Powys substation and pylons site to be announced
The preferred site for a controversial electricity substation in Powys and the route for over 100 high voltage pylons will be unveiled later.
Opponents say the substation and the pylons, to service wind farms, will disfigure the countryside.
Two sites at Cefn Coch, near Llanfair Caereinion, and Abermule, near Newtown, have been earmarked for the substation.
National Grid said there had been "extensive consultation" ahead of its announcement at 10:00 BST.
Pylons, some measuring 154ft (47m), will carry electricity to the transmission network in Shropshire.
The National Grid announced its preferred locations for the 19-acre (7.6ha) substation more than a year ago.
It has held a number of public exhibitions, attended by more than 6,000 people.
But the plans prompted protests, including 1,500 campaigners gathering at the Senedd in Cardiff Bay in May last year against the plans, aimed at connecting with about 10 wind farms.
National Grid said mid Wales had been identified as an important location for onshore wind and a number of wind farms were proposed by several companies.
A National Grid spokeswoman said: "National Grid will be announcing its preferred option to provide a connection for new wind farms in mid Wales.
"This will include the proposed area where the substation will be built and the route the connection will take through Powys and Shropshire.
"The preferred connection has been selected following extensive consultation with local communities and specialist bodies, and detailed assessments to look at the potential effects of the proposals on the landscape, environment, heritage, and local communities.
"It is National Grid's role to provide a connection for these wind farms to the national electricity network."
Dr Craig Lowrey, an energy consultant at the independent consultancy Utilities Exchange, described the issue of picking a route for the pylons as "emotive".
"It's something that people get incredibly passionate about and justifiably so," said Dr Lowrey.
"The challenge that National Grid has in terms of putting this project together is ensuring that the energy that comes from these wind farms is delivered across the country to the UK."
Dr Lowrey said there was clearly a need to reinforce and reinvest in the country's electricity infrastructure, both in terms of new pylons and upgrading existing pylons.
He added: "It certainly looks as though the construction will go ahead, with the decision about what the route will ultimately be being based on this extensive consultation procedure, looking at areas such as the environment, cultural, technical and cost implications of each of the relevant routes."
Alison Davies, of the campaign group Conservation of Upland Montgomeryshire, has claimed that more than 10 wind farms are in the pipeline, which could mean mid Wales had 800 turbines in the future.
Speaking on BBC Radio Wales, she said: "All the National Grid is putting forward at this stage is a proposal and that proposal will depend entirely upon whether the wind farm applications are approved.
"If the wind farm applications are not approved then there is no need for the hub and the transmission lines."
Llywelyn Rhys, deputy director of Renewable UK Cymru, said each wind farm application had to go through the planning process.
He added: "There is a need to upgrade the grid throughout the UK.
"There is a grid system in north Wales, south Wales, which is probably adequate for what's being generated now. In mid Wales, for the ambition the Welsh government has stated for onshore wind, the grid there isn't adequate."
Work on the substation could be finished by 2015.