Geoscience Reference
In-Depth Information
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Doppler Weather Radars and Wind Turbines
Lars Norin and Günther Haase
Swedish Meteorological and Hydrological Institute
Sweden
1. Introduction
In many countries the number of wind turbines is growing rapidly as a response to
the increasing demand for renewable energy. The cumulative capacity of wind turbines
worldwide has shown a near 10-fold increase in the last decade (Global Wind Energy Council,
2011) and in the coming years many more wind turbines are expected to be built. Existing,
older wind turbines are likely to be replaced by larger, next generation, turbines.
Modern wind turbines are large structures, many reach more than 150 m above the ground.
Clusters of densely spaced wind turbines, so called wind farms, are being built both on- and
offshore.
The continued deployment of wind turbines and wind farms is, however, not unproblematic.
Radar systems, for example, are easily disturbed by wind turbines. Interference caused by
wind turbines is more severe for many radar systems than interference caused by, for example,
masts or towers. This is due to the rotating blades of the wind turbines. Many Doppler
radars use a filter that removes echoes originating from objects with no or little radial velocity.
However, these filters do not work for moving objects such as the rotating blades of wind
turbines. Wind turbines located in line of sight of Doppler radars can cause clutter, blockage,
and erroneous velocity measurements, affecting the performance of both military- and civilian
radar systems.
Even though both radars and wind turbines have been in use for many decades it is only in
the last few years that the interference problem has received substantial attention. The reason
for this is simple; in recent years wind turbines have increased in number and size and at the
same time radar systems have become increasingly sensitive.
In this chapter we present a brief review of some of the work made to investigate the impact of
wind turbines on Doppler weather radars. Starting with a historical overview we outline the
evolution of wind turbines and early studies about their impact on Doppler radars in general
and Doppler weather radars in particular. Three major interference types for Doppler weather
radars are identified: clutter, blockage, and erroneous velocity measurements. Observations,
models, and mitigation concepts for all three interference types are discussed.
In particular, we present results from a study on average wind turbine clutter, based on
long time series of data. We show that modelling wind turbine clutter using the radar cross
section of a wind turbine can lead to erroneous results. We further argue that blockage due
to wind turbines is difficult to analyse using operational reflectivity data. An alternative way
