atw 2019-02

atw Vol. 64 (2019) | Issue 2 ı February
Serial | Major Trends in Energy Policy and Nuclear Power
Wind Energy in Germany and Europe
Status, potentials and challenges for baseload application:
European Situation in 2017
Thomas Linnemann and Guido S. Vallana
Introduction Wind power is a cornerstone of rebuilding the electricity supply system completely into a renewable
system, in Germany referred to as “Energiewende” (i. e. energy transition). Wind power is scalable, but as intermittent
renewable energy can only supply electrical power at any time reliably (security of supply) in conjunction with
dispatchable backup systems. This fact has been shown in the first part of the VGB Wind Study, dealing with operating
experience of wind turbines in Germany from 2010 to 2016 [1],[2]. This study states among other things that despite
vigorous expansion of on- and offshore wind power to about 50,000 MW (92 % onshore, 8 % offshore) at year-end 2016
and contrary to the intuitive assumption that widespread distribution of about 28,000 wind turbines, hereinafter
referred to as German wind fleet, should lead to balanced aggregate power output, no increase in annual minimum
power output has been detected since 2010, each of which accounted for less than 1 % of the relevant nominal capacity.
The annual minimum power output reflects the permanently
available aggregate power output (secured capacity) of the
whole German wind fleet by which conventional power plant
capacity can be reduced on a permanent basis. Or in other
words: In every year since 2010 there was always at least one
quarter of an hour in which more than 99 % of the nominal
capacity of the German wind fleet was not avail able and, for
all practical purposes, a requirement for 100 % dispatchable
backup capacity prevailed, although its nominal capacity
had almost doubled at the same time. Intuitive expectations
that electricity generation from widespread wind turbines
would be smoothed to an extent which in turn would allow
the same extent of dispatchable backup capacity to be
dispensed with has therefore not been fulfilled.
Dispatchable backup capacity is essentially necessary
to maintain a permanently stable balance between
temporal variations of outputs from wind turbines and
other power plants fed into the power grid and consumerdriven
temporal demand variations extracting power from
the grid (frequency regulation).
To maintain power grid stability, ancillary services such
as primary control capacity or large rotational inertia are
also necessary to limit widely oscillating frequency
deviations (grid oscillations) − properties that con ventional
power plants with their turbo generators per se possess [3],
but which must be provided separately as additional ancillary
services in case of a largely renewable power supply
system based on wind and solar energy ( photovoltaics).
For grid stability, a secured capacity of power plants
including grid reserve and standby capacities for backup
purposes of currently about 84,000 MW is required in
Germany at the time of annual peak load occurring
between 17:30 and 19:30 during the period from November
to February [4].
If electricity generation from wind power is further
expanded in line with the objectives of the German federal
government, the nominal capacity of the German wind
fleet should exceed this secured capacity of power plants in
several years’ time. From that point on, the dispatchable
backup capacity to be maintained would have to be capped
at about the level of this secured capacity of power plants
which is sufficient for grid stability reasons.
Solar energy (photovoltaics) as a further scalable and
politically designated cornerstone of the German Energiewende
is always 100 % unavailable during the times of
year and day relevant for the annual peak load, as well as
year-round at night, and therefore per se cannot make any
contribution to the secured power plant capacity [4].
At year-end 2017, almost 1.7 million photovoltaic
systems with around 42,400 MW nominal capacity (peak)
were installed throughout Germany, supplying 40 TWh
of electricity year-round [5]. By comparison, net power
consumption amounted to around 540 TWh. This amount
does not include the balance of electricity imports and
electricity exports of almost 55 TWh [6], the auxiliary
electric load of power plants of about 34 TWh [7] or grid
losses at all voltage levels of around 26 TWh [8]. Photovoltaics
therefore contributed around 7.4 % towards
meeting the domestic net power requirement.
Analyses of quarter-hourly time series of power output
from wind turbines and photovoltaic systems in Germany
over several years, scaled up to a nominal capacity of an
average 330,000 MW to obtain 500 TWh electricity from
these two intermittent renewable energy systems (iRES) per
year, lead to a continued high need for dispatchable backup
capacity of 89 % of the annual peak load [9],[10]. This average
iRES nominal capacity includes 51 % of onshore wind
power, 14 % of offshore wind power and 36 % of photovoltaic
systems. The annual electrical energy amount of
500 TWh reflects Germany’s net electricity consumption
plus grid losses minus predictable renewable energy systems
(RES) such as run-of-river and pumped storage power
plants, biomass and geothermal power plants.
The saving in backup capacity of 11 % of the annual
peak load under these conditions is essentially attributable
to the regular night-time load reduction, as high backup
capacities are seldom necessary during the daytime with
electricity generation from solar power. From 2015 to
2017, an average 13 % of the annual hours in which iRES
power outputs of less than 10 % of the iRES nominal
capacity arose were accounted for by daytime hours
between 08:00 and 16:00.
As, at around 130 TWh, slightly more than one quarter
of the iRES annual electric energy would occur at times of
low demand (surplus) and therefore not be directly usable,
the dispatchable backup system would have to provide the
equivalent of these surpluses temporally delayed with a
very low capacity factor of a maximum 20 %.
From one year to the next, weather-related fluctuations
of iRES annual electric energy of at least ±15 % would
have to be factored in [9], with repercussions on the
backup capacity in case of continued efforts to maintain
the current high level of security of supply.
According to annual outage and availability statistics
compiled by the Forum Network Technology/Network
Operation of VDE as German Association for Electrical,
Part 1 *
*) Part 2
to be published
in atw 3 (2019)
SERIAL | MAJOR TRENDS IN ENERGY POLICY AND NUCLEAR POWER 79
Serial | Major Trends in Energy Policy and Nuclear Power
Wind Energy in Germany and Europe ı Thomas Linnemann and Guido S. Vallana