I found information about a windmill park in the region of Shabla, which is in the most north-eastern part of the country, but couldn't dig up technical data. No info about those three or four windmills I've spotted near Stara Zagora either.

Check this out:

Windmill experts are searching for the most dense currents (not the fastest ones) on a height of 10m. Using that, experts depicted the perfect spots for windmill power in Bulgaria. The darkest areas are the most efficient spots, the lighter ones are not efficient for windmill energy production.

So we have the eastern part of the country (next to the Black Sea - Burgas and Varna, but with natural reservations)and the mountain areas, which are hardly exploitable. The northern part of Bulgaria has a lot of gray areas, which are perfect for windmills (only plateaus there).

Stara Zagora, is in one of the lighter areas - what's up with that? Are people richer there, or are they trying to get the best out their land? Maybe they are better informed (supposedly there is big EU grant for development of clean energies in the region).

Be careful! Is it classified?