Decentralized power generation

from Wikipedia, the free encyclopedia
Decentralized energy sources wind energy , photovoltaics and biomass in rural areas

With decentralized power generation , electrical energy is generated close to the consumer, e.g. B. within or near residential areas and industrial plants by means of small power plants . The efficiency of the power generation systems is usually only designed to cover the energy needs of the power consumers connected directly or in the immediate vicinity. Island networks too , d. H. the interconnection of smaller, fewer electricity producers and consumers in remote locations that are not connected to the public electricity network is part of decentralized electricity generation. Likewise, wind parks and solar parks commonly counted as part of the decentralized power supply, but here the transition to centralized power generation is fluid, especially with larger systems.

General

In contrast to centralized power generation, with the decentralized power supply, the electrical energy is not fed into the high-voltage network, but into the medium and low-voltage network . An important advantage of decentralized power generation is therefore the greatest possible avoidance of losses during transformation to other voltage levels and transmission losses through high-voltage lines . Between 2000 and 2015, transmission losses in Germany fell from 34.1 to 25.8 TWh, a decrease of around 19.7%. This decline is largely attributed to the decentralized energy generation, which was greatly expanded during this period. Further z. B. by combining wind power and photovoltaic systems with controllable biomass power plants, the variable power feed of the first two types of generation are stabilized.

Decentralized power generation is often seen as a partial aspect of the energy transition and associated with the conversion from fossil-nuclear power generation to renewable energies . However, the two are not necessarily linked. So z. B. Combined heat and power plants are operated with both renewable biogas and fossil natural gas , at the same time there are also central approaches to energy generation from alternative sources. Examples of this are offshore wind farms and the Desertec concept, in which the construction of large solar power plants with an output of several gigawatts is planned in North Africa.

Since the beginning of 2010, mayors of over 20 German cities have been meeting for a dialogue on strategic issues relating to the “sustainable city”. The Lord Mayors are particularly committed to sustainable development in their cities. This resulted in u. a. the paper "Making the energy transition a success story with strong municipalities" on municipal energy policy in order to decentralize energy supply.

According to the Institute for Ecological Economic Research, two thirds of the value added from renewable energies (2012: 25 billion euros) benefit cities and municipalities and contribute to the development of structurally weak areas. In addition, jobs in renewable energies are spread across the whole of Germany.

Decentralization as a structural feature of the electricity industry

While the structural feature of decentralization in the electricity industry has reached a high level on the consumer side, particularly through the expansion of the power grid in industrialized nations, decentralization on the producer side will only become the dominant structural feature in the course of the energy transition. This is mainly due - although not mandatory (see above) - to the increasing use of renewable energies , which have a lower spatial concentration and their carriers have a lower energy density than fossil and nuclear energy. Further drivers towards greater decentralization are social and economic factors (local or regional added value, broader participation and citizen participation, autonomy through extensive self-sufficiency, greater acceptance, reduction in the need for expanding the transmission network). Politically, the liberalization of the electricity market since the 1990s and, in Germany in particular, the Renewable Energy Sources Act since 2000, has brought more than 1.5 million solar and around 27,000 wind turbines as well as 9,000 small power plants based on biogas into the public domain Feed into the grid (as of 2017). The increasing decentralization of the electricity market requires a changed topology of the electricity network (see also intelligent electricity network and virtual power plant ). Since generation and consumption must be balanced, but this is not possible at every place and at any time for technical, economic, environmental or social reasons, this compensation must be technically via power grids, energy storage , controllable producers or load management such as. B. through economic incentives (fees, taxes, charges) for producers and consumers to ensure their "grid-friendly behavior". A distinction must be made between three situations: (1) Generation and consumption without using the public grid (self-consumption), (2) Generation and consumption within a region (compensation in the distribution network) and (3) supra-regional compensation of generation and consumption (compensation in the transmission network ).

