How is electrical energy created

Electrical power

Lexicon> letter E> electrical energy

Definition: Energy that is transmitted or stored with electricity

More general terms: energy

English: electrical energy

Categories: electrical energy, energy carriers, physical principles

Author: Dr. Rüdiger Paschotta

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Original creation: 03/19/2010; last change: 04.08.2020


Electrical power, often inaccurate as electricity or electricity called, plays a very important role in modern energy technology. Although it can only be stored directly in relatively small quantities (especially in capacitors), it can, however, be converted into various other forms of energy with often high levels of efficiency and, conversely (with often lower levels of efficiency), can be obtained from other forms of energy. It represents pure exergy (energy capable of working). Another advantage of electrical energy is that it can be transmitted very easily with cables, even over long distances - with high-voltage direct current transmission even over thousands of kilometers with moderate energy losses.

Generation of electrical energy

Electrical energy is a high-quality, versatile form of energy, but its generation in thermal power plants is lossy.

Electrical energy is obtained in large quantities in various types of power plants; one speaks briefly but imprecisely of Power generation. In most cases, mechanical energy is converted into electrical energy with the help of a generator, which is possible with a very high degree of efficiency (often well over 90%). The mechanical energy is either taken directly from nature (mostly as water power or wind energy) or obtained from thermal energy in heat engines. In the latter case, the conversion takes place with moderate efficiencies (often between 30% and 50%), which are limited by the second law of thermodynamics, but in practice can still be well below this limit. Higher overall efficiency levels can be achieved with combined heat and power, i. H. with simultaneous use of waste heat.

Methods that are still less widespread today are photovoltaics (direct generation of electrical energy from sunlight) and the use of fuel cells for the direct conversion of chemical into electrical energy. There are also thermoelectric generators that can convert heat directly into electrical energy, whereby a temperature gradient is required just as with heat engines and the conversion efficiency is limited.

Transmission of electrical energy

Electrical energy can be transmitted in the form of electrical power using overhead lines and cables. Here is the electrical power (Amount of energy per unit of time) the product of the current strength and the electrical voltage. For example, a current of 3 A (ampere) at a voltage of 12 V (volts) leads to an output of 3 A * 12 V = 36 W (watts), and within 2 hours an amount of energy of 72 Wh (watt hours) is transferred . Amounts of electrical energy are often measured in kilowatt hours (= 1000 watt hours), with larger amounts also in megawatt, gigawatt and terawatt hours.

The transmission of high powers requires high voltages in order to keep the energy losses low.

Since electrical lines have the higher the power losses, the higher the current intensity, high outputs with moderate currents, but very high voltages with Power lines transfer. The voltages used are usually hundreds of kilovolts (kV), sometimes even over one megavolt (MV).

The most common is the transfer of Alternating current, in which the current and voltage with a frequency of z. B. oscillate 50 Hz. (You then have 50 oscillations of current strength and voltage per second.) Opposite that Direct current Alternating current has the advantage that the voltage can be brought to a higher or lower level relatively easily with the help of transformers. However, high-voltage direct current transmission is becoming increasingly important, especially for high power and long distances, as it enables lower transmission losses, especially with underwater cables. Modern power electronics can convert alternating current into direct current with very low losses (with rectifiers) and vice versa (with inverters).

Storage of electrical energy

Electrical energy can be transmitted well and used in many ways, but it is difficult to store. The article on storage for electrical energy gives an overview of the possibilities.

Electrical energy can only be stored in capacitor storage in small quantities. So-called Super capacitors (Super caps) can e.g. B. store energy recovered when braking in an electric car (→Recuperation) and release again when accelerating.

Various other methods are used to store larger amounts of energy, in which the electrical energy must be converted into another form of energy:

  • Accumulators (rechargeable batteries) store energy in chemical form - with often high efficiencies in the order of 90%, but in very limited quantities. B. far below that of gasoline.
  • With electrolysis can z. B. win hydrogen with electrical energy, and later this hydrogen can be used again with a fuel cell to generate electricity. In this case, however, the energy losses are significantly higher (often over 50%).
  • Electrical energy can be easily and almost completely converted into mechanical energy with electric motors and generators, and vice versa. Mechanical energy can be stored in flywheels or as potential energy (positional energy), for example. The latter method is used in storage and pumped storage power plants, in which water is stored in a reservoir at a high altitude and, if necessary, “turbined” (used to generate electricity in a turbine). Another possibility are pressure accumulators, e.g. B. in the form of large underground storage facilities for compressed air (→ compressed air storage power plant).

