High Tide or Low Tide

In high seas or in low seas

I’m gonna be your friend

High Tide Low Tide

I’m gonna be your friend

In high seas or in low seas

I’ll be by your side

High Tide Low Tide

I’ll be by your side

High Tide Low Tide

— Bob Marley

and the Wailers, 1973

We have used the movement of the seas for centuries to gather energy. Early navigators knew there were predictable movements in the ocean currents, and they used them to determine when they would leave or arrive back to port. The collection of waves, tides and currents is collectively known in the alternate energy realm as “ocean energy.”

All this energy is produced by the changes in temperature in and on the oceans and seas, thermal upheavals in the ocean’s bottom, such as earthquakes, and gravitational pull of the sun and the moon. Ocean energy, according to Real Engineering, could theoretically provide for 50% of America’s energy supply. Today there are companies that manufacture various types of underwater and surface water devices to produce electricity based on the predictability of ocean currents, but they face many challenges.

Tidal energy

I more imagine Mr. Marley enjoying a carbonizing tobacco product while composing this song for a friend, as opposed to considering the causation of the high and low tides. None the less, the ebb and flow of tides, is truly a friend to tidal energy. When my father and I went to Alaska and took a cruise off the coast, I recall the massive swells that occurred not very far off shore. The boat would rise about 45 feet at any given instant. That would make a roller-coaster ride seem like a drive around Keuka Lake. No doubt Alaska has the greatest potential in ocean energy.

In this column, I want to discuss one of the upcoming technologies in alternate energy. What is interesting about this form of alternate energy compared to other forms is its 100% predictability hence uniform consistency of delivering power. It is dependent on the highly predictable rotation and orbits of the earth and the moon around the sun. This gravitational relationship causes tides to occur four times a day right on schedule.

Let’s slosh!

There are two main tides: the “spring tide” and the “neap tide.” The spring tide is when the moon and the sun are aligned and combine their gravitational forces to produce a greater rise and fall of the tides, hence more energy can be extracted during this time. The neap tide is when the moon is 90 degrees to the projection of the sun. When this occurs tides are minimal. These forces causes a rise in tide and “picture if you will ...” (this is as good as my Rod Serling imitation gets), a volume of water in a shallow plastic bucket. Next the bucket is being tilted to the left then back again. The swell of the earth pulling toward the sun acts like the bucket being tilted one way then being pulled in a different direction by the moon, as the earth and moon rotate while the oceans act like the water in your bucket. Not to be a tidal bore but this my best way of explaining this energy. It performs this action four times a day. Unlike a train schedule, you can count on it.

One of the caveats of this technology, as you are about to see, is that they are location specific. It requires a natural reservoir that funnels, a naturally obtained high volume of flow, through a narrow channel. These sites are not that common and need a great deal of geological research to ensure these energy collecting systems are effective and not an environmental hazard.

Tidal barrages

Currently there are only two major tidal wave energy plants in the world: Rance in Northern France and Sihwa in South Korea. These tidal plants are known as Tidal barrages. From a distance they look like any typical hydroelectric plant except they rely on the real time flow of water caused by the tides trapped and channeled to produce a higher flow of water. They produce about 250 megawatts each. The caveat is two fold: 1) they are very expensive to build; 2) they have an ecologically negative effect on the regional aquatic life.

SeaGen, Meygen projects

Just inside the coast of Ireland at Stangford Lough was the Seagen Project by Semic Atlantis Company. This was an undersea tidal project designed to correct the problems with the Rance and Sihwa projects by designing an underwater turbine that would not be as costly and be eco-friendly to the local sea life.

These turbines resemble wind turbines. As you may recall from my first column on wind turbines, the mass flowing through a turbine is a major factor in the energy extracted from the force of the medium, now in this case not air but water. Because of this factor, the propeller size is much reduced. This prototype reached full capacity in 2008 and ran until 2016. It had a very high “capacity factor” CF. The CF reached 59% at its peak, over twice that of wind turbines in Ireland.

With this success, a second project called Meygen began in 2014 in the planning stages and was put into operation in April 2018. In its first 18 months, it put 22gw back into the grid. This project proved the economic and ecological value of this technology.

Conclusion

These projects have merit, but I believe they are limited because they rely on a specific type of geological location that naturally funnels water to create the velocity that other such hydroelectric projects create by structure. These projects will be far less effective in open tidal waters. I think that these turbines are cheaper to build and easier to install and maintain than the larger wind turbines. *In my very humble opinion these machines have a future, but they must prove their viability in the less effective tidal waters. Permits for a second project outside of Normandy, France has been initially approved. The waters there are much deeper. Let’s hope they can!

* (To my new readers, my opinions are always very humble, just ask!)

James Bobreski is a process control engineer who has been in the field of electric power production for 43 years. His “Alternate Energy” column runs monthly. He lives with his life partner, Sherry, in Penn Yan.

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