Solar Energy
Solar Pond
A lake with saltly water at the bottom and fresh water at the top can act as a solar collector. Sun shines through all the water and heat is absorbed at the bottom, if the water is clear enough. The salty water is heavier than the fresh water, so it cannot rise. The upper layers of water insulate the system, so stored heat is still available at night.
In a hot climate, the bottom of the pond can reach 90oC. A heat exchanger with refrigerant can run an organic rankine cycle engine to make electricity.
However, water evaporates, so a continual supply is needed. Desalination could be a good use of the heat, to supply fresh water and make-up water.
Patent: Aquaculture in nonconvective solar ponds