OTEC facts

OTEC runs on warm and cold seawater instead of burning a fuel.
OTEC can only work naturally all year round in the Tropics because it is there that the largest natural temperature differences can be found.
The quoted minimum temperature difference required is 20 degrees but a little less could be possible.

Natural OTEC requires around 2.5 litres per second of deep-sea-cold-water to produce around 1 kw of electricity.
The cold water must be taken from 750-1000 meters below the sea-surface if the system is to work ‘naturally’.



Hybrid OTEC facts

The net power output of a plant can be increased with extra heat from a source other than seawater.
With the use of extra heat, a site well outside of the tropics can usefully use seawater and additional heat.
If this process is used then the diameter of the hoses and the size of the heat exchangers can decrease for a given net power requirement.



SWAC facts

SWAC is more flexible than OTEC.
Cold water source cooling is working in Canada for example, it could also work in the mountains.

SWAC can be made to work on smaller scales than OTEC.
SWAC is not limited in the same way OTEC is by the laws of thermodynamics because there is no ‘Phase change’, this means all the heat transferred is ‘usable’.

Water has a higher specific heat capacity than air; Changing 1 litre of water by 1 degree can change approximately 4 cubic meters of air by 1 degree!
This means that SWAC installations can be far cheaper per KW of cooling than OTEC can be per Kw of net power.



Pumping and plumbing facts

The faster you pump the water the more energy is required to pump.
The slower you pump the water the less energy is used to pump.
Slower pumping speeds means larger diameter hoses are required, but that much less energy is taken by pump motors.

Larger hoses are better value for money than small ones.
This is because if you double the diameter of the hose, you quadruple the volume, and only double the area.

Smaller hoses warm up due to the surrounding water temperature and friction faster, meaning that they must be insulated and are potentially an impossible means of making OTEC or SWAC work well.
Hoses over around 30 cm in diameter begin to lose the insulation requirement even over long distances, however, insulation may still be desirable.

The more dilated you can make the OTEC or SWAC system the better it would work.
Hoses are very attractive because they can mean that very large diameters are affordable and easy to install.

The low pressure in the system means that materials like PVC coated polyester are possible.  This kind of material is inexpensive; long lengths are easy to manufacture, transport and install.




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