Appropriate-technology pyramid solar still: Experimental performance and TRNSYS validation

Abstract

Water scarcity remains a global challenge that directly affects rural communities. The objective of this study is to design, build, and validate a pyramid-shaped solar distiller using appropriate technology for the decentralized supply of fresh water in Bucaramanga, Colombia. We combined a nine-day experimental campaign (April 1-9, 2025) with a TRNSYS (Type 66a-EES) simulation, evaluating two simulation models: a simplified energy balance model (MS01) and a variant that includes the efficiency of the Hottel-Whillier-Bliss (HWB) collector (MS02). Ambient temperature, direct normal irradiance (DNI), and four internal temperatures were measured every five minutes with calibrated sensors during the experimental process. The prototype reached tank/steam temperatures of 42-49 °C and produced 225-750 ml/day, with a total of 3,861 ml; the peak of 750 ml on a day of low irradiance was due to thermal inertia and reduced losses. Both simulation models reproduced the thermal and production trends with relative errors between ±0.012 and ±0.040. The cumulative yield on April 9 was 3765 ml (?2.5%) for MS01 and 3995 ml (+3.5%) for MS02. In summary, MS01 adjusted the tank/steam temperature values slightly better, while MS02 improved the distillation output prediction and offers greater calibration potential through the HWB parameters (FR, UL, (??)e). The results indicate technical feasibility and scalability for rural contexts, and point to simple design improvements (sealing, leak control, thermal management) to increase daily production. Overall, passive desalination is a practical alternative.