Empowering Smart Renewable Cities through Hydropower Technology in Urban Drinking Water Supply Systems ^†

Abstract

Nowadays, the need to improve the efficiency and sustainability of cities is crucial. Considering that the urban water cycle is one of the most energy-demanding services, it is essential to find ways of management that minimize the use of resources and provide an environmentally friendly supply. To tackle this issue, pressure management within water distribution systems is an effective method for reducing energy consumption. LIFE TURBINES aims to address this challenge by implementing turbine systems that recover energy and regulate pressure in drinking supply networks, thus contributing to cities with low greenhouse gas emissions.

1. Introduction

Our economy still relies heavily on non-renewable sources of energy, the main culprits behind greenhouse gas (GHG) emissions that are thus directly responsible for climate change. The energy consumption of water distribution systems accounts for 7% of the global energy intake [1]. In many municipalities, water distribution and treatment services can represent up to 30–40% of the energy consumption, becoming a significant source of GHG emissions. Furthermore, this figure is expected to increase in the next 25 years in all regions of our planet. Immediate, rapid, and large-scale reductions in GHG emissions and net zero CO₂ emissions can limit climate change and its effects.

In this context, it is essential to increase the energy efficiency of all production and distribution processes, starting with drinking water distribution. The LIFE TURBINES project proposes harnessing the energy currently dissipated in potable water supply networks by leveraging the variation in flow rates and pressures at certain points within the network. The project is carried out by a multidisciplinary consortium formed by 10 entities, 4 of them belonging to the Global Omnium group: Aguas de Valencia S.A. (AVSA), as the project coordinator; Empresa Mixta Valenciana de Aguas S.A. (EMIVASA); Empresa Mixta Metropolitana S.A. (EMIMET); Empresa Municipal Serveis Publics S.A. (Aigües de Tortosa); the Tortosa City Council; Instituto Tecnológico de la Energía (ITE); AeioLuz energy cooperative; the European Innovation Network (REDINN); Acquedotto del Fiora S.P.A.; and the Polytechnic University of Marche.

2. Materials and Methods

In conventional practice, issues of excessive pressure are typically addressed through the installation of pressure-reduction valves or other control devices, wherein the surplus pressure is dissipated in the form of heat, resulting in energy wastage across numerous points in the networks [2]. The following graph illustrates how water pressure is controlled and regulated in the water supply network of the city of València and its metropolitan area from the Supply Control Center located in Vara de Quart (València).

In Figure 1, the red dashed line represents a hypothetical system pressure in the absence of the supply control center. During off-peak hours, the pressure would be excessively high, leading to leaks and pipe breaks. Conversely, during peak demand periods, some areas would experience inadequate pressure. The dataset represented by a blue line represents the demand curve of the system. This demand curve presents a modulation characterized by three consumption peaks, corresponding to the morning peak, a second peak at midday coinciding with lunchtime, and the third peak toward the end of the day. A green line represents the purpose of the supply control center. Through the regulating elements located in the network, the control room operators are responsible for maintaining the pressure as stable as possible, considering all the variations in consumption that occur daily in the network.

In the last decade, equipment generally known as PATs (pumps as turbines) or turbines have appeared on the market, allowing the surplus energy dissipated in supply networks to be used while helping to regulate pressure, without compromising the supply [3]. This equipment uses the potential energy of the water between two points at different piezometric heights (the sum of the potential energy and the gauge pressure) and transforms it into mechanical energy. This transformation is carried out by means of the mass of water in movement circulating inside the pipes. In turn, the mechanical energy produced in the turbine shaft, coupled to an electric generator, is transformed into electrical energy. Although these technologies have been extensively proven in cases with nearly constant flow rates and pressures, the same cannot be said for integrated systems within distribution systems with varying flow rates and pressure setpoints over time. In such scenarios, the development of system selection, design, and regulation is less advanced both theoretically and in application to real-world cases [4]. In this regard, LIFE TURBINES aims to transcend mere energy recovery applications, maximizing the long-term production potential of these machines. This approach seeks to enhance the hydraulic and electrical regulation of these devices, with a view toward maximum replicability in pressurized networks exhibiting flow and pressure variability.

