Oceanic Thermal Energy
A great amount of thermal energy (heat) is stored in the world’s oceans. Each day, the oceans absorb enough heat from the sun to equal the thermal energy contained in 250 billion barrels of oil. Ocean Thermal Energy Conversion Systems (OTEC) systems convert this thermal energy into electricity — often while producing desalinated water. The use of heat engines is pivotal for this utilization of energy.
In common parlance heat engines are commonly associated with engineering, and nearly all energy utilized by humans uses these heat engines in some form. How this works is that the engine is placed between two reservoirs with extreme temperature differences. As heat flows from one to the other, the engine extracts some of the heat in the form of work. This same general principle is used in steam turbines and internal combustion engines, while refrigerators reverse the natural flow of heat by “spending” energy.
The difference between ordinary thermal energy sources and oceanic thermal energy is that instead of using heat energy from the burning of fuel, OTEC power draws on temperature differences caused by the sun’s warming of the ocean surface.
Three types of OTEC systems can be used to generate electricity:
1. Closed-cycle plants circulate a working fluid in a closed system, heating it with warm seawater, flashing it to vapor, routing the vapor through a turbine, and then condensing it with cold seawater.
2. Open-cycle plants flash the warm seawater to steam and route the steam through a turbine.
3. Hybrid plants flash the warm seawater to steam and use that steam to vaporize a working fluid in a closed system. OTEC systems are also envisioned as being either land-based (or “inshore”), near-shore (mounted on the ocean shelf), or offshore (floating).
