I believe it's difficult in Oman to get the most output from PV. This is because the temperature is very high especially in summer where the temperature reaches more than 50 degrees.
My question: Is there any means or technologies that can be used to cool down the cells even in summer which will help to increase the maximum voltage??
The most cost effective way to deal with the heat is to mount with air spaces between the PV and the structure if it is on a building or if it is a ground mount, there are already air spaces. The other way to deal with this is plan on adding a little more PV to make up for the loss in production.
There are many PV systems in hot places and usually hot places are the best places for PV, since the reason there is hear is because of a lot of solar energy.
In many places where it is not so hot, the high summer temperatures are around 38C, which is 12C cooler than 50C. With a typical temperature coefficient of power of -0.45%/C the decrease in power due to heat will be:
0.45%/C x 12C = 5.4% decrease in power
The benefit that you have is the solar energy hitting the earth can be 20% greater than in the place where 38C is the high design temperature, so the penalty for the heat is worth the benefits of the extra solar energy.
I have heard of people contemplating fans, but it would be less expensive to just buy 5% more PV.