Technologies

Cogeneration units

The Baden biomass cogeneration plant generates the electricity and heat requirements of 10,000 households and can thus supply the households in Baden near Vienna independently

The advantage of the very low transport losses is offset by the disadvantage of the generally lower power generation efficiency in small power plants in relation to large power plants . However, this does not apply to the combined generation of electricity and heat in the combined heat and power plant, where the overall efficiency is significantly higher when both forms of energy are used. Biomass power plants and biogas plants are z. B. built at the location of the primary energy source biomass and avoid high transport costs by limiting the catchment radius. In the case of combined heat and power plants, the waste heat can be used in the form of district heating .

Small systems, such as those used in decentralized arrangements, generally lead to higher specific investment sums . The decentralized value creation through renewable energies in German cities and municipalities reaches approximately 6.8 billion euros annually.

These systems also have lower electrical efficiencies in the case of combined heat and power, for example , which, however, is usually more than compensated for by the use of waste heat. The degree of efficiency describes the freely available share of electrical energy and any freely available thermal energy in relation to the primary energy used . If the system is operated without combined heat and power (CHP), the other part of the primary energy used is irretrievably lost due to the entropy generated . With CHP, the overall efficiency of the system is usually higher than that of large central power plants, in which the waste heat generated is often not used at all. In the case of combined heat and power plants, due to the high degree of utilization , in which the primary energy is converted into both electrical energy and useful heat, the efficiency is usually significantly greater than in large-scale systems that do not have a combined heat and power system. So went z. As early as 2007, for example, the VDE assumed that the expansion of the decentralized energy supply could increase the efficiency of power plants by 10%, thus saving primary energy, reducing the dependency on energy raw material imports and lowering CO 2 emissions .

With the change in the energy supply system as a result of the energy transition, decentralized block-type thermal power stations also assume the function of providing control energy in order to provide electricity, especially when there is little wind and / or solar power available. In order to guarantee the heat supply at all times, the systems are equipped with heat buffers and heating rods so that heat can be generated electrically even at times when the supply of volatile energy sources is high and the block-type thermal power station is not required to generate electricity. Combined heat and power plants equipped in this way would be able to generate or consume electrical energy as required, which means they can play an important role in ensuring grid stability.

Photovoltaics

Solar modules integrated into the house facade

Using photovoltaics, electrical energy is generated directly from electromagnetic radiation (here: sunlight ) . Although it has been used to supply energy to spacecraft since 1958, it only became important for power generation in Germany through the reduction in system costs triggered by the Renewable Energy Sources Act (EEG). Even if there are larger photovoltaic ground-mounted systems with a peak output in the middle double-digit or lower three-digit MW range from the construction period before 2015 , a large part of the photovoltaic systems will be installed decentrally. Classic examples are rooftop systems that are installed on the roof of residential, commercial and industrial buildings and whose electricity is consumed to a relatively large extent. For this reason, a decentralized feed-in is standard for photovoltaic systems. While typical rooftop systems of residential buildings usually only produce a few kW peaks, the peak power of solar systems on industrial and commercial buildings extends into the MW range. Smaller open-space solar parks also generate decentralized electrical energy. Only larger ground-mounted photovoltaic systems mark the transition to a central power supply.

In the case of photovoltaic systems, electricity generation can generally be reliably forecast, but currently (2012) they are only rarely coupled with storage options and cannot be regulated. They are therefore not suitable as the sole power generator, but work in conjunction with other power generators. However, through photovoltaics, electricity is only generated during the day, when it is most needed. The local consumption of the generated electricity is therefore ensured. Even in the winter months, when the amount of electricity generated is significantly lower, photovoltaics relieve the other producers and the transmission networks during the day and dampen the prices for peak-load electricity.

In order to reduce the strong regional fluctuations in PV power generation and to increase the proportion of direct self- consumption, solar batteries can be used, i. H. Storage systems consisting of solar inverter and memory storage batteries . These storage systems also offer the possibility of an uninterruptible power supply and thus an increase in the security of supply for electricity customers. The grid feed-in through decentralized PV power generation is smoothed and decentralized self-consumption is optimized. These decentralized small storage systems for electrical energy, together with other storage technologies as well as the expansion of regenerative power generators and power grids, are assigned an important role in the energy transition.

