Electric Power Generation from Water Waves

There have been many hundreds of concepts that have tried to capture some of the energy from ocean waves breaking on a seashore. Few have even generated any productive electricity at all, and nearly all were quickly destroyed by storms and other natural problems. Some interesting ideas were tried in the 1920s and 1930s, all of which soon became total failures. People today think they have come up with 'new ideas' for such things, but if they would do any Research into US Patents, they would certainly discover the thousands of various ideas which have already been Patented long ago, but which were, like most Patent concepts, totally without merit!

This is an entirely different approach, which is far more efficient at capturing energy, and also much less susceptible to being damaged or destroyed by storms.

Previous concepts generally EITHER attempted to capture the potential energy of rising-falling motion (often with giant floats which bobbed up and down and which were mechanically connected with levers and shafts to transfer the power to a location where electricity might be generated; OR attempted to capture the kinetic energy of the water motion, again using mechanical levers or shafts to transfer the power. There have been pneumatic and hydraulic concepts tried, similar to the concept of the hydraulic ram water pump, but that intrinsically has very low overall efficiency.

The variety of ideas thought up, and occasionally tried, is entertaining to look through. Patent Applications of thousands of different ideas are all in the Public Record! The majority of them show such ignorance of basic laws of science that they are laughable. But a few show actual thought and actual logic, but again, the Inventors seemed to not be aware of logic or the Engineering equations that must be analyzed to determine whether any such idea might actually have any merit.

AFTER I had invented this concept in 1996, I noticed that a European company was bragging that they had invented a device to do similar (around 2006, as I recall). They imagined a very long 'snake' that would have dozens of flexible couplings every hundred feet or so. They had decided that they could install hydraulic cylinders inside their 'snake' which would alternately pump hydraulic fluid as though they were hydraulic pumps. Then they decided they could send that pressurized hydraulic fluid the thousands of feet along the entire length of their 'snake' to a conventional hydraulic motor, which would drive a gear-box to increase the rotation speed to drive an alternator to produce electricity.

An interesting idea, but certainly not actually thought through and certainly not Engineered! Their 'snake segments' were of fixed length, which made the thing only capable of capturing energy from a very specific wavelength of ocean waves. Since they described doing this in deep ocean water, no one there seemed to be aware that the deep ocean wavelengths are necessarily many hundreds of feet long, so all their segments would have to be extremely long, and their whole device would have to be several miles long. In very shallow water near the coast, the configuration they described might do something, but their device would be a terrible Maritime Hazard to ships and boats! The durability of anything resembling what they described would be questionable, due to all the many rubber seals in the hydraulic cylinders and the mechanisms they thought would work out there. Next, they clearly had NO idea that using hydraulic cylinders and hydraulic fluid is NOT very efficient, and even if they could get the huge thing to produce any hydraulic pressure, running that thick hydraulic fluid through miles of piping (including many flexible sections which are more likely to fail), creates a lot of frictional heat, meaning most of the collected energy gets lost as friction. Next, the efficiency of hydraulic motors is not very good, so the amount of electricity that an Alternator might produce would be minimal, even WHEN the waves happened to have the right wavelength!

And finally, they described having this thing hundreds of miles out in the ocean, and they are clearly unaware that, even when designed well, long electrical distribution wires waste a lot of the electricity put in! So their claims of being close to convincing the government of Portugal to give them many millions of dollars to build one of their 'snakes', would barely have ever gotten any electricity to get to anywhere in Portugal! For their millions of dollars of investment, Portugal might have eventually gotten $10 of electricity per hour, if they were lucky!

Their idea had glimmers of merit in it, but they clearly had never done any of the Engineering or Physics to determine if it might be practical! It wouldn't! Their people were amazingly arrogant that they KNEW ALL THE ANSWERS, so they were not even interested in any FREE HELP I offered them! Fine with me!


