IEEE Spectrum May, 2013 - 38

CuttiNg aCroSS the griD:

germany's
transmission-syst e m o p e r at o r s h ave p r o p o s e d fo u r h V D C l i n e s
(along three corridors) that would cut across the country's aC grid
and help ship power from the wind-rich north to the south, which is
more reliant on nuclear energy. in 2011, germany shut down eight
of the country's nuclear reactors [red dots]. the nine remaining reactors
[blue dots] are slated to cease operating by 2022.

Offshore wind farms, planned and
operating, with subsea HVDC cables

Corridor A

Corridor C

Corridor D

Berlin

Stuttgart
AC lines

Munich

If Germany moves forward with such
HVDC lines, it could help pave the way for
something much bigger, a "supergrid" of
interconnected DC lines capable of transporting electricity on a continental scale,
ferrying energy from North Sea turbines,
dams in Scandinavia, or Mediterranean solar farms to wherever demand is greatest
at that moment. The European Commission is counting on this sort of flexibility to
meet its goal of an 80 percent renewable
power supply by 2050. Corridor A could
be the first step.
the idea for hVdc lineS started to gain

traction two years ago, when the Fukushima
nuclear accident in Japan led German chancellor Angela Merkel to shut down 8 of her
country's 17 nuclear reactors and revive plans
to phase out the rest of them by 2022. Although this will eliminate just 16 percent of
the country's annual electricity generation,
the share comes to nearly half in the southern
states of Bavaria and Baden-Württemberg, of
which Stuttgart is the capital. Stuttgart will
have to make up part of the loss by drawing on distant sources of wind power and
38

may 2013

north american

fossil-fueled power plants. All told, some
10 gigawatts of power will need to be moved
from northern to southern Germany once
the last nuclear plant is closed. And the grid
simply isn't up to the challenge.
Renewable energy is already getting
dumped because of it. In 2010, for example, German wind farms let some
127 gigawatt-hours of energy, enough to
supply more than 30 000 German households for a year, fly on by. There was no
grid capacity to deliver that power. The
grid is so stressed that Bundesnetzagentur
(BNetzA), Germany's federal networks regulator, recently departed from typically
dry language in its annual report to warn
that the accelerated shift from nuclear to
renewables has "brought the transmission
systems to the brink."
Like many German cities, Stuttgart has a
complex energy portfolio. The city generates one-eighth of its own electricity and gets
most of the rest from elsewhere in BadenWürttemberg. Solar panels are the fastestgrowing supplier in both the city and the
state, thanks to premium prices set by the
federal government. PV alone could account

SPectrUm.ieee.orG

Open nuclear reactor

for as much as 18 percent of the energy produced in Baden-Württemberg by 2020.
Little of that power will arrive in the winter, however, and none overnight. At the
same time, solar generation is flattening
peak power prices, undermining the profitability of natural gas and coal power plants.
The Düsseldorf-based power company E.ON
blamed the weakened market last November
when it mothballed two natural-gas plants
and shelved plans for a state-of-the-art coal
plant; all happen to be in the south.
Using less coal and natural gas is a key plank
in Germany's response to climate change.
But the pace of change is unsettling for
BNetzA, which oversees the power grid and
counts on fossil-fuel plants that deliver power
on demand to maintain its stability. BNetzA
is so concerned that for the past two winters
it has paid owners of several older gas-fired
power plants in southern Germany and Austria to keep their plants on standby.
In principle, wind power in the south could
take up some of the slack-but not much.
Winds are generally slower in the south. Turbine construction to exploit what wind is
available requires clearings and roads, and
map by

Bryan Christie Design

source: www.entsoe.eu

Closed nuclear reactor

http://www.entsoe.eu http://SPectrUm.ieee.orG

Table of Contents for the Digital Edition of IEEE Spectrum May, 2013