The Energy

The stored work performance is referred to as energy according to the work expended. For example, when an object is heated, this stored heat is present as thermal energy. When the energy is released into the environment, work is performed again. Energy is therefore the ability of an object to perform work. As described above, it is a conserved quantity, which means that energy can neither be created nor destroyed. This chapter deals in detail with the concepts of energy conservation, the idea of different forms of energy and methods of storing it.

1 The law of conservation of energy

The law of conservation of energy states that the total amount of energy in a closed system remains constant, even though energy can be converted between different forms. This means that energy can neither be created nor destroyed, but can only be transferred from one form to another.

A clear example: when a ball is dropped from a height, its potential energy (the energy it has due to its position) is converted into kinetic energy (the energy of motion) as it falls. When it reaches the ground, some of this kinetic energy may be converted into other forms of energy, such as heat or sound, but the sum of all these forms of energy remains equal to the ball’s original potential energy. This illustrates how energy is conserved even when it changes form.

2 The different forms of energy

In physics, energy describes the ability to perform work and occurs in various forms, each with specific properties and applications.

Kinetic energy is determined by the movement of an object. Energy depends on the mass and velocity of the object and is important in mechanics. Potential energy refers to the position of an object in a force field, such as the Earth’s gravitational field. A ball that is thrown into the air transforms its potential energy into kinetic energy as it falls.x Thermal energy, oder Wärme, ist die Energie, die aus der Bewegung der Teilchen eines Objekts resultiert. Sie ist in Wärmekraftmaschinen und anderen thermodynamischen Prozessen von entscheidender Bedeutung. Electrical energy entsteht durch die Bewegung von Elektronen in einem elektrischen Feld und ist fundamental für den Betrieb technologischer Geräte. Chemical energy ist in den Bindungen von Molekülen gespeichert und wird bei chemischen Reaktionen freigesetzt. Sie wird zur Bereitstellung von nutzbarer Energie und in der Medizin genutzt. Nuclear energy entsteht durch Veränderungen im Atomkern, zum Beispiel durch Kernspaltung oder -fusion. Sie wird zur Bereitstellung von nutzbarer Energie und in der Medizin genutzt.

3 Electrical energy

Energy is the potential to perform work, for example, to accelerate charge carriers for a certain period of time. An energy source can only release as much energy as has been supplied to it beforehand. This corresponds to the time during which work was performed, i.e. an energy exchange took place. Since energy cannot exist without prior work and work cannot be performed without energy, causality is complex and mutually dependent. For this reason, the following assumes the existence of an energy source that can then perform work.

Energy \(E\) is generally defined over the integrated distance between two points \(P_\mathrm {1}\) and \(P_\mathrm {2}\) via a force \(\vec {F}\).

\begin {equation} E = \int _{P_\mathrm {1}}^{P_\mathrm {2}} \vec {F} \cdot \mathrm {d}\vec {s} [E] = \text {1 Joule = 1 J = 1 Nm} \label {eq:Fds} \end {equation}

An electric force \(\vec {F}_\mathrm {{el}}\) is present when a charge \(Q\) is exposed to an electric field \(\vec {E}\). Multiplying both quantities yields the following expression:

\begin {equation} \vec {F}_\mathrm {{el}} = Q \cdot \vec {E} \end {equation}

Inserted into the formula 1, integration over the electric field strength \(\vec {E}\) yields the electric energy \(E_\mathrm {{el}}\). Since the amount of charge \(Q\) does not depend on the distance, it can be moved outside the integral.

\begin {equation} E_\mathrm {el} = Q \cdot \int _{P_\mathrm {1}}^{P_\mathrm {2}} \vec {E} \cdot \mathrm {d}\vec {s} \end {equation}

From Module 1, we know that the integral over an electric field under constant conditions is the voltage \(U\). This results in the following simplified representation.

\begin {equation*} [E_\mathrm {el}] = \text {1 Joule = 1 J = 1 Ws} \end {equation*} \begin {equation} E_\mathrm {el} = Q \cdot U \end {equation}

4 Electrical energy storage

Electrical energy storage devices are characterised by the fact that they store energy in electrical or magnetic fields. The basic storage devices of this type are capacitors and coils. The advantages of these energy storage devices are fast energy release and high efficiency. In practice, however, they have limited storage capacity and are expensive. Capacitors can undergo many charging cycles, but have a low energy density. In order to store energy in a coil, current must flow through it continuously, which is technically challenging and only possible in special cases..

Figure 2 shows the two basic types of electric energy storage. On the left, energy is stored in an electric field. This is achieved by placing charges with different signs on the capacitor plates. On the right-hand side, a coil is shown which, according to Lenz’s law, generates a magnetic field due to a current flow. The topics of coils and capacitors are covered in more detail in Module 3. Since a current flow is required to maintain the magnetic field, a coil does not constitute a storage device in which electrical energy can be stored outside a circuit through which current flows. A capacitor, on the other hand, can store electrical energy for a long time even without a connected circuit. This means that a capacitor can continue to release energy long after an electrical circuit has been switched off. For example, the rear light of a bicycle can continue to be supplied with electrical energy even when the dynamo is stationary at a red traffic light. This effect is undesirable in circuits with higher voltages, for example, as the electrical energy present in the capacitors can pose a hazard to people even after the systems have been switched off if there are no appropriate protective circuits.

Batteries are therefore often used for medium-term storage of larger amounts of energy (see Figure 3). Batteries store energy chemically, can store larger amounts over longer periods of time and are versatile, making them ideal for powering mobile applications.

Although batteries are versatile, they also have some disadvantages: they are often expensive to purchase and maintain, have a limited lifespan, and their manufacture and disposal can cause significant environmental pollution due to the raw materials used.