atw 2019-02

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

<strong>atw</strong> Vol. 64 (<strong>2019</strong>) | Issue 2 ı February<br />

Serial | Major Trends in Energy Policy and Nuclear Power<br />

Wind Energy in Germany and Europe<br />

Status, potentials and challenges for baseload application:<br />

European Situation in 2017<br />

Thomas Linnemann and Guido S. Vallana<br />

Introduction Wind power is a cornerstone of rebuilding the electricity supply system completely into a renewable<br />

system, in Germany referred to as “Energiewende” (i. e. energy transition). Wind power is scalable, but as intermittent<br />

renewable energy can only supply electrical power at any time reliably (security of supply) in conjunction with<br />

dispatchable backup systems. This fact has been shown in the first part of the VGB Wind Study, dealing with operating<br />

experience of wind turbines in Germany from 2010 to 2016 [1],[2]. This study states among other things that despite<br />

vigorous expansion of on- and offshore wind power to about 50,000 MW (92 % onshore, 8 % offshore) at year-end 2016<br />

and contrary to the intuitive assumption that widespread distribution of about 28,000 wind turbines, hereinafter<br />

referred to as German wind fleet, should lead to balanced aggregate power output, no increase in annual minimum<br />

power output has been detected since 2010, each of which accounted for less than 1 % of the relevant nominal capacity.<br />

The annual minimum power output reflects the permanently<br />

available aggregate power output (secured capacity) of the<br />

whole German wind fleet by which conventional power plant<br />

capacity can be reduced on a permanent basis. Or in other<br />

words: In every year since 2010 there was always at least one<br />

quarter of an hour in which more than 99 % of the nominal<br />

capacity of the German wind fleet was not avail able and, for<br />

all practical purposes, a requirement for 100 % dispatchable<br />

backup capacity prevailed, although its nominal capacity<br />

had almost doubled at the same time. Intuitive expectations<br />

that electricity generation from widespread wind turbines<br />

would be smoothed to an extent which in turn would allow<br />

the same extent of dispatchable backup capacity to be<br />

dispensed with has therefore not been fulfilled.<br />

Dispatchable backup capacity is essentially necessary<br />

to maintain a permanently stable balance between<br />

temporal variations of outputs from wind turbines and<br />

other power plants fed into the power grid and consumerdriven<br />

temporal demand variations extracting power from<br />

the grid (frequency regulation).<br />

To maintain power grid stability, ancillary services such<br />

as primary control capacity or large rotational inertia are<br />

also necessary to limit widely oscillating frequency<br />

deviations (grid oscillations) − properties that con ventional<br />

power plants with their turbo generators per se possess [3],<br />

but which must be provided separately as additional ancillary<br />

services in case of a largely renewable power supply<br />

system based on wind and solar energy ( photovoltaics).<br />

For grid stability, a secured capacity of power plants<br />

including grid reserve and standby capacities for backup<br />

purposes of currently about 84,000 MW is required in<br />

Germany at the time of annual peak load occurring<br />

between 17:30 and 19:30 during the period from November<br />

to February [4].<br />

If electricity generation from wind power is further<br />

expanded in line with the objectives of the German federal<br />

government, the nominal capacity of the German wind<br />

fleet should exceed this secured capacity of power plants in<br />

several years’ time. From that point on, the dispatchable<br />

backup capacity to be maintained would have to be capped<br />

at about the level of this secured capacity of power plants<br />

which is sufficient for grid stability reasons.<br />

Solar energy (photovoltaics) as a further scalable and<br />

politically designated cornerstone of the German Energiewende<br />

is always 100 % unavailable during the times of<br />

year and day relevant for the annual peak load, as well as<br />

year-round at night, and therefore per se cannot make any<br />

contribution to the secured power plant capacity [4].<br />

At year-end 2017, almost 1.7 million photovoltaic<br />

systems with around 42,400 MW nominal capacity (peak)<br />

were installed throughout Germany, supplying 40 TWh<br />

of electricity year-round [5]. By comparison, net power<br />

consumption amounted to around 540 TWh. This amount<br />

does not include the balance of electricity imports and<br />

electricity exports of almost 55 TWh [6], the auxiliary<br />

electric load of power plants of about 34 TWh [7] or grid<br />

losses at all voltage levels of around 26 TWh [8]. Photovoltaics<br />

therefore contributed around 7.4 % towards<br />

meeting the domestic net power requirement.<br />

Analyses of quarter-hourly time series of power output<br />

from wind turbines and photovoltaic systems in Germany<br />

over several years, scaled up to a nominal capacity of an<br />

average 330,000 MW to obtain 500 TWh electricity from<br />

these two intermittent renewable energy systems (iRES) per<br />

year, lead to a continued high need for dispatchable backup<br />

capacity of 89 % of the annual peak load [9],[10]. This average<br />

iRES nominal capacity includes 51 % of onshore wind<br />

power, 14 % of offshore wind power and 36 % of photovoltaic<br />

systems. The annual electrical energy amount of<br />

500 TWh reflects Germany’s net electricity consumption<br />

plus grid losses minus predictable renewable energy systems<br />

(RES) such as run-of-river and pumped storage power<br />

plants, biomass and geothermal power plants.<br />

The saving in backup capacity of 11 % of the annual<br />

peak load under these conditions is essentially attributable<br />

to the regular night-time load reduction, as high backup<br />

capacities are seldom necessary during the daytime with<br />

electricity generation from solar power. From 2015 to<br />

2017, an average 13 % of the annual hours in which iRES<br />

power outputs of less than 10 % of the iRES nominal<br />

capacity arose were accounted for by daytime hours<br />

between 08:00 and 16:00.<br />

As, at around 130 TWh, slightly more than one quarter<br />

of the iRES annual electric energy would occur at times of<br />

low demand (surplus) and therefore not be directly usable,<br />

the dispatchable backup system would have to provide the<br />

equivalent of these surpluses temporally delayed with a<br />

very low capacity factor of a maximum 20 %.<br />

From one year to the next, weather-related fluctuations<br />

of iRES annual electric energy of at least ±15 % would<br />

have to be factored in [9], with repercussions on the<br />

backup capacity in case of continued efforts to maintain<br />

the current high level of security of supply.<br />

According to annual outage and availability statistics<br />

compiled by the Forum Network Technology/Network<br />

Operation of VDE as German Association for Electrical,<br />

Part 1 * <br />

*) Part 2<br />

to be published<br />

in <strong>atw</strong> 3 (<strong>2019</strong>)<br />


Serial | Major Trends in Energy Policy and Nuclear Power<br />

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

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!