two points here:
one, your panels will be hottest when the days are the longest. hence your loss of efficiency is offset by the length of the day.
two, you could just get a hose and soak those suckers down once in awhile. or what about a solar pump that sprays a mist onto the back of your panels. cheap!
(three, i was kidding about number two)

The other day, the sun was kinda hazy, so I was amazed to see all my PV was putting out a lot of power.
They were running very close to 95% of their max ratings.
Then, I checked the outdoor temperature. It was down around 30F.. :)
Normally, these panels put out between 70 and 80 percent of max ratings.

yesterday, the coldest day of the year so far, saw 61.19 volts from my 48 volt panels (rated 57.5). the highest voltage yet. I also saw current limiting at 909 watts out of my 800 watt max system. still not enough to get my batteries through 2.5 hrs of absorption. 68 minutes of absorption though, so very close to fully charged.

Cooling solar panels is very important. It increases the power production of your solar panels. If you try to cool your solar panels with water for a purpose you might see some gain but its more water usage per day. The other option for cooling solar panels is try spraying a hose on my roof panels on a hot day.