With bottlenecks in transmission capacity for wind generated electricity in northern Germany continuing, tensions are rising between wind farm operators and network operator E.on Netz. Frustrated by what they say is an overwhelming lack of progress on network strengthening to accommodate growing volumes of wind power, wind companies are taking on the task of transmission cable development themselves.
Upgrading the network in north Friesland is particularly urgent, says German wind association Bundesverband Windenergie (BWE). E.on's system between Breklum and Flensburg can cope with a maximum capacity of 310 MW. However, 535 MW of rated capacity is already connected to it, with this figure set to rise to 600 MW by 2006. For now, wind turbine operators voluntarily participating in a load management scheme cut output at critical times to ensure the system is not overburdened. However, they receive no compensation for doing this, even though Germany's renewable energy law places a legal obligation on network operators to expand the transmission network to ensure all renewable energy generated power can be accommodated.
E.on Netz is planning a new overhead transmission line for the Breklum to Flensburg route, but opposition to the scheme is increasing with local people and communities rejecting an idea which would see more transmission masts across their property. They argue an underground cable system would be a better option, but E.on rejects this saying it would be too expensive. BWE supports the underground option.
Cost of transmission lines
BWE says an underground cable could be authorised within one or two years, while in contrast gaining consent for an overhead cable could take up to eight years. If the overhead option is followed, the potential losses wind operators could accrue due to load management measures could add up to more than the cost of the network expansion itself, argues the association. Frustrated wind developer Geo mbH of Enge-Sande has taken the bull by the horns, progressing plans for an underground cable which would more or less follow E.on's earmarked route. Moreover, the developer has already signed contracts with affected property owners or users.
To support Geo's action, BWE has commissioned a study comparing the costs of overhead transmission lines to an underground cable over a theoretical 30 kilometre distance. The author of the study, Heinrich Brakelmann, professor at the University of Duisburg/Essen, has previously carried out commissions for E.on. His report rejects the idea that an underground cable would inevitably be the more costly option. It would be cheaper, it says, if a single cable system, rather than the usual two, is used. E.on is reluctant to contemplate a single cable system because this would contravene the German Transmission Code and the rules of the European network operator organisation UCTE. These both require a dual cable system for security of supply reasons. Brakelmann suggests, however, that as the cable would be used predominantly for wind energy transport, a degree of security of supply comparable with the overhead double cable system could be achieved if suitable wind energy load management measures are put in place.
Brakelmann's report also raises the possibility that bottlenecks in other regions could be eased, if not completely relieved, without necessarily building new transmission capacity. For example, E.on Netz says new 110 kV cables are required between Heide and Pöschendorf and from Göhl to Lübeck. However, according to Brakelmann technical solutions applied to the existing networks could possibly avoid that. Under extreme conditions, consisting of high temperatures of around 35 degrees centigrade and low winds, overhead cables could be operated above rated capacity for just a few minutes, he states. Cable load, he adds, is pitched to cope with this extreme at any time. If the cable temperature were continually monitored, overhead cables could carry up to 30% more capacity than the rated figure, he suggests, which would at the very least reduce the bottleneck and enable more wind power to be delivered.
With a substantial amount of offshore wind capacity from projects in the North and Baltic Seas also to be accommodated in the future, there is an additional need for new long distance transmission cables to be developed by Germany's largest network operators, E.on, RWE and Vattenfall Europe. But again, the wind industry is critical of progress to date and has taken the initiative. Windland Energieerzeugung has set about planning a high voltage electricity network which will be able to deliver the electricity from its proposed Meerwind offshore plant as well as other projects. The planned network's capacity limit is 3 GW to ensure network stability.
Under the proposal, cables would connect the landing points at Dornum and Wilhelmshaven on the North Sea coast of the state of Lower Saxony with an existing high voltage network T-junction at Conneforde, about 40 kilometres south of Wilhelmshaven. The two proposed high voltage links would run for 60 kilometres and 40 kilometres, respectively. From Conneforde, Windland proposes an additional 110 kilometre cable route southwards to reach an existing east-west cable connection which links the RWE and E.on networks. The project could be divided into a number of phases to gradually meet growing demand as offshore projects are brought online, says the company. However, Windland's plans for the southwards cable route from Conneforde compete with E.on's existing plans for a connection between Bremen-Gandersee and Diepholz, "which is one year further advanced than our project," acknowledges Windland's Joachim Falkenhagen.
Windland says the task of securing planning consent and financing is expected to take 5-10 years, and adds its project will be designed to be a "people's high voltage transmission cable system." The EUR 200 million project will be financed largely by a fund structure similar to the popular German wind fund mechanism used to raise equity for wind stations. In this way, people close to the cable will profit and contribute to the local economy, it says.