A public inquiry into plans to build Wales' tallest onshore wind farm on common land in Swansea is due to end.
The Planning Inspectorate Wales is considering an appeal by RWE npower renewables to build 19 turbines up to 127m high at Mynydd y Gwair, Felindre.
As the inquiry hears final submissions, BBC Wales has learnt that wind turbines have more than doubled in height since the first was built in Wales in 1992.
The Welsh Assembly Government is due to announce its decision later this year.
Swansea councillors rejected the Mynydd y Gwair scheme in January on the grounds that the turbines were 27m higher than guidelines for the area.
Wales' first wind farm, Rhyd Y Groes, on Anglesey, had height of 46m when it was built in 1992. The average height of turbines built between 2007-2010 is 95m.
The proposed 127m structures at Mynydd y Gwair would be would be 20mhigher than Wales' tallest building, the Meridian Quay tower in Swansea.
They would be more than 30m taller than Big Ben's tower, which stands at 96m, and slighter shorter than the London Eye, which is 135m high.
Mynydd y Gwair was identified as a suitable location for a large-scale wind farm due to its strong and persistent winds.
Swansea council's planning committee said its visual and landscape impact was unacceptable and the proposed route for construction traffic was inadequately justified.
But the council had taken more than a year to reach this decision and last October RWE started the appeals process on the basis the decision was taking too long.
A RWE spokesman said Mynydd y Gwair was the right location for the development.
"We feel all sides had the opportunity to present their views; we were pleased there was an evening session to allow local residents every chance to be heard by the inspector and we await the decision," he said.
He added: "Having listened to the evidence from all parties, we remain of the view that the wind farm represents a high quality development in the right place, has been designed sympathetically to fit with the local environment and that it will bring substantial clean energy and climate change benefits."
Geoffrey Sinclair, advocate for campaign group Save Our Common Mountain Environment (SOCME), said the wind turbines would be larger than 15 110m turbines given planning permission at nearby Mynydd y Betws.
"This would be adding a larger number of much larger turbines in an area much more open to view and used by more people," said Mr Sinclair.
"It's very visible from a huge area; an area with considerable recreational value for people from Swansea, Pontarddulais and Pontardawe.
"Also, it is common land and the graziers feel that to move their flocks would have an enormously disruptive effect."
Swansea council said it would comment when the assembly government announces its decision.