White walls inside basin type solar still

The first prototype solar water still, simple basin type, was tested recently:

https://bkhome.org/news/201911/first-test-basin-type-proto-1.html

And the inside was coated with black silicone (except for some grey patching, and the photo below also shows some reflected clouds):

What has nagged at me though, is why are the side walls coated black? Because that is the way it is done in all the designs that I have seen so far!

This morning, I typed some appropriate keywords into Google search engine, to see if there are any arguments for a different colour, such as white, or even a reflective surface. Got hits!

OK, it seems that the rationale for painting the side walls black is to prevent condensation on the walls.

However, that also means the walls will absorb heat, and will need to be extremely well insulated. In my prototype, they are not.

I found a couple of research papers, where the authors painted the sides white, down to the water level:

https://www.sciencedirect.com/science/article/pii/S2213020916300453

https://scholar.google.com/scholar_lookup?title=Improved%20solar%20still%20for%20water%20purification&publication_year=2012&author=C.%20Tenthani&author=A.%20Madhlopa&author=C.Z.%20Kimambo

...the second author is claiming an efficiency improvement of 6.8% when the side walls are coated white.

There are a lot of variables in this analysis, but I reckon that I will go for white walls in prototype #2. 

Tags: nomad