Ocean Power Generating Systems—Going Nowhere Fast
Written by Dr Klaus L E Kaiser
The number of companies that hoped in vain (some still do) to harness ocean power for “free energy” is steadily increasing.
One of the latest outfits not doing so well is Ocean Power Technologies, Inc. (OPT) of Monroe Township, NJ, USA.
According to its website ( https://oceanpowertechnologies.gcs-web.com/ ), it “is a pioneer in renewable wave-energy technology that converts ocean wave energy into electricity” and they have several patents to prove it.
Indeed, OPT was founded more than twenty years ago. In 2007, its shares on the NASDAQ stock exchange, adjusted for several stock share consolidations since (1[new]-for-10[old] shares), traded in the neighborhood of $4,000 per share. Right now you can get them for about $3 a piece, clearly, a hot investment.
Let’s look at the range of basic ideas to harness ocean power
Power from Wave Energy
That’s probably the most common attempt for power generation from the oceans. After all, there are nearly always and everywhere small (0.5 m) waves to be found at any shore. A variety of stationary (firmly placed in the on the bottom) and floating designs have been proposed. For example, the floating Pelamis Wave Power idea of sizable, partially water-filled, elongated tanks would create internal swapping back and forth of the water (like your kid making waves in the bathtub) and would drive an internal turbine. It didn’t work out and the company folded.
The OPT idea also has floating devices, in the shape of bottom-anchored buoys. Their technical specifications do not actually give details on how the wave energy is to be converted to electricity.
Another, stationary concept was thought of by the SeWave wave farm project in Nípanin, Faroe Islands. The (rising) water was to compress a fixed airspace in the rock onshore that would drive an air turbine. It was to be in place by 2010. It has not been heard of since.
The same idea, actually built in 2000, was the Islay LIMPET, then claimed to be the world’s first commercial wave power device. It has been decommissioned since.
Power from Salinity Gradients (Osmosis)
That idea relies on the long-recognized concept of osmosis, which is the natural process of salinity equilibration between water of low salinity (freshwater) and high salinity (saltwater). It requires both, in similar quantities and a semi-permeable membrane that allows water molecules to pass through, but not the salt-ions. It was tested in a pilot plant in Norway several years ago. It may work well in a laboratory setting with clean water but not so with actual ocean water. The tiny membrane pores get readily plugged with other materials and the system was not found to be commercially viable.
Power from Tidal Currents
In 2016, with considerable fanfare, the Cape Sharp Tidal (CST) company launched its “long-awaited” underwater test turbine in the Bay of Fundy. The Bay of Fundy in Nova Scotia, Canada, has among the largest tidal sea level changes in the world and, for that reason also nearby strong tidal currents. The project built a large underwater turbine that was to convert the tidal in-and-out flows to electric power.
The euphoria didn’t last long. In late 2018, CST, co-owned by Nova Scotia’s Emera Inc. (EI), and the Irish company OpenHydro Ltd. (OH), a subsidiary of the French co. Naval Energies, (NE), have hit the end of the road. Both CST and OH filed for bankruptcy.
It didn’t surprise me. The large underwater turbine, placed somewhat offshore where the bay is approximately 500 m or more wide, could not possibly deliver the anticipated power. The current had plenty of room to flow around the “obstacle” of the turbine without creating much power.
Power from the Tides
There are a few well known tidal power plants that actually work. They are in Canada, France, South Korea, and the UK. All have large barriers that allow the incoming tide to raise the water level behind them and drive regular water turbines at low tide. They operate essentially in the same way as any dam that uses the energy of the different water levels in the upside reservoir and the lower release point.
Still, such systems also have their limitations and other problems. One limitation is the nearly constant change in the tides. To begin with, the time windows around the high (to fill the reservoir) and low tides (to generate power by emptying it), where the most energy can be had, is quite short. Then, such structures interfere with other activities, like marine traffic to a harbor and a healthy range for fish to seek forage or to spawn. In addition, the occasional humpback whaleand possibly other “flotsam and jetsam” can cause problems.
In summary then
Ocean power is not easy to harness. So far, only a few tidal power plants exist that actually produce a reasonable amount of electric power—at predictable intervals. All attempts at getting constant power generation from waves and currents have failed to deliver anything close to the promises. Of course, wind power generating systems are not much different.
The reasons have been known for a long time.
As stated on a UK government site in 2006:
The main problem with wave power is that the sea is a very harsh, unforgiving environment. An economically-viable wave power machine will need to generate power over a wide range of wave sizes, as well as being able to withstand the largest and most severe storms and other potential problems such as algae, barnacles and corrosion.
But don’t give up on your “free ocean energy” dreams yet—there are still plenty of tax dollars to be had to foster them.
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