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
'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.
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.
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
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
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
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Manuel Sanchez Jimenez
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
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.