Energy firm Energiekontor UK Limited was initially granted planning permission for two turbines on the site to the north of the village of Rhydcwmerau by Carmarthenshire County Council in March 2016.
The consent was subject to a condition that the turbines would be only 100 metres high, but the company later applied to the vary the condition and raise their height to 125 metres.
The council refused but, last winter, planning inspector Janine Townsley granted permission for the taller turbines (DCS Number 200-007-313), despite objections from local resident John Finney and campaign group Villages Against Supersized Turbines (VAST).
Opponents of the scheme complained that the turbines would be not only taller but also much more bulky than those originally proposed. Blade lengths would be increased by 43 per cent and the area swept by the rotating arms would go up by 104 per cent, they contended.
Challenging the inspector's ruling at Cardiff High Court, Finney's lawyers argued that she had exceeded her powers.
They maintained that she had no power under section 73 of the Town and Country Planning Act 1990 "to amend a condition pursuant to which a prior planning permission had been granted which had the effect of directly contradicting the description of the development permitted in that earlier permission".
They also claimed that the inspector had failed to consider whether the application before her constituted a "fundamental alteration" of the previous permission.
However, senior judge Sir Wyn Williams yesterday dismissed their complaints, ruling that the inspector correctly applied the law. The challenge, he said, was based on an "over-technical" and "inflexible" approach to the inspector's powers to change the planning condition.
In the judge's view, the inspector had carried out a "meticulous planning appraisal" of the larger turbines compared with the smaller ones initially approved. He said he had "no doubt" that she had specifically considered whether varying the condition would fundamentally alter the original plans.
Legal experts said the ruling was a useful clarification of the scope of section 73 applications, which allow planning conditions to be altered or removed.
Specialist planning law firm Town Legal tweeted: "Important judgment by Sir Wyn Williams on scope of section 73 permissions. Can alter description of proposed development as long as not a fundamental alteration to the proposed development the subject of the original permission."
Planning barrister Zack Simons, of Landmark Chambers, said in a tweet: "A useful judgment on section 73 variations. Confirming (following Wet Finishing Works, and departing from Collins J in Vue Entertainment) that a s73 consent CAN vary the terms of the operative part of a planning permission."
Yesterday, a Warwickshire farmer failed in a High Court effort to overturn a council's decision to discharge a planning condition stipulating that the developer of a neighbouring barn conversion must install acoustic fencing to prevent possible noise complaints from future residents of the property.
Last week, an Oxfordshire council failed in a High Court challenge to block plans for a housing development on the edge of a village after a judge rejected its arguments that an inspector had ignored critical parts of its emerging local plan.
Also last week, a Leicestershire man failed in a High Court challenge against a planning consent to convert a local shop into a Domino's pizza outlet, after a judge rejected his arguments that the decision had not taken account of relevant local planning policies and had breached equality legislation.