Planning inspector Alwyn Nixon has dismissed an appeal lodged by REG Windpower Limited over Powys County Council's refusal to give approval for three wind turbines at land at Pentre Tump, at Llanfihangel-Nant-Melan, near New Radnor.
Members of the Alliance campaign group, which is battling separate plans for huge windfarms in other parts of Mid Wales, say the inspector's decision, and the reasons for it, back up their arguments. Powys County Council rejected REG Windpower Limited's application in December 2012.
The firm wanted to build three wind turbine generators with a blade tip of 103.5 metres as well as related infrastructure.
The company appealed to the inspector after the council rejected its plan.
But Mr Nixon said the council's decision was correct. He added: "
The proposed development would unacceptably adversely affect the environmental and landscape quality of Powys, and would unacceptably adversely affect the enjoyment of the public rights of way network, especially bridleways."
The decision has been welcomed by members of the Alliance, an organisation made up of several environmental and campaign groups opposed to plans to build five large scale windfarms in Powys.
The windfarm proposals are currently subject to a planning inquiry.
Jonathon Wilkinson, from the Alliance, said the key difference between the Mid Wales turbines scheme and the New Radnor project was that the Mid Wales turbines were within the region's Strategic Search Area, areas of land which have been ruled as suitable for windfarms.
But he added: "That is an important distinction. However, the principle remains exactly the same.
"The inspector has confirmed every negative aspect of the development and they were only looking at three wind turbines.
"What we have in Mid Wales could be between 600 or 700 wind turbines.
"Those negative aspects the inspector has found are exactly the same negative aspects we say the Mid Wales project will bring."
The Alliance is taking part in the ongoing planning inquiry into plans for five large scale windfarms in Mid Wales.