Hi Steve.
Yes the scientific answer would be quite nice. Thanks.
DISCLAIMER: Do not read if you are not interested in solar panel cleaning (cos this might get boring!) or if you are just gonna argue with me at the end!
There are various types of glass, which is made in a whole host of ways. Some has a very rough finish, some has a very smooth finish. All look the same to the naked eye, but under a microscope, they look completely different.
Dirt accumulates on glass at a microscopic level to begin with, then gathers to the point where we can see it.
Self cleaning glass is either hydrophobic, meaning the water beads on it or it is hydrophilic, meaning the water sheets on the glass. Hydrophobic glass needs a very high static water contact angle in order to be self-cleaning effectively. Solar panels are hardly, if ever laid at this angle. So although the glass itself is self-cleaning and has the capability of being self cleaning, the angle it is laid at is often incorrect for the scientific process of self-cleaning to happen.
Why does hydrophobic glass not work?
To make glass hydrophobic, waxes or polymers need to be applied, which is a timely and costly process. The finish is often hazy which makes it unsuitable for the majority of windows.
What is hydrophilic glass?
Hydrophilic glass is coated with Titania which enables sunlight to chemically break down the dirt and then the rain washes it away. So, hydrophilic glass is the stuff to use then eh? No.
Why does hydrophilic glass not work?
It again is costly, which has held it back from commercial use. Secondly, the cleaning is a two stage process. You need photocatalysis and hydrophilicity to be present for the self-cleaning process to be activated. In order to accelerate both processes, university scientists are trying to develop substances to do just that. The technology is very much in its infancy and good quality products are at least 5 years from the market place.
It is the development of such products, specifically in the field of solar panels which we hope to shortly be involved in with some Welsh universities.
To conclude, there is self-cleaning glass on the market. However, it's functional use in solar panels is limited at best, which is great news for all of us!
Hope that gives a satisfactory answer to the question dd.