Environmental Engineering Reference
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expansion decisions: amount and type of RES available in the future, electricity
demand levels, the level of hydro in
ows, and fossil and renewable fuel costs.
Models must also be multi-criteria, meaning that some of the main quanti
able
objectives to be achieved as a result of the reinforcement of the grid will have to be
somehow incorporated into the expansion problem objective function. Main system
variables to be optimized shall relate to the reliability of system operation, trans-
mission network losses, conventional and RES-based generation CO2 and other
pollutant gas emissions, the environmental (visual and other) impact of the trans-
mission grid itself, and transmission grid investment and variable operation (power
production) costs.
Given the long lead times considered in the planning problem, the model will
typically consider only the so-called DC approximation to the load
ow equations,
assuming that voltage and reactive support problems can be addressed in shorter-
term grid expansion planning analyses as well as in the operation time frame.
However, the decision on which level of detail to adopt for the representation of the
ow of power in the network is to be made in the light of the size and technical
characteristics of the problem to be solved.
Expansion planning algorithms may be based on a functional decomposition
between a
rst module aimed at the automatic generation of network expansion
plans, using optimization techniques or meta-heuristics ones, and a second module
that evaluates each plan and computes its cost and reliability metrics. For a review
of some of the most relevant publications on transmission expansion planning see
[ 14 ].
There are several projects funded by the European Commission to study the
transmission planning of the European grid from several perspectives: Realisegrid,
SUSPLAN or E-highway2050. Feasibility studies on the integration of the North of
Africa and European electricity systems have been launched by the Dii and Med-
grid consortiums, see [ 6 , 8 , 15 , 24 , 26 ].
3 Access to the Transmission Grid
Long-term transmission rights will have to be made available to both RES-based
and conventional generation. Research is needed on how the availability and format
of these rights will affect transmission capacity allocation algorithms.
In order for markets to allow RES generators to better address imbalances caused
by the intermittency of their output, short time markets will probably need to move
closer to real time. This fact, together with the increase in demand for long-term
transmission capacity products will certainly condition the schemes for allocation of
available transmission capacity in the different time frames when it is offered.
Regarding the regulation of connection to the grid, the number of connection
requests will probably increase, at least in those areas with abundant renewable
primary resources. At the same time, RES generation will probably be provided
priority access to the grid. Mechanisms to deal with very large numbers of requests
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