Ocean Thermal Energy
The energy in the ocean waves is a converted form of concentrated solar energy. The energy which comes from the sun is transferred through Complex wind electromagnetic wave interactions. The effect of Earth’s temperature variation due to solar heating combined with a multitude of atmospheric phenomena (variation in temperature and pressure). It is used to power generation or wind current, around the globe.
The conversion of thermal energy is devised by a French engineer Jacques D’ Arsonval in 1881, on the basis of temperature difference the surface of the ocean, and deep in the ocean. In order to build a power station on the basis of temperature difference, a temperature difference of at least 36°F to 38°F is required.
Ocean Thermal Energy Conversion (OTEC)
Ocean Thermal Energy Conversion (OTEC) makes use of the temperature difference between the warm surface of the ocean and the coldest layer underneath. Due to solar heating, the amount of energy available in the temperature gradient between Hot and Cold seawater can be substantially larger than the energy required to pump the cold seawater up from the lower layers of the ocean.
Since the efficiency in the Carnot cycle is given by n=1-T1/T2 so when there is a large difference in the temperature of the warm surface of the ocean and deep cold water efficiency will be large. For a typical 36°F, the efficiency of the conversion is 6.77%.
The Ocean Thermal Energy can be converted to useful form by following three means:
- Open cycle OTEC system.
- Closed cycle OTEC system.
- Hybrid system.
Open cycle (OTEC) system
This system uses a warm surface to make electricity. When warm seawater is placed in the low-pressure container it boils. The expanding steam drives the turbine and hence the generator attached to it. The steam is pure water, leaving behind the salt in low-pressure containers. The steam is condensed back into a liquid by exposing it too deep ocean cold water.
Closed cycle OTEC system
This system uses fluid with low boiling points i.e ammonia. The warm water of the surface is pumped through the heat exchanger where a low boiling liquid is evaporated. These expanded vapours rotate the turbo generator. Then cold deep seawater is pumped into a second heat exchanger, where it condenses the fluid into liquid form, which is then ready for the next cycle.
This system has a combined feature of both open and closed-cycle OTEC. Open system work on the low-pressure container while the closed system works with a fluid of low boiling point.
Advantages of ocean thermal energy
- Very low and environmental impact.
- The byproduct is pure and freshwater.
- The waste cold water contains nutrient which can be used for mariculture near the seashore.