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Mining towards renewable Stantec examines how pumped storage can be an ideal solution at mine sites

The Dinorwig ine sites can offer the ideal pumped storage infrastructure for the devel- scheme in Mopment of pumped stor- north , UK age hydropower projects post clo- sure and have the potential to add a considerable amount of to the power grid. Pumped storage is the modified use of conventional hydropower technology. Projects store and generate energy by moving between two at different elevations, as shown in Figure 1. The system is a ‘closed loop’, which eliminates the need to a . Pumping the water uphill for tem- porary storage creates a ‘recharge- able battery’. During periods of high demand, water is released back through the to gener- ate energy like a conventional hydropower station. Pumped storage projects are via- ble as they often use low-cost As governments push for higher cally ranging from 1MW up to excess ‘grid’ power to pump and renewable penetration percentages, 1,300MW. generate power when the arbitrage the need for ultra-fast energy stor- Planning for pumped storage at price of power exceeds the cost of age response becomes crucial to the existing mine sites has already pumping. reliability and security of the power begun in some cases. For example, grid. In fact, the existing 161,000MW Stantec, along with SCI, is involved PROVEN TECHNOLOGY of pumped storage capacity is cur- in the development of pumped stor- According to the International rently forecasted to grow by age projects on abandoned and Hydropower Association, pumped 78,000MW by 2030. operating mine sites located on First storage accounts for over 94% Nation throughout Canada. (9,000 gigawatt hours) of installed EXISTING MINE SITES The joint venture has agreements global capacity, and Due to the infrastructure, location with 11 First Nations to manage the retains several advantages, such as and water storage capacity at exist- development (design, permitting, lifetime cost, levels of sustainability ing mine sites, private developers financing, construction management and scale. are proposing that a significant por- and operations) of seven pumped Pumped storage is available at tion of the global pumped storage storage projects, which if developed almost any scale. The largest operat- capacity be used at these sites. will deliver 6,400MW of generating ing pumped storage is just As seen in Figure 2, existing mine capacity. over 3,000MW and the smallest sites offer a unique opportunity to A notable example is the plant is less than 1MW. Storage evaluate the potential of mine pits 1,728MW Dinorwig pumped storage volumes and generation times range post closure for use as flooded res- scheme in north Wales (UK), as seen from several hours to a few days. ervoirs for pumped storage. Current in the image. Fully commis- “Pumped Other renewable , such as pits that were developed for , sioned in 1984, the station is a prime storage wind and , tend to stop aggregate and gold are example of an abandoned slate and start abruptly, causing steep being evaluated and considered for quarry being utilised to develop accounts MW per second ramp rates to occur. pumped storage. pumped storage generation. for over When the power grid is not in Post closure, the presence of The Dinorwig pumped storage 94% of perfect supply and demand bal- either one or two pits offers scheme includes an underground ance, frequency or voltage problems companies the opportunity to con- powerhouse that supplies the installed occur. sider the value-added opportunity National Grid in the UK. When the global However, pumped storage allows of the pits for use as upper and plant officially opened in 1984, it grid operations to manage the grid lower reservoirs at new pumped was regarded as one of the most energy response to changes almost instan- storage projects. Many mine sites imaginative and envi- storage taneously, to generate power when around the world are being consid- ronmental projects in the world, and capacity” needed and to be a load consumer ered for use as pumped storage to this day, it remains the largest in times of oversupply. sites, with generation output typi- project of its type in Europe.

