You'd be lucky to have that 25 watt solar panel power a fan much less an AC unit. Most in-window a/c units take about 600 - 1200 watts. They also run on A/C power, not DC which is what you get from solar panels. Getting enough amperage from a solar panel is going to be difficult.
Unless of course you were to put some isolation in those tents (or regular buildings, for the matter).
The ingenious building style in hot countries revolves around few windows, light colors and thick walls. With that, there is not much need for air conditioning.
But then again, the US has a track record of building inefficient houses, so this should not surprise anyone.
Making mud huts doesn't seem very realistic in the middle of a sandy desert, a war zone or a disaster area. Nor are they entirely easy or quick to build & their ability to cool would be temperamental & inconsistent.
There aren't any bases literally in the middle of a sandy desert, as what are you defending in that case? They're usually somewhere on more solid ground. If there's dirt, there's material for building. There are no bases of any consequence in the middle of the Sahara. Iraq isn't Saudi Arabia.
Rammed Earth construction (http://en.wikipedia.org/wiki/Rammed_earth) is an ancient practice made easy with modern equipment. The tents the American forces use are better suited to a European climate, not the intense heat of the desert. They're also going to resist mortars a lot better than some flimsy canvas tent.
The military could invest in compact, easily constructed tents or it could rely on the possibility that mud is available in the area & that they have the time, the personnel & the heavy equipment free to build them. Huts that you can't deconstruct and take with you.
Also we're not just talking about military purposes. You could put up an industrial grade tent in an hour for disaster relief. How long would a mud hut take to build in a disaster area? How about at a festival or fairgrounds?
It looks like in some areas the army is re-purposing tents for semi-permanent housing. Tents are already on hand. Their specs are known. I am not aware of an army approved mud hut. Perhaps the army should look into it, but there are many varying factors that can go wrong in constructing a mud hut vs a standard issue tent.
Also I don't think a quickly build mud hut is going to fair a whole lot better than a tent to a mortar round. Additionally the tents are being sprayed with insulating foam on the outside which makes them almost airtight. Though I'd question if there is the ability to re-purpose the tent after it's been sprayed.
How difficult would it be to do a geo-thermal like system? Instead of coolant + heat exchanger, can you just force warm air down some pipes buried in the earth (running some distance) and having the thermal exchange occur "naturally" to surface as cool air at the other end of the pipe? In which case, (solar) fans might be all that is needed to run the system (though burying the pipes would require some work)
You are talking about a Ground source heat pump. Once you are down about 10m the temperature of the ground is fairly constant at about 10-14 degrees C. You can exploit this temperature difference for either heating or cooling using a heat pump.
Indeed though the ones I've read about uses some type of liquid coolant for heat/cool interchange. Just curious if circulating just air through the piping would suffice as a poor-mans implementation thus reducing the need for the above ground exchanger.
You would probably need about 4 of these: http://www.ecodirect.com/ProductDetails.asp?ProductCode=Cana...
Then maybe you could start talking about powering something like a 5,000 BTU air conditioner.