Would it play any positive role in reversing the desertification?

Some of this depends on how you view desertificaiton.

A: The arbitrary definition for desert usually is 'an area receiving under 10 inches of precipitation a year" By this definition the arctic is a cold desert, and is very wet.

B: Our mental image of desert is 'hot, dry, sparse vegetation, very sparse habitation'

C: Desertification is usually viewed as a process that changes an arid region to one of deserts. There are various causes of this:

• Overgrazing. Herbivores (goats and sheep often, but also camels, cows...) Reduce the biomass. Because plants aren't transpiring, overall rainfall drops, more clear days means wider temperature swings, harder for plants to get re-established.

• Rain pattern shifts -- either time of year, or prolonged drought.

In the early days of LandSAT, scientists found a perfectly regular pentagon of green vegetation in the sub Sahara. On sending out field agents, they found that some enterprising person had fenced in several square miles of desert scrubland. At the centre was a well. He grazed livestock on each triangle in succession on a 5 year rotation. Because the land had 4 years to recover, it worked.

The well wasn't used to irrigate the fields, but only to supply water for the stock.

One of the potential issues with farming solar power: Solar cells are quite dark, and while some 20% of the energy that hits them is converted to electricity, the rest is converted to heat. The net effect is an decrease in the overall reflectivity, and an overall heating up of the region.

Hot air rises, so now you have a thermal column rising from the solar farm. Depending on local humidity, this can create an overcast layer that interferes with the solar farm. Small units (a mile or do across) won't shade themselves, but really massive farms may create their own interference.

OTOH, some of the ground is shaded, at least part of the day. Lower temps = lower water demand by plants. You may be able to grow plants you otherwise couldn't grow.

On the third hand, if you are close to the sea, it may be possible to harvest that surplus heat to evaporate sea water. This moderates temperatures, but increases humidity. Can you get fresh water out of this?