Wild land charity the John Muir Trust insists SSE's Coire Glas scheme cannot be classed as a renewable source of green energy, and warns if it gets the go-ahead in the hills to the north-west of Loch Lochy and the Great Glen it would simply attract other developers wanting to build wind farms nearby.
The scheme, which is capable of powering up to one million homes, would be a pumped storage operation using water descending from an upper reservoir to drive turbines during period of high demand. During periods of low demand, electricity would be used to pump water from the lower loch back to the upper reservoir.
Ben Cruachan at Loch Awe was the last such new scheme to be built in Scotland, opening in 1965, but 10 years later the conventional scheme at Foyers on Loch Ness reopened as a pump storage station.
The cost of the Coire Glas scheme is currently estimated at £800 million and it would be one of the largest construction projects in Scotland, creating about 150 jobs.
It would require the construction of a 300ft dam and upper reservoir at Loch a' Choire Ghlais. A powerhouse complex would be constructed underground, together with a series of tunnels to provide access and convey water between the lower reservoir (Loch Lochy) and the upper reservoir, thereby reducing the visual impact.
However, an administration building and jetty, tunnel portals and tailrace structure would be built on the shores of Loch Lochy.
Because of its size, it will be ministers who decide whether it gets the green light, and SSE lodged an application with the Scottish Government in February. But by law, the local planning authority has to be consulted and today Highland Council's local planning committee will visit the site. Tomorrow it will decide whether to object, and automatically trigger a public inquiry.
The council's planning officials have recommended councillors do not object, subject to a long list of conditions.
However, the John Muir Trust believes the scheme should be opposed, because pumped storage is not a renewable technology. It believes the proposed development would have a major detrimental impact on the area.
In its submission, the Trust says pumped storage uses more electricity to pump the water to the upper reservoirs than is generated when it flows down.
"The Trust believes that if the minister grants planning permission for the Coire Glas scheme it will lead to further inappropriate and unnecessary development in the surrounding landscape," the submission states. "This may come from developers keen to build wind farms close to a source of energy storage, or from others who see this as an opening for further development in the area.
"This precedent would make it increasingly difficult to challenge proposals in future, leading to the potential encirclement and encroachment of wild land by development."
An SSE spokesman argued energy storage was vital to the development of green energy.
He said: "We believe increased pumped storage capacity has an important role to play in balancing the grid – using surplus energy when demand is low and makingit rapidly available when itis needed.
"Both conventional and pumped storage hydro schemes already have a strong track record of providing clean, flexible electricity generation for Scotland."