The hydropower sector is responding to challenges created by concerns over climate change, water availability and other environmental issues, writes Didier Mallieu
|Karakaya hydropower plant in Turkey
Hydropower is the only large-scale renewable electricity source which can be financed without the help of state subsidies. It decreases dependency on fossil fuels for the countries where it is installed, positively impacts local employment and allows balancing of other renewable energy sources. It is, so far, the cheapest way to store energy.
Hydropower technology is mature, and thus plants have a very long and predictable lifetime, with minimal O&M costs. So the future is definitively rosy for the hydropower industry, which should see its capacity doubling to 2000 GW by 2050 according to the International Energy Agency, not to mention the huge potential of repowering existing sites and small hydro.
However, as for most other large infrastructures, sustainability gives rise to considerable challenges. Climate change and its impact on water inventory have brought some uncertainty, but this is not without opportunities. The financial crisis triggered additional efforts to reduce project implementation duration and to limit or offset cost increases linked to additional environmental regulations. These fast changes have transformed the hydropower industry from a low-paced, mature science into an exciting area for innovation.
Environmental protection is paramount, and engineering and O&M companies active in hydropower have worked hard to ensure that their operations comply with new regulations. Hydropower has successfully integrated sociology, hydrology, geology, and civil and electromechanical engineering, and this winning hand has been enriched in recent years by climate modeling, biology, electricity market economy and water resource management.
Underlying such changes is a more hidden transformation related to modern design and simulation tools. From computerized fluid dynamics to computer-aided project management, modern engineering techniques treat enormous amounts of data in an integrated way, leading to significant improvements in project design, development and operation.
For the ‘Y-generation’ of engineers, who have developed strong social and environmental skills and consciousness, such an enlarged multidisciplinary scope provides new opportunities to grow and learn continuously, often extending their specialities into adjacent disciplines. Provided that engineering companies can work efficiently as multidisciplinary teams – which is not always straightforward – these innovations will continue and we’ll see hydropower plants which are sensitive to the environment whilst still being economical, balanced and optimized for all uses.
Hydropower is the most proven renewable energy source. Plants constructed 50 to 100 years ago are still operating today. Experiences from previous decades can be combined with new innovations to create transformational hydropower developments in many developing countries. What’s important is that state-of-the-art integrated solutions are seen as the best choice by these high-growth nations – for both economic and sustainability reasons. Globalization of knowledge and of the hydropower industry makes it easier for all developers, decision-makers and influencers to access such technology, with their own specific objectives.
Responding to challenges
In some of the latest developments in the hydropower industry, engineers have responded to challenges with solutions and innovations.
Over the last decades, concern has increased that water availability and, consequently, energy production will be significantly affected by climate change, which is often seen as a negative risk. However, the impact of climate change on plant performance can be very variable, depending on location and project type.
Detailed studies have shown that climate change can also lead to an increase in production under certain conditions. Recent research in Switzerland, for example, has revealed that, for high-lying catchment with medium glaciation in some regions, a marked increase in average annual runoff is expected. Because of the spatial variability of climate change’s impact on inflow, a project-specific assessment on a catchment scale is required. Complex modelling, covering the processes from climate change through hydrological inflow to energy production, must be carried out.
Closely following advances in the atmospheric sciences, Pöyry´s team of hydrologists has developed extensive know-how in estimating inflow and electricity generation under current and future conditions. This includes coupling of regional climate models with hydrological models to predict reservoir inflows for different climate change scenarios, as well as the application of complex river basin models to consider the impact of upstream developments and other water users.
Even for remote areas with limited hydrological data, Pöyry has developed advanced modelling techniques to derive robust hydrological estimates based on satellite data and water balance studies, producing the best possible energy forecasts from a few hours to decades.
This trend takes two forms: more precision in both input data and modelling for the classical hazards like earthquakes, but also consideration of new hazards like the retreat of regions affected by permafrost due to global warming, which leads to increased risk of landslides impacting into reservoirs. Using cutting-edge analytical methods, the effects of such impacts on the maximum possible impulse wave and the run-up on the affected dam can be simulated in detail with three-dimensional numerical modelling. This was done by Pöyry for the existing Göscheneralp earth-core rockfill dam in Switzerland.
