Renewable Energy and Transmission Networks - Green Energy and Efficiency: An Economic Perspective - page 373

may be more abundant and economical than in the IEM, like the North sea to the
North of Europe, or Northern-Africa to the south of Europe, see [ 5 , 7 ].
Some of the latter issues will be discussed when re

ecting on the allocation of

transmission rights in the long term.

2.3 Upgraded Algorithms for Network Expansion Planning

Given the intermittent nature of the output of most RES generation and the non-
homogeneous distribution of primary renewable energy resources, the deployment
of large amounts of this generation is expected to result in a signi cant increase in

the size and diversity of power ows among areas in a region comprising several

systems. These directly result from the rise in the variability of system conditions
over the entire region. This will increase the number of operating conditions to be
considered in whatever planning procedure that is adopted.
If very large amounts of power have to be transported from distant places —

offshore wind production from the North Sea, solar power from Northern Africa to
Europe, large wind resources from the sparsely populated Midwest in the USA

—
and very broad market integration is an objective, then just reinforcements of the
existing high-voltage grid (400 and 220 kV in Europe) may not be sufcient and
some sort of overlay or super-grid may have to be built, perhaps using higher
voltage levels and direct current (DC) technology. As a consequence of this, a large
number of technology options will have to be considered in the planning process,
ranging from small but numerous incremental AC reinforcements to the existing
grid, to large HVDC corridors that may or may not be part of a regional super-grid,
including higher-than-conventional-voltage AC lines.
The development of the network for all the systems in a region will probably
have to be planned in an integrated way, since bene ts from the required rein-

forcements will not accrue to a single area or system but to several of them. Lastly,
due to the fact that the size of reinforcements to undertake in the long term future is
huge, network investments already undertaken in the short-to-medium term should
be consistent with long-term objectives, and therefore represent an intermediate step
towards the achievement of the integration of very large amounts of RES-based
generation (almost completely replacing conventional one on a daily basis).
In this new context, computing the optimal expansion of the transmission net-
work in a region ideally requires making use of highly ef

cient computer tools, able
to automatically produce a coherent ensemble of network reinforcements in several
time horizons that are consistent among them and can be deemed robust against the
multiplicity of scenarios that may unfold in the long-term future. The expansion
planning tools must be dynamic, meaning that a sequence of coherent sets of
reinforcements to be deployed in different time horizons, instead of just for a single
target year, must be computed. The model must be also stochastic, so that it may
consider several stochastic parameters that can in

uence the optimal transmission