Dark doldrums

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In the energy industry, dark doldrums refer to the situation in which wind energy and photovoltaic systems in a region produce little or no electrical energy due to doldrums or weak winds and darkness at the same time . The dark doldrums are particularly important for energy systems that are largely or exclusively based on fluctuating renewable energies , and is thematically related to the security of energy supply . Suitable measures for bridging dark doldrums are, for example, the provision of conventional power plants as well as base- load renewable energies such as biomass power plants , geothermal power plants and solar thermal power plants with heat storage , the expansion of the power grids for extensive networking of regions with different weather conditions, sector coupling , the use of energy storage and the flexibilization of Consumers, for example with smart grids .

term

Phases of low wind and solar power feed-in lasting several days are referred to as dark doldrums , which can no longer be compensated for by the use of short-term storage and load management alone. So-called “cold dark slacks” are particularly problematic, as situations in winter when, on the one hand, little electricity is generated from wind and solar energy due to the calm and darkness, but there is particularly high electricity demand due to cold climatic conditions.

Frequency of occurrence

A two-week dark lull occurs in Germany on average once every two years. The period from January 16 to 25, 2017 is often cited as an example of such a dark doldrums. There was no prolonged dark lull in 2018.

According to the German Meteorological Service , there were situations in Germany from 1995 to 2005 on average twice a year in which large-scale lulls and times with little sun over 48 hours occurred together. When looking at the European level, the frequency of occurrence is reduced to 0.2 situations per year.

background

Wind energy and photovoltaics are considered to be the world's most important sources for a largely or complete supply of renewable energies, which is aimed at with an energy transition. This applies in particular to Germany, where only wind energy and photovoltaics have the potential to provide sufficient energy. Other renewable energies such as hydropower or biomass , on the other hand, have already largely been expanded, so that there are only few opportunities for further expansion. Since the above-mentioned producers are dependent on the weather in their electricity production, measures must be taken to guarantee security of supply at all times, even if only low yields are generated due to the weather.

Nowadays it is not assumed that there is a capacity problem in the power plant fleet. In Germany , the conventional power plants do not have to feed in all of the available power, even in the dark, in order to guarantee security of supply. At present, Germany can export electricity to neighboring countries even in the dark. Therefore blackouts are not to be feared. In October 2014, Europe-wide overcapacities were stated to be at least 100 GW, of which around 60 GW are in the grid area that is relevant for Germany. Overcapacities are therefore expected in the electricity market for years to come. For Germany itself, the overcapacities in the period 2014–2017 were put at around 10 GW.

In order to ensure that enough power plants are always available, the Reserve Power Plant Ordinance was passed in Germany. This ordinance grants the Federal Network Agency the right to prohibit the decommissioning of power plants relevant to the system security and, if necessary, to build new power plants in the future that are also necessary for security of supply.

Fluctuation in wind and solar power feed-in

Dark slacks occur especially in late autumn and winter. This is due to the short day length , the low position of the sun and the often cloudy winter weather . In addition, snow-covered PV systems cannot produce electricity even when the sun is shining. Although the wind usually blows more often and stronger in the cold season than in summer, there are also lulls in autumn and winter .

In geographically very small areas such as B. related to Germany, d. H. Without extensive exchange, the generation of wind energy fluctuates between very high feed-in capacities during stormy days and very low values ​​during lulls. The feed-in of the photovoltaics does not provide any electricity at night. In a publication by Agora Energiewende , the minima and maxima for 2015 are itemized. Accordingly, November 3, 2015 was the day on which the least amount of electricity was generated from renewable energies. At 2 p.m., wind turbines in Germany only fed in a total of around 0.2 gigawatts - the lowest value of the year. At 5 p.m., when photovoltaics were hardly supplying any more energy, electricity generation from renewable energies (in addition to wind and sun, also biogas and hydropower) reached a total output of 7.3 gigawatts (of which 0.5 GW from wind power), and thus only a share of less than ten percent of the total electricity production. The maximum values ​​were reached on December 21, 2015. On this day, wind turbines fed in an average output of 36.7 GW; this corresponded to 91.5 percent of their installed nominal output of 40.6 GW. On April 21, 2015, the photovoltaic systems in Germany achieved a maximum of 28.5 GW at midday. That was 73 percent of the installed capacity of around 39 GW.

Up-to-date feed-in data (for Germany) for the years from 2011 onwards are freely accessible on the Internet.

Problem-solving opportunities

Since climate protection measures will make it necessary to dispense with conventional power plants in the future and these will no longer be available to compensate for this in the long term, alternatives must be available in a renewable energy system to ensure security of supply. There are numerous possibilities to adapt the variable generation to requirements. These include, among other things: the interconnection of geographically widely distributed variable generators, the safeguarding of variable renewable energies with base load capability (e.g. wind energy through biomass), the use of intelligent energy systems, the oversizing of converters, the storage of energy by producers or consumers and the use of Vehicle-to-grid storage. These individual options each have different advantages and disadvantages, so that in the future they should be used in combination with one another in the most expedient manner. If the energy system is designed accordingly, the occurrence of dark lulls does not represent an obstacle to a 100% regenerative energy supply, even if this is based largely or exclusively on fluctuating renewable energies.

