Ambient Water-enabled Energy Harvesting for Novel Smart Window System

Abstract

With increasing global energy consumption and climate concerns, building energy efficiency particularly through windows is critical. Smart window (SW), which possesses dynamic opto-thermal regulation, offers significant potential in building energy saving. Among all, electric-responsive SWs are ideal candidate for modern buildings due to their rapid response, on-demand regulation, and integrability. However, their reliance on external power for transmittance changes makes their universal applicability challenging. Although immense progress has been made in developing self-powered smart windows based on environmental energy harvesting technologies such as triboelectric nanogenerator (TENG) or photovoltaics, they suffer from fundamental limitations such as requirement of external force input, poor durability or environmental pollution. This thesis proposes harvesting ambient water-enable energy—from raindrops to atmospheric moisture—to achieve fully self-powered smart windows, addressing limitations of existing self-powered smart windows.

Here, we first develop a fully self-powered smart window by integration of the droplet-based electricity generator (DEG) for extracting energy from abundant rainwater. Distinct from the traditional self-powered approaches, our DEG allows for the spontaneous and ecofriendly energy harvesting from environment. Driven by DEG, the liquid crystal (LC) based SW exhibits rapid response and high transmittance regulation between the transparent and hazy states, both stable without power, and can be reversibly switched by gentle pressure.

World climates present alternating sunny/rainy periods. For all-weather operation,
a droplet-solar hybrid generator (DSEG) is adopted to develop self-powered smart window system. The DSEG, combining a solar cell with DEG structure, allows for hybrid energy harvesting from droplet/solar to drive smart window regardless of whether restrictions. The resulting smart system achieves 51% visible and 25% NIR light modulation, yielding notable indoor temperature regulation, and supports privacy protection applications in energy-free mode.

Facing arid environment, we propose a novel approach by fusing atmospheric water collection technology and droplet-based electricity generator to develop self-powered smart windows, enabling operation of SW even in low-humidity conditions. Based on adsorbents, a liquid-repellent but breathable PTFE framework with an interfacial solar module was developed as atmospheric water collector, which can effectively convert atmospheric water into liquid water. Through a flow regulator, we achieved tunable fluidic parameters of droplets that contacts the DEG surface for on-demand electrical output. The integrated SW simultaneously collects water and generates electricity, offering solutions for sustainable buildings or agricultural settings, especially in arid areas.

We believe that the design and methods of integrating water energy harvesting and smart window can open new path and provide certain foundation for their application in energy-efficient buildings, smart agriculture, and beyond.

Date of Award	8 Oct 2025
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Steven WANG (Supervisor) & Zuankai Wang (External Co-Supervisor)