08-12-2012, 06:44 PM
OCEAN THERMAL ENERGY CONVERSION AND THE PACIFIC ISLANDS
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EXECUTIVE SUMMARY
The idea of using thermal energy from the ocean is not new. A French scientist, J.
D’Arsonval first thought about the idea more than a century ago but it was only in early 1970
when research on this technology started to take shape.
The Pacific island countries are heavily dependent on fossil fuels to meet their increasing
energy needs for economic development. The high costs associated with fossil fuels are
placing an increasing strain on the economies in the region.
A significant factor in energy usage patterns in Pacific island countries has been attributed to
the availability of energy sources as early as the fifteenth century where pollution control was
not an issue. People have used what they have been able to get, be it coal, oil, natural gas,
wood, etc. However, within the last two decades warnings of global destruction and climate
change have become major issues. The growth of environmental awareness and the rising
demand for energy has urged researchers to identify other sources of renewable energy.
The heat stored in the ocean can be converted into electricity by means of a process called
Ocean Thermal Energy Conversion (OTEC), which uses the ocean’s natural temperature
gradient to drive a turbine connected to a generator which produces electricity. Apart from
electricity, there are other useful by-products from the OTEC process like fresh water, chilled
water and nutrient-rich water. To date there are basically three types of OTEC systems
developed to harness the ocean heat – a closed-cycle, an open-cycle and a hybrid-cycle.
The economics of energy production have delayed the financing of permanent OTEC plants.
At present, the cost per kWh from OTEC is more than that of the electricity generated from
fossil fuels and decreases with increasing capacity of the power plant.
The environmental impact of the introduction of OTEC plants to the Pacific region is a
significant concern to our small island countries. The laying of pipes and discharging of cold
water at huge volumes in the coastal waters may cause damage to the marine ecosystem.
INTRODUCTION AND BACKGROUND
This paper is the result of discussions held during the Regional Energy Meeting (REM) 2000
and the SOPAC STAR Energy Working Group 2000 meeting which noted the need to
provide technical information on “New Energy Technologies”, in particular, hydrogen fuel,
ocean thermal energy conversion (OTEC) and space solar power generation.
As Pacific island countries vary widely in terms of natural resource endowment and energy
use patterns, they still remain heavily dependent on fossil fuels to meet their increasing
energy needs. The relatively high costs associated with fossil fuels have encouraged
research into indigenous resources as an alternative source of energy. However, the
potential of indigenous resources is yet to be fully realised and exploited.
The excessive use of fossil fuels by industrialised countries2 has not only increased the
carbon dioxide and other ozone-depleting gases in the atmosphere, but has also contributed
to global warming, sea-level rise and climate change, all of which the Pacific island countries
are vulnerable to. The Pacific islands view this as a major disaster and have openly criticised
the industrialised nations for not taking serious measures to reduce the pollution of the
atmosphere and their greenhouse gas emissions.
HOW OTEC WORKS?
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. It
is desirable that the temperature difference between the warm surface water and the cold
deep water be at least 200C (680F).
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.
There are basically three types of OTEC systems developed that can utilise sea water
temperature differentials – they are: a closed-cycle, an open-cycle and a hybrid-cycle.