A protest meeting is taking place against plans to build a 19-acre substation in Powys that would connect electricity produced by 10 planned windfarms.
Huge pylons, some measuring 154ft (47m) and spanning 26 miles, are also to be built.
Opponents say they cannot be justified because wind turbines are under performing, while supporters say the machines are reliable and effective.
About 1,000 people are expected at Wednesday’s Welshpool meeting.
The meeting, organised by Montgomeryshire MP Glyn Davies, will be at the livestock market at 1900 BST.
Two sites – at Abermule, near Newtown, and Cefn Coch, near Llanfair Caereinion – have been suggested.
Campaigners claim the huge wind turbines will blight the rural landscape.
Alison Davies, of the campaign group Conservation of Upland Montgomeryshire, claimed that more than 10 wind farms were in the pipeline, which she said could mean mid Wales has 800 turbines.
She told BBC Radio Wales: “Then (there will be) pylons from the wind farms to the substation, then more pylons from the substation to the main (transmission) line to Wrexham and Ironbridge, near Telford (Shropshire).”
Mrs Davies claimed wind power was unreliable, that it did not produce enough energy, and that it was not a viable alternative power producer.
“We know that wind farms are not producing what they are supposed to produce, and many are producing under 25%.”
But John Woodruff, chairman of Renewable UK Cymru which represents wind farm developers, said the farms were effective and reliable.
“Wales’ wind farms are designed to operate at 30% capacity,” he said.
“Older wind farms in Wales do operate at a lower level, but Wales has the potential to do a lot better than Denmark, Germany and Spain and become a centre for excellence for wind and tidal energy in the future.
He said there were always impacts of any development, but the planning application process was very stringent.
“Wales has a better than average wind resource than England, and wind farms in Wales would be expected to be more productive.”
He added that the wind power industry was worth £160m to Wales.
The Welsh Assembly Government could not comment because of the assembly pre-election period.
But in 2005 it unveiled seven areas across mid and south Wales, known as TAN 8, which had been chosen for the development of wind farms.
TAN 8 was part of the UK Government’s energy policy to increase the amount of electricity from renewable sources to 10% by 2010, but Wales has exceeded this and produces about 13%.
The National Grid has organised 48 public exhibitions about the substation. It has said it has no preference which site is chosen.
A National Grid spokeswoman said: “What we are trying to find is a solution that best suits most people but we do have to build the substation if the wind farms are going ahead.”
Another protest meeting is planned at Welshpool Town Hall next Tuesday.
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