Output duration curve offshore (North Sea), source: TenneT TSO GmbH
Output duration curve 2011, source: German Renewable Energy Law-data and data of the TSOs.
There is no wind on the North Sea on at most two to three days a year. At the same time, balancing effects result from the large number of decentralised feeders. Renewable energy sources produce electricity in Germany every hour of the year.
The systematic expansion of renewable energies to 50 percent by 2030 will mean that only 6 GW of conventional base load will be needed. According to the Bundesnetzagentur (German Network Agency), the figure for 2011 was 29 GW from coal and nuclear power plants.
The demand for base-load power stations declines in regions with a high proportion of renewable energy, such as the network area of the utility EWE AG today, by almost 80 percent! This does not take into account the fact that conventional power stations consume 8 percent of the energy they generate.
At the same time, it has been established that the annual offshore energy generation in a weak wind year compared to a reference year with a good level of wind (2007) is only 8.5 percent lower (2007 compared to 2006). On the other hand, the difference for onshore generation is 23 percent (2007 compared to 2004). The cumulated frequency of availability of more than 50 percent of the installed output is 46 percent in offshore generation and so far only 14.7 percent from onshore farms (see graph). Furthermore, due to the higher energy availability and more constant wind speeds at sea, the output duration curve is well above that for onshore and is also more linear. Model calculations (development scenario 2020) for future North and Baltic Sea wind farms indicate the generation of at least 15 percent of installed output for 7,000 hours (see IWES, Endbericht DENA-Netzstudie II), and 53 percent of the installed output for at least 4,000 hours. This is the working range of a medium-load power plant (see TAB, Regenerative Energieträger zur Sicherung der Grundlast in der Stromversorgung, Endbericht, 2012). Therefore, offshore wind farms are base load-capable.
Our neighbouring country Denmark proves that energy supply can function without problems with a high proportion of fluctuating renewable energy, above all wind energy. Denmark's wind energy share in 2011 was some 28.1 percent. According to an IEA study in 2011, the share of fluctuating renewable energies can be expanded to more than 60 percent without causing problems in the transmission network. This is mainly because Denmark took the necessary decisions early enough. The electricity transfer with the neighbouring countries Norway and Sweden, including the use of hydropower potentials, storage systems and due to early membership in the Scandinavian electricity exchange Nord Pool, totals 30 percent of the electricity generated per year.
The share of combined heat and power plants is 45 percent. Additionally, excess wind energy is converted into heat in local storage systems.
Ubbo de Witt, Managing Director of the Projekt group of companies, is confident that "now the new state government in Lower Saxony will take the right and necessary steps within the community of coastal countries; Denmark is a good example of how wind energy can today already be optimally included in the energy supply of the future."
Sources and relevant links:
* According to the operating result of alpha ventus in 2011 and probably a similar result in 2012: alpha ventus website: 2011 Annual Review
Nordwest-Zeitung of 8.5.12 (German): "Borkum: Offshore-Windpark alpha ventus liefert mehr Strom als erwartet"
Nordwest-Zeitung of 9.5.12 (German): "Alpha-Ventus erfreut Forscher und Unternehmer"
Büro für Technikfolgen-Abschätzung beim Deutschen Bundestag (TAB, German): "Regenerative Energieträger zur Sicherung der Grundlast in der Stromversorgung, Endbericht, 2012"
International energy agency: "Energy policies of IEA countries: Denmark 2011, Review"
Danish energy agency: "Renewables now cover more than 40% of electricity consumption"