Post the Eighth: Wave and Tidal Energy

Easily my favorite alternative energy.

http://continuouswave.com/whaler/cetacea/images/18OutrageOceanWaves520x334.jpeg

Probably the least known form of alt-energy, wave/tidal technology uses the potential energy constantly sloshing around every day in the ocean.

Wave and tidal energy are really two different technologies. Tidal energies and wave energies are similar in that they both utilize the potential energy of the ocean, but each operates based on distinct principles. Wave energy is created by generating electricity from ocean waves, which is created by winds passing over the water.

Tidal energy, on the other hand, is derived from the rising and sinking of sea levels to generate electricity, and is considered the only form of energy to come from the gravitational relationship between the sun and the moon.

The technology has only been recently explored; the last significant development was Salter’s Duck in the 1970s. Funding of Dr. Salter’s project was shut down in the early 1980s under curious circumstances.

Tidal Energies

Barrage / Dam

Tidal Barrage

As neatly summarized by the U.S. Department of Energy,

A barrage or dam is typically used to convert tidal energy into electricity by forcing the water through turbines, activating a generator. Gates and turbines are installed along the dam. When the tides produce an adequate difference in the level of the water on opposite sides of the dam, the gates are opened. The water then flows through the turbines. The turbines turn an electric generator to produce electricity.

Tidal Turbine

Similar to wind turbines, tidal turbines are installed on the ocean floor in rows like wind farms. Again quoting the U.S. Department of Energy,

The turbines function best where coastal currents run at between 3.6 and 4.9 knots (4 and 5.5 mph)… Ideal locations for tidal turbine farms are close to shore in water depths of 20–30 meters (65.5–98.5 feet).

A fancypants new design brought to you by Tidal Energy, Ltd.

Wave Energy

First, a link to a great History Channel video on hydropower (which I suppose is the correct general term) that covers both barrages and turbines, and also the invention below.

The Pelamis Wave Energy Converter

Each individual Pelamis is an interconnected series of metal tubes. When swayed by ocean waves, rams in the hinges pump oil at a high-pressure through hydraulic motors. Electricity is sent ashore via a subsea cable.

According to the Pelamis website, each machine is 180 meters long, 4 meters in diameter and is rated at 750 kW. Each machine can power approximately 500 homes.

–> A nifty interactive video on the Pelamis.

The Aquabuoy, the Powerbuoy

Aquabuoy. It's so cool

These are two very similar inventions that function around a partly submerged buoy that bobs up and down. As it bobs and bobs, water pressurizes a piston which generates electricity.

–> A 1 minute video on the Aquabuoy. Very tiny.

–> A 3 min. video on the Powerbuoy by some Philly CBS station.

Oyster

This one is pretty cool.

The Oyster is a massive underwater metal “flap” that opens and shuts by wave movement. As the Oyster shuts, seawater is pumped at high-pressure to an onshore generator. Each oyster can generate 600 kW each. What’s smart about the Oyster is it keeps the sensitive bits onshore, with only the most robust mechanical elements in the harsh cold seawater.

To give you an idea of the size of one of these suckers:

There is also an Oyster prototype that is designed to power an onshore desalinization plant, which will provide fresh drinking water.

The Limpet

The Limpet is a large chamber installed by the coast, where waves crashing into/onto the chamber’s exterior force air up through the chamber, driving a turbine. As the water recedes, air is sucked back into the chamber, driving the turbine even further.

Diagram of the Limpet at Isley island in Scotland

The Limpet provides 500 kW of electricity to the island.

There’s also a “wavecam” with four different views at the Limpet website. It’s a little wonky though.

So what gives?

The advantages to tidal and wave energies are the generally low visual and ecological impact, although this depends on the technology. In addition, the “fuel” for wave energy is free and virtually unlimited. On top of that, the U.S. Department of Energy estimates there is 2 terawatts’ worth of power in wave energy—a considerable amount when put into the context of a 16TW global power consumption. In fact, hydropower is often seen as a good way to power local desalinization plants (such as the Oyster.)

The ocean has a lotta energica.

The disadvantages to tidal/wave energies are amplified by the fact the technology is still young. For one, the cost of construction is very high and increases the time it takes for investors to receive their money back. Secondly, there is little infrastructure in place to transport such energy. Thirdly, the vessels needed to install equipment are generally booked by oil companies, and as such are often expensive. In addition to these obstacles, the stressful conditions that tidal/wave energy equipment is placed under are considerable — seawater is a tad corrosive. Lastly, the number of sites suitable for tidal energies is limited.

So, I say we all git hopping and start making some waves.

The bigger the belly, the better you bloat.

Advertisement