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A WIN-WIN benefits. Although development some of these issues but The main attraction for developing a costs will be required to establish could become complex. pumped storage scheme at an the upper and lower storage A clear understanding open-cast mine site is the utilisation reservoirs, the offset rehabilitation of both aspects is of the existing infrastructure. costs could be substantial, and an necessary to Underground tunnels and caverns ongoing beneficial asset is ensure a success- can be used for the storage, created. The development of a ful project. The criti- although these are not as common pumped storage scheme could cal path for hydro- as open-cast sites. Positioning an become a central feature of the power projects upper storage pond on the mine closure plan. typically passes surrounding elevated positions at an Leveraging synergies existing mine site can help to between mine operations and develop a differential head with the the development of the main pit. Using the main pit as the potential pumped storage lower storage eliminates facility can help reduce capital the need to construct a dam to form costs and minimise the lapse the lower storage. The greater the between completion of mining difference in elevation profile and activities and the net , the less water is commissioning of the plant. required to generate the same Using the mine fleet to cut energy output. back the pit slopes as they As a result of previous mining develop to a profile that operations, mine sites have a meets the long-term civil good chance of already being engineering design understood geologically and geo- parameters will likely cut costs technically. Additionally, the lithol- compared to revisiting and ogy, structural and hydrogeological stabilising the steep mine cut aspects of mine sites are typically slopes at the end of mine documented as well, which can operations. through civil construction of the Figure 2: expedite studies. The costs of additional done powerhouse, installation and com- Pumped storage The transformation of a mine site by the mine fleet should be taken missioning of the electromechanical potential at to a pumped storage facility may into consideration when evaluating plant and equipment. If the earliest existing mine also present an opportunity to pumped storage economics. For commissioning date possible is the sites restore the to a safe, stable and example, utilising the mine fleet to target for an active mine site and self-sustaining condition with due place waste rock material in loca- it is possible to commence civil consideration to the surrounding tions favourable to the construction construction prior to completion of environment and communities. of the pumped storage structures, mining activities, it is possible that Mine sites often have in place such as an upper reservoir embank- the critical path may shift to com- suitable access, an electricity ment, could offer cost savings. pletion of the mining activities, con- transmission grid connection and Integrating mine planning with struction of the lower reservoir other site services, offering hydropower planning for a pumped intake structure and completion of significant cost and permitting storage scheme will help address the tailrace conduit.

Figure 1: A schematic of a project storing and generating energy by moving water between two reservoirs at different elevations www. .com November 2019 20 POWER / REMOTE POWER

pared to a mine site with two pits The image of the Rocky Mountain pumped storage project with suitable elevation differential. in , US showcases the elevation differentiation All of the 10 criteria should be given needed for a successful pumped storage project additional attention as budget permits.

AN OPPORTUNITY The efficient use of energy resources is a significant societal demand. While the benefits of this energy are recognised, achieving these aims within an integrated electricity grid poses a number of technical challenges. These challenges are often mitigated by grid operators through systems planning, and management via pumped stor- age hydro. Other forms of energy storage, such as lithium batteries, lack the reliability that grid operators depend on. Mine sites come with preceding site data and offer ideal infrastructure for the development of pumped storage projects post IDEAL PUMPED STORAGE SITE given site, but in general all of them closure. The below table lists 10 basic should be considered. For example, Landowners are beginning to criteria that can be used by mine topography would apply to a mine give these sites considerable inter- operators to identify potential sites site where only one pit exists; the est as they may be able to extract and to rank one site versus another. other reservoirs must be created additional revenue from their Some of these may not apply to a but would not be as critical com- investment.

Characteristic Preferred Situation Rationale Length to head ratios Length to head – the smaller the better; less Total waterway length from upper to lower res- than 10 preferred. ervoir intake, divided by gross head (average Gross head – the larger the better. upper reservoir water elevation minus average Ideal 200m to 600m (minimum 100m, lower reservoir water elevation). Minimises maximum 700m). costs and project footprint. Topography Varied topography. Allows for reservoir construction with minimal excavation or embankments. Geology , unfractured, consistent, limited faulting. Limits reservoir leakage and foundation prepa- ration requirements; provides suitable local construction materials. Power capacity Maximum megawatts. Increases revenue potential. Pump loads are greater than generation. Energy storage potential MWh, increases revenue potential and opera- Product of plant capacity in MW and the hours tional flexibility. Typical minimum hours of stor- of available storage (MWh); or age is four hours, average is 6-8 hours, but can associated with the upper body of water in be 24 hours or more. relation to the lower storage space. Construction Powerhouse can be in a shaft or in a cavern. Below 100MW often can have a shaft power- Water transfer pipe can be a tunnel or surface house. Larger schemes require a cavern. buried line. Water availability Plentiful, available, and nearby. First fill impor- Reduces costs and risk exposure for first filling tant, and annual top up for evaporation. and replenishment water. Environmental, regulatory Closed loop, limited environmental exposure, Reduces costs, risk exposure, permitting and desirable land ownership. requirements and development duration. Electrical power transmission Nearby and available transmission capacity. Reduces potential costs of new T-lines and/or Higher the kV class of line the better. grid upgrades. Power marketing Large spreads, suitable partnership Increases revenue potential and ease of opportunities, multiple offtakers. marketing; reduces risk exposure.

November 2019 www. .com