WO2022197470A1

WO2022197470A1 - A device for extracting energy from slow moving water utilizing a variable geometry, reciprocating drag machine

Info

Publication number: WO2022197470A1
Application number: PCT/US2022/019027
Authority: WO
Inventors: Robert Reynolds TIPTON
Original assignee: Tipton Robert Reynolds
Priority date: 2021-03-14
Filing date: 2022-03-04
Publication date: 2022-09-22

Abstract

The disclosed device is capable of extracting mechanical work from slow moving water, such as ocean currents, and converting it to useful forms of energy at a Life Cycle Cost (LCC) of 0.076 cents / KWH to 0.11 cent / KWH. This is 2%, or less, than the LCC of the best existing technologies in 2020. The device uses predominantly off the shelf components and works with a variety of collection units. The device is sustainable, scalable in size and number, poses minimal risk of harm to sea life and is easily recovered for recycling or reuse at the end of its useful life.

Description

A Device for Extracting Energy from Slow Moving Water Utilizing a Variable Geometry,

Reciprocating Drag Machine

Description

The device described in this application collects energy from slow moving water, such as ocean currents. The mechanical energy collected may be converted into other forms of energy such as electricity, gravitational potential energy or compressed gases.

The primary utility of this device is it’s very low Life Cycle Cost (LCC) expressed in US cents per Kilowatt Hour (KWH). Calculations show the device can generate electricity at less than 0.08 cent / KWH. The average LCC of electrical generation in the USA is presently 11 cents / KWH and natural gas is 5.4 cents / KWH. This results in the device’s LCC being less than 2% of the lowest cost forms of electrical generation presently in use. Since the device is powered by naturally occurring moving water, it is also sustainable and renewable.

The most common and accepted method for extracting mechanical work from moving water is the rotary turbine. Turbines require the water to be moving at moderate to high speed in order to function effectively. Below a certain speed there is insufficient force to spin them.

The device described in this application makes use of a Variable Geometry, Reciprocating Drag Machine (VGRDM.) This can be best visualized as the piston of an internal combustion engine operating without a cylinder. The collector is a device which can change geometric shape; one shape is high drag while the other is low drag. The change in shape is accomplished by a controller. The controller may be passive, active, mechanical or electromechanical and it’s details are not pertinent to this application. In the remainder of this application the high drag state of the shape shall be referred to as the closed state while the low drag shape shall be referred to as the open state.

The device described in this application is composed of a collector, controller, control line(s), anchor, tether, optional secondary controller and optional float.

The device operates in a two stroke cycle similar to a piston engine.

1. The cycle begins with the entire system submerged in slow moving water, anchored and tethered to the bottom with the collector located near the main controller.

2. The main controller closes the collector.

3. The drag force on the collector, due to the moving water, pulls the collector which in turn pulls the control lines.

4. When the collector reaches the end of the power stroke, the controller opens the collector and pulls it back to the starting position by force. This is the recovery stroke which consumes energy.

5. When the collector returns to the starting position the controller repeats the cycle by closing the collector.

The force and motion of the collector, transmitted by the control lines, produces useful mechanical work. This work can be converted to other forms of energy such as electricity. Because the work generated during the power stroke is much greater than that expended during the recovery stroke the system generates net useful mechanical work. It is also possible to operate two collectors as a ‘push-pull pair.’ In this configuration, the force from the power stroke of one collector is used to recover the other. When the cycle completes, the collectors change roles.

The device described in this application may be used singly or by operating multiple devices in conjunction. If multiple devices operate synchronously, they form a phased array and their net drag force and power output increases. It is expected that most devices will be deployed in groups but this choice is not relevant to the operation of the device described in this patent application.

Example Collectors

There are a multitude of possible designs of the collector, three of which are described in this application.

Sails With a Supporting Frame

This design is made of a rigid frame with fabric sails. When the controller causes the sails to open they go slack and present minimal area and coefficient of drag to the flow. When the controller causes the sails to close they present maximal area and coefficient of drag to the flow.

Figure 1 - Image of an ocean energy using a rigid framed with fabric sails

This design is the simplest and lowest cost of the three described in this application.