Making producers and consumers more flexible

In order to smooth out peaks in demand, there are options for making consumers more flexible, for example with intelligent power grids . Load shifts are particularly important in this context . Even if these are only possible in the range of hours to a few days, they are considered an excellent way of adapting demand to supply in a renewable energy system, which is why they should be used with preference. Their great advantage lies in their great energy efficiency , as they can be used with very little or even loss-free in contrast to storage power plants. Their functionality achieves the same effects as the use of a storage power plant: the increase in load (switching on the load in the event of excess electricity, for example by power-to-heat ) corresponds to the charging of a storage system, the later load reduction corresponds to the storage unit discharge. Therefore load shifter acts as "virtual storage".

Additional flexibility can be achieved by using biomass, which was previously mainly converted into electricity in base load operation, to fill gaps in demand in dark periods.

Offshore wind power

In addition to the mutual complementation of photovoltaic systems and onshore wind power, the security of supply through renewable energies can be significantly increased through the use of offshore wind power . According to a study by the German Meteorological Service , favorable conditions for dark doldrums occur twice a year when all three forms of generation are used, compared with thirteen times a year when only photovoltaics and onshore wind power are used. A period of at least 48 hours was regarded as a period of time that favored a dark doldrums.

Unlike onshore wind power and photovoltaics, offshore wind power has only been increasingly expanded in Germany since 2015. In November 2019, offshore wind turbines with a total output of 7.6 GW were installed in Germany. Another 4.3 GW are under construction or in planning (see: List of offshore wind farms ).

Network expansion

The submarine cable projects NordLink , NorGer and NorNed (not shown here) serve both to expand the network and to connect long-term storage facilities in Scandinavia.

Large-scale networking across several weather zones is advantageous . By reciprocal electricity transport across national borders, balancing effects can be used that both increase security of supply and reduce storage requirements. Since the costs for grid expansion are significantly cheaper than the costs for energy storage, transnational grid expansion is an important factor for a cost-effective renewable energy system. It is noted that it is “technically illusory to want to guarantee security of supply through national autonomy”. A key technology for connecting distant regions is high-voltage direct current transmission , which enables low-loss power transmission over long distances. Storage power plants can also smooth the variable feed-in, but these are more expensive than HVDC connections.

In addition, the network expansion also enables better linking of production and consumption centers with storage facilities, for example pumped storage power plants in the Alps or Scandinavia. There, surpluses that occur during times of high wind or solar power production could then be stored and then withdrawn again during times of low production and corresponding demand. Norwegian and Swedish pumped storage facilities with 84 and 34 TWh capacity, respectively, offer high storage capacities. Provided that there is sufficient line capacity, these could make energy storage in Germany almost completely superfluous, according to the Council of Economic Experts for Environmental Issues . With Northern Link and NorGer are with stand 2016 two submarine cable with a transmission capacity of 1.4 GW under construction or planning.

Long-term storage

Long-term storage systems are important for fully renewable energy systems. Storage in the form of synthetic gases obtained from renewable energies, i.e. hydrogen or methane , is particularly suitable as long-term storage . Including the cavern and pore storage facilities planned for 2013, the storage capacity of the German natural gas network is around 332 TWh. In 2011, natural gas consumption was 760 TWh. If power-to-gas systems were increasingly used for seasonal long-term storage in the long term, gas consumption could rise further. Nevertheless, the natural gas network including the planned storage facilities would be sufficiently dimensioned for a secure full supply based on renewable energies. With power-to-gas it is possible that gas power plants currently fired with fossil natural gas can continue to be operated with synthetic methane or hydrogen in the long term; Alternatively, operation with refined biogas is also possible. In the event that the total required annual peak load in Germany of 85 GW were completely secured with base load-capable gas turbine power plants , the electricity costs would increase by approx. 0.5 ct / kWh. Since this route is subject to quite high energy losses due to the relatively low efficiency of the electricity - hydrogen / methane - electricity energy chain, which in turn leads to an increased demand for wind power and photovoltaic systems, a future energy system should be designed in such a way that there is only a low long-term storage requirement .

literature

  • Patrick Graichen, Mara Marthe Kleiner and Christoph Podewils: The energy transition in the electricity sector: State of affairs 2015. Review of the main developments and outlook for 2016 . Ed .: Agora Energiewende. January 2016 ( agora-energiewende.de [PDF]).