See the article on electrical energy storage for more details.

Adjustment of electricity generation and demand

Since electrical line networks store practically no electrical energy, the total electrical power generated must be adapted to the current consumption (supplemented by certain line losses) at any time. This is not easy for several reasons:

  • The demand for performance can fluctuate rapidly, and these fluctuations are only partially predictable.
  • If a power plant z. If, for example, it fails due to a defect, a major service may suddenly be missing without any warning. Similar problems can arise in the event of a sudden failure of large pipelines.
  • In particular, wind turbines and solar power plants deliver fluctuating performance, depending on wind and solar conditions, which are only partially predictable.

To compensate for unforeseen fluctuations Control energy required, either in the form of energy storage or quickly controllable generation capacities. The need for (often expensive) balancing energy can be reduced significantly using various methods, which are discussed in the article on balancing energy. To cover longer-term bottlenecks you also need reserve power plants, e.g. B. in the cold reserve.

Power plants with different characteristics are used to cover the base load (constant demand), medium load (with daily and seasonal fluctuations) and peak load. Part of the load is covered by non-controllable power plants; the rest is the residual load that has to be covered by controllable power plants (and partly by energy storage). Many power plants (especially large power plants) also supply balancing energy in addition to the planned amount of electricity.

Different value of electrical energy

The economic value of electrical energy e.g. B. from a power plant depends on many circumstances - in particular on how the electricity generation takes place over time and to what extent it can be adapted to demand.

The economic value of electrical energy depends on whether it can be made available as needed.

The highest value per kilowatt hour is found in electricity generation that can be carried out in a targeted manner according to the respective demand, or at times when other power plants are not performing as well. Such energy can be sold relatively expensively on the electricity market to cover peak loads or as balancing energy. Base load current, which occurs evenly over a long period of time - is not based on demand, but is reliably available at least. Electricity that occurs sporadically and in an uncontrolled manner has an even lower value, whereby it still plays a role whether it is often supplied at times with consumption peaks (e.g. from photovoltaic systems at lunchtime) or at times when demand is lower.

A similar distinction can be made for different types of electricity demand. The highest costs per kilowatt hour are caused by an electricity demand that is limited to short time intervals and that may still occur at times of peak load. (This is the case, for example, for antifreeze electric heaters.) It is much cheaper to meet even demand, e. B. with constant power for day and night, summer and winter. (This is the case for the standby consumption of devices.) A demand that only occurs during off-peak times or, better still, can be flexibly adjusted to the respective power supply - ideally with the use of only temporary surpluses is even cheaper. By designing the electricity tariffs, one tries to evaluate these differences financially.

There are technical means to increase the above-described value of generated electrical energy:

  • Large gas-fired power plants and coal-fired power plants (especially with hard coal) can be operated specifically during the day and more in winter than in summer. The operators of such medium-load power plants achieve higher revenues per kilowatt-hour than for base-load electricity. However, the investment and capital costs are more significant when the number of full-load hours per year is lower.
  • Large water storage power plants are equipped with powerful turbines and generators, for the year-round continuous operation of which the available water quantities would not be sufficient. They are mainly used at times of high electricity demand, i.e. mainly in winter and during daily consumption peaks, and do not produce at all at other times.
Pumped storage power plants allow electrical energy to be “refined”.
  • Pumped storage power plants use z. B. cheap night electricity and generate electricity with the stored energy at other times, which can be sold much more expensive to cover peak loads. So it arises despite a certain energy loss of z. B. 20 to 25% a financial advantage for the operator, which reflects the higher value of the peak load in terms of the energy industry. This procedure is called Power refinement designated.
  • Combined heat and power plants are often operated purely heat-driven, without taking into account the electricity demand in the public power grid. After all, this leads to increased production in winter, where the electricity demand is higher, but often not to electricity production that is optimally distributed over the day. Such a feed-in tariff would not be honored even if the feed-in tariff was not time-dependent. In future, however, financial incentives will probably be created to increase the energy-related value of electricity production through more targeted use. Many operators will then design their CHP units to be a little stronger and provide them with buffer storage in order to be able to better meet the fluctuating demand for electricity.
  • Storage systems for electrical energy (some of which have already been mentioned above) can temporarily absorb excess electrical energy and then release it again when it is most urgently needed. If such storage facilities were available on a large scale, could be built and operated inexpensively and also caused only minor energy losses, this would lead to a general leveling of electricity prices because the timing of electricity generation would hardly matter. In addition, the need for interregional power grids would then be much lower. However, a storage technology that could meet all of the requirements mentioned is not yet known.
In principle, both extensive storage facilities and strong power grids can provide a good balance between generation and consumption. In practice, however, this only works with power grids.
  • Strong interregional power grids - for example in the form of a European supergrid - would also have the effect of making the timing of power generation much less important, as this would enable generation and demand to be balanced in a much larger area. The energy losses and costs involved would also be quite low, and the technology to do this is already available. That is why strong power grids (as opposed to extensive energy storage systems) are a very realistic option to increase the usability (and thus also the economic value) of fluctuating power feeds and to reduce the need for peak load generation.