The goal of LIFE TURBINES is to develop a methodology facilitating intelligent energy recovery alongside machine efficiency optimization while promoting renewable energy production within drinking water supply networks. This initiative aims to establish it as a sustainable, autonomous, and decentralized technology capable of addressing the energy consumption needs of the population. This will be made possible through the development of a digital tool for turbine and PAT selection and sizing. This tool will ensure operational modes for delivering the maximum available energy in real time between points with varying demands. Additionally, it will assist managers or promoters of such technologies in selecting the most suitable commercial hydroelectric system for installation and defining the most profitable exploitation model.

3. Results

The LIFE TURBINES project has its origins in several studies carried out within the framework of the Aguas de Valencia Chair linked to the improvement of the energy efficiency of the supply network through the use of PATs, in various supply systems operated by Global Omnium [4]. These studies were intended to move away from the conventional applications of PATs and turbines in supply networks. The work led to the installation of a 24 kWh turbine in the supply network of the city of Valencia, positioning Global Omnium at the forefront of the installation of turbines that take advantage of pressure changes in the network, applying time-varying regulation setpoints, and also as a pioneer due to its characteristics and great potential. The flow of water that the turbine continuously transfers is adjusted according to demand and reduces the service pressure to the needs of the supply at any given moment, leaving the regulating valve in the main pipe to compensate for the rest. The energy generated is currently used to power an electric vehicle charging station and a refrigerated fountain. The energy produced is equivalent to the consumption in 66 homes. These figures represent 6.45 Tn CO₂eq avoided per day.

LIFE TURBINES will catalyze the deployment of energy recovery installations in large-scale drinking water networks, applying different case studies with different flow rates, pressure jumps, type of turbine to be used, and even the use of the final energy consumption. The aim is to demonstrate that hydroelectric energy can be produced at any point at which there is a pressure difference and that its use in supply networks within cities is possible. The project will be carried out in four different locations in Spain and Italy.

3.1. Tortosa

In the La Ribera sector in Tortosa (Catalonia, Spain), there is currently a pressure reducing valve that will be replaced by a turbine to take advantage of the energy dissipated and act as a regulating element for the network. It is planned that a participatory process will be developed in schools in which students will be able to decide how the energy generated in this case study will be used.

3.2. València

The second case study is in the city of València (Spain), where action will be taken in several hydraulic sectors. 9 of the 10 points will have an average power of 1 KWh, the tenth point will have an average power of 4 KWh. Moreover, the regulation valve located in the Benimàmet neighborhood will be replaced by a turbine capable of generating almost 4 kWh of power, which will be used for the installation’s own self-consumption.

3.3. Scansano

Scansano is a municipality in the province of Grosseto, in the Italian Tuscany region, with a population of about 4600 inhabitants. In the supply network of this municipality, there is an existing control valve that will be replaced by a turbine that exploits the electrical potential by generating almost 43 kWh of energy. The existing valve is located in a rural area surrounded by agricultural estates, farms, and wineries. The energy generated by the turbine will be used to consolidate an energy community that will feed the surrounding rural establishments and agro-tourism businesses.

3.4. Metropolitan Area of València

The metropolitan area of Valencia (Spain) is made up of 48 municipalities surrounding the city. In this area, there are large changes in flow and pressure. Precisely in the area near the International Trade Fair, the hydraulic jump makes it possible to install a turbine to regulate the pressure and use the energy generated to recharge electric vehicles. Considering the characteristics of the point, 74 kWh of power is expected to be generated. This energy will be used for the installation of electric vehicle charging points and, when the chargers are not being used, the energy will be used for the self-consumption of the supply system.

4. Conclusions

Society at large is facing a medium to long-term process that will progressively manifest the effects of climate change. Mitigation responses will hardly be adequate and effective without the active participation of the people and communities affected or capable of responding to the risks identified. In this sense, the mitigation processes must include appropriate formulas that allow the involvement of society in the diagnosis, the definition of objectives, the identification or design of measures, their implementation, and the evaluation of the process. LIFE TURBINES aims to demonstrate that all changes, no matter how small, add up in the transformation of cities. The potential of hydropower and its use in supply networks within cities is possible, cost effective, and sustainable, and hydropower need not exclusively be obtained from large dams or reservoirs. Contributing to the transformation of our cities is a commitment that lies in the hands of all citizens.