Apparently this has been going on since 2016. I don't know how I missed it, usually I'm on top of everything solar and nautical. I've written no small amount in the past about the unique suitability of watercraft for pure, direct solar power of their propulsion motors.
The 2018 race spanned three days, all of which will be seen here. I became aware of it by searching for examples of small, fast solar powered boats because of my interest in a project 
Taking place between July 12 and July 14, the race proceeded according to this programme. The winners of the various classes are listed here. The modern solar boat races in Monaco are a continuation of a local motorboat racing tradition stretching back to 1901.
There were different classes for one, two and three seater watercraft. Some of the most successful, or at least the quickest, were hydroplaning boats that lifted themselves up out of the water on what amounted to water skis. This decreased the surface area in contact with the water, which in turn decreased drag.
The challenge, then, was generating enough power to hydroplane. That's no trivial task. The emergence of hydroplaning solar electric boats signifies a leap forward for clean energy watercraft technology. Perhaps one day I'll build myself a solar electric hydroplaning boat for use up at the lake. :)
Stay Cozy!