A solar thermal collection system is another great way to take advantage of the free energy the sun provides us with. Though it is obviously less effective than a solar panel, it is a much cheaper alternative if you are thinking about harvesting solar energy and it will have a significant effect on your water heating expenses.
The technology heats water by running it through black pipes and in to a holding area. And when placed in a sunny spot for example on the roof of your building, it can be quite effective.
(A black, metal water tank on the roof of a building in a sunny area will also do the trick to some extent)
Examples: Adrena Sport Hostel in Belo Horizonte