Building-integrated solar tube-driven membrane distillation for rooftop potable water production

Overview

This solution integrates hollow fiber vacuum membrane distillation (HF-VMD) directly inside evacuated solar tubes, creating a compact, building-integrated system for rooftop potable water production. Conventional solar thermal water treatment systems rely on physically separated solar collectors and treatment modules, requiring heat exchangers and complex plumbing that increase capital cost, footprint, and complexity. By coupling two proven technologies—evacuated tube solar collection and membrane distillation—into a single unit, the system delivers a lower-cost, space-efficient alternative suited to factory and office rooftops in regions with water shortages and high solar radiation. Prototype testing has demonstrated permeate production of approximately 8 litres per square meter per hour, with a levelized cost of water around $40 per 1,000 US gallons, in line with major beverage industry targets.

Technical specifications

• Integrated design: Hollow fiber membranes submerged directly inside evacuated solar tubes, eliminating the need for separate heat exchangers and complex plumbing.
• Vacuum membrane distillation: Uses a vacuum on the permeate side to drive vapor flux across the hydrophobic hollow fiber membrane, enabling operation at lower temperatures than conventional distillation.
• Solar thermal drive: Evacuated tubes capture solar radiation and convert it to thermal energy, providing the heat source for distillation and reducing external energy requirements.
• Transient solar handling: Designed membrane distillation configurations manage variable solar conditions throughout the day, maintaining stable performance under fluctuating irradiance.
• Performance targets: Salt separation below 200 mg/L and total dissolved solids below 500 mg/L, meeting EPA drinking water standards.
• Compact footprint: Single-unit integration reduces installation space, enabling deployment on building rooftops where conventional systems are impractical.
• Feedwater flexibility: Tested with realistic feedwater inputs under both steady-state and transient solar thermal conditions.

Technology readiness level

The technology has progressed through prototype validation, with peer-reviewed results confirming permeate flux and levelized cost of water performance consistent with industry benchmarks. A pilot-scale ST-VMD module is planned for construction and testing against EPA drinking water standards, including salt separation and small organics fate. Subsequent tasks will generate normalized performance curves as a function of solar irradiance, flow rate, and ambient temperature, followed by a techno-economic feasibility study extrapolating findings to commercial-scale deployment at industrial facilities. The system is positioned for pilot trial engagement and co-development with an industrial manufacturing partner to enable production at scale.