PUMPED STORAGE TUNNELS | INSIGHT
● Tunnels and shafts: Waterway, surge, access, ventilation, cable, drainage, and other types of tunnels and shafts are required to service all the requirements. The waterways form the backbone of the tunnels and shafts. They need to be able to handle the very high internal pressures along with high water velocities and surge pressures. For performance and economic reasons, the powerhouse should be close to the mid- point of the waterway tunnel system. This shortens the high-pressure tunnels but also makes the water in the tunnel more stable for quickly starting and stopping. These extreme challenges dictate many requirements from in-situ stress conditions, rock quality, consolidation grouting, excavation methods to limit rock damage, and robust lining with reinforced cast-in-place concrete and steel, with membranes used in some cases.
● High voltage transformers and cables: Placing transformers in underground facilities can be difficult but siting them on the surface can be more desirable to the operations. If placed underground, these components represent some of the largest and heaviest elements to install. So, the access tunnel needs to be designed so they can be carried in with a grade of typically less than 10%. This element drives a significant portion of the requirements to keep the access tunnel short for construction scheduling or the need for early construction access tunnels. The high voltage power must then be brought from the transformers to the surface in its own cable or shaft system.
● Safety precautions: Safety is paramount, from design to construction to operations. Fire and life safety during operations calls for extensive ventilation, isolation, and suppression systems. Ventilation systems can include dedicated shafts and tunnels with fans along with complex requirements for electrical power plants with high voltages. With the high-pressure water and caverns being below water levels, significant dewatering and sump systems are integrated into the complex.
● Geotechnical: Not only are we looking for good geotechnical conditions, but the investigation requirements are extensive with a geologic model needing to be developed with borings that can be very deep, time-consuming, and expensive to install. Several upfront stages are also needed. These can take years to complete from development through permitting execution and reporting. But it is also common to have an exploratory adit targeting the powerhouse where additional drilling and testing can be performed.
KEY CHALLENGES As with any complex design, there are many challenges we face when developing pumped storage hydropower projects. From cost to siting to transmission infrastructure, engineers have a lot of problem-solving to do to ensure the successful implementation of these facilities, including:
● Time and cost: With the upfront licensing and permitting, infrastructure, design, and construction time, these projects typically take a minimum of seven to eight years to complete. With many roadblocks, that time can be greatly extended. When it comes to cost, these projects can cost billions of dollars. While justified, it is hard to develop in a capital improvement plan. The need is certainly there to augment renewables, but other technologies with lower up front capital costs, such as battery storage, can seem more attractive. The two types of power storage can overlap, but the long duration capacity of pumped storage projects far exceeds that of batteries, and the delay in financing may only delay the inevitable need for larger long duration storage. A typical pumped storage project has 8 to 12 hours of storage with some plants having over 20 hours at full power. Batteries tend to be better suited at less than 4 hours. Also, the life of pumped storage projects is over 100 years, regardless of how often it is discharged. A battery plant is substantially less than 15 years depending on how often it is discharged. The longer the storage duration and the longer the time horizon, the more favored pumped storage hydropower becomes.
● Building enough to meet demand: Many pumped storage facilities are needed to augment renewable energy. With capacity demands ever so close to capacity output, the potential for power shortages exists right now. Building enough pumped storage projects to meet demand is a formidable task, especially given the long lead time for full development to operations.
● Procurement and scheduling: Procurement includes finding a contractor to build and, in some cases, design the projects. Early lead item procurement, such as the pump-turbine generators designed and manufactured specifically for each application, are also needed. These projects can use complex delivery methods with EPC being the most common approach. Sometimes these methods can tie-up multiple entities for years during the procurement process, leading to longer schedules.
● Finding the right site: Pumped storage projects need elevation over short distances, access to water, sites for upper and lower reservoirs, appropriate geotechnical conditions, proximity to transmission facilities, and more. They also must be suitable for the public and government oversight agencies. The number of feasible sites becomes greatly limited, so much so that developers need to have multiple sites being developed as many factors can delay or eliminate a site.
● Proximity to communities: These projects need to be near existing transmission facilities and substations to avoid transmission problems as the cost and impacts for installation of new transmission lines can be significant. The transmission installation becomes its own project in addition to the power plant. Also, the closer they are to major load centers, such as a
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