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image European Research News Centre > Energy > The essential integration
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image image image Date published : 02/10/2001
  image The essential integration
  How can we increase the amount of renewable energy sold in a liberalised electricity market? If green energy sources are to take off, a major innovation effort will be needed to make them part and parcel of Europe's power grid.

THERE can be no sustainable development without increased use of renewable energy resources. That is the maxim - now strengthened by the threat of climate warming - which has guided European energy policy for the past 20 years or more. The Union's objective is to boost the share of renewables to 12% of total energy consumption, or double the present level.

'There was an initial failure to fully gauge the extent of the problem,' believes Michel Crappe, a professor at the Electrotechnical Laboratory at the Faculté Polytechnique de Mons (B). 'To achieve a more sustainable energy model it was thought to be enough to make more efficient windmills, develop fuel cells and promote cogeneration. But if you want renewable generation - which by its very nature is highly decentralised - to become an increasingly competitive resource, then it must be integrated into the global electricity distribution system.'

The problem is that the logic of this system, being based on very large nuclear or fossil-fired plants generating upwards of 1 000 MW apiece, is the very opposite of that of renewable energy production. Connecting a very large number of small power plants - ranging from just a few dozen kW to 150 MW - to such a system is rendered all the more difficult as the power produced from sources such as the wind or sunlight inevitably fluctuates a lot.

Electrical solidarity

In an electricity distribution network it is essential for all the sources to operate at the same 'electrical speed' - the famous 50 hertz alternating current standard for which all European mains devices are configured. If a 1 000 MW power plant fails, the overload imposed on the other generating sources causes them to 'go slow', and this threatens the synchronisation of the network.

'Electricity is not a commodity like any other because it cannot be stored on a large scale, so supply must match demand at all times,' explains Michel Crappe. 'That's why we have interconnected our networks throughout Europe, from Stockholm to Lisbon and from Dublin to Vienna. This enables us to deal with consumption peaks and supply failures.'

This electrical solidarity, now centralised and fully automated, must not last longer than 15 minutes, as otherwise there is the risk of contagion as the strain is passed on to other parts of the system. This quarter of an hour allows the affected network to take the necessary measures to restore its autonomy, either by starting up reserve generators or disconnecting part of the network (some companies agree to be occasionally cut off in return for special low rates). These electricity trade-offs between the countries of the UCTE (Union for the Coordination of Transmission of Electricity) reached 173 TWh (terawatt-hours) in 1999, which is 8.4% of Europe's total electricity output.

Added complexity

Plant and equipment (generators, high-tension lines, transformers, circuit breakers, etc.), computer systems, control procedures, regulations: everything must be designed in accordance with the network structure, within which the location and power of the generating plants are carefully planned. The loads within this enormous grid are balanced by remote control from a central unit.
Decentralisation adds to the complexity of such an architecture, owing to the small size of the units. In the case of renewables, the geographical location of the generating plants is no longer determined by the network's overall needs, but according to local demands and the geographical availability of the resources, whether wind, sun, biomass or rivers. What is more, the fluctuating nature of these sources means that the networks must be able to absorb the decentralised production when it is active, and draw on alternative supplies when it is at rest.

As long as renewable energy sources make a negligible contribution to a system, these fluctuations are not really a problem. But above a certain threshold, managing the balance between production and consumption becomes difficult. The Danes, who are at the forefront of wind power, estimate this crucial threshold to be 20%. Above this, a probability-based approach to system management must be adopted, as well as great flexibility in the power flow between the centralised and decentralised parts of the network.


Apart from the network operation design itself, the integration of renewables requires many specific technical adjustments. 'The lack of standardised interfaces between the decentralised production units and the distribution network is a particular problem,' explains Manuel Sanchez Jimenez, a scientific officer at the Research DG. 'Managing their integration also requires some major, complex computer developments.'

The Commission recently signed a research contract with 37 European companies and laboratories. Known as Dispower,(1) this four-year project represents a total investment of euro17 million. It aims to support the decentralisation of the electricity market on the basis of new knowledge and new technological developments. Its objectives include the development of hardware and software for the optimum functioning of a large number of decentralised electricity generators, the agreement of strategies for network stability and control systems, the creation of infrastructures to carry out life-size pilot tests, and training for electricity network operators.

Another aspect of research is focusing on the most promising new technologies for the storage of energy from intermittent sources. The Investire(2) network, for example, comprises 35 European companies and laboratories working in this field. 'To date, it is lead batteries which are most widely used for storing electricity, mainly of photovoltaic origin, as they provide best value for money,' explains Paul Lucchese (CEA - France). 'But new avenues are being explored, both in the form of electrochemical accumulation - lithium or nickel batteries which have shown their worth in portable electronics - and by using the energy to electrolyse water, producing hydrogen which can be stored and then generate a current in fuel cells. It is also possible to store the energy in supercapacitors, in flywheels or by compressing air.'


(1) Distributed Generation with a High Penetration of Renewable Energy Sources
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(2) Investigation of Storage Technologies for Intermittent Renewable Energies
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Manuel Sanchez Jimenez
Research DG


'Renewable' tariffs

The Electricity Tariffs and Embedded Renewable Generation project is looking at the delicate issue of charges for energy that is produced on a decentralised basis. 'Decentralised energy production has a certain advantage. It is closer to the consumer, which permits savings in the electricity transport and distribution infrastructures,' explains its co-ordinator, Goran Strbac. 'But the present market organisation does not allow this benefit to be passed on to the consumer.' A significant conceptual contribution by the project has been to develop a framework for a cost-benefit approach to energy planning and tariffs.


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On the Web

Association of European
Transmission System Operators (ETSO)

Cogen Europe

European Renewable Energy
Centres Agency (EUREC)

Union of the Electricity Industry

Union pour la Coordination du
Transport de l'Electricité


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The Research DG is holding a conference on the Integration of Renewable Sources and Distributed Power Generation in Energy Systems on
25 and 26 September in Brussels.



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