I recently read that Peltier TEGs (thermoelectric generators) are less efficient than conventional electromechanical systems such as turbines/generators. Mayak pointed out that TEGs could be used to generate power by using the difference in temperature between the surface and deep water of the ocean. I found the Wikipedia entry on this, called OTEC, which apparently doesn’t consider TEGs, probably because they’re less efficient than conventional systems. Here is the link to NREL’s OTEC entry. According to them, OTEC has been around for more than a hundred years.