Analytical hill chart towards the maximisation of energy recovery on water utility networks with counter rotating micro-turbine

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Loïc Andolfatto, João Delgado, Elena Vagnoni, Cécile Münch-Alligné, François Avellan

Thursday 2 july 2015

11:00 - 11:15h at South America (level 0)

Themes: (T) Water engineering, (ST) Hydraulic machinery and industrial flows

Parallel session: 11C. Engineering - Industrial

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Almost all of the large scale hydroelectric potential is already harnessed in developed country. An increase of sustainable hydraulic energy production mostly rely on the development of new technologies dedicated to harvesting the small scale hydroelectric potential. For instance, the Swiss yearly small hydro power production – produced on stations with a nominal power below 300 kW – is expected to grow from 0.3 TWh to 1.3 TWh between 2010 and 2050. The condition for such small power stations to meet economical profitability is to minimise the required capital expenditure while maximising the efficiency of the installed hydraulic machine. Environmental impact should also be kept as low as possible to allow a massive and sustainable field implementation. Harvesting the hydroelectric potential on existing installation such as water utility networks limits both the investment and the environmental impact associated to new infrastructure. The concept of counter rotating micro-turbine features a compact axial architecture ensuring a lean in-line installation on existing facilities. Variable runners’ rotational speed allows to cover the consumer-driven wide range of discharge usually experienced on water utility networks. It is therefore an interesting candidate for energy recovery on drinking water network. The best efficiency of the hydraulic machine is very likely to be reached with the two runners rotational speed set independently. But finding the optimal speed combination for each operating point is not a straightforward problem. In this paper, a generic procedure to build an efficiency hill chart out of experimental measurement is presented. The entire domain of rotational speeds is investigated. Analytical models are used to identify the optimal rotational speed command laws. The benefit of the method is illustrated through the case study of an instrumented pilot site with an average of 9.5 kW of available hydraulic power. The annual energy production is estimated with and without individually optimised runner speeds. The proposed method leads to a 5% enhancement of the yearly averaged efficiency.