Power and Efficiency Investigation of Compressors as Turbines (CATs) for Pico-Hydropower Plants
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Keywords
Compressor as turbine (CAT), turbocharger, pico-hydropower application, output power, turbine efficiency
Abstract
This study investigates the power and efficiency performance of compressor as turbine (CAT) units for pico-hydropower applications using laboratory experiments under varying head conditions. Motivated by the increasing demand for low-cost, pico-scale hydropower (<5 kW) units and the limited availability of conventional turbines for remote areas, this work evaluates six nearly similar Garrett turbocharger compressors as turbines using different models with different sizes from a single compressor PC family (PC78US-6, PC130-7, PC200-6, PC300-6, PC400, and PC500) due to their geometric similarity to Francis-type turbines. The experiments were conducted using a pump-circulated test rig commonly used for assessing pico-hydroturbine-generator characteristics, with measurements of output power and efficiency at head levels of 6, 8, 10, and 12 m. The tests show that all CAT units exhibit a parabolic efficiency–rotational-speed relationship for a reaction turbine, with head-constant best-efficiency points (BEPs) ranging from 52% to 70%, occurring at a rotational speed range of 1750–2100 rpm and a discharge range of 0.004515–0.009442 m3/s. At a head level of 12 m, the smaller units (PC78, PC130, and PC200) reach turbine-individual maximum powers of 373–486 Watt with peak efficiencies of 60–65%, while the larger units (PC300-6, PC400, and PC500) achieve performances of 508–774 Watt with 67–70%. The results clearly suggest that the CAT characteristics are significantly influenced by runner size and hydraulic head. The resulting test graphs can serve as a practical guideline for selecting a PC-family compressor model for pico-hydropower sites based on the available water head and discharge, as well as on the specific rotational speed. Based on this study, low-cost, mass-produced turbocharger compressors used as turbine alternatives instead of a specially designed turbine have favorable prospects for inexpensive pico-hydropower systems.
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