The influence of hydroelectricity on the habitats and migration activities of fish as well as aquatic microbes is of the utmost importance. Provision of adequate residual flows and fish migration facilities, as well as mitigation measures for the reduction of surge effects due to storage release or peaking power operations, require special attention.
In order to provide near-natural conditions in residual flow, the application of dynamic water release patterns is now commonplace. Fish migration systems are being designed to the specific needs of the targeted species in the affected river. This aspect is investigated on a case-by-case basis in close cooperation with specialized biologists. Upstream fish migration, for example, is extremely well investigated and can be solved successfully by providing species-specific fish ladder designs. Downstream fish migration is more complex, as the fish need to be kept away from the power water intakes by special screen-type racks, and to be guided to the corresponding bypass system.
Felix Oberrauch, senior project manager, says: “Considerable efforts and research have been done and are ongoing within the hydropower industry and universities in order to provide adequate technical solutions for successful downstream fish migrations. First prototypes for such devices are already in the realization phase.
“Surge effects due to changing tailwater discharges of power stations are resulting in fluctuating water levels and flow velocities in the receiving water course, which has a stressing impact on the aquatic fauna. In the case of the Chlus Hydropower Project in Switzerland, Pöyry is in charge of designing all the mentioned mitigation measures.”
Land use and visual impact
As with any man-made activity, hydroelectricity has an impact on land use and on the overall appearance of the landscape. These visual impacts are an understandable area of concern in project sites close to urban or touristic areas that, rightly, call for mitigation or project optimization measures. In most cases, such optimization is a compromise between the technical optimization of the plant layout and the overall acceptability of the project. The latest visualization techniques are very helpful tools and have transformed project consultation, as they allow for a more active discussion between project teams and involved stakeholders (see Figure 1).
|Figure 1. Example of a visualization of Lateral-Coanda-Intake. Current situation (top); predicted situation (bottom)
Technical mitigation concepts include, for example, shifting a weir or dam location to a more remote place which has a positive impact on visibility in the landscape as well as a reduction in use of valuable land. On the flip side, such a revised concept leads to a reduction in the capacity of the reservoir and/or the gross head of the plant.
Other mitigation measures include, for example, changing the plant concept from a storage scheme to a more runoff-type scheme with a reduced need for reservoir volume and a more limited plant flexibility. Further possibilities include the more frequent use of costly underground or cut-and-cover structures instead of surface civil works. Desanding facilities, power waterways and powerhouses are the most suitable elements of a hydropower scheme to be realized as subsurface constructions. Thanks to the implementation of such sustainable optimization concepts, even the realization of new-build hydropower projects within natural preserves is becoming feasible.
An important example in this respect is the intake and plant concept for the Kukule Ganga Hydropower Project in Sri Lanka, where Pöyry was part of the Designer Engineers’ Consortium.
Rehabilitation and repowering
The need for rehabilitation and repowering of existing hydropower plants is growing in importance as more and more schemes reach their end-of-concession period, which normally lasts in the range of 60 to 80 years. A further trend, due to ongoing changes in the economic environment, is the transfer of ownership of hydropower plants originally designed and built for feeding the electricity demand of industrial consumers like smelters or chemicals industries to utilities, with a change in operational requirements for the future grid supply of such plants.
In most cases, rehabilitation projects consist not only of replacing ancient electromechanical and/or hydromechanical equipment with the latest machinery, but also exploring the upgrade potential of the entire scheme, including the plant layout as well as some civil structures. Typical aims of upgrade projects are increases in power generation, peaking power capabilities and storage capacities, as well as more flexible operation.
Pöyry has wide experience in all types of hydropower rehabilitation projects, especially in the Alpine region (Austria, France, Germany and Switzerland) as well as in Turkey and the CIS countries.
|Löntsch hydro plant in Switzerland: the Alpine region is prime hydropower territory
Hydropower plants can deliver multiple benefits besides energy production, such as irrigation, flood mitigation, water supply, navigation or fish farming. To ensure public acceptance, new hydropower plants should consider and publicize these different goals. For multipurpose projects, it is essential to assess the benefits with a holistic approach. A transparent assessment of the various advantages and impacts should be carried out by subject matter experts.
