Innovation in Dealing with Drought
The idea of “shade balls,” i.e., black plastic balls that float on a body of water to minimize evaporation, is all over the news nowadays, especially as California comes up with increasingly innovative solutions to deal with its drought. But why black? I would think we would want the incident sunlight to be reflected rather than absorbed. What am I missing here?
Perhaps they figure that the black balls won’t send the heat back up into the sky, and wouldn’t have a large impact on the ozone?
No, you want the radiation to be reflected rather than absorbed (though, true, due to the “greenhouse” effect, some will be re-reflected back down to Earth).
It’s also true that the black balls will heat up the water beneath which will cause more evaporation.
I have to assume that someone has tested this to make sure it works in real-world conditions, but it’s a bit unclear how they chose this design.
My guess is that the black is down to carbon black being added to the plastic to make the balls UV resistant. Still, I would have thought that a mirrored finish would have been preferable.
Regards the plastic, I have seen comment elsewhere that the balls may not be 100% UV resistant, and that there may be a risk of contamination with chemicals and small particles wearing or leaching off the balls over time.
An alternative approach taken by flexiblesolutions is to spread a powder made of a water soluble bio-polymer WaterSavr™ which has been shown to reduce evaporation by 15% without adverse effects on water quality.
http://cts.businesswire.com/ct/CT?id=smartlink&url=http%3A%2F%2Fwww.flexiblesolutions.com%2F&esheet=51027426&newsitemid=20150127006196&lan=en-US&anchor=www.flexiblesolutions.com&index=2&md5=6990268a2e179172f2cb5eb19e022bdd
Incidentally, this same product is excellent at reducing humidity, heat requirement and water consumption at indoor swimming pools.
Why black was my first thought also for the same reasons as you had. The second thought was are they weighted so they stay right side up as it were or can the rotate and drag water along their surface which would evaporate. Not sure this is a good idea. I guess we’ll find out.
There is also a theoretical maximum associated with a single layer of balls (whose cross-sections are circles) arrayed on top of a flat surface. I’m having trouble calculating it, but it’s in the neighborhood of about 85%. I have a feeling that this is going to work very poorly in the real world.
The calculation would in fact be significantly more difficult as we are talking about the interaction of spheres – the black spheres on the lake, the large rotating sphere of the Earth and the even bigger sphere of the sun. That being the case, and California not being on the equator, the sun is not ever at 90 degrees to the lake surface.
The evaporation reduction would not be entirely down to the percentage of the lake covered as the balls would also tend to reduce wind speed at the lake surface.
The black spheres may increase the amount of heat absorbed by the lake, again hard to analyse due to the insulating effect of the air in the balls (I understand the balls are part filled with water for ballast)
My guess is that the water would in any case become warmer as a result of the loss of evaporative cooling – with consequences for oxygen content in the water.
I think it would be worth carrying out a controlled experiment on identical two swimming pools as near together as possible – monitoring temperature before and for several weeks after the balls are added.
I agree 100%. I’ll bet the gain, if there is one at all, will be far less than anticipated due to all these factors, especially hotter water.
Here are my calcs at the theoretical maximum of circles arrays on a flat surface (~ 97.45%): https://2getemp.files.wordpress.com/2015/08/scan0180.pdf
This is much higher than I expected. Did I do something wrong?