The place of production can also be important for the economic value. For example, electricity that is produced in large quantities in remote locations is of less value because it can only be used through costly transport. Accordingly, electricity consumption in remote locations causes higher costs.

Electrical energy and climate protection

The generation of electrical energy is often done in a way that is highly harmful to the climate. Particularly high carbon dioxide emissions arise worldwide in a large number of coal-fired power plants, which cover approx. 42% of the world's electricity generation (as of 2007). Because of the high conversion losses in power plants, the generation of one kilowatt hour of electrical energy is often associated with significantly higher emissions of greenhouse gases than when the same amount of heat is generated in a boiler. Probably the most climate-damaging way of heating buildings is electric heating with electricity from coal.

Although the generation of electricity is in many cases still very harmful to the climate, electrical energy can become even more important than before in the context of climate protection.

Nonetheless, electrical energy is likely to play an essential role in the endeavor to make the entire energy supply less harmful to the climate and less dependent on the limited availability of fossil fuels. Various sources of renewable energy (in particular hydropower, wind energy, photovoltaics and biogas) can contribute to almost CO2-free or CO2-neutral electricity generation can be used. The same is true of nuclear energy, although there are several serious concerns about it. Even if fossil energy is temporarily used in the power plants, for example, the generation of heat using electric heat pumps in connection with the generation of electricity in highly efficient gas-fired power plants allows a significant amount of CO2-lower generation of thermal heat than the use of fossil-fired boilers - even in cases without waste heat utilization (combined heat and power) in the power plant. The switch to green electricity or at least an improved electricity mix can then reduce the CO2- Another significant reduction in emissions. For such reasons, further electrification in the heating and transport sectors can definitely be an effective strategy for climate protection if sufficient efforts are made to generate electricity that is more energy-efficient and climate-friendly.

Power source

Is it even possible to determine where the electricity in the power grid is coming from?

Most electricity consumers are supplied with electrical energy via the general supply network of energy supply companies (EVU). It is then physically impossible to assign a specific consumption or energy supply to a specific producer. Allocation takes place almost in terms of accounting, so that the payment for the electrical energy that a consumer calls up is not distributed evenly to all producers, but rather goes to his energy supply company. This can of course only sell as much electrical energy as it feeds into the grid or purchases from other producers or electricity traders (minus grid losses of a few percent). If a consumer decides to buy green electricity (electricity from environmentally friendly power plants), the money will ultimately go to the operators of environmentally friendly power plants and should support the further expansion of corresponding generation capacities. This is why the choice of energy supplier has an impact on electricity generation in the medium term, even if the energy flows from different power plants can no longer be physically separated.

According to an EU directive, energy supply companies are obliged to inform end users about the type of generation of the electrical energy they supply (obligation to Electricity labeling).On this basis, consumers can decide whether to buy energy from the respective company or which electricity product they choose.

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See also: energy, electrification, electrical voltage, electrical current, exergy, power plant, kilowatt hour, base load, medium load, peak load, annual maximum load, electricity market, control energy, balancing energy, secured power plant output, storage for electrical energy, energy supply company, security of supply, power gap, power failure, climate protection , Green electricity, electricity mix, energy efficiency, load management, electricity generation, switching electricity providers, electromobility
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