Predictive modeling and validation of water in glass evacuated tube solar heaters

Mendoza Orbegoso E.M.; Alva Alcántara J.; Julca Verástegui L.; Asto-Rodriguez E.; Bengoa Seminario J.C.; Leiva Calvanapón Y.; Silvera Otañe J.; Marcelo-Aldana D.; La Madrid Olivares R. · Solar Energy (2026) · DOI: 10.1016/j.solener.2025.114125

Resumen

This research work presents a predictive modeling and validation framework for water-in-glass evacuated-tube solar water heaters that couples (i) a shading-aware, array-level incident-energy model parameterized by tube spacing B and tilt β, with (ii) CFD-derived thermosiphon correlations that include an explicit tilt factor. These models coupled to fundamental conservation equations of mass and energy and heat transfer formulations to develop a predictive numerical tool implemented in an open Python tool (SolarTherm Designer) to enable transparent, location-specific parametric sweeps. Field validation was conducted on a Peruvian coastal city by comparing a geometry-optimized prototype (30 tubes, B=116mm, β=15∘) with a commercial unit of the same tube count (B=84mm, β=25∘, tube diameters and length were identical in both systems. Performance was assessed using an energy-based interval efficiency ηk=Eu/Ein over synchronized ±15 min windows and a daily efficiency ηday. Across three test days, the prototype achieved ηday values of 0.666, 0.736, and 0.741 versus 0.590, 0.640, and 0.624 for the commercial system, i.e., 13%–19% relative gains at constant tube count. The results demonstrate that coupling shading physics and tilt-explicit thermofluidic correlations in a reproducible tool can guide geometry (B,β) to deliver measurable gains without changes in tube technology or the use of concentrators or additives.

Instituciones: Universidad Nacional de Trujillo; Universidad de Piura