Unsupported Sails

The unsupported sails design utilizes sails with shroud lines and no frame. This is similar to a parachute or spinnaker sail. Starting in the closed state, with sails filled, the controller spills the sails and reels them into a small, streamlined container. This can be performed using a furling mechanism or by reeling the sails into a container. The method chosen is not significant to this application. To close the collector, the controller releases the packed sails, akin to deploying a parachute and the sails fill.

When in the packed configuration, the container presents low frontal area and coefficient of drag. Note that in this design the closed collector corresponds to sails being deployed which would normally be thought of as being ‘open.’ Many readers will find this terminology to be logically reversed, but it keeps the terminology consistent across designs.

Figure 2 - Image of an ocean energy collector with unsupported sails and predicted C_d of 2.3 or higher

This design has the maximum Cd of the designs studied and the smallest frontal area in the open (furled) state. CFD analysis shows the design in figure 2 has a Cd of 2.3 or higher. A full discussion of this analysis is contained in citation 1 of SB0008b attached.

Array of Multiple Rigid Vanes

This design of the collector is an array of multiple rigid vanes. In the open state the vanes are oriented parallel to the water flow resulting in low frontal area and drag coefficient. In the closed state the vanes are oriented to impede the flow of water as much as possible resulting in high frontal area and coefficient of drag.

Figure 3 - Image of an ocean energy collector using multiple rigid vanes

This design would be the largest and most expensive. It is also more robust, requires less maintenance and has longer useful life.

Controller

The controller is a pod containing an electronic control module and actuators to control the state of the collector. The controller would operate the collector by varying the length of the two control lines as shown in figure 3. It is also possible to have a secondary controller located on the collector, with its own actuators.

The controller may also contain a device(s), such as an electric generator, to convert the mechanical work into a more useful form of energy and apparatus to transmit or store that energy. While the two controller, master-slave, configuration is simpler in concept, the secondary controller would need to communicate with the main controller and have its own power supply. As a result it is unclear whether one or two controllers is preferable and the choice is not relevant to the operation of the device described in this patent application.

In installations where the pod is suspended from above, it would have negative buoyancy. If anchored from below it requires positive buoyancy. This discussion focuses on the bottom anchored installation but both are covered by this patent application.

The pod is designed to have positive buoyancy so it will operate at relatively constant depth. Positive buoyancy would also cause it to float to the surface if accidentally detached from the anchor to ease recovery and repair. The controller can achieve positive buoyancy singly or by using a separate float, described later.

Figure 4 - Image of a Concept Pod With Block And Tackle Line Control Mechanism

Figure 4 shows an exploded view of the controller’s pod. It consists of a pulley, dual line control mechanism, electric generator and the enclosing pod.

Control Line(s) and Associated Control Mechanism

The collector is connected to the controller by means of one or more control lines. The control line transmits the force on the collector to the controller where that force can be used to power an electric generator, air compressor or other means of converting or storing the mechanical work produced by the collector into a useful form.

It may be desirable to use redundant lines in place of a single line to reduce the risk of losing a collector due to a line breaking. This discussion treats redundant lines performing the same function as a single line. When controlling a passive collector, there is a second control line which is used to open and close the collector. This is done by changing the distance of the end of control line 2 relative to the end of control line 1. Since the sum of forces on the two lines is equal to the force on the collector, this changes the relative force between the two lines. The difference between these forces is used to open and close the collector. In this arrangement both control lines are load bearing and combine to produce mechanical work.

The relative length of line 2 may be changed by using an inverted block and tackle or dual pulley with phase adjusting gear mechanism. This is discussed later.

If only one control line is used some other method must be provided to inform the collector when to open and close. This can be done mechanically, optically, electronically, acoustically or by means of an inertial control system. In this configuration the main controller would send a signal to the secondary controller, located on the collector, to open and close the collector.

Figure 5 shows an enlarged view of the reverse block and tackle mechanism (without lines). In most applications a block and tackle is used to increase force by means of mechanical advantage. It does this by a system of pulleys which cause a small force on the input rope to produce a larger force on the output rope. One consequence of this is that the input rope moves a much greater distance than the output rope.

Figure 5 - Detail of Block And Tackle Line Control Mechanism

In this mechanism the roles of input and output are reversed. A large force acting over a short distance produces a small force acting over a long distance. As a result, the block and tackle ‘consumes’ more rope, or in this case control line. This has the result of making line 2 effectively shorter.

