Here in Central New York we experienced 68% of totality during the August 21, 2017 solar eclipse.  There seemed to be general agreement among observers that there wasn’t a significant perceptible reduction in ambient light during the event.  But check out the reduction in solar PV output during the ~1:30 to ~3:30 PM timeframe and the peak at 2:38 PM in the plot below.  The reduction in output is significant, but comparable to a cloudy period based on a comparison with the cloudy afternoon of August 15 the previous week.

Solar power on Eclipse Day.