Truro, UK — How can the potential negative legacy of a mine site be converted into a positive inheritance for the wider environment and local communities? Recent imaginative renewable energy projects give good grounds for confidence that many former mine sites can be ideal locations for developing alternative energy generation facilities, simply by looking in a new light at some of the qualities that made them problematic in the first place.
Possibilities range from wind, solar photovoltaics (PV), geothermal, hydropower and energy crops to test-beds for a variety of more experimental power generation technologies.
As with any development, mine site conversion to renewable energy generation must of course take due account of impacts on the local environment and communities. But when done well, these can provide ongoing and long term value in the form of an alternative income stream well after mining operations have ceased. Specific benefits can include the mitigation of cleanup costs, reusing infrastructure to reduce decommissioning cost, enabling re-employment of a skilled mining workforce and/or new local employment opportunities, and a clean and usually quiet after-use for a mine site that can also create a potential source of carbon credits with tradable value.
So why might mine sites prove to be ideal locations for the generation of renewable energy?
First, and maybe most obviously, mine sites often cover extensive areas of up to thousands of hectares or more where wind and solar power structures will have less environmental impact and are therefore less likely to meet with opposition. Mine sites often already have the necessary electricity transmission lines and transport infrastructure in place, avoiding extra capital costs. Land transaction costs are generally lower and the process can be simpler because brownfield areas tend to be owned by fewer landowners than a similar area of greenfield. Brownfield redevelopment for green energy can also reduce development pressure on greenfield sites, maintaining their carbon sink benefits. Furthermore, other forms of redevelopment may not be an option due to the remoteness of the site, or the environmental conditions may rule out residential or commercial use without significant extra development cost.
Large-scale wind energy projects are an increasingly common alternative energy use on former mine sites, particularly in Europe and the US. Just one example is the largest wind farm planned in Virginia. With 166 turbines sited on over 4000 hectares of land disturbed by coal and hard rock mining activities, 99% of the land remains usable for other activities including farming. In Scotland, Black Law Wind Farm near Forth covers 1850 hectares of abandoned coal mine land, grazing land and commercial forestry, with 42 wind turbines generating 97 MW, and plans for expansion potentially increasing the total generating capacity to 193 MW.
The visual impact of wind turbines may be less controversial in areas already affected by mining landscapes. Mineral waste dumps often give increased elevation and exposure to enable increased output, while underlying land can also still be used for other purposes. However, there may be technical challenges to overcome due to the nature and stability of the dump material and constructing adequate foundations for turbines.
At the Hazlehead Wind Farm site in West Yorkshire, wind power is now being generated on the site of a former clay quarry spoil tip and landfill site, with three turbines and a proposed installed capacity of 6 MW. A community benefits fund will run alongside the wind farm when it is fully operational, providing support for local community groups, environmental and voluntary projects to help ensure a long-term positive impact on the area. Engineering and environmental consultancy Wardell Armstrong carried out an initial feasibility study, detailed site investigation, geotechnical testing and slope stability work. The results were used to determine the practicality of siting the turbine foundations within the tipped material mudstone material, as well as creating a suitable landform.
In 2009 a study of former coal mining land across the UK was undertaken to examine its potential for wind power generation. This was based on identifying suitable sites of sufficient area, far enough from existing habitation, with an annual average wind speed >6.5m/sec, reasonable access, free of other constraints and the potential to link to the grid. 106 sites were identified, with the potential for nearly 4 GW of generating capacity, some 10 TWh/year. If developed, this would displace the output of a typical coal-fired power station. However, there would be significant UK permitting hurdles to overcome. Also, the ground conditions on most of the sites, being man-made ground, means that engineering costs for foundations would be higher than for greenfield sites, which would affect the economics.
Former mine sites can be ideal locations for solar energy generation, thanks to their often expansive and exposed positions, especially in areas with an aspect facing the sun. Germany is utilising its old mine sites in this way. The Geosol solar plant at Espenhain, Leipzig, constructed on a former lignite mine ash site, generates 5 MW and saves around 3700 tonnes of CO2 every year. The site of the former Göttelborn coal mine in Saarland, southwest Germany, has been converted into a solar energy park – the largest of its type when opened. It generates 8 MW from 50,000 photovoltaic panels covering 165,000 m2.
Other countries are following suit, with the UK’s first large-scale solar PV farm developed by Lightsource Renewable Energy now live on the south-facing site of the former Wheal Jane tin mine near Truro in Cornwall. The solar farm houses 5680 panels with a peak generating capacity of 1437 MWh. To bring this project to fruition, a detailed landscape management plan was created. There was also pre-consultation; screening and scoping; feasibility studies including specific studies on glint, glare and ecology; a full environmental impact assessment; planning submission and post-submission consultation. There are now plans for further development to create the UK’s first earth science park using energy from solar, wind, hydro, and shallow and deep geothermal sources, as well as an 18,288 m2 business park.
Since the ambient temperature of the Earth increases with depth, underground mine workings provide a convenient collection point for groundwater. This resource may be sufficiently warm to raise the starting temperature of the water used for heating and hot water in buildings and horticulture, often involving ground-source or water-source heat pumps. Mine and quarry sites can also offer opportunities for access to deep geothermal resources, involving hotter water or even superheated steam power generation via a turbine.
Rosemannowes Quarry in Cornwall, UK, was an ideal location for the hot dry rocks deep geothermal energy research project undertaken by the UK government during the 1980s. Its exploration of the possibility of exploiting the high heat gradients in the local granite to produce superheated steam to generate electricity was, at the time, an enticing but unproven theory. Today, after decades of research and recent advances in technology, it’s set to become reality with the go-ahead given for Britain’s first geothermal power station.
