http://www.newscientist.com/article/mg20026836.000-plumbing-the-oceans-could-bring-limitless-clean-energy.html?full=true

Plumbing the oceans could bring limitless clean energy

FOR a company whose business is rocket science Lockheed Martin has

been paying unusual attention to plumbing of late. The aerospace giant

has kept its engineers occupied for the past 12 months poring over

designs for what amounts to a very long fibreglass pipe.

It is, of course, no ordinary pipe but an integral part of the

technology behind Ocean Thermal Energy Conversion (OTEC), a clean,

renewable energy source that has the potential to free many economies

from their dependence on oil.

"This has the potential to become the biggest source of renewable

energy in the world," says Robert Cohen, who headed the US federal

ocean thermal energy programme in the early 1970s.

This has the potential to become the biggest source of renewable

energy in the world

As the price of fossil fuels soars, private companies from Hawaii to

Japan are racing to build commercial OTEC plants. The trick is to

exploit the difference in temperature between seawater near the

surface and deep down (see diagram).

First, warm surface water heats a fluid with a low boiling point, such

as ammonia or a mixture of ammonia and water. When this "working

fluid" boils, the resulting gas creates enough pressure to drive a

turbine that generates power. The gas is then cooled by passing it

through cold water pumped up from the ocean depths via massive

fibreglass tubes, perhaps 1000 metres long and 27 metres in diameter,

that suck up cold water at a rate of 1000 tonnes per second. While the

gas condenses back into a liquid that can be used again, the water is

returned to the deep ocean. "It's just like a conventional power plant

where you burn a fuel like coal to create steam," says Cohen.

The idea of tapping the ocean's different thermal layers to generate

electricity was first proposed in 1881 by French physicist Jacques

d'Arsonval but didn't receive much attention until the world oil

crises of the 1970s. In 1979, a US government-backed partnership that

included Lockheed Martin, lowered a cold water pipe from a barge off

Hawaii that was part of an OTEC system generating 50 kilowatts of

electricity. Two years later, a Japanese group built a pilot plant off

the South Pacific island of Nauru capable of generating 120 kilowatts.

In the first flush of success, the US Department of Energy began

planning a 40 megawatt test plant off Hawaii. Then in 1981, the

funding for ocean thermal technologies began to dwindle. It dried up

altogether in 1995 when the price of oil began to drop, eventually

falling below $20 a barrel.

Now rising fuel costs have revived interest in this neglected

technology. In September, the Department of Energy awarded its first

grant for ocean thermal energy in more than a decade, giving Lockheed

Martin $600,000 to develop a new generation of cold water pipes.

Cohen believes this could eventually lead to 500 MW OTEC plants on

floating offshore platforms sending electricity to onshore grids via

submarine cables, and factory ships "grazing" the open ocean for power.

Lockheed's first goal is to get a test facility up and running. The

company has got together with Makai Ocean Engineering of Waimanalo,

Hawaii, to build a 10 to 20 MW plant, most likely off Hawaii, that it

hopes to have up and running in the next four to six years. The plant

- including a 1000-metre pipe some 4 metres in diameter - would feed

electricity to the island's energy grid via submarine cables.

While Lockheed gears up for its test facility, a plant for the US

military could come online even sooner. OCEES International, based in

Honolulu, is finishing designs for an ocean thermal facility to be

built off the island of Diego Garcia in the Indian Ocean, which is

home to a major US military base.

The plant would provide 8 MW of electricity and would also power the

desalination of 1.25 million gallons of seawater per day. OCEES says

it could be up and running by the end of 2011.

At the moment Diego Garcia is powered entirely by diesel fuel, and

base commanders see ocean thermal as a means to energy independence.

"It's a strategic military installation in the middle of the Indian

Ocean," says Harry Jackson of OCEES. "They don't want to rely on

others to provide their power."

"I think OTEC has the potential to develop sufficient power output

much quicker than wave buoys or tidal power would," says Bill Tayler,

director of the US navy's Shore Energy Office. "It would take a lot of

buoys to produce 8 to 10 MW of power. We're looking at them all but

have our hopes on OTEC."

Still, both teams will have to work out issues such as how to connect

the floating, bobbing platforms to fixed submarine power lines. Heat

exchangers will have to be designed in a way that prevents excessive

buildup of algae, barnacles and other marine organisms that could clog

the system.

If these test plants are a success, larger, commercial-scale plants

could transform the energy equation on Hawaii, where nearly 77 per

cent of electricity is generated by burning oil. "It will be the major

energy game changer for our state and elsewhere in the world if we can

get OTEC working well at the 100 MW level or larger," says Lockheed

collaborator Reb Bellinger of Makai Ocean Engineering.

But scaling up won't be easy. "A 100 MW plant might have a pipe 30

feet in diameter suspended 3000 feet. That's not a small challenge.

You've got this huge structure vertically suspended. You've got a lot

of stresses and strains from current, from the movement of platform on

the surface - how you are going to anchor it and install it?" asks

Bellinger.

Smaller designs have already run into trouble. In 2003, Indian

engineers building a 1 MW ocean thermal plant attempted to lower an

800-metre cold water pipe into the ocean from a barge in the Bay of

Bengal only to lose the pipe in 1100 metres of water. A new pipe met

the same fate the following year. "Both times there were some winch

problems and it fell to the bottom of the sea," says Subramanian

Kathiroli, director of India's National Institute of Ocean Technology.

"I don't think we will ever be able to go beyond 5 to 10 MW with

present knowledge," he says.

Yet the technology will have to be scaled up if OTEC is ever to make a

significant impact on the green power market. Hans Krock, who has

worked on OTEC designs for the University of Hawaii, the US Department

of Energy and others since 1980, says he's tired of testing. "Pilot

tests have been done," Krock says. "It's not a matter of design, it's

a matter of getting the economics right."

Krock, who founded OCEES in 1988, recently left to start Energy

Harvesting Systems, a firm with ambitious plans to build a 100 MW OTEC

plant off the coast of Indonesia. The electricity it generates will be

used to produce hydrogen, a green fuel that could be used to power

zero-emission vehicles. Krock says he has funding for the $800 million

plant and it could be up and running within two years, once building

contracts are finalised.

For Cohen, who has also waited decades for ocean thermal to come into

its own, such a large plant seems overambitious, especially as it is

coupled with the production of hydrogen, whose distribution structure

is still largely undeveloped.

"Scaling up so quickly could be risky," warns Cohen. "I'd like to see

us move fast on ocean thermal but I think we have to be careful."

As governments and private companies around the world look to

capitalise on ocean thermal energy, an offshoot of the technology is

already up and running. Instead of trying to harness cold, deep water

for electricity production, the city of Toronto in Canada uses water

from the bottom of Lake Ontario to cool its buildings. Makai Ocean

Engineering of Waimanalo, Hawaii, recently helped construct the city's

cold-water air conditioning system that will save 60 megawatts of

electricity when it is fully connected to buildings in the city's

centre. The system works by pumping water at a temperature of 4 °C

from a depth of 80 metres and then sending it to buildings within the

city via three pipes, each5 kilometres long. The cold water is then

used to cool air.Makai is working on a similar cold-water air

conditioning system for Honolulu in Hawaii. "Ocean thermal energy is

the big prize, but cold-water air conditioning can play a major role

in cutting energy needs, and it can do it today," says Reb Bellinger

of Makai.

posted by Ross to ClimateConcern