Planning approval is being sought for the Coire Glas project in Scotland – the first pumped storage scheme in the UK for decades, reports Patrick Reynolds

Scottish and Southern Energy (SSE) has submitted a planning application for the Coire Glas pumped storage scheme, which it proposes to construct with an installed capacity up to 600MW near Loch Lochy, in Scotland.

The project would lay claim to a number of plaudits. It would be the first pumped storage scheme to be built in the UK for decades, the largest hydro project in Scotland and also one of the country’s biggest construction projects. It would not, though, be the UK’s largest pumped storage plant – that crown will still be held by Dinorwig, in Wales.

Depending on planning progress, SSE doesn’t expect to address the final investment decision ‘before 2014 at the earliest,’ the utility’s renewables division – SSE Renewables Developments (UK) Ltd – said in February when the application was submitted

Coire Glas – UK context

As noted in the Scottish Government’s “Energy Storage and Management Study”, published in October 2010, pumped storage is the largest, project-based energy storage technology globally.

In the UK there was pumped storage from the 1960s, and in the EU much of the construction of these assets happened in 1970s and 1980s during which 21.5GW of capacity was installed. Since then, however, only about a fifth of the capacity has been added in the EU.

In Scotland, one of the countries to push hydro early, there are only a few pumped storage schemes, such as Cruachan and Foyers. Elsewhere in the UK, the prime pumped storage scheme in Dinorwig and Ffestiniog, in Wales. All the schemes hail from the 1960s-1970s, leading the wave of pumped storage development in Europe.

The moves to undertake new projects represents a late resurgance for pumped storage in the UK, as part of a bigger push to develop renewables more widely, including wind, marine and offshore technologies. To support Scotland’s goal to cut carbon dioxide emissions by at least 42% by 2020 compared to 1990 levels, the country has a renewable generation target of 50% by 2020.

SSE says: ‘Whilst pumped storage itself is not a renewable energy technology, it is recognised as a facilitator that allows greater and more efficienct use of renewable energy sources in our electricity supply.’

The anticipated array of pumped storage projects for SSE in Scotland are schemes at: Balmacaan (300MW-600MW) at Loch Ness near Invermoriston; Sloy (72MW) near Loch Lomand and next door to the existing 152MW Sloy hydro plant; and, Coire Glas (300MW-600MW) at Loch Lochy, near Fort Augustus.

Pumped storage – global resurgence

Pumped storage is undergoing a resurgence. In many countries there are plans for projects, in terms of type and scale, that would see more such assets available to, classically, help meet peak loads but also have greater energy storage roles and provide dynamic, ancillary services, support to electricity grids.

Projects range from new schemes, like Coire Glas in Scotland, and the 1GW Parker Knoll closed-loop project in the US, to expansions – sometimes of projects still in construction, such as Nant de Drance in Switzerland – to more novel approaches seeking to flexibly address the questions of water resource, elevation and location, such as: concepts exploiting coastal or river waters with underground lower reservoirs; or, deep vertical “piston” storage shafts arranged in clusters, not in rural areas but, untypically for pumped storage, next door to load centres almost anywhere (like Gravity Power LLC’s proposed offerings).

A common trigger to many schemes, though, is the need to have much more capacity that operates in a reliable and fast manner to counter the intermittant output that would come from wind power, which is seeing huge investment for massive expansion. In so many cases, pumped storage is the preferred solution.

On this aspect, the “Energy Storage and Management Study” notes that, ‘in the short to medium term, pumped hydro represents the best storage option to address the potential excess renewable generation in Scotland.’

However, while the technical need is apparent there is always the matter of project economics, to be determined usually on a case-by-case basis.

The Study comments that, ‘the average costs needed to justify a number of large pumped storage schemes are marginally greater than the value of the excess generation. This will limit the economic case for pumped storage as the only solution to the excess generation as only the lowest cost sites will be economic.

‘Hence, increased interconnection, demand side measures and generation constraints will have a part to play in managing the level of generation in Scotland.’

The study noted that among demand side management there could be counted the low cost options of heat pumps, electric heating and also charging electric vehicles – ‘that would reduce the requirements for electricity energy storage.’

Interconnections, though, are a key option being explored and is, in fact, a vital component in what would be, in terms of scale, the grandest and most strategic approach to tapping the potential benefits of pumped storage to support the grid and provide storage: the possibility of much of Norway’s hydro infrastructure, at least in the south of the country, being tied-in to the European grid, especially Germany.

The massive scheme that would see Norway as the so-called “green battery” of Europe is being explored to examine how existing hydro infrastructure, to be extended with some additional inter-basin infrastructure works, would help soak up excess output from the colossal increase in wind and solar capacities under construction, and planned, in Germany and other parts of Continental Europe. The grids would be linked through interconnections run through Denmark, it is envisaged.

Coire Glas – Planning

SSE says there are few sites in the UK suitable for pumped storage exploitation, chief among them being Coire Glas and Balmacaan in the utility’s territory. The plant would have an energy storage capacity of up to 30GWh. A key difference of Coire Glas compared to the four other pumped storage plants in the UK is its much longer period of continuous generation or pumping – approximately 50 hours in total.

The utility issued its preliminary environmental scoping for the scheme in late 2009, the Scottish Government replied half a year later, and then the environmental impact statement (EIS) was submitted, for the planning application, in February 2012.

