RENEWABLE ENERGY

Innovative Turbine Developments

In traditional run-of-river power plants, Kaplan turbines or Francis turbines are commonly used. Due to their high efficiency, there is little room for development in terms of energy efficiency. New turbine developments, for example, focus on reducing fish mortality when fish want to descend over the turbine. The “fish-friendliness” of turbines can be achieved through slowly rotating turbines or through an optimized design of the runner blades. Another research focus is on the development of sediment-passable turbines, where, in addition to the question of the right “coating,” the structural design and the position in relation to the hydropower plant are also crucial. Hydrokinetic turbines utilize the kinetic energy of the flowing water without damming it up. The intervention in the flowing water is thus significantly less than with run-of-river power plants, but this also applies to the annual energy output. The hydropower test stand of the BOKU hydraulic engineering laboratory offers the possibility to test innovative turbine developments at (near) 1:1 scale.

Optimization of Hydropower Plants

Existing hydropower plants often have a need for optimization due to new technical and construction requirements, necessary adjustments to (climate change-related) hydrological changes, or for the purpose of re-granting water rights. A key aspect of optimization is the renewal of outdated turbines, generators, control, and regulation technology. For example, despite increased residual water discharge, performance increases of the plant can often be achieved, thus creating a “win-win” situation from a technical, ecological, and socio-economic perspective.

Furthermore, new hydrological conditions, such as stronger and more frequent extreme events, require adaptations of hydraulic engineering elements of the power plant facility. This includes, in addition to the optimization of weir crest and stilling basin geometry, changes to existing bed protections in the upper and lower water, trash rack systems, or steel hydraulic engineering elements.

Reservoir Management and Design

The sediment continuity of many rivers in the Alpine region can be disrupted by hydropower plants, as a large part of the sediment load is often retained in the reservoir during storage operation. Possible consequences include an increased flood risk, technical problems during plant operation, and a sediment deficit downstream, associated with erosion problems. Therefore, the development of sustainable sediment management strategies is necessary. For example, naturally occurring flood discharges can be used for flushing to selectively mobilize sediments deposited in the reservoir and transport them to downstream sections. The discharge value for initiating a flush should represent a compromise between flushing efficiency and ecological aspects (concentration of suspended solids and organic material). Furthermore, repeated reservoir drawdowns during moderate, sediment-effective discharges can allow for the sluicing of sediments through the reservoir. Efficiency can be increased through construction measures (sediment guiding structures, sediment channels, etc.) and optimized operating methods (reservoir drawdown concepts for power plant chains, reaction diagrams for power plant operation). In addition to measures in the actual reservoir area, bypass systems (bypass channels, bypass tunnels, etc.) can further improve sediment passage.

Fish Migration Aids

Fish migration aids are integral components of a run-of-river power plant. They are designed to ensure the safe passage of fish and other organisms both upstream and downstream. Key elements of fish migration aids include their detectability and location, a sufficiently strong attraction flow compared to the competing discharge, adherence to maximum velocities and water level differences depending on the target fish species, as well as their functionality over long periods of the year (e.g., 300 days a year). From an energy economic perspective, the residual water allocation for electricity production is lost. Innovative developments of residual water turbines combine fish migration and energy utilization equally. An example is the Fishcon fish migration aid, which is characterized by a compact, space-saving design and passability in both directions. Fishcon was developed from 2016 – 2020, among others, at the BOKU River Lab.

Solid Matter Budget

Sediment is transported from the surrounding areas into the river through erosion processes within a river’s catchment area. In an undisturbed state, this sediment is carried along the river over time and eventually ends up in the sea. However, power plants and other structures disrupt these transport processes, leading to an excess in the reservoirs and deficits downstream. This results in reservoir capacity losses and reduced efficiency of power plants, as well as increased land loss in coastal regions. The goal of a regulated solid matter budget is to increase the sediment passage of dams to balance the sediment budget again. Various technical and organizational solutions can be employed for this purpose. These can act in 3 areas: prevention of sediment entry into the reservoir (catchment management, bypasses, etc.), reduction of how much of the introduced sediment settles (sluicing, etc.), and removal of already deposited sediment (flushing, dredging, etc.). Which methods are sensible depends on the local conditions and must be determined, but the individual methods can also be further optimized.

Flood Risk Management at Hydropower Plants

Climate change-induced and natural changes in the hydrological conditions of alpine rivers require a continuous adaptation of flood risk management strategies for the safe operation of hydropower plants. This includes, on the one hand, the improvement of existing reservoir drawdown concepts for individual plants based on new extreme value statistics and the corresponding conveyance curves, and on the other hand, a holistic optimization of decision diagrams for the operation of power plant chains, taking into account integrative objectives of flood control, sedimentology, and aquatic ecology. In addition to management measures to minimize flood risk, it usually requires structural optimizations to the existing power plant facilities to ensure the safe and damage-free discharge of extreme flows (see Optimization of Hydropower Plants).