Are you anxious to feed the hungry, combat the rise in atmospheric carbon dioxide concentration, and see the desert bloom? If so, this piece, Greening the Sahara, outlining a scheme to do just that by irrigating the ten million square kilometers of the Sahara desert using solar power as the sole driving energy source may be of interest.
The scheme involves the use of geodesic spheres as gigantic, lighter-than-air cloud-containment structures that carry water-saturated air from the coast inland on the sea breeze, deposit the water over the desert during the cool nighttime and return to the coast either on the predawn land breeze or perhaps drawn by camels.
I had intended to add a cost analysis of the scheme but it is some months since I worked on the idea and the details about cost now escape me. As I recall, however, the thing was not altogether unfeasible. In fact, with some ingenuity in the construction of the hot air dirigibles, it seemed to me that the idea could payoff quite well.