Figure 6 - Reverse Block And Tackle Line Control Mechanism Figure 6 shows a schematic diagram of how an actuator changes the position of the moving pulleys of the block and tackle, thus increasing the path length of the upper line. In this diagram 1 unit of change in the actuator line results in 4 units of change in the upper line. This changes the distance between the ends of the first and second control lines. This change in distance, and resulting force, is used to open and close the collector.

The mechanism in Figure 5 is using plates with slider holes in place of the pulleys shown in Figure 6.

While Figure 5 shows a controller using a single pulley storing both lines, it is also possible to use a divided pulley or multiple pulleys.

Figure 7 shows a Phased Dual Pulley Line Control Mechanism. It consists of two pulleys synchronized by a gear chain made up of two sets of bevel gears. One set of the bevel gears is rigidly connected to a phase control gear which adjusts the phase angle between the two pulleys. As the phase control gear is rotated, the phase angle between the two pulleys changes which in turn changes the distance between the ends of the two lines. The phase control gear is rotated by an actuator (not shown). Both pulleys are synchronized on a common shaft which opens and closes the collector.

Figure 7 - Schematic of Phased Dual Pulley Line Control Mechanism

Anchor and Tether

One advantage of this device is that it does not require a rigid pylon or base and can operate using an anchor and tether. The anchor can be made of any dense material or combination of materials such as metal, crushed stone or concrete. While the tether may be constructed of materials such as rope or metal cable, if it is made of a neutrally buoyant material it does not have to support its own weight. Using such a neutrally buoyant material the tether can be of any length and can operate in any water depth. This would allow the device to operate in large, low velocity flows such as the Gulf Stream or Kuroshio Current. Neutrally buoyant materials of this type are already in widespread use. Spectra- Dyneema is one example - the rope that floats.

One feature of the device described in this application is that it can use an existing structure as an anchor. Possible structures include bridge caissons and offshore drilling platforms.

In addition to cost, the anchor and tether design produces a small footprint on the seafloor with low environmental impact. If the device requires service, it can be detached and taken back to shore. One way to accomplish this is by using an Underwater Remotely Piloted Vehicle (UROV). AUROV can descend to the anchor and detach the tether. Then the entire device - sans anchor - can then be transported to shore for maintenance. The same method can be used to reattach a tether.

Optional Float or Weight

While it is possible to design the controller’s pod to have the required buoyancy and keep the collector at the desired depth, some installations may choose to achieve the desired buoyancy by means of a float, weight or surface vessel.

Mechanics

The forces on the controller, anchor, tether and other components are not significant to the operation of the device described in this patent application.

The force on the device’s collector is expressed as

Eq l F = ½ p Vr² CdA

Where

F is the force p is the density of the water

Vr is the velocity of the water relative to the device Cd is the coefficient of drag and

A is the frontal area

The power extracted by the device is expressed as

Eq 2 P = F Vm

Where Vm is the velocity that the collector is moving relative to the controller.

Substituting Eq 1 for F in Eq 2 yields

Eq 3 P = ½ p Vr² CdAVm

It is convenient to express Vr and Vm relative to the velocity of the water as

Eq 4 Vm = k V and

Eq 5 Vr = (1 - k) V

Where k is a constant between 0 and 1 and V is the velocity of the water. Substituting equation 4 and equation 5 into equation 3 and simplifying the result yields

Eq 6 P = ½ p k (1 - k)² Cd A V³

Figure 8 - Relative Power Generated as a Fraction of Water Velocity (k)

Figure 8 shows the effect of k on generated power. It can be shown that maximum power is extracted when k = 1/3. This corresponds to the Betz derivation for a turbine where the fluid velocity is slowed to 1/3 of the free stream velocity. Substituting k = 1/3 into equation 6 yields

Eq 7 PMax = ½ p 4/27 Cd A V³

References and analysis show that the value of Cd in the open state is roughly 0.3 and in the closed state is 1.4 to 2.5. 1.4 is a typical value for a parachute, 1.6 for a sailboat spinnaker and 2.5 for a sail optimized for high drag as described in appendix A.

Assuming that the sail with frame configuration has a span of 100 cm and the frames have a frontal chord of 0.5 cm, the area of the closed square is 10,000 cm² and the frontal area of the frame is 199 cm². This results in a closed/open area ratio of 50.