This invention is entirely different. It actually captures part of both types of energy and generates electricity directly, without significant mechanical mechanism. It is NOT directly attached mechanically to the seafloor or any equipment on shore, but more resembles the semi-freedom of navigation buoys. They DO have a leash of sorts that keeps them in a general location, but they are also fairly free to bob around due to any storms.

Main Structure

Two standard massive concrete buoy supports represent the end points of the assembly. Two heavy ("1/2quot; or thicker) marine steel cables span the distance between the two concrete piers, parallel to each other and 4 feet apart. The space between the two concrete piers will here be assumed to be 500 feet.

Sixty-three identical assemblies are affixed to both cables with standard U-bolt clamps. Each assembly is as follows:

A four-foot cubic box of 10 gauge marine-compatible steel, waterproof, is between the two cables, such that the cable clamps are at all four of the very bottom corners of the box. They maintain the spacing of slightly over 4-foot distance between the two main cables, and also secure the position of the cubic box. The 63 such boxes are spaced at 8-foot intervals along the main cables, such that they equally space the entire 500 foot clear space between the concrete piers.

If there were no other parts, this assembly could be seen as representing a series of floats which would keep the cables just slightly below the surface of the water, but otherwise the positions and integrities of everything are secure, as long as the two main cables do not break. This is NOT the configuration it works in, but is the emergency configuration in case major damage occurs to any parts of any of the assemblies.

Each assembly has outriggers welded across both ends of the cubic box. These outriggers are standard marine-compatible U-channels, of the standard 40-foot length. They are welded such that the outriggers extend equally on both sides of the cubic box, that is, 18 feet beyond the sides of the cubic box where the cable clamps are attached. The U- shape is positioned upside-down, such that water would never be trapped inside of it regarding corrosion.

This now provides a pair of 18-foot-long outrigger arms on each side of the cubic box.

Each assembly includes two pontoon floats, which will attach on the underside of the outrigger arms. The pontoon floats are 7'6" by 4' by 1'. The one-foot dimension is vertical, and the longest dimension is parallel to the main cables. When all the 63 assemblies are properly attached to the cables, these floats appear as nearly a pair of continuous float sidewalks, from the one concrete pier to the other, with a six-inch gap between each of the 63 segments.

The cubic box is therefore supported mostly above the outrigger U-channel pieces, which rest on top of the pontoon floats. This means that the cubic box and the outrigger channels are generally ABOVE the water, and therefore the cables connecting the assemblies are also visible just above the water surface. One pontoon of these dimensions has 30 cubic feet of volume, and so two of them could support around 3800 pounds by their displacement. The actual total weight of an assembly is planned to be around 2000 pounds, (box around 400, outriggers around 600, pontoons around 500, box contents around 500) so each pontoon float is expected to normally be around half submerged.

The pontoon floats need to be positioned at a specific distance from the cubic box. This positioning is related to an equation that determines the surface wavelength to the local depth of the water. This basic adjustment should not be necessary, except on first installation and if the contour of the ocean bottom changes enough to alter the wavelength of the incoming waves.

During the common 13-hour cycle of the Tides, a sinusoidal variation occurs in the water depth so this system needs to have a regular adjustment of the length of the outrigger arms. Threaded shafts can be provided along all four outriggers, such that the pontoons might be very easily and automatically adjusted in this way.

Functionality

At the location where the specific assembly is to be installed, the wavelength is determined by observation. As an example, say it is 72 feet, crest-to-crest. Half of a wavelength would then be 36 feet. The pontoon floats would then be positioned so that their centerlines were 16 feet out along the outriggers, so their centerlines were 18 feet from and parallel to the centerline of the line of cubic boxes.

When one pontoon float is on top of a wave crest, the other pontoon float is in the adjoining trough, half a wavelength away. This situation causes the cubic box to experience the maximum amount of angular motion/displacement due to the waves.

When unusually strong storm-driven waves come in, the weight of the assemblies limit how much power can be recovered. When unusually large wave crests come in, the entire assembly is partially lifted up out of the water, with the pontoon that would normally be resting in the trough then being above the water surface.