Web links

Individual evidence

  1. ↑ a b Cold dark doldrums: robustness of the electricity system in extreme weather. (PDF) June 29, 2017, accessed June 30, 2017 .
  2. ↑ Dr. Patrick Graichen, Frank Peter, Dr. Alice Sakhel, Christoph Podewils, Thorsten Lenck, Fabian Hein: The energy transition in the electricity sector: State of the art 2018. Review of the main developments and outlook for 2019. Ed .: Agora Energiewende. 2019, p. 61 .
  3. ↑ a b German Weather Service: Reduce weather-related risks of electricity production from renewable energies through the combined use of wind power and photovoltaics. German Weather Service, March 6, 2018, p. 1 , accessed November 30, 2019 .
  4. ↑ Sarah Becker et al .: Features of a fully renewable US electricity system: Optimized mixes of wind and solar PV and transmission grid extensions . In: Energy 72, (2014), 443–458, p. 443, doi: 10.1016 / j.energy.2014.05.067 .
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  6. ^ Matthias Günther: Energy efficiency through renewable energies. Possibilities, potentials, systems . Wiesbaden 2015, p. 134.
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  8. ↑ Thomas Unnerstall: Fact check energy transition. Concept, implementation, costs - answers to the 10 most important questions. Berlin Heidelberg 2016, p. 148.
  9. ↑ The energy transition in the electricity sector: State of affairs 2015 ( Memento from August 26, 2016 in the Internet Archive ). Agora Energiewende website. Retrieved January 13, 2017.
  10. ↑ Energy Charts. Fraunhofer ISE , accessed on November 15, 2016 .
  11. ↑ EEX Transparency (German). (No longer available online.) European Energy Exchange , archived from the original on November 15, 2016 ; Retrieved on November 15, 2016 (up-to-the-minute information on the feed-in of electricity in Germany (share of PV and wind power and from other "conventional" sources)). 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. @1@ 2Template: Webachiv / IABot / www.eex-transparency.com
  12. ^ Nicola Armaroli , Vincenzo Balzani : Towards an electricity-powered world . In: Energy and Environmental Science 4, (2011), 3193-3222, p. 3217, doi: 10.1039 / c1ee01249e .
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  14. ^ Brian Vad Mathiesen et al .: Smart Energy Systems for coherent 100% renewable energy and transport solutions . In: Applied Energy 145, (2015), 139–154, doi: 10.1016 / j.apenergy.2015.01.075 .
  15. ↑ Dmitrii Bogdanov, Christian Breyer: North-East Asian Super Grid for 100% renewable energy supply: Optimal mix of energy technologies for electricity, gas and heat supply options . In: Energy Conversion and Management 110, (2016), 176–190, doi: 10.1016 / j.enconman.2016.01.019 .
  16. ↑ Matthias Günther, Energy efficiency through renewable energies. Possibilities, potentials, systems , Wiesbaden 2015, p. 141.
  17. ↑ Nele Friedrichsen, consumption control , in: Martin Wietschel, Sandra Ullrich, Peter Markewitz, Friedrich Schulte, Fabio Genoese (ed.), Energy technologies of the future. Generation, storage, efficiency and networks , Wiesbaden 2015, pp. 417–446, p. 418.
  18. ↑ Christian Synwoldt, decentralized energy supply from renewable energy sources. Technology, markets, communal perspectives. Wiesbaden 2016, p. 257.
  19. ↑ Volker Quaschning : Regenerative Energy Systems. Technology - calculation - simulation . 8th updated edition. Munich 2013, p. 49.
  20. ↑ See DP Schlachtberger et al .: The benefits of cooperation in a highly renewable European electricity network . In: Energy . tape 134 , 2017, p. 469-481 , doi : 10.1016 / j.energy.2017.06.004 .
  21. ↑ Don't be afraid of the dark doldrums. avenir-suisse.ch, October 2, 2016, accessed on October 19, 2016 .
  22. ↑ Alexander MacDonald et al .: Future cost-competitive electricity systems and their impact on US CO2 emissions . In: Nature Climate Change 6, (2016), 526-531, doi: 10.1038 / nclimate2921 .
  23. ↑ See Michael Sterner, Ingo Stadler: Energy Storage - Demand, Technologies, Integration . Springer, Berlin 2014, p. 108.
  24. ↑ Volker Quaschning: Regenerative Energy Systems. Technology - calculation - simulation . 8th updated edition. Munich 2013, p. 51.
  25. ↑ Volker Quaschning: Renewable energies and climate protection . Munich 2013, p. 332.
  26. ↑ Holger Rogall : 100% supply with renewable energies. Conditions for global, national and local implementation . Marburg 2014, p. 98.
  27. ↑ Expert Council for Environmental Issues 2013: Shaping the electricity market of the future. Special report , p. 67. Retrieved April 7, 2018.
  28. ↑ Günther Brauner: Energy systems: regenerative and decentralized. Strategies for the energy transition . Wiesbaden 2016, p. 89.