Analyses of possible synergies between energy recovery and water management are essential for achieving sustainable improvements in the performance of irrigation water networks. Improving the energy efficiency of water systems by hydraulic energy recovery is becoming an inevitable trend for energy conservation, emissions reduction, and the increase of profit margins as well as for environmental requirements. This paper presents the state of the art of hydraulic energy generation in drinking and irrigation water networks through an extensive review and by analyzing the types of machinery installed, economic and environmental implications of large and small hydropower systems, and how hydropower can be applied in water distribution networks (drinking and irrigation) where energy recovery is not the main objective. Several proposed solutions of energy recovery by using hydraulic machines increase the added value of irrigation water networks, which is an open field that needs to be explored in the near future.Keywords: irrigation water networks; water-energy nexus; renewable energy; sustainability and efficiency; hydropower solutions; water management Hydropower GenerationSociety's energy consumption worldwide has increased by up to 600% over the last century. This increase has been a direct result of population growth since the industrial revolution, in which energy has been provided mainly by fossil fuels. Nevertheless, today and in the near future, renewable energies are expected to be more widely implemented to help maintain sustainable growth and quality of life and, by 2040, to reduce energy consumption down to the 2010 levels [1].Sustainability must be achieved by using strategies that do not increase the overall carbon footprint, considering all levels of production (macro-and microscale) of the different supplies. These strategies' development has to be univocally linked to new technologies [2]. Special attention must be paid to those new strategies that are related to energy recovery. These new techniques have raised interesting environmental and economic advantages. Therefore, a deep knowledge of the water-energy nexus is crucial for quantifying the potential for energy recovery in any water system [3], and defining performance indicators to evaluate the potential level of energy savings is a key issue for sustainability, environmental, or even management solutions [4].Energy recovery, with the aim of harnessing the power dissipated by valves (in pressurized flow) or hydraulic jumps (in open channels), is becoming of paramount importance in water distribution

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Abstract:Water irrigation systems are required to provide adequate pressure levels in any sort of network. Quite frequently, this requirement is achieved by using pressure reducing valves (PRVs). Nevertheless, the possibility of using hydraulic machines to recover energy instead of PRVs could reduce the energy footprint of the whole system. In this research, a new methodology is proposed to help water managers quantify the potential energy recovering of an irrigation water network with adequate conditions of topographies distribution. EPANET has been used to create a model based on probabilities of irrigation and flow distribution in real networks. Knowledge of the flows and pressures in the network is necessary to perform an analysis of economic viability. Using the proposed methodology, a case study has been analyzed in a typical Mediterranean region and the potential available energy has been estimated. The study quantifies the theoretical energy recoverable if hydraulic machines were installed in the network. Particularly, the maximum energy potentially recovered in the system has been estimated up to 188.23 MWh/year) with a potential saving of non-renewable energy resources (coal and gas) of CO 2 137.4 t/year.

The use of pumps working as turbines (PATs) connected to the electric system, in the replacement of pressure reduction valves to reduce the excessive pressure in water distribution networks, have been studied for the last years. The introduction of PATs is very important in the water-energy nexus to promote the increase of the energy savings. As consequence, the majority of the water systems does not have access to the electrical grid and, therefore, the need to study the PATs operation off-grid is necessary. In this line, the novelty of this research is the application and optimization of a PAT in water systems when the recovery solution is off-grid type. To operate correctly, the induction machine requires an external source of reactive power, which is typically provided by the electrical grid. To supply the required reactive power, a bank of capacitors is installed at the machine terminals, so-called self-excited induction generator (SEIG). The analytical model, simulation and experimental works were performed, to analyse the SEIG behaviour. The results were applied in a SEIG-PAT system obtaining the global efficiency of the system for different speeds and loads. The global efficiency decreases 47% when off-grid operation, showing the need to optimize the electrical parameters of the generator to operate as off-grid with acceptable efficiency levels. In this framework, a tuning methodology for the SEIG capacitor bank values was developed to be automatically adjusted according to the operating point of the PAT to maximize its efficiency.