Analysis

When a wave crest encounters the first (outermost) pontoon float, that float is lifted up, by the power of the wave. The opposite pontoon float is simultaneously falling, and not providing any support at that instant. A torque (Moment) is therefore created in the device. The instantaneous lift is the 1900 pounds of floatation lift that that pontoon can provide, and the total lever arm is 36 feet (numbers from our example.) This therefore creates an instantaneous torque (Moment) of 68,400 ft-lb.

If the waves come in at 10 per minute (one per every six seconds), this torque increases to 68,400 ft-lb, drops to zero, reverses to -68,400 ft-lb, drops to zero, and returns to 68,400 ft-lb, every six seconds. This is a sinusoidal variation. This therefore represents an amount of mechanical power equal to an average of around a constant 8,000 ft-lb/sec. This is equal to around 14.5 horsepower or 11 kW.

This device does NOT require the waves to break. In general, if this system is installed farther out, the waves are less tall, but the wavelength is also generally longer. A different configuration would then be needed, but the same amount of torque (Moment) would still be available. Breakwaters tend to be installed where it is shallow enough to be able to economically pour all that concrete. This concept allows for additional flexibility, in being able to place the breakwater devices farther from shore, but with similar benefits regarding wave reduction and electricity production.

The items inside the cubic box are expected to recover around 1/2 of this energy or about 5.5 kW per device. The 63 assemblies in that 500 foot stretch would therefore have around 350 kW of power available, nearly all of which can be converted directly into electricity.

Where a mile long breakwater would normally be used, ten of these sets of assemblies could be used instead. Collectively, they would provide a reliable and constant 3.5 megaWatts of electricity, WITHOUT BURNING ANY FOSSIL FUELS OR USING ANY IMPORTED URANIUM.

The power that is captured is removed from the strength of the incoming waves. Therefore, the primary function of a breakwater is produced but without the many environmental impact effects of permanent concrete breakwaters.

In an area where waves come in that are generally rather powerful, a second row of this device and even a third could be used. The amount of electricity generated by each succeeding line of devices is less, because power had already been removed from the incoming waves! But after several stages of this energy removal, waves approaching the shore can be subdued to nearly any desired level, while gaining large amounts of electricity in the process.

It must already have been noted that the main cables will also support the main electric distribution lines that will bring all that electricity to either end pier and then to land. The adjoining town and landowners would then probably receive free electricity forever.

As to the aesthetic appearance of this: The structures are certainly no taller or larger than a conventional concrete breakwater. From the shore, it would certainly be noticeable that there was oscillating movement, but the overall appearance does not seem to have any unpleasant aspects. There are no additional marine hazard issues than if a standard concrete breakwater was in that location. Fishermen might dislike it because it would not be safe to go out on to fish, because of all the motion!

Inside the Cubic Boxes

A fairly heavy (400 pounds), fairly generic gyroscope is primarily what is in the cubic box. The gyros shaft is started out with its axis of rotation being vertical. Consider a such a gyro that has a 3-foot diameter and where nearly all of the 400 pound weight is at that 18" radius. (mass is 12.5 slugs). Rotational Inertia is therefore around 28 slug-ft2 (or 38 kg-m2.)

If the gyroscope has good bearings, a rotational speed of 3000 rpm should be conservative and reasonable. That is 50 rps or 314 radians/sec angular speed. (The outer edges of the gyro rotor would then be moving at around 470 ft/sec or 320 mph, not an outrageous speed.) The Angular Momentum would then be 11,900 kg-m2/sec which is the same as 11,900 nt-m-sec (8,800 ft-lb-sec).

This is the Angular Momentum of the gyro rotor, which attempts to keep its orientation in a fixed vertical axis direction.

The effect of the pontoons is to cause a rocking of the assembly, which constantly would cause the gyro axis to be perturbed.

