Optimization of low-head hydropower recovery in water supply networks

Small scale hydropower is emerging as a decentralized source to satisfy local demand for electricity. The interest in micro-hydropower, which refers to installed power below 100 kW, is increasing since this is a solution with low environmental impact. Water supply systems are one of the main manmade water systems presenting potential for micro-hydropower. Although some applications already exist in adduction lines, the urban distribution networks remain unexplored. Because these are complex systems in which flows and pressure vary constantly, specific technology and installation schemes for energy recovery are lacking. This work accesses the potential for hydropower within water supply networks (WSN) and presents an arrangement of micro-turbines specially conceived for this type of installation. The arrangement is based on a novel inline turbine suitable for pressurized systems and its best location within the networks is studied. The five blade tubular propeller (5BTP), preliminarily designed in the framework of the European Project HYLOW, was further developed and tested in this work. An experimental campaign was conducted with a large range of heads and torque measurements to access its characteristic curves and to obtain hill charts. The relative positioning of the turbine-generator shaft regarding the pipe bend was modified from a downstream position to an upstream position. Efficiencies of around 60% were found. The adequate locations in WSN for micro-hydropower plants are identified using an optimization algorithm which considers both the assessment of the energy production and sizing of the main equipment and works. A concept for the implementation of the 5BTP in the field was developed, consisting of an arrangement with up to four turbines inline within a buried chamber created around an existing pipe. Two objective functions, energy production and economic value respectively, are used. A simulated annealing process is developed to optimize the location of a given number of turbines. This procedure takes into account the hourly variation of flows throughout an average year and its effect on the turbine efficiency. The optimization is achieved by considering the characteristic and efficiency curves of a turbine with different impeller diameters and simulating the annual energy production in a coupled hydraulic model. After a convergence analysis for different restrictions and numbers of installed turbines, the algorithm was applied to analyze the feasibility of the proposed arrangement in two case studies in Switzerland: a sub-grid of the city of Lausanne and the complete WSN of the city of Fribourg. In both cases, the implementation of the proposed energy recovery solution seems to be feasible. A detailed analysis of the cost breakdown revealed that the cost of additional pipe work, which are required in each layout to guarantee a by-pass supply in case of maintenance, may have an important role on the investments. Also, the pressure reduction valves locations, if they exist, are likely to be the optimal solutions. Finally, a methodology to quantify the potential for hydropower based on the excess energy in a WSN is proposed and applied to case studies. It allowed to conclude how much the proposed arrangement can extract from the networksâ energy potential. In addition, an attempt was made to produce an expedite method to estimate the energy produced with one 5BTP based on network parameters and dimensional analysis

Optimal location of micro-turbines in water supply network

Micro-hydropower is currently expanding as a solution to improve the efficiency of water systems by using energy excesses which are typically lost. In the particular case of water supply systems, often excessive pressure exists in zones of the network connected to other areas situated at higher altitudes. Pressure reducing valves are commonly used as a mean for dissipation of this excess energy. In this work, the installation of micro-turbines in a closed water supply network is analyzed as a way to recover the existing surplus of energy by converting it into electricity. The flow in water supply systems is highly variable, with a direct impact on the efficiency of the turbine and, as most water-supply networks are meshed, the optimal location of the energy converters is not straightforward and needs assessment by simulation processes. For this purpose, an optimization tool based on the application of an evolutionary algorithm was developed to select the best location, model and runner size of a selected number of turbines to install in a network. Using the characteristic and efficiency curves of a micro-turbine and a database of flow demand given every hour, a simulated annealing process is applied to maximize the energy production while pressure restrictions imposed by regulation must be respected. The methodology was applied to a case study in a sub-grid of the water supply system of the city of Lausanne, Switzerland, and the considered micro-hydro converter was a five blade tubular propeller. This study is focused on the simulation problem and the convergence to optimal solution is analyzed under different restrictions and number of turbines to install

Feasibility assessment of micro-hydropower for energy recovery in the water supply network of the city of Fribourg

In water supply systems there is potential for hydropower production at several scales, from small hydro to micro. The energy recovery within the urban water supply networks is a type of micro-hydro that may be useful for the control of excessive pressures. On the other hand, local decentralized production of electricity may have multiple uses, considering self-consumption at local grid level or storage. However, there is still a lack of technologies and specific solutions for such applications, since the flows are highly variable and the available heads are small and limited to service pressures. A scheme specially conceived for water supply networks making use of a micro turbine is proposed.Adequate positioning conditions are identified using a search algorithm which considers both the assessment of the energy production and sizing of the main equipment and works. Typical schemes are proposed where the installation of up to four turbines is possible within the same buried chamber created around an existing pipe. Preliminary results obtained for a network case study show that the implementation of the proposed energy recovery solution is feasible. The installation of a by-pass revealed to have a key role in the feasibility of each solution, demanding customized engineering judgment. Further testing of the search algorithm as well as a first in-situ implementation of the scheme may be foreseen in the near future