Geothermal Engineering Ltd is creating a 10 MW geothermal power plant at United Downs near Redruth. By drilling down into large ‘welds’ or faults running across granite 5 km underground — the deepest onshore welds in Britain — it will generate sustainable electricity which can be fed into the national grid. As a by-product, it will also produce 55 MW of heat which can be used for the local community.
The world’s first mine water power station opened at Heerlen in the Netherlands in 2008. It uses water at 32°C extracted from underground coal mine workings through boreholes in what was once the Netherlands’ coal mining heartland. It heats 350 homes and businesses and is estimated to reduce CO2 emissions by 55 percent compared to conventional water heating systems.
Geothermal heat is also expected to come on-stream in the very near future from the heat stored in the water at the flooded former underground coal mine workings at the Cape Breton site that once supplied half of Canada’s coal. With average water temperatures of 12°C, investigations are under way into how best to capture the heat stored in the mine water using a loop system, and use it in the former coal mining communities.
Pumped storage for power generation in the underground workings of closed or abandoned mines or surface open pits are an emerging option for the generation of hydroelectricity. This technology is not yet operational, but projects are being planned or in development. They generally involve high capital expense, but avoid the potential environmental impacts of storing water at the surface. Two underground pumped water storage projects that have been proposed in recent years include an underground limestone mine in Ohio, and the underground workings of an abandoned iron mine in New Jersey, both in the U.S.
At the former Wheal Jane site, flood control is now being combined with a potential new renewable energy initiative. Under the management of the UK Environment Agency, water is pumped to keep it below a level where it might leak, treated at the surface to precipitate any metals, and then discharged as clean water to run downhill into a nearby river – with the possibility of recovering some of the energy in the form of hydropower.
Another option still at an early experimental stage, on sites where there are former mine workings running under the sea with shafts exposed at sea level, is that of wave shaft technology. This involves the use of oscillating water column devices and air compressed by wave action expelled under pressure to generate electricity through a turbine system.
A criticism often levelled at renewable energy programmes is, of course, that the energy they generate — from wind and solar for example — is variable, reducing their ability to reliably match demand. But former mining sites can again lend themselves to providing an answer to this challenge, in the form of energy storage.
Built around the old slate quarries in Snowdonia, Wales, Dinorwig Power Station was regarded as one of the world’s most imaginative engineering and environmental projects when it was commissioned in 1984. It’s still the largest scheme of its kind operating in Europe, with six generating units that stand in Europe’s largest man-made cavern. Drawing on water high up in a mountain lake through 16 km of underground tunnels, Dinorwig’s reversible pump/turbines are capable of reaching maximum generation in less than 16 seconds.
Compressed air energy storage (CAES) systems use cheaper off-peak energy to inject air underground to be stored under pressure as potential energy. When electricity is required at peak periods the air is withdrawn under pressure and used in conjunction with fuel to operate turbines. The world’s first CAES plant was commissioned in 1978 at Huntorf, Germany, where compressed air is stored in underground salt caverns created by the solution-mining of salt. A broadly similar system exists at McIntosh in Alabama, US, commissioned in 1991. At Norton, Ohio, a proposed CAES plant will use a worked-out limestone cavern (which produced limestone for the glass-making industry) to store the compressed air. Ultimately the system will generate 2700 MW through gas-operated turbines, with emissions equivalent to a conventional gas turbine power plant of 600 MW capacity, its backers claim.
Post-mining land, such as from large scale strip mining, can offer a more sustainable model for growing energy crops than using existing agricultural land or clearing natural vegetation cover. Biomass crops typically include fast-growing trees planted at high densities and perennial tall grasses, while biofuel crops are subsequently processed to derive fuels. Jatropha, for example, produces an inedible oil that can be used to produce biodiesel and is the subject of much interest for growing on mined lands in China, the Philippines, Australia, Germany, Eastern Europe and elsewhere. There are also potential additional or combination benefits with less intensive energy crops, such as for biodiversity and/or providing a carbon sink or offset as forest biomass or soil improvement with ‘biochar’, which could qualify for carbon credits.
The US Environmental Protection Agency’s programme Re-powering America’s Land: Renewable Energy on Contaminated Lands and Mining Sites aims to meet a significant proportion of the nation’s 31% growth in renewable energy demand over the next 25 years by encouraging this kind of development. The EPA has identified 480,000 such sites covering 6 million hectares across the country, of which 345,000 hectares have been cleaned up or protected long-term and are available for development. The EPA and the National Renewable Energy Laboratory (NREL) have produced a series of on-line maps showing the renewable energy potential of nationwide contaminated and mined lands.
Although interest is increasing, the re-use of mine sites for alternative energy generation remains at a small scale. Stringent planning or permitting conditions can affect many developments, especially in relation to visual impact. A more sensitive land and development planning and permitting regime, particularly relating to the reuse of brownfield sites, could be given a higher priority.
As national governments address their climate change obligations by moving more toward renewable energy, this kind of support will be critical in encouraging the development and implementation of renewable energy generation programmes from low-carbon sources in the early years.
Many new technologies, although developing fast, are still in the early stages of commercial viability, often relying on assistance from government incentives or green energy subsidy schemes. But as they become more economical and commercially viable, and as financial institutions grow more amenable to providing debt and equity finance, the long term future of mine sites could be very different and far more promising than the reality of today.
Peter Whitbread-Abrutat is principal environmental scientist and Nick Coppin is managing director at Wardell Armstrong International.