So, this story comes from a paper in a reputable science journal, Angewandte Chemie
Reference: Q. Tang, X. Wang, P. Yang, B. He, Angew. Chem. Int. Ed. 2016, 55, 5243.
A Solar Cell That Is Triggered by Sun and Rain - Tang - 2016 - Angewandte Chemie International Edition - Wiley Online Library
(paywall, or talk to your local science librarian)
This story is based on real measurements in the laboratory. However, the time from laboratory study to adoption ranges from years to infinity (i.e. never happens), with the latter being more probable. It's a neat idea. It likely will never come to commercial fruition.
Some notes from the paper:
1.) The salt concentrations used for the rainwater solutions are significantly higher than regular rainwater.
The tests used solutions with a concentration of 0.6, 1.0 and 2.0 moles NaCl / litre water. The most dilute solution (0.6 moles NaCl / litre) requires ~36 g of salt (more than an ounce) dissolved in 4 cups of water. This is roughly the concentration of seawater.
In contrast, typical rainwater has a concentration of ~10 mg Na+ / litre (0.0004 moles NaCl / L), or a concentration about 1,500 times lower than the lowest concentration used for this text.
2.) The rainwater active surface is on the back-side of the solar panel: "On rainy days, the new solar cells can be reversed with [the] rGO film upward, creating current and voltage outputs under the persistent dropping of raindrops."
So, not conventional mounting
3.) The power output is low, on the order of picowatts. I'm not going to make a quantitative comparison to silicon photovoltaics, as power output should scale with area, and I don't know the area used for these studies.
I'm more excited about the science than I am the possible technology, but that's an occupational hazard for me. I'm a physical chemist with conventional silicon photovoltaics on my trailer