CityUHK develops “Liquid Droplet Mops” for solar panel cleaning, saving over 80% of water globally each year
With the rapid expansion of the global solar energy industry, the number of solar panels has surged in recent years. However, dust and pollutants accumulating on panel surfaces can significantly reduce energy conversion efficiency while traditional cleaning methods are highly water-intensive.
In response to this challenge, an international research team led by the Department of Mechanical Engineering at City University of Hong Kong (CityUHK) has successfully developed a breakthrough technology, called “Liquid Droplet Mops”, which only uses a minimal amount of water to effectively remove dust and pollutants from solar panel surfaces, significantly enhancing cleaning efficiency while conserving water.
The study was led by Professor Steven Wang, Associate Vice-President (Resources Planning) and Associate Professor in the Department of Mechanical Engineering and the School of Energy and Environment. The project was conducted in collaboration with Professor Omar Matar from the Department of Chemical Engineering at the Imperial College London. The findings were published in the prestigious journal Nature Sustainability.
High‑pressure liquid jets are commonly used to clean solar panels, but they require an enormous amount of water, globally exceeding 12 billion gallons per year. The research team discovered that cleaning efficiency depends on droplet energy in a non‑monotonic manner, meaning that stronger impact does not necessarily yield better cleaning efficiency; instead, optimal cleaning performance occurs at moderate energy levels rather than maximum force.
The innovative “Liquid Droplet Mops” technology precisely controls droplet impacts to effectively remove contaminants from solar panel surfaces, achieving a particle removal efficiency of up to 99.9%. It successfully tackles the challenge of high-density dust, including heavy particles with densities 6–10 times greater than water. Compared to conventional methods, this approach reduces water usage by 6–10 times, potentially reducing the total annual water consumption required for global solar panel cleaning by more than 80%.
The technology leverages the physics of droplet spreading and recoiling upon impact with the panel surface, generating targeted hydrodynamic forces that drag and lift pollutants away. This breakthrough is particularly promising for large-scale solar farms in arid desert regions, alleviating water stress and enhancing the sustainability and viability of renewable energy deployment worldwide.
Professor Wang explained that the technology draws inspiration from natural phenomena, such as butterfly wings and plant leaves, which achieve self-cleaning through raindrop impacts. “We hope this groundbreaking technology will help conserve global water resources, improve the efficiency of renewable energy utilisation, and ultimately generate significant economic and environmental benefits,” he said.
He added that this is a simple yet highly impactful research outcome. It not only validates a new cleaning mechanism but also provides important insights for future engineering design of solar panel cleaning devices.
Lo Wai-kin, one of the research team members and a PhD student in the Department of Mechanical Engineering at CityUHK, explained that they tested droplets repeatedly using sand particles of various sizes to simulate actual desert conditions. The study found that within the typical range of sand particles sizes deposited on solar panels, droplet impact can effectively coalesce and remove the particles, enabling each droplet’s impact energy to be more efficiently utilised to carry away contaminants, resulting in a highly effective and stable cleaning mechanism.
Amid major global environmental challenges, including the clean energy transition and water scarcity, CityUHK remains committed to developing innovative technologies that offer practical solutions to address global issues. As this technology advances toward broader promotion and application, it will contribute significantly to achieving more sustainable and efficient use of renewable energy.
Media enquiries:
Him Chak, Communications and Institutional Research Office, CityUHK (Tel: 3442 6807)
In response to this challenge, an international research team led by the Department of Mechanical Engineering at City University of Hong Kong (CityUHK) has successfully developed a breakthrough technology, called “Liquid Droplet Mops”, which only uses a minimal amount of water to effectively remove dust and pollutants from solar panel surfaces, significantly enhancing cleaning efficiency while conserving water.
The study was led by Professor Steven Wang, Associate Vice-President (Resources Planning) and Associate Professor in the Department of Mechanical Engineering and the School of Energy and Environment. The project was conducted in collaboration with Professor Omar Matar from the Department of Chemical Engineering at the Imperial College London. The findings were published in the prestigious journal Nature Sustainability.
High‑pressure liquid jets are commonly used to clean solar panels, but they require an enormous amount of water, globally exceeding 12 billion gallons per year. The research team discovered that cleaning efficiency depends on droplet energy in a non‑monotonic manner, meaning that stronger impact does not necessarily yield better cleaning efficiency; instead, optimal cleaning performance occurs at moderate energy levels rather than maximum force.
The innovative “Liquid Droplet Mops” technology precisely controls droplet impacts to effectively remove contaminants from solar panel surfaces, achieving a particle removal efficiency of up to 99.9%. It successfully tackles the challenge of high-density dust, including heavy particles with densities 6–10 times greater than water. Compared to conventional methods, this approach reduces water usage by 6–10 times, potentially reducing the total annual water consumption required for global solar panel cleaning by more than 80%.
The technology leverages the physics of droplet spreading and recoiling upon impact with the panel surface, generating targeted hydrodynamic forces that drag and lift pollutants away. This breakthrough is particularly promising for large-scale solar farms in arid desert regions, alleviating water stress and enhancing the sustainability and viability of renewable energy deployment worldwide.
Professor Wang explained that the technology draws inspiration from natural phenomena, such as butterfly wings and plant leaves, which achieve self-cleaning through raindrop impacts. “We hope this groundbreaking technology will help conserve global water resources, improve the efficiency of renewable energy utilisation, and ultimately generate significant economic and environmental benefits,” he said.
He added that this is a simple yet highly impactful research outcome. It not only validates a new cleaning mechanism but also provides important insights for future engineering design of solar panel cleaning devices.
Lo Wai-kin, one of the research team members and a PhD student in the Department of Mechanical Engineering at CityUHK, explained that they tested droplets repeatedly using sand particles of various sizes to simulate actual desert conditions. The study found that within the typical range of sand particles sizes deposited on solar panels, droplet impact can effectively coalesce and remove the particles, enabling each droplet’s impact energy to be more efficiently utilised to carry away contaminants, resulting in a highly effective and stable cleaning mechanism.
Amid major global environmental challenges, including the clean energy transition and water scarcity, CityUHK remains committed to developing innovative technologies that offer practical solutions to address global issues. As this technology advances toward broader promotion and application, it will contribute significantly to achieving more sustainable and efficient use of renewable energy.
Media enquiries:
Him Chak, Communications and Institutional Research Office, CityUHK (Tel: 3442 6807)