of energy. However, radioactivity is also produced, which is very harmful to humans and can only be protected from with great effort. Furthermore, the problem of the millennia-long disposal of radioactive waste has not yet been solved anywhere in the world. When converting into electrical energy, around 70% of the heat is lost, which leads to the heating of the rivers. The sun's radiation is produced by nuclear reactions on the sun.

Radiant energy (light, solar energy)

The energy of light can be seen in sunburn. The light energy of the sun is the form of energy that flows in large quantities from the outside onto the earth. However, the amount of energy per square meter (energy density) is relatively small. All other regenerative (renewable) forms of energy, with the exception of geothermal energy, are created from solar energy through conversion. The occurrence of solar energy on earth, however, particularly in Germany, is heavily dependent on the weather, the day / night rhythm and the season. The astrophysicists estimate that the sun will continue to shine for about 5 billion years.

Chemical energy

This form of energy is found in all fuels and foods. The chemically bound energy can be converted into other forms of energy by burning coal, wood, oil, gas or by using it in living beings. As a rule, heat is also released, which is either used directly for heating or further converted into mechanical energy (car engine) or electrical energy (coal-fired power station). Energy can be stored particularly well in the form of chemical energy (small volume, low weight → high energy density).

Classification according to conversion steps

Forms of energy that occur directly in nature are referred to as Primary energy. Through the energy conversion, possibly over several steps (secondary energy), the form of energy desired by the human being arises, the Final energy. Actually, however, it is not the energy itself that is the goal of all activities, but that which people want Energy benefitse.g. a warm room. This can often be achieved without using energy, for example through better thermal insulation.


Energy balance of the earth

In addition to the energy from radioactive decay in the interior of the earth, solar energy is the only form of energy that is supplied to the earth's surface in large quantities. Part of the energy that has flown onto the earth in a few million years is stored in the earth's crust in the form of fossil fuels (coal, crude oil, natural gas). At the moment, mankind is consuming this energy at a rapid pace. It cannot be restored in human time. Almost all energy conversions ultimately lead to thermal energy. This thermal energy is released back into space from the earth. Energy radiation from the sun and energy output are in equilibrium, so that the temperature on earth does not change.

When fossil fuels are burned, carbon dioxide is produced. This is not a pollutant created by side reactions that can be reduced by taking appropriate measures, but alongside water actual product of burning and therefore not to be prevented.

fossil fuel + oxygen in the air → carbon dioxide + water (vapor)

The increase in carbon dioxide in the atmosphere, like a sweater, adds additional thermal insulation to the earth, which increases the temperature on the earth. This results in climate changes with hardly manageable consequences.

All in all, the renewable forms of energy occurring on earth are a multiple of the energy used by humans.


Measurement of amounts of energy

The quantities of energies are given in the various forms of energy by different units, which can all be converted to one another. To illustrate, some activities are given in which about this amount of energy is consumed.

1 kWh =

3 600 KJoules =

860 Kcal =

3,600,000 Nm

Kilowatt hour

Kilo joules

Kilo calories

Newton meter

electrical power

chemical energy in food

Thermal energy

Position energy

Operate the kettle for 0.5 hours

1.9 l Coca-Cola

Heat 10 l of water by 86 °

Carry 360 kg 1000m high

6-8 h to watch TV

Calorie consumption per day during heavy physical work

1 x shower

Mountain hike with a heavy backpack at an altitude of 4000 meters

For very rough rough calculations you can remember that the following amounts of energy of the usual energy sources are roughly the same:

1l petrol ~ 1l diesel ~ 1 l heating oil ~ 1m³ natural gas ~ 10 kWh electricity ~ 2kg dry wood ~ 1kg hard coal

By the way: 1 permanent standby consumption of 1 W by a device leads to an annual consumption of 8.76 kWh!

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further information at:

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