13-08-2012, 01:31 PM
OTEC
OTEC.ppt (Size: 2.04 MB / Downloads: 48)
What is OTEC?
OTEC or Ocean Thermal Energy Conversion is an energy technology, which uses the ocean’s natural temperature gradient to drive a turbine, which is connected to a generator. Itis desirable that the temperature difference between the warm surface water and the cold deep water be at least 200C (680F).
Basic Principles
An OTEC plant consists of a heat engine that converts thermal energy into mechanical work through the temperature gradient
between a “heat source” and a “heat sink”. Although this temperature gradient is relatively small compared to a steam
engine, the principle is the same. The OTEC technology is divided into three categories: closed-cycle, open cycle and
hybrid-cycle.
I the closed-cycle system, the most common of the three, the temperature difference is used to vaporize (and condense) a
working fluid (e.g. ammonia) to drive a turbine-generator to produce electricity. See Figure 1. In the open-cycle system,
warm surface water is introduced into a vacuum chamber where it is flash-vaporized. The produced water vapor drives a
turbine-generator to generate electricity. The remaining water vapor (essentially distilled water) is condensed using cold
water. The condensed water can either return back to the ocean or be collected for the production of potable water.
The Basic Process
OTEC systems rely on the basic relationship between pressure (P), temperature (T) and
volume (V) of a fluid, which can be expressed by the following equation:
where pressure, temperature and the volume of a fluid can be closely controlled by manipulating the other two variables.
Hence the differential in temperature of the fluid can be used to create an increase in
pressure in another. The increase in pressure is utilised to generate mechanical work.
LIMITATION’S OF OTEC
land-based OTEC plants is the need for a 3 km long cold water pipe to transport the large volumes of deep seawater required from a depth of about 1000
m. The cost associated with the cold water pipe represents 75% of the costs of current plant
designs. Studies show that OTEC plants smaller than 50 MW cannot compete economically
with other present energy alternatives. A 50 MW plant will require 150 m3/s of cold water
thus, the 3 km long cold water pipeline has to be at least 8 m in diameter.
Summary and Conclusions
Consider methods to reduce system cost, consider:
Sell directly to city to remove “middle-man”
Platform cost savings: less-robust design, shorter CWP
Recommend Africa installation after OTEC is ‘proven’ at large scale
Alternative technology approaches increase possible installation area to include colder water regions
Way Forward Recommendations
Meet early and often with environmental policy teams regarding licensing and permits to ensure compliance and a clear path ahead
Begin talks with Nigerian government to express interest in developing OTEC near Lagos; Establish a partnership with power distributor
Verify ocean temperatures & geography; Consider university research