Overtopping wave energy systems are one of the pathways being investigated to capture this potential renewable energy source. An interesting an innovative approach has been adopted by the Norwegian company Wave Energy, which is now doing a technical feasibility study for building such a system in Oregon’s famous and famously stormy Tillamook Bay. Waves form a potentially large world-wide energy resource, estimated at more than 2 Terawatts, but formidable technical challenges have long stood in the way of realizing this potential.
Ocean energy is one of the most concentrated forms of renewable energy that exists and it has the potential to provide a significant contribution to the electric energy needs of many regions that border on the world’s great oceans. The world is estimated to contain some 2 terawatts of potential wave energy – although much of this is probably not recoverable for one reason or another. Ocean energy is not applicable on every coastline of course, but in many regions the energy potential contained in waves is in fact significant and if it can be harvested it could provide a fairly steady and reliable source of power. Wave energy does vary of course – ultimately depending on the winds that impart energy to the rippling ocean surface, but it varies less than wind energy and its variance is also more predictable over the time scales that it varies upon. This is important because it enables the – hopefully smart – grid ample time to respond to predictable peaks and troughs of power production.
Wave energy has lagged behind hydro, wind, solar, biofuel/biomass, geothermal because it also presents significant challenges to anyone who seeks to harvest it. For starters the salt water environment is itself very tough and corrosive – as any marine engineer can attest to. Many materials that are commonly used do not survive well or for very long in this saline and watery environment. Not only is salt water itself a problem, but any structure that is immersed in the ocean itself becomes a platform for colonizing and hardy species such as barnacles or muscles and these can become a problem in and of themselves (again as anyone who has ever had to clean a hull can surely testify to). AND as if this was not enough the ocean can become at times a very scary and violent place. Ocean storms can reach levels of energy that will rip apart structures and smash things to pieces. In fact this is also one of the principal challenges faced by designers of ocean wave energy harvesting engines.
In large part because of the combination of these issues wave energy has largely remained an elusive dream. A few pioneering companies such as Pelamus Wave Power Ltd have tried and met with some limited success and unfortunately significant setbacks as well (sadly it seems there installation off the coast of Portugal is on hold). Ocean Power has announced that it is building a PowerBuoy 150 – with peak power output of 150kW – in Reedsport, Oregon; a project that is being funded by Pacific Northwest Generating Cooperative. However it should be also noted that in the past other wave power buoys have met with untimely ends in the rough Pacific Northwest seas. Hopefully this one will demonstrate the feasibility of these devices.
It would be nice if I could report a rosier picture, but the news is still decidedly mixed. However the fact remains that waves and ocean swells are some of nature’s most concentrated energy carriers, with many regions containing more than 30 kw per meter of shoreline.
A Norwegian company called appropriately enough Wave Energy is now carrying out a study for a slightly different type of wave energy collection device that I found quite interesting. It has been funded to carry out a technical feasibility study of the possibility for a full-scale implementation of a Wave Energy-structure in connection with the jetty reconstruction project at the Port of Garibaldi in Oregon.
Their technology is interesting in several ways. It is based on the wave overtopping principle with an interesting twist. Fully utilizing the entire spectrum of different wave heights is one of the main challenges in wave energy designs. In order to achieve a higher total utilization of the potential energy contained in varying wave conditions Wave Energy (the company) employs a patented system of three separate reservoirs placed on top of each other, in which the potential energy of the wave will be captured and stored. The water that is captured in these stacked reservoirs will then run a turbine thus generating electric energy. By utilizing three reservoirs with overtopping apertures placed at strategically varying heights above one another the overall efficiency will be significantly higher as compared with an overtopping system that has a single overtopping level. In other words lower energy waves will still be able to generate power, overtopping at the lowest energy level; while higher energy waves will overtop at higher levels as well.
The cutaway diagram clearly shows the inclined wave energy intercepting ramp and the three stacked overtopping reservoirs that will capture as much energy from waves as possible. As a wave is intercepted by the structure it will – just like in a breakwater – rush up the inclined ramp, and as it does it will fill the various overtopping reservoirs. The big high energy waves will overtop a significant amount of water into the highest energy upper reservoir (as well as the two lower ones of course); while more common lower energy conditions will still overtop at one or more of the two lower energy reservoirs.
What I also found unique an interesting about their idea is that it can be incorporated – as in fact is being studied in Port of Garibaldi, Oregon into a breakwater or jetty. The wave energy harvesting system in this way serves the additional important function of sheltering an area of much calmer water lying behind the wave energy intercepting barrier it forms. This robustness – after all it is also a breakwater – seems like it will ensure that this system can handle the very roughest of ocean storms a big problem with many offshore buoy systems that have in fact been damaged or even destroyed by big ocean storms.
Another interesting idea that has been developed by this company is a multi stage turbine that will be able to utilize the energy contained in the three water columns (reservoirs) that have been stacked above each other as outlined in the diagram. By being able to utilize a single turbine wheel only a single turbine shaft and generator is needed to convert power from all three of the reservoirs. In this manner the overall system complexity and cost is kept down.
I am fascinated and have long been fascinated by the potential of wave energy; there is something so visceral and dynamic in ocean swells pounding on the coast with thunderous retorts that can be heard even from far off. I would love to see Oregon take the lead in this particular renewable energy sector; it certainly has the wild seas to power it.
© 2011, Chris de Morsella. All rights reserved. Do not republish.