Thermal methods require energy, it seems like this substrate is effective at maintaining its solar-thermal absorbing properties better than a material that will attract salts

> Testing their solar-thermal desalination technique using samples of water from the Pacific, Atlantic, and Indian Oceans, Guo and his team were able to make the surface self-cleaning. In other words, it extracted freshwater and directed the remaining salts to the passive region where they could be later collected without reducing the panel’s efficiency.

This is not "large" this is a moderate improvement. Albedo is likely only marginally affected, and the solar power input over area is the same.

Depending on this cost of this process it could very likely be a wash in terms of NPV