Page 4 - Risorse_Energetiche_Favignana_2005

Proposal APERTURES. PART B Priority6.1.3.1.1.2 - FP6-2005-TREN-4 p 4 of 49
B.1 Scientific and technological objectives of the project and state of the art

B.1.1 Background and state of the art
Renewable energy and energy efficiency technologies are key to creating a clean energy future not only for Europe,
but for the world.
In November 1997 the European Commission adopted the Communication “Energy for the Future: Renewable
Sources of Energy (RES)”, a White paper for a Community Strategy and Action Plan. The purpose of this White
Paper is to contribute, by promoting renewable energy sources, to the achievement of overall energy policy
objectives: security of supply, environment and competitiveness, and to improve and reinforce environmental
protection and sustainable development.

This means that it is necessary to incorporate significant energy resources supplied by renewable energy generation
into already existing grids in order to reduce the percentage of carbon based fuel generation.
This would abate the energetic European dependency and in addition would contribute both to better energy
security and lessen CO 2.emissions and therefore help to meet the EU’s international obligations.

Almost all the electricity currently produced is generated from a centralised power system designed around
large fossil fuel or nuclear power stations. This power system is robust and reliable but the efficiency of power
generation is low, resulting in large quantities (around 60%) of primary energy being wasted as heat.

For the reasons explained above, it is claimed that smaller scale power supply networks could deliver substantial
environmental benefits via higher energy efficiency and by facilitating the integration of renewable sources. There
is now a trend towards developing smaller generators, with emphasis on high efficiency and low emissions.

These distributed generators (DG) connected to the distribution network do not fit easily into the traditional power
generation hierarchy. There are problems caused by the intermittent nature of the generation: the output from a
wind farm or a photovoltaic array depends on the climatic conditions, and Combined Heat and Power (CHP) plants
are usually controlled by the production of heat.
Microgrids offer a solution which can provide a stable and reliable power supply despite a high penetration of
intermittent renewable energy sources and despite the seasonal variation of the power demand.
A microgrid is a small-scale power supply network that is designed to provide energy for a small community. The
‘small community’may be a typical housing estate, an isolated rural community, a mixed suburban environment, an
academic or public community such as a university or school, a commercial area, an industrial site, a trading estate,
or a municipal region or a small island.
The key concept that differentiates this approach from a conventional power utility is that the power generators are
small (often referred to as microgenerators, of a similar size to the loads within the microgrid). They are also
located in close proximity to the energy users. The generators, and possibly also loads, are then managed to achieve
a local energy and power balance
Microgrids promise substantial environmental benefits through higher energy efficiency and by facilitating the
integration of renewable sources such as photovoltaic arrays or wind turbines.

By virtue of a good match between generation and load, microgrids have a low impact on the electricity network,
despite their potentially significant level of generation.
However, to achieve this, a number of technical, regulatory and economic issues have to be resolved before
microgrids can become commonplace.

There needs to be power balance within microgrids, on a timescale ranging from milliseconds to years.
Over a short timescale, the power balance is linked to the question of control and frequency; over longer time
scales, one needs to consider the relationship between energy supply, demand and storage. Sufficient energy
must be available from the generators to ensure energy balance over longer time scales.
A diversity of generation matched to the load will need to be employed if the microgrid is to be capable of
stand-alone operation. Microgrids can exist as a remote power system in regions where utility supply is not
available. They may, on the other hand, be embedded in a larger electrical utility – this would be the typical
scenario in Europe with its mature utility power system.
In this case the use of intelligent control and fast switching power electronic systems to match the RES to the
grid provides an opportunity for a more flexible, and possibly more intelligent RES interface which is capable of
maintaining power quality within a microgrid. The optimization process can be usually performed at two levels: a
local and a global one.