Small hydro still has big potential

Small hydroelectric power schemes offer valuable sources of green electricity to countries seeking to meet national and international renewables targets. New technological developments are offering better ways of exploiting this potential.

The UK government’s determination to meet the Kyoto directives for reducing carbon emissions and the introduction of Renewable Obligation Certificates (ROCs) has given companies increased opportunities to invest in their hydroelectric power generation portfolio, as the legislation is rewarding electricity production from renewable sources. The UK government’s renewable target is 10 per cent generation by 2010 and 20 per cent by 2020. Hydro is regarded as a renewable if it is new build (except pumped storage), refurbished (new runner and guide vanes) and rated below 20 MW.

Figure 1. Tailwater at the Nussdorf Hydromatrix plant
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The Obligation has boosted the refurbishment market in the UK, particularly in Scotland, since its introduction in 2001. Many projects have been completed and almost all of the ROC-qualifying stations in the UK have been equipped with, at minimum, new runners and guide vanes. However, there is still a huge potential for upgrades and refurbishments – a hydro-power trend worldwide, as well as in the UK.

As most of the UK hydro portfolio was built between 1900 and 1950, refurbishment has become necessary. Like other power generators, the UK hydro market has been affected by competition under the privatized market place. The resulting low electricity prices mean operators have to consider efficiency improvements in order to keep investments financially viable.

Refurbishment of Culligran

Scottish and Southern Energy (SSE) in Scotland, the owner of over 60 hydro stations, is one company that has embarked on an overall refurbishment programme to improve the efficiency of its existing hydro power stations.

One of the refurbishment contracts was for the Culligran hydro power station, which was awarded to an alliance of VA Tech Hydro and Weir Engineering Services in 2003.

The scope of work of this turnkey refurbishment project comprises the overall refurbishment of the main turbine generator sets including replacement of turbine runners (Deriaz type), guide vanes and governor oil plants, along with performance test, generator overhaul and new brush-less exciter machines. The smaller unit will be equipped with a new runner and a complete new generator set. The electrical control, protection and excitation systems for the entire plant will also be renewed. This includes new digital governors, as well as a replacement of the medium and low voltage switchgear and balance of plant. Finally, civil and building works and new main inlet valves guarantee high reliability and life extension for at least 30 years. The main site activities started in September 2004 and work at the stations will be completed at the end of 2005.

Figure 2. The Nussdorf Hydromatrix plant (top left of complex)
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The Culligran units will also benefit from a shift to oil-free runner design, as are already installed at Aigas, Kilmorack and other stations in the UK. The runner hub is designed to operate without oil filling and all bearings, bushes and guide strips within the turbine runner hub are self-lubricating. The runner blade servomotor and high-pressure oil head (120 bar) are located on top of the generator. This design will avoid oil spillage into the rivers.

Improving efficiency

Retrofits and refurbishments not only extend the lifespan of hydro power stations and increase their reliability and availability at a low cost and with minimal environmental impact, but can also increase the output of the power station.

VA Tech Hydro has been involved in numerous upgrades for SSE over the years, including the Rannoch power plant, which saw a major refurbishment of generators, turbines and inlet valves. The refurbishment has given the 75 year old Rannoch power plant a life extension of 20 to 30 years, and an increased output of 5 per cent, at rated head.

New technology

Uprating allows additional hydropower to be generated from existing units. In other cases, new small hydro projects can capture energy currently being dissipated. In Austria, for example, VA Tech Hydro, in a consortium with Porr Technobau and Verbundplan, were awarded a contract to provide a small-scale hydropower plant near the Schemerl Weir at the intake of the Vienna Danube Canal in Nussdorf. The contract sent an important signal around the world concerning the best possible use of hydropower as a renewable source of energy. The Nussdorf small-scale hydropower plant project utilizes the currently unused discharge of the Danube Canal for generation of electricity in an ecological and economical way.

The idea of a hydropower plant had been considered at the end of the 1990s but at the time it was not pursued, for financial reasons. However, following an innovative concept worked out by the project partners and the availability of VA Tech’s new Hydromatrix technology, the project has today become economically viable.

The small-scale hydropower plant consists of a 30 m long, approx. 12 m wide and 7 m high over-flow hollow body weir, with attached pneumatically operated spillway gates, twelve Hydromatrix turbine-generator units and an operation building.

Figure 3. Water intake through the Nussdorf plant
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The Hydromatrix concept has also made it possible for the project partners to secure the required flow for navigation in the Danube Canal and to comply with the existing weir operating procedure. Another important feature of the project was that it had to be integration carefully into the existing Nussdorf Weir building complex, which was designed by the famous Jugendstil architect, Otto Wagner.

The Hydromatrix plant is scheduled to supply the first electricity in summer 2005 and will meet the needs of approximately 10 000 households.

The Hydromatrix concept is an innovative application of well-proven hydropower technologies. Its standardized modular design makes it possible to employ efficient factory assembled small turbine-generator units in a “grid” or module. It uses existing weir structures and therefore requires no new civil construction, and incurs no extra geological risk or additional land usage. Project schedules using the Hydromatrix are short (12-18 months) and the concept boasts low costs and high availability.

A large-scale Hydromatrix power plant is currently being completed in Jebel Aulia in Sudan.

Realising hydro potential

Austria is a major user of hydropower technology and has been at the forefront of developments in efficient technologies for small hydro electricity generation. Cooperation between VA Tech Hydro and Energie AG Upper Austria has formed the basis for a new application development: the StrafloMatrix. This was first implemented at a small hydropower plant in Agonitz on the Steyr river, back in 2004. The small hydropower plant at Agonitz, which will supply approximately 4500 households with green energy, is equipped with one vertical Kaplan turbine and one StrafloMatrix unit, and will produce almost 16 GWh annually. The two turbines have a total output of 3.1 MW, which corresponds to an output increase of 350 per cent, compared to the power plant it replaces. For Energie AG, the expansion and reconstruction of small hydropower plants will continue to play an important role in strengthening the share of power the company generates itself, thereby further securing the electricity supply in Upper Austria.

Simple operation

In addition to its extremely compact design, the ease of operation is another feature of the StrafloMatrix. As the water flow from which the StrafloMatrix generates electricity is constant, it operates without expensive regulation technology. The turbine is lowered into the water flow and immediately generates electricity with the integrated generator. The StrafloMatrix in the Agonitz power plant is designed for a water flow of approx. 10 m3 / second and has an output of 700 kW. In the coming five years, the StrafloMatrix will prove its practical capabilities under tough commercial operation conditions. Irrigation dams and weir systems throughout the world that are not yet used for energy production are targeted as application sites.

Figure 4: Schematic of the Hydromatrix installation
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In addition to third world countries, where the StrafloMatrix turbines are advantageous in particular because of their simple operation, utilities from USA and Canada have already expressed their interest. Agonitz is therefore set to become an international meeting place for power plant technicians during the coming years. While environmental concerns and restrictions are likely to impose a constraint for the large hydro segment, there remains enormous scope for the development of small and micro hydro applications.

Ursula Scheidl, VA Tech Hydro, Austria

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