Could sea power solve the energy crisis?
Thermal Energy Conversion (OTEC) may be an idea whose time
has come. The theory is very simple: OTEC extracts energy
from the difference in temperature between the surface of
the sea (up to 29C in the tropics) and the waters a kilometre
down, which are typically a chilly 5C. This powers a "heat
engine": think of a refrigerator in reverse, in which
a temperature difference creates electricity.
OTEC plant was constructed by the French inventor Georges
Claude in 1930 in Matanzas Bay, Cuba, where the sea plunges
to great depths close to the shore. After several failures
- including the loss of two of the pipes used to suck up cold
water from the sea - Claude produced 22,000 watts of electricity
from this early prototype. This is a very small amount, enough
to heat five well insulated houses. But it confirmed that
his calculations worked, and that both electricity and drinking
water could be produced by the sea. When a later version was
installed on a converted boat in Brazil, Claude found a use
for this desalinated water: he froze it to make ice, a valuable
commodity at the time. The boat, however, was damaged in a
storm and the project abandoned.
There are two basic versions of the technology. The
first operates in a "closed cycle", using
warm surface water to heat ammonia, which boils at a
low temperature. This expands into vapour, driving a
turbine that produces electricity. Cold water from the
depths is used to cool the ammonia, returning it to
its liquid state so the process can start again.
second, "open cycle" version offers the added
benefit of producing drinking water as a by-product.
Warm seawater is introduced into a vacuum chamber, in
which it will boil more easily, leaving behind salt
and generating steam to turn a turbine. Once it has
left the turbine, the steam enters a condensing chamber
cooled by water from the depths, in which large quantities
of desalinated water are produced - 1.2 million litres
for every megawatt of energy.
modern OTEC plant could meet much of the world's energy
needs, without generating polluting clouds of carbon
and sulphur dioxide. A 250MW plant (a sixth of the capacity
of the new coal-fired power station that has recently
won planning permission in Kent) could produce 300 million
litres of drinking water a day, enough to fill a supertanker.
Using electrolysis, it would also be possible to produce
have beset many subsequent attempts to turn principle into
practice, but with oil at $100 a barrel, and with pressure
growing to arrest the effects of climate change, the conditions
are right for OTEC to make a comeback. And - if you are going
to build an offshore platform, it makes sense to harness its
space to create an "energy island" - a facility
that uses a variety of alternative energies, such as wind,
wave and solar, to generate enough power to pump the huge
quantities of water from the sea and run the vacuum pumps
of the OTEC plant.
would these "islands" be self-sufficient, but several
could be linked to generate energy outputs of around 1,000MW,
rivalling the output of a typical nuclear plant. The cost,
according to our models, would be roughly double that of a
nuclear power station. This might seem expensive, but an OTEC
plant would not involve the waste-treatment or astronomical
decommissioning costs of a nuclear facility. Also, it would
offset its expense through the sale of the desalinated water.
This is in addition to the other advantages: carbon-free energy
production and no generation of heat. In fact, the plants
would cool the seas and oceans by the same amount as the energy
extracted from them.
produce enough drinking water to ease drought-stricken tropical
areas like Ethiopia
islands would mainly be built from reinforced concrete, using
corrosion-resistant metals, but they would come in different
sizes and with different functions: some would be simple energy-generating
platforms, while others would be larger installations, linked
to the land by cable, along which the electricity could be
distributed (this would involve superconductors, materials
that lose all resistance to electricity when cooled, minimising
energy loss in transmission).
generation would not be their only function. Larger islands
could support fish farms that used the plankton pumped up
along with the cold seawater, as well as pods for heliports,
greenhouses, accommodation and maintenance areas, facilities
for producing sea salt and harbours and mooring for supertankers
to collect the desalinated water or the hydrogen produced
by electrolysis to ship to energy- and water-scarce parts
of the world.
have a clear idea where to build these powerful islands. For
the system to function, the gap between the surface and the
depths must be at least 20C. Maps of the oceans show which
waters contain the necessary temperature gradients -and China,
India and Brazil, the three countries projected to have the
greatest economic and population growth this century, and
therefore the most pressing energy requirements, all have
are now sponsoring serious research on renewable marine power.
50,000 energy islands could meet the all world's energy requirement
while providing two tons of fresh water per person per day
for its six billion inhabitants. That would be a legacy of
which Georges Claude could be proud.
Dominic Michaelis is an architect and engineer. He and his
architect son Alex are developing the energy island concept
with Trevor Cooper-Chadwick of Southampton University.
Telegraph 8th Jan 2008
go to top