The Century-Old Renewable You’ve Never Heard Of

Good News Notes:

Japanese island of Kumejima to work as an English teacher after graduating from a business school in landlocked Arizona. Now he runs a power plant fueled by ocean water. “I don’t have an engineering degree, and I do all the maintenance for our electricity,” he said. “It’s relatively easy.”

The plant, which looks like a cross between a lighthouse and a jungle gym, generates a negligible amount of power, only about 100 kilowatts. It was built in 2013 to demonstrate a process called ocean thermal energy conversion, or OTEC. The idea behind OTEC isn’t new, and it’s deceptively simple. Like most power plants, the facility uses vaporized liquid to spin a turbine and generate electricity. The difference is that instead of burning fuel, the plant gets its energy from Sun-warmed water from the ocean’s surface. Cold water pumped up from a depth of several hundred meters cools the vapor again, creating a heat engine.

For now, Kumejima depends mostly on diesel fuel, shipped in at a premium, to provide electricity for its 8,000 residents. But residents of the island hope someday to sever that dependency by building a 5-megawatt OTEC plant that with a bit of solar, could cover all of its energy demand.

Such an endeavor would be expensive, and the plan is to help pay for it by sharing the cold-water intake pipe with the various cold-water industries already thriving on the island—from prawn farming, to a deep-sea water spa, to greenhouses in which the water chills the soil so that it’s the optimum temperature for growing spinach. Cold seawater can even be used for air-conditioning.

“Our research center is cooled by deep-sea water, which reduces the amount of power we need for cooling by about 90%,” said Martin, who also serves as secretary general for the Ocean Thermal Energy Association, a group with members from around the globe who want to see OTEC deployed and expanded in the power sector.

On paper, they’re right to be optimistic. The theoretical potential of OTEC is vast. It could produce at least 2,000 gigawatts globally, rivaling the combined capacity of all the world’s coal power plants on their best day. And unlike many renewables, OTEC is a baseload source, which means it can run 24/7 with no fluctuation in output.

But the conditions necessary to make the process viable—at least a 20°C difference between surface and deep water—occur only near the equator, far from most of the world’s power demand and much of its wealth.

That’s why, despite its simplicity and decades of small, successful demonstrations, OTEC has yet to take hold in the renewable power industry. Its high initial capital costs have kept investors away, especially as other renewables like solar and wind get cheaper by the minute.

But places like Kumejima and dozens of small island states, many of them among the poorest countries in the world, could benefit enormously from ocean thermal power. If they can raise the money to get started, energy independence and carbon neutrality may be literally at their doorstep.

“The island hopes to be 100% carbon free by 2040,” Martin said of Kumejima. “But we need OTEC to get there.”

More of a Warmth Engine

The universe runs on contrasts and the forces of entropy. Thermal power, for instance, isn’t generated by heat but by its ability to do work as it cools. Even a modest amount of heat can do the job, as long as there’s a temperature gradient to be exploited.

Most OTEC systems use liquid ammonia, which has a very low boiling point, as what’s called the “working fluid.” Warm water from the ocean surface flows into a heat exchanger, where it causes the ammonia to evaporate. (Other “open” systems use the seawater itself as the working fluid, first exposing it to a vacuum to lower its boiling point.) As the vapor expands, it flows around the blades of a turbine. The vapor then enters another heat exchanger, where cold water pumped up from the deep ocean causes it to condense again. The pressure differential between the two chambers on either side of the turbine pulls vapor from one to the other, spinning the turbine and generating electricity. Some of that electricity is used to run the pumps. What’s left can feed the grid.

At first glance it looks like a painfully inefficient process; only about 2%–3% of the energy in the seawater is converted to electricity. But the fuel is free and virtually infinite. Output is limited only by how much water you can pump at a time.

And there’s the rub. For OTEC to be viable—that is, for it to be competitive with other renewables like wind and solar—the plants need to be huge. To get anywhere near wind’s or solar’s average cost of 0.02–0.06 cents per kilowatt-hour, an OTEC plant would have to keep the equivalent of four Niagara Falls flowing through its heat exchangers at all times.

A 100-megawatt OTEC plant (the equivalent of about 500 acres, or 202 hectares, of solar panels) would need a cold-water intake pipe that’s 7–10 meters in diameter to work efficiently. Just to scale up to a modest 1-megawatt plant, Kumejima expects to spend between $60 million and $80 million on a 1.5-meter pipe.

So far, funding for that kind of leap of faith has proven to be elusive. “OTEC can be cost competitive,” Martin said. “It’s just no one’s done it yet.”

The Curse of the First

The concept of using warm and cold ocean water to generate electricity is about as old as the generation of electricity itself. French scientist Jacques-Arsène d’Arsonval theorized the process in 1881, just as the notion of using a steam engine to rotate coils of copper wire around a magnet was emerging as a source of commercial and industrial power. His student Georges Claude, a rebellious and hardheaded entrepreneur who got rich selling neon lights, built the first OTEC plant in Cuba in 1930. At first cockily optimistic, he eventually admitted that running it cost about 4 times more power than it generated.

And Claude had a lot of trouble with the cold-water pipe. He sank a handful of failures in Matanzas Bay, losing a million dollars with each attempt. The one that finally worked was destroyed by a hurricane.

The moral of Claude’s story is that when it comes to big, novel machines, failure is expensive. And before Claude had even begun his less-than-convincing demonstration, coal had become ubiquitous as the fuel for large-scale power plants. Unlike two-temperature seawater, coal (and, later, oil and natural gas) was perniciously easy to ship anywhere in the world.

Predictably, global interest in OTEC has followed oil prices. After the crises of the 1970s, President Jimmy Carter signed a bill calling for 10,000 megawatts of OTEC capacity to be up and running by 1999. Then oil prices stabilized, administrations changed, and other than a few demonstration projects, nothing happened.

OTEC projects began to crop up again after the 2008 financial crisis, coupled with growing concern over climate change. Makai Ocean Engineering, based in Hawaii, was the first to connect an OTEC plant to the U.S. power grid. But like Kumejima’s facility, it was a temporary demonstration, generating only enough electricity to run about 120 homes. The cold-water pipe is still operating, though, allowing a local fishery to grow and sell Maine lobsters.

Plans for a score of small-scale OTEC projects have been announced, including in Bora Bora, where one resort is already using deep-sea water for air-conditioning; ChinaMartinique; and Puerto Rico. But this time, the meteoric rise of wind and solar power has simply overtaken marginal renewables like OTEC.

The main advantage of wind and solar is their modularity. The technology can be proven at full scale with a single turbine or panel; scaling up is a matter of simply manufacturing more of them. OTEC, on the other hand, requires a huge investment—and the risk that goes with it—before even the first kilowatt is generated….”

View the whole story here:

Leave a Reply