This story from the Daily Mail is incorrect on 2 counts:
1- The unit is not solar powered.
2- The concept of evaporative cooling has been around for centuries. A teacher in Niger, Mohammed Bah Abba, redeveloped the concept for an impoverished Nigeria and set up a large-scale production facility. The pots they produce currently cost less than 50 cents. His story was featured on NPR a few years ago.
This boon allows the girls in the villages to go to school on a regular basis. Before they were going to market every day before the harvested food spoiled.
Make your own: a large unglazed terracotta pot, a second vessel preferably with a lid (this can be almost any material that will conduct the cool) that will fit inside and allow wet sand to be placed in the space between the vessels.
Soaking the terracotta pot helps too.
However. I give this young woman the Genius accolade for using what she had on hand to make something both functional and useful.
And if you are interested, you can use the same idea to make a fast, quick and cheap air conditioner. LifeHack is on the case.