Posts tagged clean energy

Tidal Turbine Array

Companion video animation to our popular Honey, I Sunk the Turbine post.

The animation shows an array of SeaGen tidal turbines operating during a flow tide, pausing during slack tide, and restarting during an ebb tide. It finishes showing how the turbine blades can be raised above sea level.

Note: No Audio

Filed under energy hydro clean energy

Honey, I Sunk the Turbine

SeaGen Tidal Turbine at Strangford Lough, Northern Ireland

Tidal Turbines Start Making Waves

Tidal turbines look and work a lot like submerged wind turbines. Technically, both are fluid-driven devices—one uses air while the other uses water. Tidal turbines are installed in undersea locations that have high-velocity tidal currents—or with fast enough continuous ocean currents—to extract large quantities of energy from these huge volumes of flowing water.

Today, there are no operating tidal turbine power plants in the United States. Conditions are ideal for tidal power generation in both the Pacific Northwest and the Atlantic Northeast. Good news: pilot projects are underway.

Nendrum Paddle Configuration

The world’s first commercial-scale tidal turbine was the SeaGen deployed at Strangford Lough in Northern Ireland. It was connected to the grid in 2008 and continues to deliver electricity today.

Is harnessing tidal power new? No. Coincidentally, Strangford Lough was also the site for the Nendrum Monastery Mill— the very first known tide mill in the world dating back to 787 AD. Oddly enough, its paddle configuration is similar to today’s blade approach.

Tidal energy is intermittent but extremely predictable because tidal currents can be calculated many years into the future. Its proponents are typically quick to stress that tidal power is more predictable than wind and solar.

Thanks to the Moon’s gravitational pull, the Earth’s coastal areas invariably get two high and two low tides about every 24 hours—so potential energy assessments and projections are easier than for both wind and solar projects that must consider variability. Obtaining bankable data for financing tidal projects appears much less challenging and less expensive.

According to the U.S. DOE, the difference between high and low tides should be at least five meters, or more than 16 feet, to harness those differences and transform them into electricity. They estimate about 40 sites on the planet with tidal ranges of this magnitude. Despite what some might consider a siting limitation, many believe tidal energy is another valuable form of renewable energy definitely worth pursuing. And, new technology advances can take advantage of smaller differences in tidal heights.

The DeltaStream

Eco2 is a proponent. They’re backing the aptly-named firm Tidal Energy to develop the DeltaStream, a 1.2MW tidal turbine which sits on the seabed without the need for a positive anchoring system. It generates electricity from three separate horizontal axis turbines mounted on a common frame.

Go Green’s Chris Kelsey recently looked at various tidal energy generation methods. Here’s an excerpt that contrasts tidal energy with wind energy:

"The vast difference between tidal power and wind is predictability. It’s easier for business modelling, for design purposes and to know exactly when power is coming which is important for the grid and important from a business perspective," said Chris Williams, development director of Cardiff-based Tidal Energy.

He added: “If you measure tidal flow over a lunar cycle you know how much energy you’re going to get for a project’s life. For wind you might need to measure wind flow over a whole year and even then you’re only getting a probability of what you’re likely to get.”

The relative consistency of tidal flows, without the powerful gusts that can affect wind turbines, means that you can design a tidal turbine to operate through the entire process according to Mr Williams.

"That’s what we’re looking at now, to make sure we can gather the maximum amount of power available in the water. That might not mean getting the peaks—we’re trying to gather the highest proportion of power that’s available over the tidal cycle," he said.

Tidal turbines can be arrayed in rows to create underwater wind farms. Other designs look less like bladed wind turbines. The design shown below is from OpenHydro for an energy pilot project in Puget Sound in Washington. It differs, although it is similar to some land-based designs.

OpenHydro’s Open-Centre Turbine

Today’s new tidal turbines are relatively expensive. Analysts compare the industry’s efforts to where wind was five to ten years ago. Supporters are bullish. They anticipate costs to go down, technology to advance, and adoption to grow. They fully expect tidal power to be a valuable addition to the renewable energy mix—we wish them much success.

We in the wind space are a bit envious though. Tidal turbines are immune from many of the complaints made by NIMBYs against wind turbines. Tidal turbines are completely or partially submerged so there is no visual impact. There is no noise or shadow flicker issue. They pose no known threat to birds, bats, or marine life. No such malady as Tidal Turbine Syndrome exists.

Lucky guys.

UPDATE: Tidal Turbine Array Video Animation

Filed under NIMBYhydrowind energyclean energyenergy