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

Wind Energy in Germany and Europe ı Thomas Linnemann and Guido S. Vallana

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