Assuming that the sails of the unsupported configuration are square with a span of 4 meters and can be packed into a cylinder with a 15 cm diameter, the area ratio would be roughly 2,000.

Since the area in the closed state is roughly 50 to 2,000 times greater than in the open state. Using a conservative assumption that the product (Vr² Vm) during the recovery stroke is 10 times higher than during the power stroke, the energy required by the recovery stroke is 0.06% to 4.6% of the energy collected during the power stroke. Assuming that the collector is operating near 1/3 of the water velocity, the total cycle would operate at 95% to 99.5% of theoretical efficiency. This is not including losses in the generator.

Assuming that the device operates with Cd closed of 2.3, it would have a theoretical efficiency of 34%. Atypical horizontal axis turbine operates at between 30% and 45%. This shows that the device described in the application can operate on par with a typical horizontal axis turbine.

However, drag devices are insensitive to flow velocity when the generator is adjusted for RPM by means of a transmission. This adjustment keeps the collector operating at near 1/3 the free stream velocity. Therefore, the device described in this application will operate near optimum efficiency across a broad range of water velocities. According to the US Energy Information Agency, the average LCC in the USA in 2020 was 11 cents / KWH, for wind it was 5.6 and natural gas it was 5.4. Estimates show it is possible to produce a version of the device described in this application capable of generating 3KW for $500 and it would have a useful life of 25 years. Based on those figures it’s LCC would be 0.076 cents / KWH. Even if that LCC is doubled for repairs and maintenance, the LCC would be 0.15 cents / KWH. This shows that the device described in this application would generate electricity at 0.7% to 2.8% of present methods.

A larger version of the device, using the array of rigid wings design, operating in a 5 knot current, generating 40KW would cost $9,676. Table 2 shows a breakdown of this estimate. These values are based on online catalog prices for the various components.

Table 2 - Cost Breakdown of a Representative Rigid 40KW Device

This version of the device would have an estimated life of 25 years resulting in an LCC of 0.11 cent / KWH. This is 1% to 2% of current technologies.

While there are presently systems in place for extracting energy from ocean currents, the best known are in use in Scotland, these systems currently have LCCs of 18 cents/KWH which is 2 to 3 times what the best technologies cost today.

The device described in this application produces electricity at less than 0.4% to 0.85% of the best available ocean methods and 1.4% to 2.8% of the best of all present methods. Further, this device is in its infancy and these estimates are conservative. When the device described in this application is fully refined, these values of LCC should be substantially lower. In addition, the device’s collector unit fully impedes the water flow. While it looks like a net which would be likely to ensnare sea life or be fouled by debris, the blockage it creates in the flow causes the free stream flow, and anything within it, to pass around the device. This characteristic of the flow makes it unlikely that the device will ensnare sea life or trap debris.

Prior Art

Virtually no prior art could be found for this type of device. The general concept, on land, is shown in most text books on wind energy, but as shown in the attached reference document, there has never been significant research into maximizing drag or using those effects to collect energy.

A search of the ePCT terminology list shows that this class of machine is not listed. It operates something like an open, positive pressure piston pump; however it has no cylinders and does not match that category.

Prior art loosely relating to this application is listed here

• Patent number 9416796, Jan 292014, Hydrostor, “Energy accumulation apparatus.”

• Patent number 8,169,101, May 1, 2012, Canyon West Energy, LLC (Canyon, TX), “Renewable energy electric generating system”

• Patent number 9,909,491, March 6, 2018, Bromberg, et al., “Engine reformer systems for lower cost, smaller scale manufacturing of liquid fuels”

• Patent number 8,721,868, May 13, 2014, Kelly, et al. “Integrated solar-powered high-pressure hydrogen production and battery charging system”

• Patent number 5,733,422, March 31, 1998, Lin, “High-pressure gas producing electrolysis tank

Claims

Claims I claim the following about the device in this application.

1. The device is well suited for collecting energy from slow moving water at all depths

2. Has Life Cycle Cost of energy generation less than 2% of the best present technologies

3. The device poses low risk of harm to sea life

4. The device has very low complexity

5. The device does not require a supporting base or pylon.

6. The device can be designed to float to the surface for recovery and repair if lost.

7. The device is easily recovered for recycling or reuse at the end of its useful life.