Design and Evaluation of a PV-Direct DC Surface Pumping System for Multi-Storey Residential Water Supply in Uzbekistan

Rapid urbanization and rising electricity costs are putting pressure on legacy water supply systems in Central Asian apartment buildings. Today, many dwellings rely on small flat-level booster pumps, which raise lifecycle costs, create noise, and increase the risk of uneven or interrupted service. This paper introduces a PV-direct DC surface multistage pumping architecture combined with rooftop storage tanks and N+1 duty-rotation for reliability. The approach eliminates inverters and batteries, reducing complexity while shifting pumping loads directly to solar power. A three-objective optimization problem is formulated— daily energy use, lifecycle cost, and PV area—subject to hydraulic constraints of ≥30 m head and ≥34 m<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>/day demand. The problem is solved using the Non-dominated Sorting Genetic Algorithm II (NSGA-II). A case study of a four-storey, 48-apartment building in Jizzakh (43 occupied) demonstrates that the centralized PV-direct design can cut electricity use by over 95% and reduce annual costs from 11.6 million UZS to under 0.3 million UZS. At the same time, duty-rotation and automatic switchover improve service continuity. The study also provides pump datasets, sizing equations, and guidelines for controller and reservoir operation. The results suggest that PV-direct pumping is a practical option for engineers and policymakers in regions with high solar potential, offering a path toward reliable water supply and renewable energy integration.

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