IEEE Power & Energy Magazine - July/August 2016 - 51

compensation) and partially equipping local distribution
transformers with regulating devices.
a notable example at a larger scale is the collection of
studies of the european climate foundation examining the
road for a decarbonized power sector in europe, "Power
perspectives 2030" and "Roadmap 2050," where the need
for serious transmission reinforcements is shown in the presence of large volumes of renewable generation. The study
does not make a clear distinction between distributed and
centralized estimates for deployment of wind and solar
power production.
The International energy agency, in the report "Repowering Markets:. Market Design and Regulation During the
Transition to low-carbon Power systems," examines the
issue of transmission planning in the presence of large
volumes of renewable resources. Modeling a transmission
network for the future involves assessing modifications to
complex network structures in an uncertain and changing
world, choosing from many possible choices with multiple
dimensions under huge uncertainty. one of the most important variables for network planning is the share of intermittent renewables envisaged in the system and their location.
The clearer the criteria and goals, the easier it will be to
design a network plan that meets the future requirements of
the energy system.
While variable renewable resources such as wind and
solar, whether centralized or distributed, can generate an
impressive amount of electricity, they are typically not
as dependable as conventional energy generation. Interconnectors remain by far the most cost-efficient solution
to combining a high share of variable renewable energy
with the need to maintain a highly secure electricity supply. Transmission lines reduce the need for new generation
capacity to balance the system. The development of low
carbon renewable generation depends on the location of
the best natural resources, since deployment of renewables,
also for distributed generation, tends to happen more rapidly in windy and sunny locations. These patterns increase
the benefits of market integration over larger geographic
areas because cross-border trade contributes to reducing
the overall cost of the electricity system by exploiting the
complementarities between demand patterns and cost differences between electricity systems. Market integration
offers savings in overall dispatching costs. The overall
generation cost is therefore lower when dispatching over a
broader and more diversified portfolio of plants. Transmission infrastructure can smooth out the variability of wind
and solar power across large geographic areas. The aggregated load factor of renewables over large areas, in terms of
percentage of peak generation, is higher than the individual
load factor of one specific plant.
a clear example of the relevance of renewables in transmission planning is the Ten-year network Development Plan
(TynDP) that enTso-e publishes biannually to identify
transmission expansion reinforcements that are necessary to
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ieee power & energy magazine

facilitate eu policy goals. The last TynDP indicates that
interconnection capacity all over europe should double by
2030 to deliver social and economic welfare, characterized
by enTso-e as the ability to reduce congestion between
two electricity markets to trade power in an economically
efficient manner. Depending on the scenario, between 44
and 80% of the projects in the TynDP lead to an increase
in renewables being available in the energy system, either
by enabling new connections or by reducing congestion in
the network.

DERs as Sources of Local Flexibility
a less obvious topic is whether DeRs could be a source of
local flexibility that could solve problems at the nodes of
the transmission network. emerging technologies on the
distribution grid (whether DeRs, digital communications,
sensors, control systems, digital "smart" meters, or greater
customer engagement) present both technical and policy
challenges and opportunities for the delivery of energy
services. Power grids evolved organically in a bottomup manner, as opposed to a centrally coordinated master
plan. This build-up has led to large-scale legacy investments that require significant operating margins to maintain system stability, as opposed to more refined margins
enabled by the rapid and precise control offered by new
and emerging technologies.
The office of energy Policy and systems analysis of the
u.s. Department of energy has performed a thorough analysis of this issue by sponsoring and reviewing a large collection of studies on the subject; see the Quadrennial energy
Review (QeR). a summary of the broad conclusions can be
found in chapter 3, "Modernizing the electric grid" of the
main QeR document. Regarding the relationship between
DeRs and transmission expansion, two relevant findings
deserve to be mentioned.
✔ The QeR concludes that flexible grid system operations and demand response can enable renewables and
reduce the need for new bulk-power-level infrastructure. end-use efficiency, demand response, storage,
and distributed generation can reduce the expected
costs of new transmission investment. Increased electric system flexibility can come from a portfolio of
supply- and demand-side options, including grid storage, more responsive loads, changes in power system
operations, larger balancing areas, flexible conventional generation, and new transmission.
✔ analyses conducted for the QeR examined transmission capacity needs in 2030 that could accommodate high deployment of low-cost DeRs, using
low-cost solar PVs as a proxy for all types of distributed generation. The scenario modeling results
show that changes in transmission requirements
through 2030 for a high-distributed PV case vary by
region, but in most regions 2030 transmission needs
are similar to those in the reference case, indicating
july/august 2016

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - July/August 2016