Liquid droplet mops

Surface contamination is pervasive across various industrial systems, especially photovoltaic systems, and degrades system performance. Cleaning practices are essential to tackle this problem but remain water intensive due to low water utilization efficiency, particularly in photovoltaic fields. Here we found that cleaning efficiency depends non-monotonically on the water droplet energy and can be maximized for intermediate droplet energy values, which can be utilized to improve water utilization efficiency in surface cleaning. Our experiments and theory demonstrate that particulate removal mechanisms are governed by droplet impact velocity and particle–droplet interfacial interactions. This mechanism enables removal of contaminants with varied densities from superhydrophobic surfaces. Leveraging this mechanism, we developed the ‘liquid droplet mops’ method to efficiently clean superhydrophobic-coated solar panels, achieving 99.9% removal with only 10% of the water consumption of standard liquid jets. Our findings not only advance the fundamental understanding of surface cleaning but also offer a simple yet efficient water-saving strategy for surface cleaning in the water-scarcity context. © The Author(s), under exclusive licence to Springer Nature Limited 2026.