Pöyry covers all the main disciplines required for such a holistic approach, and has extensive experience on more than 60 multipurpose projects around the world. Currently Pöyry is one of the leading engineering companies for the Uma Oya Multipurpose Development Project in Sri Lanka.
The construction of a dam on the Uma Oya River in the Puhulpola region has been under consideration since 1991, when one of the main objectives of the project was defined as water conveyance from the Central Highlands to irrigate the dry lands of Sri Lanka. The Uma Oya project will enable the diversion of 145 million m3 per year of water from Uma Oya to Kirindi Oya through a total of approximately 23 km of tunnels. The water will be used to irrigate some 5000 ha of new lands in the South East Dry Zone of Sri Lanka and to generate around 120 MW of electricity for the national grid. The project is currently in realization and is planned to begin operation in 2016.
|The need for rehabilitation and repowering of existing hydropower plants is growing in importance
Credit:Emerson Process Management
Storage and pumped-storage hydropower plants play an important role in supplying peak electricity and balancing services for the grid, thus contributing significantly to its stabilization. In most European countries the variable renewable energy sources, mainly wind and solar, will be further extended. Because of these highly fluctuating electricity sources, it is expected that the system importance of pumped-storage power plants will increase.
A clear trend is for waterways and power caverns of new pumped-storage schemes to be designed as underground structures. Besides topographical and geological aspects, this significantly minimizes the visibility of such large structures, which are often situated in beautiful mountainous areas, and therefore increases public acceptance.
Pöyry is in charge of the design and site supervision of the underground works at the 900 MW Nant de Drance pumped-storage hydropower plant in Switzerland, one of the largest pumped storage schemes currently under construction. The two main caverns of the power station are positioned between two reservoirs, around 600 metres below surface level. These will house the pump turbines and the transformers. The twin waterways consist of two pressure tunnels, approximately 1500 metres long, with an internal diameter of nearly 8 metres, plus two vertical shafts 450 metres in height. The two vertical shafts will be lined with concrete.
Martin Aemmer, Pöyry’s Head of Hydropower, EMEA, says: “This concept allows a substantial cost saving compared to a conventional steel liner. Another significant cost and time saving was achieved by designing the large valve chambers with a shotcrete lining instead of in-situ concrete.
“Another example of the tailored engineering of a pumped-storage scheme was the success of the Limberg II project in Austria, where Pöyry helped to significantly reduce the original design of the power cavern for the tender and construction stage. The excavation volume of the cavern was reduced by more than 35 per cent, which led to a significant cost reduction and shortening in construction time.”
Effective cost and project management are key considerations for any investor, especially as the up-front costs for hydropower projects are high. In order to keep within these economic constraints, engineering and project management services of high quality are required.
Wide interdisciplinary experiences in the design, construction and operation of hydropower plants, combined with the specific use of modern engineering tools and construction techniques like finite element models or underwater concrete castings, are mandatory for any project’s economic success.
An important example is the design and construction of the 100 MW New Rheinfelden run-of-river hydropower project at the German/Swiss border, where Pöyry was part of the Designer’s Engineer Consortium. Based on innovative design and engineering concepts developed prior to the detailed design phase, the investment costs for this project could be reduced compared to initial budgets by a further €50 million ($67 million), to a total in the range of €350 million.
Large hydropower plants can be cost-intensive and require high up-front investments. Therefore it is essential to ensure reliable energy production over the complete lifetime of a plant.
Hydropower plants designed by Pöyry more than 50 years ago are fully amortized and still operate efficiently today. For example, the five Swiss hydropower plants – Andermatt (which began operation in 1961), Calancasca (1951), Göschenen (1962), Mauvoisin (1958) and Wassen (1949) – are constantly producing renewable energy at low operation and maintenance costs.
Didier Mallieu is Vice President of Hydropower and Renewable Energy at Pöyry.
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