Vienna’s two mountain spring pipelines not only supply fresh drinking water to the city. Because they are designed as gravity flow conduits, they also generate eco-electricity.
The Austrian capital has a fairly advanced system of eco-electricity generation. Part of this electricity is also generated by the drinking water conduits of Vienna’s water supply system, both in the source areas and in the city itself. The key to this are special small hydropower plants, commonly referred to as “drinking water power plants”. They are equipped with turbines which use the build-up of gravitational pressure along the two water supply lines. This provides electricity for the operation of technical equipment also in remote source areas.
In Vienna, the drinking water power plants mainly serve for pressure control. The surplus current was, and is again, sold to the power utilities. Electricity supply was suspended in the 1970s when energy prices were stagnant and this form of power supply became increasingly uneconomical. The turbines in the drinking water power plants were subsequently by-passed with new pipes and pressure control was taken over by special fittings.
Turnabout in the 1990s
When electricity prices recovered and renewables became increasingly important as a source of energy, a turnabout took place in the mid-1990s which led to the reactivation of existing infrastructure and the construction of new plants. The drinking water power plant at Mauer along the Second Mountain Spring Pipeline marked the beginning. Currently, 14 such plants within and outside the city area are operated with drinking water from the Vienna Waterworks.
This allows the water utilities to sell their surplus eco-electricity. In 2011 more than 65 million kWh of electricity were generated. But the central goal still is to supply the population with fresh mountain spring water, as it was one century ago. Thanks to external bearings and food-safe lubricants, the quality of drinking water is in no way impaired by electricity generation.
Reithof 2 will be connected to the grid before the end of the year
The Vienna Waterworks’ most recent contribution to the EU renewable energy targets is the second upgrade of the drinking water power plant at Reithof. The plant is located along the First Mountain Spring Pipeline near the community of Nasswald. It was built back in 1929 with a capacity of 45 kW. In a first upgrade, the capacity of the old power plant was increased to 240 kW. In a second upgrade, water volume was added to increase the flow rate to 1.000 l/sec. and a 500-m-long section of the gravity flow conduit was converted into a pressure conduit. This helped to further increase capacity to 340 kW. Thanks to the pressure conduit, the head could be raised by eleven metres.
Cost-saving technology at Wienerberg
The last of the scheduled projects shall be executed within the city limits of Vienna next year. Eco-electricity is recovered at the intake of the drinking water reservoir at Wienerberg. Kurt Schlesinger, Head of Department 4 of the Vienna Waterworks (technical infrastructure, tanks and lifting stations), explains the special features of the 40 kW plant: “This time we are not installing conventional turbines but reverse-rotating centrifugal pumps. While turbines, with their high efficiency and good control mechanisms, are advantageous for water supply operations, they are custom-made and there - fore quite expensive. Reverse-rotating centrifugal pumps – which operate on the basis of the ‘pumps as turbines’ principle – are much cheaper.
The lack of control mechanisms and the lower efficiency is compensated by installing two units at a water flow ratio of one-third to two-thirds, which ensures that the tank is always optimally filled to match consumption needs. The reverse-rotating centrifugal pumps are installed on either side of the pipe string. The local pumping station and the public power utilities, Wien Energie, derive their electricity from our system.” The Vienna Waterworks calculate that the € 300,000 drinking water power plant at Wienerberg has a payback time of thirty years, depending on changes in the feed-in tariffs. Detailed planning is underway.
With the two new drinking water power plants Reithof and Wienerberg, Vienna is continuing on its path to meet the renewable energy targets. The double benefit of this technology – pressure control AND eco-electricity generation – more than offsets the lower electricity output compared to other Viennese initiatives. Environment City Councillor Ulli Sima believes that the plants are also important role models. For this reason, other potential sites where such plants may be erected are currently under investigation.
(Source: , Christof Hahn)