For the Defence Forces, the areas most problematic are along the borders, as well as wind parks planned comparatively close to radars.
As admitted to Postimees by defence ministry press rep Andres Sang, the army has encountered hardships with already existing parks.
«At certain heights, the turbines may interfere with air surveillance radars. This happens in two ways. Firstly, the rotating blades pose as fake targets. The radar identifies these as aircraft and will try to identify their future location, unnecessarily encumbering the radar. Secondly, a blind spot is created behind the rotating blades where flights are not visible for radars,» explained Mr Sang.
The closer to a radar, the less height is allowed for a turbine in order to not mess with the image.
The air force radars are the only ones to detect Russian military aircraft flying in international air space near Estonian borders with transponders switched off. For civil radars, these are invisible. The air force surveillance system being part and parcel of NATO’s integrated NATIENADS showing the picture to allies, the problem is not Estonia’s alone.
Mr Sang said wind parks aren’t a unique problem in European sense as such problems are also evident in nations like the UK, France, Denmark and Finland. The issue may be mitigated by reducing reflection off blades, but the blind area is created nevertheless – regarding that, only distance between radar and park helps.
Elsewhere in the world, developers have paid for additional radar posts in order to cover the blind areas created. This is very costly, however, and not allowed by Estonian law. Also, a hypothetical extra radar will for various technical reasons not solve problems in East Viru County.
«Air force experts have calculated maximal heights of turbines according to distance from radar. This not being public information, defence ministry may not publish the data,» said Mr Sang.
He added that with justified need to know, developers, local governments and others may see the materials at the ministry.
These past weeks, defence ministry has been explaining the wind park problems at economic, environmental and national defence committees of the Riigikogu, as well as the governmental security committee.
Environmental committee chairman Rainer Vakra (Soc Dems) says the problem needs to be solved by cooperation of ministries and wind park developers, it being «expedient that defence ministry must okay all plans regarding wind parks to be built. Regrettably, current rules exclude any agreement between developers and a ministry, for which reason the state says no to lion’s share of the plans,» said Mr Vakra.