The construction of a small-scale hydropower plant in the community of Strallegg in eastern Styria made the operator Ernst Schweighofer largely independent of the public power grid.

The plant, which was constructed largely independently, covers ­almost all the electricity demand for several residential and commercial properties and a heating plant which is likewise owned by the operator. The surplus power is fed into the grid operated by Energie Steiermark, from which power can also be sourced if the water level is low. The power plant, which was constructed in the space of five months in 2017, is based on the classic diversion principle. Via a Tyrolean weir, up to 130 l/s of water are collected from the River Arbesbach and directed via a penstock that is around 1.3 km long to a 3-nozzle Pelton turbine. All of the piping in the form of highly durable ductile cast-iron pipes was provided by the professional sales company Geotrade from Upper Austria. Thanks to the flexible socket system, it was ­possible to lay the entire pipeline without installing any pipe elbows. After being commissioned in March 2018, the plant celebrates its first anniversary of operation this spring.

Ernst Schweighofer, who is today 21 years old and comes from Strallegg in the district of Weiz in eastern Styria, developed his interest in hydropower at an early age. It was back in 2009 that the then twelve-year-old drew his first designs for the construction of a hydropower plant on his parents’ property. However, the cost of constructing a plant with a maximum output of 5 kW was considered to be too high. Once the family had taken up the initiative to receive advice on small-scale hydropower plants in 2014, the plans for a hydropower plant of their own were again fleshed out. As part of the advice provided, the potential to generate around 200,000 kWh a year was identified. But as the focus of the Schweighofer family was and still is on supplying energy for their own needs, the project was put back on ice. “This changed in 2015 when we started operating our own biomass plant. The large amount of electricity that the heating plant used meant that the construction of a hydropower plant once again made a lot of sense,” explains Ernst Schweighofer.

Power plant construction approved in very short time
The application to construct a small-scale hydropower plant on the River Arbesbach was submitted to the relevant authorities in December 2015. The project was planned and developed by the engineering firm Mosbacher from Lower Austria, which specialises in small-scale hydropower. Schweighofer stresses that the landowners, owners of fishing rights and public officials were involved in the project right from the start and it was possible to quickly reach an agreement with all the parties involved. This also explains the short approval phase, with the building permit being issued just a few months after it was submitted in May 2016. As an ecological counterbalance, one section of the body of water at the mouth of the river was made accessible to fish by installing low-water groynes.

Penstock made from ductile cast-iron pipes
The actual construction works started with the excavation of the powerhouse at the beginning of June 2017, and the concrete structure of the building was hoisted into place in around three weeks. This was followed by the laying of the around 1.3 km long penstock which, like the groundworks and the hydraulic steel construction works, was overseen by Schweighofer himself with assistance from fitters to help with the assembly work. The upper section of the penstock was laid with a dimension of DN350 and, following tapering, the remaining section of around 950 m towards the powerhouse had a DN300 design. Also laid at the same time were empty conduits for the power cables and fibre optic cables, each routed separately, for providing power to the water catchment. When it came to the material for the pipes, the operator opted for ductile cast-iron pipes from the manufacturer Jindal SAW which were supplied by the sales specialist Geotrade from Upper Austria. The high-quality pipes are renowned for their high compressive strength, resistance to harmful environmental effects, optimum flow conditions thanks to their ultra-smooth inside surfaces, and they are suitable for very tough installation conditions. In addition, the pipes can be laid without any additional bedding material in the ground. Thanks to the ability of the pipe joints to deviate within the connecting sockets, the system allows expansive changes of direction to be designed into the pipeline without using specific piping fittings. This was also the case with the penstock for the Arbesbach power plant, which was laid, including a river underpass, entirely without any pipe bends in around 1.5 months.

Pelton turbine optimised for partial load
The water catchment was equipped by Schweighofer with a Tyrolean weir which he fabricated himself, and a slide valve integrated into the transverse structure is used for residual water discharge. In the weir cabin in which the electrical engineering components were housed, an additional fine trash rack can be used for winter inflow. Following entry, the works water is fed into a de-sanding basin, and the power descent begins immediately after this. “As the maximum extraction water quantity of 130 l/s was set relatively high, the turbine should be able to cover the widest possible operating volume. In addition, the level-controlled unit had to be adapted to a second-hand, refurbished synchronous generator from Hitzinger,” says Schweighofer. Maschinenbau Unterlercher GmbH from East Tyrol manufactured a 3-nozzle Pelton turbine with a horizontal shaft that was optimised for this intended use. The connection between the turbine and generator shafts is provided by a belt drive which is also used at the same time for speed transmission. With a gross drop of 64 m, the turbine produces a bottleneck capacity of 70 kW. When the amount of water available reduces due to the different seasons, the three electrically regulated nozzles ensure a maximum level of efficiency. A powerhouse crane from the company Mayrhofer from Wenigzell makes it easier to carry out maintenance on the technical equipment. The fish ponds which were created next to the powerhouse before the plant was constructed source their supply of water from the residual water section.

Independent power source since 2018
As well as providing a dedicated energy supply, the power plant’s ability to operate independently was also an important point for the operator. This requirement was safeguarded by the items supplied by SOWA-Control GmbH, which was responsible for the electrical engineering and control. The electrical engineering in the powerhouse and the power feed were likewise designed by Schweighofer himself. To connect the cogeneration plant and the properties spread around the local area to the dedicated supply grid, the operator laid around 4 km of power cables. If a sufficient amount of water is available, the properties are supplied with power completely independently; if the power plant stops operating, power is automatically sourced from the grid operated by Energie Steiermark. After the plant began operating normally in March of last year, Schweighofer is very happy with the production capacity that has been achieved to date: “Although the power plant was shut down for several months, around 80 percent of our own energy requirement was met in 2018. In addition, around half of the electricity produced was fed into the public grid.”