Feature - Smart grids help reduce German wind costs

GERMANY: Germany's 31.3GW fleet of wind turbines is connected mainly to the electricity distribution network and fed in about 45TWh of Germany's total generation of 671TWh in 2012.

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Add to this the approximately 32GW of solar generation supplying local networks with around 28.5TWh in 2012, and the networks are dealing with around 73TWh of variable generation for which they are, as yet, scarcely equipped.

On top of the renewables input, mini gas-fired co-generation plants are becoming increasingly popular for family housing, public buildings, hospitals and other users. These also feed electricity into the local networks.

At the same time, the number of consumers with higher-capacity demands on the local network, such as chargers for electric cars and heat pumps, is expected to grow over the coming years. Clearly, demands on the low- and medium-voltage grids that are meshed to create the distribution networks are changing fast.

The problem is that Germany's distribution network stretching over 471,213 kilometres was originally installed on a top-down principle. Large conventional power stations fed electricity into the high-voltage network that transmitted it down through the medium-voltage grid into the low-voltage network to reach consumers.

As the country adopts more renewable energy, medium- and low-voltage networks must become smart enough to cope with increasing fluctuation in supply and demand, and even flows of electricity changing direction depending on the time of day. The risk that individual components or sections of the meshed system could be overloaded is getting higher with each new renewables installation. But the simple systems installed today in local transmission stations can often neither register nor actively react to such threatening overloads.

More grid

An investigation into the need for expansion and innovation of Germany's distribution network to 2030, published in December by energy agency Dena, estimated that 135,000-193,000 kilometres of new distribution network would be required by 2030. This will require changes to 21,000-24,000 kilometres of overhead high-voltage networks and additional transformer-station capacities.

Investment required over the period 2012-30 would add up to €27.5-42.5 billion, the study said. The average expected annual cost of €1.5-2.2 billion is between double and triple the approximately €750 million 2012 investment in distribution networks, as reported in the first renewable-energy monitoring report published by the German economy ministry, also in December.

Adding to the challenge, the distribution network is split into smaller and larger areas operated by around 850 different network operators. "Many are simply too small to master the complex challenges," says Gero Luecking, a board member at German "green" electricity retailer LichtBlick. "A system of 25 network operators or groups of operators would be significantly more efficient."


Not surprisingly, calls for swift investment in modernising the networks are becoming ever more urgent. But a roadmap for the transformation to intelligent energy networks presented to the economy ministry by federal energy and water association BDEW in February revealed the task could take years. The roadmap defines ten steps necessary to 2022, including basic tasks such as developing a consistent legal and regulatory framework, drawing up standards and norms, and defining the borderline between the electricity market and the needs of the electricity transmission networks — as well as the interaction between the two.

One difficult task is to establish when and if curtailment of wind and solar generation is necessary, and whether compensation for the lost generation should be paid to the operator.

In December 2011, German energy regulator Bundesnetzagentur discussed what is needed for intelligent electricity networks in a paper titled "Smart Grid and Smart Markets". An overall economically sensible relationship between network expansion and curtailment measures must be found and then discussed in connection with the renewables support regime, and with the aim of maintaining the priority feed-in for renewables generation to the networks, the Bundesnetzagentur said.

It questioned the rationale of expanding the network, whether at lower or high-voltage level, to take up every last kilowatt hour of power from renewables, since outside peak generation times much of this capacity would not be in use. Meanwhile, substantial safety margins across the transmission system itself result in much transmission capacity going unused. Germany's ten-year network development plan 2012 for high-voltage networks, published late last year, said network expansion measures are planned under the assumption that they will be used at just 20% of their capacity in normal operation.

Different approaches

Clearly Germany cannot wait years for improvements to the distribution networks when solutions are needed now. Some answers have been found and implemented in North America, but these are aimed primarily at increasing efficiency in operation and maintenance and improving security of supply rather than in dealing with increasing amounts of variable wind and solar electricity feed-in, German Association for Electrical, Electronic & Information Technologies VDE said in a November report.

China too will face the same challenges as Germany with its Five-Year Plan target of 160GW of renewables by 2015. But China is tackling its problems with programmes of a scope and means impossible in Germany, whose systems have grown organically over decades.

VDE warns of future challenges in keeping operation of intelligent distribution networks secure. Wireless-sensor-based network controls could be vulnerable to attacks ranging from illegal accessing of transmitted data to manipulation or shutting down of a local distribution network.

Steps forward

Fortunately, demonstration projects are under way in Germany in which distribution grids are being swiftly made intelligent without large investment and where experience in such issues can be gathered.

German company SAG has developed a system for secure and automatic operation of low-voltage networks dubbed Intelligent Network Station, or Ines, which will be rolled out for medium-voltage networks from 2014. It is working in partnership with Wuppertal University and Frankfurt-based municipal energy company Mainova.

"We are convinced that we can reduce the costly investments in the distribution network with this system," says Peter Birkner, a board member at Mainova. The system can dramatically reduce the costs of network expansion. In a pilot project in Frankfurt-Bornheim, investment amounted to just €50,000, compared with €350,000 that had been earmarked for network expansion, says Markus Zdrallek of Wuppertal University, which is responsible for the software development.
The aim is to monitor the real-time situation on the low- and medium-voltage networks and the interfaces between them, and introduce the possibility to steer and automatically control loads on the wires so that the existing network capacity can be optimally used. Infrastructure investments can thereby be reduced or postponed.

SAG's technology makes it possible to get a complete overview of a town or parish local network by equipping and measuring only 15% of the network nodes — points where lines are connected to each other. In critical situations, the power flows can be controlled and precise measures taken to eliminate overloads, for example by steering generation plants such as wind turbines or photovoltaic plants. Interfering in consumer power use takes place only as an absolute exception.

Low impact

The technology operates automatically and existing infrastructure is left as it is. The real-time situation in the local transformer stations can be monitored continuously. This applies to electricity flow, voltage level, capacity use and temperature; data are fed to the next voltage network level for further evaluation.

The situation at a local transformer station can be visualised at any time with a traffic-light system — green for ok, amber for problems brewing and red for critical. The whole system can be retrofitted without having to interfere with existing transformer station switchgear, says SAG.

A similar system for low- and medium-voltage networks has been developed by Westnetz, a distribution network subsidiary of German energy company RWE. The initiative was launched in November 2011 and runs until January 2016. It is part of the Grid4EU innovation for energy networks, a major EU-wide project with a budget of €50 million, €25 million of which is provided by the European Union.

Working with ABB and the Technical University of Dortmund, its pilot project is in Reken in North Rhine Westphalia, a network region that is expected to see much more solar and wind power in the future. In turn, these forms of generation are expected to cause reverse flows of electricity on 70 to 80 days of the year. With such projects only recently getting under way, there is still a lot of exploratory work to be done to find the best ways to optimise existing distribution networks, minimise the need for expansion and maximise the take-up of wind and solar generation.

The distribution grid operator's role will be much broader, and co-ordination with high-voltage levels far more closely monitored. The impact of new technologies such as electricity-storage facilities, increasing demand-side management and benefits of some renewable curtailment, in as far as this is accepted, are all challenges that the distribution network operators have long envisioned but hardly expected to become priorities so quickly.

This article originally appeard in Wind Stats

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