Throughout the world, 16% of electricity production is generated by hydropower plants. Compared to wind and solar energy sources, hydropower is by now technologically mature. However, novel approaches in the design, operation, and planning of hydropower plants still exist, aiming at increasing hydropower flexibility, efficiency, lifetime, and cost effectiveness. In this article, the major challenges and innovations will be discussed.
Increase of hydropower flexibility:
Modern hydraulic turbines are faced with new challenges associated with the variable demand on the energy market. This necessitates new technologies to ensure greater flexibility over an extended range of regimes far from the best efficiency point of turbines. Some of these technologies are: stabilizer fins, J-grooves, stator installed immediately downstream of the runner, adjustable diaphragm installed in the draft tube cone, air injection/admission, tangential water injection at the cone wall, axial water injection with high/low velocity and low/high discharge, axial water injection with counter-flow tangential component, ejector power plants for the excess flow rate, and two-phase air-water injection along the axis.
Hydro generators with current-controlled rotors:
Frequent start and stop actions are required to provide regulation of turbines, which leads to additional wear on the energy-conversion components. Modern power electronics with current-controlled power supplies can provide new opportunities for the control of electrical machines. This is, for example, the case of the hydropower plant Frades II in Portugal, which is equipped with two pump-turbines and with an induction-motor generator with rotor power controlled by an AC-excitation system.
Digitalization of hydropower operation:
The objective is to gather and analyze real-world data and apply them to the actual working conditions of turbines, providing advanced grid supporting services without compromising their safety and reliability. The annual energy production coming from the world’s hydropower sector (1,225 GW) could increase by 42 TWh by investing in hydropower digitalization. This production increase corresponds to $5 billion USD annual operational savings and a significant reduction of greenhouse gas emissions. One example is within the HYPERBOLE research project, granted by the European Commission, on the 444-MW MICA hydropower plant located on the British Columbia in Canada.
Hydroelectric energy storage and variable speed turbines:
The increase of renewable energy in the electrical power system is requiring the need for energy storage power plants such as pumped storage hydropower plants (PSHPs). PSHPs continue to evolve to respond to the need for turbines to more quickly and more frequently pass from pump mode to turbine mode and vice versa. These turbines are called pump-as-turbines (PAT). Variable speed PATs are able to start up in pump mode and change the operation mode in a shorter time than turbines with constant rotational speed. The speed variation is possible thanks to the use of power electronic converters, in either of the two following ways: synchronous machines whose stator is driven with a variable frequency (converter-fed synchronous machines), and electric machines that are fed by AC currents into both the stator and the rotor windings (double-fed induction machines).
The first large variable-speed hydropower units were commissioned in Europe in 2004 for the Goldisthal PSHP. Goldisthal is equipped with four 265-MW pumped-storage units, two of which are connected to the grid through a double-fed induction machine.
Novel technologies in small-scale hydropower:
Small-scale hydropower is generally more eco-friendly and can potentially offer an alternative clean energy solution in the variable electricity market. Small hydro plays an important role in mini-grid and rural electrification strategies. The cost of small hydropower is lower and environmental impacts are not as significant as large hydro plants. In particular, novel designs of gravity hydraulic machines and turbines, along with advanced designs and operation strategies for PATs, are being introduced. For example, the 378-kW variable-speed Kaplan tubular turbine with fixed guide vanes, installed in Ingelfingen small hydro to deal with head variation.
Fish-friendly hydropower technologies:
The environmental and ecological sustainability of hydropower plants is always considered in hydropower design, with a focus on fish-friendly turbines (like water wheels in low head applications and the Alden turbine for higher heads) and on the development of water-lubricated bearings to mitigate water pollution risk.
Therefore, hydropower companies and public authorities are continuing to invest in the hydropower sector, making hydropower a potential source of profit and business. For example, through 2020, in the state of New York there will be 47 projects encompassing 62 hydroelectric developments located on 29 different rivers in nine watersheds.
Featured image courtesy of Rudolf Fritsch – Hydroconstruct/ZT-Fritsch GmbH
