The Dena study shows how the high-voltage grid needs to be expanded and optimised to the period 2020-25, assuming 39% of German electricity generation will by then be sourced from renewables and taking into account increasing electricity trading within Europe. If conventional overhead cabling is used, the report says, it will cost EUR9.7 billion to lay 3,600 kilometres of new routes, including connections for offshore wind stations.
There are two technical variations on this scenario. If the overhead cables are equipped with temperature-monitoring equipment, higher amounts of electricity can be transmitted when the weather is cold and the wind is blowing. This would slightly reduce the need for new cable routes to 3,500 kilometres. The additional cost of temperature-monitoring equipment would raise overall investment to EUR9.8 billion.
If high-temperature cable is used, transmission capacity is greater and new routes only need to be 1,700 kilometres. But 5,700 kilometres of existing cable routes would have to be equipped with the new cables at an overall cost of EUR17 billion.
The least expensive option involves new standard overhead cable routes, which would raise the network-use charge within household electricity bills by just EUR0.002/kWh, from EUR0.058/kWh to EUR0.06/kWh. The most expensive option, involving high temperature cable, would raise the network charge by EUR0.005/kWh.
Transmission system operator Tennet is sceptical about the high-temperature cable scenario - even though the requirement for new routes would drop to 1,700 kilometres. "To implement this idea, the existing high-voltage network would have to be taken out of operation within the next five years. This is not compatible with maintaining a secure electricity supply," says a Tennet spokesman, adding that this would involve longer disruption.
Germany's wind energy association Bundesverband Windenergie (BWE) welcomes the report but believes it is flawed by not taking sufficient note of the European dimension. "Germany needs a network strategy co-ordinated with network development, cross-border transmission line availability and storage capacity in the European Union," says BWE president Hermann Albers.
A separate report published by the European Wind Energy Association in the same month explores the requirements for developing the pan-European grid. Powering Europe: wind energy and the electricity grid predicts the evolution of renewable energy in the European power system from 2010 up to 2050 and the main power corridors needed (Windpower Monthly, December 2010).
To accommodate the growing amount of renewable energy coming online between now and 2050, the report envisages a new offshore grid in the Northern, Irish and Baltic seas, as well as improved connections between Spain and France, and Germany and its neighbours.
The report says that the ten-year network development plans produced by regulatory body the European Network of Transmission System Operators for Electricity should be the main tool for providing a pan-European planning vision for grid infrastructure in line with long-term EU policy targets for renewables.