Located approximately 13km south west of Fort Augustus, the scheme would be at the foot of a mountainous, lightly populated area in part of the U-shaped, fjord-like Great Glen. The project site is near the northern end of the south west-to-north east running Loch Lochy, in the mountain above its north shore.

Loch Lochy would act as the lower reservoir. The loch is currently is controlled by SSE for the Mucomir (Gairlochy) plant, although the needs of the latter would subjugated to the requirements of Core Glas operations. The scheme also involves modification works at Mucomir, including improved fish passage provision and downstream flow management.

‘Ultimately, the total volume of water passed through the barrage in a year would remain unchanged,’ adds the utility.

Construction stage activity would see temporary loss of some local areas of woodland and forestry, and amenity interruption for walking and cycling. However, once established and operational, and remedial works completed, the environmental impact would be tightly localised to the main infrastructure, such as the upper dam, tunnels portals and roads.

View from SEPA

However, a view of the plans for the project, given in late March as feedback to consultation, had the Scottish Environmental Protection Agency (Sepa) say: ‘In this case, with the information provided and the proposals as they stand, we do not think it has been demonstrated that the project could be achieved with acceptable environmental impact and further information is therefore sought.’

Sepa said it had undertaken ‘productive’ work on the project with SSE before the planning application for Coire Glas was submitted but stated its objection, at present, due to insufficient information on a range of aspects: surplus peat, surplus rock, access track construction, borrow pits and potential impacts on ecosystems dependent on groundwater.

The agency also wanted a condition attached to the consent – the requirement for site-specific construction environmental management documents being submitted for written approval at least two months before any works. Sepa called for this addition because, it says, ‘many of the works will not be regulated by us and need to be covered’. The agency would then look to be involved with a planning authority then handling the document, and it anticipates any other related agency would also be consulted.

Sepa and other agencies were involved for a few years in consultation for the projects. The Scottish Government issued a scoping consultation in late 2009.

Coire Glas – Layout

With Loch Lochy as the lower reservoir of the Coire Glas scheme, SSE proposes that a new, upper, reservoir be impounded at Loch a’ Choire Ghlais, an elevated small river basin perched just over the mountain wall of the U-shaped valley.

Like the U-shaped main valley, the natural perched basin was formed during the Ice Age. In its case, a pre-glacial hollow was carved deeper and wider by ice, and such features are known as “coire” in Gaelic, “corrie” in English and also as “cirque” in French.

Coire Glas drains to the north east, the flow running almost parallel to the axis of Loch Lochy. The northern rim of the basin edges onto the higher level Glengarry Forest. On the opposite side of the coire, the south east rim is formed by the Sean Mheall mountain and saddles to adjacent peaks. It is through and within this mountain range – which also forms a short stretch of the U-shaped wall of Loch Lochy, that the scheme’s underground works will be excavated.

SSE says that the topography enables pumped storage to be exploited by there being a large difference in elevation – approximately 500m – between the bodies of water for the relatively short distance of about 2.5km they are apart. The resulting layout enables the underground works to be less that otherwise might be the case for the headrace, tailrace and access tunnels.

Yet to be finalised, the indicative layouts of the tunnels show different arrangements of headrace and tailrace tunnels, and lengths of access and emergency tunnels. The location of the powerhouse complex also differs below Sean Mheall.

Coire Glas – Features

Coire Glas project would feature a new dam and upper reservoir, extensive underground works and inlet/outlet infrastructure at the lower reservoir, Loch Lochy.

The embankment dam would be approximately 92m high above ground level and 650m long, which SSE says would mean construction of the UK’s largest such impounding structure. Rock for the dam and concreting operations for the project would be quarried within the basin.

‘This would also reduce offsite hauling of rock fill and aggregates to the project,’ says the utility.

Underground, the tunnel infrastructure would include the powerhouse cavern, transformer cavern, headrace, penstock and tailrace tunnels, possibly a surge shaft or gallery, and associated permanent access and bypass tubes.

Preliminary options to transport spoil from the underground excavations, having been removed via the access tunnel, include: transport by road to a quarry or temporary storage for use in other projects; or transport by water (barge and canal routes) for either local or coastal use.

In its recent feedback to consultation over the planning application, Sepa had a point of objection over borrow pits. Sepa noted that ‘it is intended to excavate the rock required to construct the embankment for the upper reservoir and concrete operations at the dam,’ but expressed concren over insufficient details regarding ‘further borrow pits’ being required for construction of the outlet and the access track.

Points of concern are the location and size of the borrow pits, and volume of rock to be excavated – ‘in particular in relation to those located outwith the reservoir area.’ Sepa added, however, that with provision of extra details showing the location of the pits having minimised the potential for adverse environemntal impacts on water, peat and groundwater-dependent ecosystems.

Road ahead

Like so many pumped storage projects being built, expanded or planned at present, Coire Glas would play no little part in helping the electricity grid to accommodate, in a stable and growing fashion, the contributions from irregular renewable outputs, such as from wind farms.

Development progress of the scheme, however, in addition to outcomes from the planning application and the final investment decision by SSE, will, it says, ‘be dependent upon a satisfactory public policy and regulatory framework, including a change in transmission charging regime.’

Pending those factors, the utility anticipates that Coire Glas would take up to five years to construct, which means operations would not begin until approaching 2020 at the earliest. But with the planning submission for Coire Glas, and given the strategic pushes behind pumped storage expansion in so many nations and in so many ways, the future of the project will be a landmark in how Scotland, and the UK, deals with prospects for and challenges in hydro and renewables in the near and mid-term future.