The gyroscope axle is mounted in a ring bearing mount, where it would be able to tumble over sideways. This allows the body of the cubic box to rotate back and forth without directly affecting the gyroscope axis direction. However, a mechanism can be provided that enables this differential motion to create a reciprocating and then a rotary motion, which effectively applies a load on the gyroscope. In the same way that a toy gyroscope can "hang" in space due to a force that counteracts the weight-caused Moment, the same is true here. As long as the perturbing Moment is not greater than the Euler-calculated ability of the gyroscope to resist, the gyro axis will not be materially affected, and the applied Moment is then converted into work and power by that intervening mechanism.

In our example device, we have waves that come in every six seconds, meaning that the oscillation is at around 1 radian per second. The maximum ability of a gyroscope to resist directional change of its axis is given by M = I * omega * OMEGA. In this case, we have 28 * 314 * 1 or 8800 ft-lb (or 38 * 314 * 1 or 11,900 kg-m) for the maximum applied Moment that it can resist. We have already calculated that the device is capable of applying a maximum of about 68,400 ft-lb.

Therefore, for this size gyroscope, we would regularly be applying far more torque/Moment than the gyroscope could resist. The result would be that mechanical power and then electricity would be produced, at a very constant rate, but that the axis of the gyroscope would also be forced to rock back and forth (substantially) because that specific gyroscope was not substantial enough to absorb all of the desired Moment.

It would work fine, but it would be limited in removing an amount of power from the waves only around 1/7 of what it could remove (and convert into electricity).

A moderate amount of Engineering would be involved, following the above pattern, to determine an optimal gyroscope. For our example, if we considered a larger cubic box, where a 6-foot gyroscope could be included (with the same total weight), we would then have:

Rotational inertia: 112.5 slug-ft2 (or 152 kg-m2.)
Angular momentum: 47,600 nt-m-sec (35,200 ft-lb-sec)
Maximum amount of resisting Moment: 35,200 ft-lb or 47,600 nt-m.

Note that this still spins at the same rate, but is now able to absorb over half of the available wave-caused Moment. Similar modifications of the gyros weight, diameter or rotation speed could have other beneficial effects. Obviously, if we allowed this larger gyro to weigh twice as much, we would already be able to absorb all of the desired 68,400 ft-lb of Moment, and even a little more, around 70,400 ft-lb.


The mechanical linkage would need to have an automatic adjustment built in. When waves are of less height, the rocking motion is of less angular amplitude, and therefore a smaller angular distance must then be linked to cause circular sinusoidal motion. This is fairly easy to implement. It merely needs a feedback circuit to adjust the length of the linkage arm as a result of the extent of the rocking motion that exists at that instant.


I first invented this while sitting on a beach near Fort Lauderdale, Florida in 1996, and I did the Design and Engineering work on it in 1997. When I discovered that an impressive amount of electricity could be produced by this system, while also reducing the size and power of the waves that constantly erode all the Florida beaches (where they find it necessary to build huge and expensive concrete breakwaters to try to deal with that problem), I expected the various beach cities in South Florida to jump at the chance of being able to solve several of their main problems all at once, while also providing much of the electricity their cities need, and all for surprisingly minimal cost. I was shocked that absolutely NONE of the cities had the SLIGHTEST interest in this! As a result of that total lack of interest, I chose to NOT then include this in the various energy-related pages in my Domain. This presentation was first placed on the Internet about ten years later, in March 2006, but then only in a very SECURE section of the Domain, where no one would be able to access it. I don't mind when people USE one or more of my devices or systems, but I get offended when a lot of people treat me as though I am uneducated and ignorant! In 2013, I am easing back and I have decided to make PART of this information available in a page which is accessible. I am now tempted to think that even if some beach town sees value in it, that they are very unlikely to know any Physicists who could do the Euler's Equations for them regarding how the massive gyroscope works inside it, or any Engineers who could know how to safely Design it to get built! So this page has now become available in April 2013!


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C Johnson, Theoretical Physicist, Univ of Chicago