Energy Efficiency and Stability of Micro-Hydropower PAT-SEIG Systems for DC Off-Grids

João M. R. Catelas, João F. P. Fernandes (), Modesto Pérez-Sánchez, P. Amparo López-Jiménez, Helena M. Ramos () and P. J. Costa Branco
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João M. R. Catelas: Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal
João F. P. Fernandes: IDMEC, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal
Modesto Pérez-Sánchez: Hydraulic and Environmental Engineering Department, Universitat Politècnica de València, 46022 Valencia, Spain
P. Amparo López-Jiménez: Hydraulic and Environmental Engineering Department, Universitat Politècnica de València, 46022 Valencia, Spain
Helena M. Ramos: Department of Civil Engineering, Architecture and Environment, CERIS, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal
P. J. Costa Branco: IDMEC, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal

Energies, 2024, vol. 17, issue 6, 1-25

Abstract: Using pumps operating as turbines (PATs) offers the possibility of increasing the sustainability of water and energy systems by recovering the excess energy that would be otherwise lost in pressure-reducing valves or head loss chambers. Regarding on-grid applications, there have been many research works, and PATs have been implemented in several ways. However, more research still needs to be done on optimizing the efficiency and stability of PATs operating in off-grid systems. This work contributes to the development of stable direct current (DC) off-grid electric systems based on PATs using a self-excited induction generator (SEIG). In this context, a methodology is proposed, based on the hydraulic, mechanical, and electric subsystems, to define the PAT-SEIG operational area to maximize energy conversion and system efficiency. These limits depend highly on the capacitor value, rotational speed, and electric load. In addition, an analytical model is proposed to estimate the PAT-SEIG operation under specific conditions. With this, water managers can design and optimize an off-grid PAT-SEIG system and define the best hydraulic machines, electronic equipment, and control elements to maximize energy conversion within the target of operational limits. Two micro PAT-SEIG setups were implemented in the hydraulic laboratory of IST/CERIS under typical operating conditions to validate the proposed methodology. The system’s maximum efficiency and operational limits can be adapted using different capacitor values for the excitation of the SEIG. Considering the nominal efficiencies of the system’s components, the maximum p.u. efficiency obtained for each PAT-SEIG system was between 0.7 and 0.8 p.u.

Keywords: energy efficiency; micro-hydropower; pump-as-turbine (PAT); off-grid; self-excited induction generator (SEIG); water–energy nexus (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2024
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