NEWS

Meteorological associations around the world assess weather conditions; particularly monitoring of rainfall levels, using radar systems operating at high frequencies. Such frequencies are typically in C and S frequency bands. Meteorological radars are generally of relatively low resolution as weather tends to be an area effect. Rainfall calculations are typically made with 1-5km resolution, higher resolution being available at shorter ranges, typically up to 75km.

As wind farm development throughout the UK and around the world continues to expand, the impact of turbines on radar, for both military and civil stakeholders, remains one of the biggest constraints. Nevertheless, moving wind turbine blades do not cause the same problems on Air Defence and Air Traffic Control radars as on Doppler weather radars.

There have been increasingly growing concerns of the effects of wind turbines on Meteorological radars in many countries in Europe and North America. These have resulted mainly from numerous reports mentioning false predictions as rotating blades can show up on a weather radar screen as incoming weather, such as an area of precipitation and, on some occasions, interfering with the ability of forecasters to issue warnings, even on occasions resulting in false warning alerts. Furthermore, an increasing number of institutions and organisations have been undertaking research and publishing reports for the effects of wind turbines on weather radar such as EUMETNET, the network of European Meteorological Services. The main concerns regarding the effects of wind turbines on met radars can be summarised as Shadowing, Clutter and Doppler processing interference.

Shadowing

Wind turbines can cause met radar shadows - sometimes referred to as ‘occultation’ by meteorologists, particularly for wind turbines sited close to a radar. This may be significant for met radars as reflections from individual water droplets may be very weak, and a reduced radar signal in a shadow zone may be significant. This causes blind areas where reduced precipitation will be detected, which may affect larger areas due to the processing methods employed. Wind turbine shadows are considered to be significant by some national meteorological organisations as no or reduced rainfall will be detected in the shadow regions. This is a significant concern especially when the wind farm lies close to the radar and it is exacerbated by multiple wind turbines across a large sector.

Clutter

As with all radars, meteorological radars receive returns (echoes) from targets such as buildings, trees, communication towers and the landscape. These returns are known as clutter, but are normally readily processed out from met radars using various clutter filtering algorithms as returns from them will be constant. To some extent, this should apply to the static parts of wind turbine structures unless the wind turbine returns are strong enough to saturate the receiver. The later is possible due to the large radar cross section of wind turbines. Moving objects such as aircraft also cause clutter that is less easily processed out, but are normally transient in nature, so cause few problems. The varying returns from wind turbine blades can potentially cause problems as they may be described as persistent transient returns.

Doppler radar processing

Some meteorological radars use Doppler processing techniques to identify the horizontal velocity of water droplets and dust particles and hence wind velocities. Doppler processing interference has generally similar effects to clutter as described above, but effects are limited to the Doppler processing conducted by the radar.

As a result of this, meteorological organisations recommend wind farms not to be located within various distance ranges from their radars and object to wind farms being located in proximity to the radar. Often this can hinder whole developments from being developed or the solutions can cost several million Euros. We believe that the optimal approach in the decreasing met radar concerns is to assess the potential effects and apply necessary modifications in early stages. However, assessing the impacts of wind turbines on meteorological radar is far from trivial.

Pager Power Ltd has a successful track record of assessing the effects of wind turbines on meteorological radar, both, in the UK and abroad. Using our own bespoke software application called Sightlines we have the capability to assess the impacts of shadowing, clutter and Doppler processing. Our bespoke software also enables us to produce custom analysis adjusted to the varying nature of different proposed wind farm developments and weather radar. This is a key to maximise the effectiveness of the analysis in assessing and suggesting ways for minimizing potential impacts. Furthermore, besides the above effects we have the capability to establish and incorporate both bare terrain data as well as buildings and vegetation that may help to shield wind turbines.