Simulated Annealing in Optimization of Energy Production in a Water Supply Network

In water supply systems, the potential exists for micro-hydropower that uses the pressure excess in the networks to produce electricity. However, because urban drinking water networks are complex systems in which flows and pressure vary constantly, identification of the ideal locations for turbines is not straightforward, and assessment implies the need for simulation. In this paper, an optimization algorithm is proposed to provide a selection of optimal locations for the installation of a given number of turbines in a distribution network. A simulated annealing process was developed to optimize the location of the turbines by taking into account the hourly variation of flows throughout an average year and the consequent impact of this variation on the turbine efficiency. The optimization is achieved by considering the characteristic and efficiency curves of a turbine model for different impeller diameters as well as simulations of the annual energy production in a coupled hydraulic model. The developed algorithm was applied to the water supply system of the city Lausanne (Switzerland). This work focuses on the definition of the neighborhood of the simulated annealing process and the analysis of convergence towards the optimal solution for different restrictions and numbers of installed turbines

Turbinage des eaux usées, quel potential pour la Suisse?

Une évaluation du potentiel de turbinage sur les systèmes d’eaux usées en Suisse a été réalisée au Laboratoire de Constructions Hydrauliques (LCH) en collaboration avec le bureau e-dric.ch. Le potentiel hydroélectrique de chaque STEP a été calculé et complété par une analyse de rentabilité pour chacun des sites identifiés, ce qui a permis d’identifier 19 sites potentiellement rentables. L’étude de différents scénarios d’évolution de l’assainissement fait apparaitre 31 nouveaux sites rentables dans le futur

Energy production with a tubular propeller turbine

Micro-hydropower is a way of improving the energetic efficiency of existent water systems. In the particular case of drinking water systems, several studies have showed that pressure reducing valves can be by-passed with turbines in order to recover the dissipated hydraulic energy to produce electricity. As conventional turbines are not always cost-effective for power under 20 kW, a new energy converter is studied. A five blade tubular propeller (5BTP), assessed through laboratorial tests on a reduced model with a diameter of 85 mm diameter and a maximal output power of 300 W, is addressed in this work. Having showed promising potential for further development, since global efficiencies of around 60% were observed, the turbine has been further used to estimate the potential for energy production in a real case study. A sub-grid of the drinking water system of the city of Lausanne, Switzerland, has been used to obtain an annual energy production through hourly simulations with several turbines

Intervention concepts for energy saving, recovery and generation from the urban water system

There are numerous options for energy measures in the water sector ranging from water conservation and process efficiency improvements to new technologies and redesigning water systems. Next to energy efficiency improvements, there is a need for new concepts in which water is viewed as a carrier of energy. Municipal wastewater is a potential source of chemical energy, i.e. organic carbon that can be recovered as biogas in sludge digestion. Even more so, domestic (waste)water is a source of thermal energy. And in areas with altitude differences, installing micro-hydro technologies in water distribution systems can convert energy from the pressure and flow into electricity. This report presents intervention concepts for energy saving, recovery and generation from the urban water system. Summarised, the main outcomes of research undertaken at 9 case studies are: i) Algarve and Alcoy water supply system: by performing an energy audit, the most energy efficient operating scheme can be determined. ii) Oslo and Amsterdam water cycle: the thermal energy recovery potential from wastewater is large, and it is in particular feasible if coupled to aquifer thermal energy storage systems. iii) Schiphol and Athens wastewater treatment: the energy generation at wastewater treatment plants through biogas can be enhanced by co-digestion and thermophilic digestion. iv) Lanhirano, Athens and Algare water supply system: in a water distribution system, water and energy can be saved by integrating pressure and energy management., i.e. by installing micro-turbines.Frijns, J.; Monteiro, A.; De Graaff, M.; Carriço, N.; Covas, D.; Cabrera Marcet, E.; Lausund, E.... (2014). Intervention concepts for energy saving, recovery and generation from the urban water system. http://hdl.handle.net/10251/4662

Opportunity and Economic Feasibility of Inline Microhydropower Units in Water Supply Networks

Small-scale hydropower is emerging as a decentralized source to satisfy local demand for electricity. In water supply systems, microhydropower can be used for energy recovery associated with excessive pressure control. However, there is a lack of specific solutions for applications within networks where discharges are highly variable and there are limitations of pressure. An arrangement of microturbines specially conceived for water supply networks is proposed, based on a recently tested microturbine for inline installation in pipes. The installation of up to four turbine units is possible within a buried chamber created around an existing pipe. The location of the chambers is analyzed using an optimization algorithm that considers two objective functions: energy production and economic value. The feasibility of the proposed arrangement for a microhydropower plant was assessed through a case study of a subgrid of the water supply network of Lausanne, Switzerland. A detailed analysis of the cost breakdown revealed that further to the electromechanical equipment, the number of isolation valves required in each layout may have an important role on the investments