Hundreds of people have attended a public meeting opposing plans to build a 19-acre substation in Powys that would connect electricity produced by 10 planned wind farms.
Pylons, some measuring 154ft (47m) and spanning 26 miles, are also planned.
Opponents say they cannot be justified because wind turbines are under performing, while supporters say the machines are reliable and effective.
The meeting in Welshpool was told a protest would take place in Cardiff.
Initial estimates were that the meeting attracted more than 1,000 people, but other observers believe the number exceeded 1,500.
Two sites - at Abermule, near Newtown, and Cefn Coch, near Llanfair Caereinion - have been suggested.
But campaigners claim the huge wind turbines and the pylons 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 could mean mid Wales has 800 turbines in the future, she said.
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.
He added: "Wales has a better than average wind resource than England, and wind farms in Wales would be expected to be more productive."
Mr Woodruff said 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.
Another protest meeting is planned at Welshpool Town Hall next Tuesday.
Wednesday's meeting, organised by Montgomeryshire MP Glyn Davies, also heard that a protest would be held in Cardiff once the new assembly meets following the election on 5 May.
The planned substation has proved a controversial topic locally during campaigning for the assembly election on 5 May.
Montgomeryshire Liberal Democrat assembly candidate Wyn Williams said the plans were "just not suitable for our area" and he opposed them.
"Several much more preferable options, including using existing high voltage lines in north Wales, burying cables underground, or developing a hub in the far north of the county away from homes, all appear to have been rejected by the electricity companies on the basis of cost," he added.
The Conservatives said they were committed to promoting a diverse range of renewable energy sources but said the assembly government had championed wind farms too exclusively in Wales.
"It is typical of Labour-Plaid's tunnel vision and it is essential that we develop a full range of energy sources fit to meet the demands of a greener economy," said a spokesman.
David Senior, Plaid Cymru's candidate for Montgomeryshire, said decisions over large energy projects were not taken in Wales but in England.
He said: "This means that the decision about where these pylons go will be made in London.
"I believe that this is nothing short of a scandal. In government, Plaid will negotiate with the UK government to ensure that all functions in the areas of water and energy generation are devolved."
Welsh Labour said it was committed to a "greener future for Wales, utilising our natural environment to achieve our aim that by 2050, at the latest, almost all of our local energy needs will be met by low carbon electricity production".
"Wind energy is only part of our energy mix, alongside marine energy, sustainable biomass and other sources which will help us achieve our objective," the party added.