Wind energy

Wind energy is used by means of wind turbines . This can be done centrally, such as B. in the case of an offshore wind farm , as well as decentralized, as is often the case with onshore wind energy. Although there are also large onshore wind farms with a capacity of several 100 MW, many onshore wind farms are usually smaller, so the electricity is generated in a decentralized manner close to the consumer. Such wind farms are fed into either the medium-voltage network or the high-voltage network (distribution level). Only offshore wind farms or very large onshore wind farms feed directly into the transmission network.

Hydropower

Hydropower is used in hydropower plants. As small hydropower plants, hydropower plants can produce decentralized; hydropower plants located on large rivers are more likely to be assigned to centralized electricity generation. The largest hydropower plants on earth are also the largest power plants of all. The planned Grand Inga , then the largest hydroelectric power station in the world, will be z. B. have an output of 40 GW, which roughly corresponds to the electricity demand of Germany on weak days.

Power transmission

Thanks to decentralized electricity generation and consumption on site, electricity does not have to be transported as far. In Germany, the transport costs of electricity make up more than 20 percent of the total electricity price . Decentralized electricity generation can save transport costs, but at the same time the costs for electricity storage increase.

Power storage

With the help of electricity storage systems, electricity produced in a decentralized manner can be stored in a decentralized manner and then consumed decentrally as required. Storage power plants are available in many sizes, such as pumped storage power plants that can store electricity in large quantities, but also as battery systems, e.g. B. solar batteries for short-term storage, which can regulate the amount of storage up to house consumption.

literature

Web links

Individual evidence

  1. ↑ Energy consumption in Germany in 2015, p. 3 3 . Website of the AG Energiebilanzen. Retrieved August 12, 2016.
  2. ↑ Infographics by Thomas Gerke ( Memento of the original from November 10, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. . In: Renewables International , November 7, 2013. Retrieved November 7, 2013. @1@ 2Template: Webachiv / IABot / www.renewablesinternational.net
  3. ↑ Paper "Making the energy transition a success story with strong municipalities" ( Memento of the original from September 9, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 3.3 MB) @1@ 2Template: Webachiv / IABot / www.nachhaltigkeitsrat.de
  4. ↑ Institute for Ecological Economic Research: Value creation and employment effects through the expansion of renewable energies. 2013 ( Memento of the original from October 7, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 864 kB) @1@ 2Template: Webachiv / IABot / www.greenpeace.de
  5. ↑ Agora Energiewende : Energiewende and decentralization. On the foundations of a politicized debate . February 2017 ( agora-energiewende.de [PDF; 1,2 MB ]).
  6. ↑ Andreas Oberhammer, System Optimization of a Biomass Cogeneration Plant for the Regional Energy Demand of a Municipality - Practical Example, 2006
  7. ↑ Institute for Ecological Economic Research , September 22, 2010: Municipal value creation through renewable energies, Decentralized expansion of renewable energies brings value creation in the billions for cities and municipalities , accessed: March 14, 2011
  8. ↑ VDE press release: VDE study: Decentralized energy supply 2020 ( Memento of the original from May 3, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , accessed January 27, 2012. @1@ 2Template: Webachiv / IABot / www.vde.com
  9. ↑ Structural change in the electricity and heating market . In: VDI nachrichten , March 9, 2012. Retrieved March 9, 2012.
  10. ↑ 5 MW power plant already the second major Conergy project for the Italian exhibition center ( memento of the original from March 31, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. . Conergy website. Retrieved February 25, 2012. @1@ 2Template: Webachiv / IABot / www.conergy-group.com
  11. ↑ Cf. Volker Quaschning : Renewable Energies and Climate Protection . 3rd edition Munich 2013, pp. 139–142.