Variable-Speed Operation of Micro-Hydropower Plants in Irrigation Infrastructure: An Energy and Cost Analysis  
[PERSON]  
1 Department of Electrical Engineering, University of Oviedo, 33003 Oviedo, Spain; [EMAIL_ADDRESS] (A.B. ); [EMAIL_ADDRESS] (F.G.-G.)  
[PERSON]  
1 Department of Electrical Engineering, University of Oviedo, 33003 Oviedo, Spain; [EMAIL_ADDRESS] (A.B. ); [EMAIL_ADDRESS] (F.G.-G.)  
[PERSON]  
2 Department of Mathematics, University of Oviedo, 33003 O  
irrigation techniques has been increasing in recent years. For example, these techniques were being used on 72% of all irrigated cropland in the US in 2018 [7]. The use of these techniques has reached 100% in some Mediterranean countries [8]. This change has altered the electricity consumption profile in the agricultural sector. Renewable energies are a feasible alternative for covering the electricity needs of pressurised irrigation techniques, even in areas where no grid connection is available. Micro-hydropower plants can be used for this purpose. Hydropower is one of the most widely used renewable sources of electricity generation worldwide. In 2022, the global electricity production from hydropower was 11,300 (TWh) [9]. This represents 6.73% of global electricity generation and 47.38% of global power generation from renewable sources [9]. This technology uses a hydraulic turbine and an electric generator to convert potential energy into electrical energy. The size of the hydraulic turbine classifies the hydropower plant. It can vary from several kW to hundreds of MW [10]: small-scale, medium scale, and large-scale. Small-scale hydropower plants can be further classified into small (up to 10 (MW)), mini (up to 2 (MW)), micro (up to 100 (kW)) and pico (up to 5 (kW)) hydropower plants [10,11]. This classification depends on the country [12]. Micro-hydropower plants have been the subject of study in the European Union in the hopes of increasing the production of renewable energy from this type of hydroelectric power plant [13]. To this end, the RESTOR Hydro project (2012-2015) [14], co-funded by the European Union through the Intelligent Energy Europe Programme, identified and restored water mills, inoperative hydropower plants, dams, and irrigation structures. One of the results of the project was the RESTOR Hydro map [14]. This map shows the location and characteristics of 65,000 possible micro-mini hydropower plants. This web application is free to access and offers a user-friendly interface. The focus of this work is on micro-hydropower plants used in irrigation infrastructure. When micro-hydropower plants operate as part of the irrigation infrastructure, electricity generation is a secondary objective. In irrigation infrastructure, priority is given to the use of available water for crop irrigation. With these hydropower plants, the power plant is usually installed as a run-of-the-river system. Therefore, these hydropower plants do not interfere with river flows, making them an environmentally-friendly solution [15]. Micro-hydropower plants require a high initial investment and the estimated lifetime is several decades [16]. The latter characteristic is based on their hydropower potential, which depends on the hydrological regime and thus on local and regional climate characteristics [17]. The estimated lifetime is therefore vulnerable to the potential dangers of climate change. Some micro-hydropower plants have actually seen their lifespan truncated due to low rainfall. Most twentieth-century micro-hydropower plants were characterised by fixed-speed operation. As the electricity production of a micro-hydropower plant is directly dependent on the amount of water available, two key events occur with regard to the continued operation of a micro-hydropower plant if there ia a decrease in hydropower resources: (i) a dramatic decrease in electricity production over the entire water head range, and (ii) a noticeable decrease in efficiency in partial operation mode or in operation mode outside design conditions [18].