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Is Tidal Energy the World's Next Renewable Powerhouse?

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Is Tidal Energy the World's Next Renewable Powerhouse?

A British company has announced plans for an array of unique marine turbines that can operate in shallower and slower-moving water than current designs.

One of the new marine turbine rotor blades is floated in on a barge, ready for installation. Photo credit: Kepler Energy

Kepler Energy, whose technology is being developed by Oxford University’s department of engineering science, says the turbines will in time produce electricity more cheaply than off-shore wind farms.

It hopes to install its new design in what is called a tidal energy fence, one kilometre long, in the Bristol Channel—an estuary dividing South Wales from the west of England—at a cost of £143m (US$222m).

The fence is a string of linked turbines, each of which will start generating electricity as it is completed, until the whole array is producing power. The fence’s total output is 30 megawatts (MW) and 1MW can supply around 1,000 homes in the UK.

Power Outputs

Peter Dixon, Kepler’s chairman, told Reuters news agency: “If we can build up to, say, 10 kilometres’ worth, which is a very extended fence, you’re looking at power outputs of five or six hundred megawatts. And just to visualize that, it’s like one small nuclear reactor’s worth of electricity being generated from the tides in the Bristol Channel.”

The new Transverse Horizontal Axis Water Turbine (THAWT)—whose design is compared to that of a water mill—will use the latest carbon composite technology and should be suitable for the waters around Britain, as well as overseas.

How the rotor blades look installed in a tidal fence configuration. Photo credit: Kepler Energy

Because the turbines sit horizontally beneath the surface of the sea, they can be sited in water shallower than the 30-metre depth typically required by current designs. And because the water is slow-moving, the company says, fish can safely avoid the turbines’ blades.

Although the technology is regarded as environmentally benign, Kepler says it will still undergo a rigorous environmental impact assessment during the planning process to ensure that it poses no significant risk to marine life and to other users of the sea.

There is more good news for proponents of renewable energy after the UK government—which is no longer encouraging onshore wind and solar energy—gave the go-ahead for a large offshore wind farm that could provide power for up to two million homes.

The new wind farm is to be built near the Dogger Bank in the North Sea and will have 400 turbines.

Its developers say it could create almost 5,000 jobs during construction. And, earlier this year, they obtained planning consent for another installation nearby which, with the new development, will form one of the largest offshore wind farms in the world.

North Seas Assets

But the fossil fuel industry is far from abandoning its own interest in British waters as the energy giant BP has announced that it is to invest about £670m (US$1,040m) to extend the life of its North Sea assets.

It said it would be drilling new wells, replacing undersea infrastructure and introducing new technologies to help it to produce as much as possible from the area, whose future would be secured “until 2030 and beyond.”

In November, delegates to the UN Climate Change Convention annual negotiations will gather in Paris to try to conclude an ambitious and effective agreement on preventing the global average temperature rise caused by greenhouse gas emissions exceeding 2˚C above its pre-industrial level.

Last year, the Convention’s executive secretary, Christiana Figueres, said the world’s long-term goal was to reduce greenhouse gases to zero by 2100—a target she said would require leaving three-quarters of fossil fuels in the ground. “We just can’t afford to burn them,” she said.

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Just in time for Halloween, scientists at Cornell University have published some frightening research, especially if you're an insect!

The ghoulishly named ogre-faced spider can "hear" with its legs and use that ability to catch insects flying behind it, the study published in Current Biology Thursday concluded.

"Spiders are sensitive to airborne sound," Cornell professor emeritus Dr. Charles Walcott, who was not involved with the study, told the Cornell Chronicle. "That's the big message really."

The net-casting, ogre-faced spider (Deinopis spinosa) has a unique hunting strategy, as study coauthor Cornell University postdoctoral researcher Jay Stafstrom explained in a video.

They hunt only at night using a special kind of web: an A-shaped frame made from non-sticky silk that supports a fuzzy rectangle that they hold with their front forelegs and use to trap prey.

They do this in two ways. In a maneuver called a "forward strike," they pounce down on prey moving beneath them on the ground. This is enabled by their large eyes — the biggest of any spider. These eyes give them 2,000 times the night vision that we have, Science explained.

But the spiders can also perform a move called the "backward strike," Stafstrom explained, in which they reach their legs behind them and catch insects flying through the air.

"So here comes a flying bug and somehow the spider gets information on the sound direction and its distance. The spiders time the 200-millisecond leap if the fly is within its capture zone – much like an over-the-shoulder catch. The spider gets its prey. They're accurate," coauthor Ronald Hoy, the D & D Joslovitz Merksamer Professor in the Department of Neurobiology and Behavior in the College of Arts and Sciences, told the Cornell Chronicle.

What the researchers wanted to understand was how the spiders could tell what was moving behind them when they have no ears.

It isn't a question of peripheral vision. In a 2016 study, the same team blindfolded the spiders and sent them out to hunt, Science explained. This prevented the spiders from making their forward strikes, but they were still able to catch prey using the backwards strike. The researchers thought the spiders were "hearing" their prey with the sensors on the tips of their legs. All spiders have these sensors, but scientists had previously thought they were only able to detect vibrations through surfaces, not sounds in the air.

To test how well the ogre-faced spiders could actually hear, the researchers conducted a two-part experiment.

First, they inserted electrodes into removed spider legs and into the brains of intact spiders. They put the spiders and the legs into a vibration-proof booth and played sounds from two meters (approximately 6.5 feet) away. The spiders and the legs responded to sounds from 100 hertz to 10,000 hertz.

Next, they played the five sounds that had triggered the biggest response to 25 spiders in the wild and 51 spiders in the lab. More than half the spiders did the "backward strike" move when they heard sounds that have a lower frequency similar to insect wing beats. When the higher frequency sounds were played, the spiders did not move. This suggests the higher frequencies may mimic the sounds of predators like birds.

University of Cincinnati spider behavioral ecologist George Uetz told Science that the results were a "surprise" that indicated science has much to learn about spiders as a whole. Because all spiders have these receptors on their legs, it is possible that all spiders can hear. This theory was first put forward by Walcott 60 years ago, but was dismissed at the time, according to the Cornell Chronicle. But studies of other spiders have turned up further evidence since. A 2016 study found that a kind of jumping spider can pick up sonic vibrations in the air.

"We don't know diddly about spiders," Uetz told Science. "They are much more complex than people ever thought they were."

Learning more provides scientists with an opportunity to study their sensory abilities in order to improve technology like bio-sensors, directional microphones and visual processing algorithms, Stafstrom told CNN.

Hoy agreed.

"The point is any understudied, underappreciated group has fascinating lives, even a yucky spider, and we can learn something from it," he told CNN.

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