Tethered propgen

[0001] 1. Field of the Invention

[0002] The invention relates to a hydroelectric power generating device submerged in relatively slow moving water, as in a river or tidal basin. Keeping the device in an optimal water channel velocity during tidal cycles, as well as propeller and shaft orientation with respect to water channel flow are the chief design goals for maximizing the generating capacity factor in a river or tidal basin.

[0003] 2. Description of the Prior Art

[0004] Power generation efficiency within a natural and variable medium requires that the turbine propeller maintain a perpendicular relationship to the water's direction. Past examples of river or tidal basin energy conversion devices have depth and level control in moving water that is regulated by the system's fore and aft wings. Using a system of wings for control is only effective in a dynamic environment—action and reaction. When water is at standstill no control is possible, necessary leveling and depth control is not achieved and bottoming can occur. Other tethered devices have characteristics which prevent bottoming, but are fixed in one direction, and cannot yaw to face water from opposite directions, as in a tidal basin. Additionally, tethered devices that sense only depth are not suited to tidal basin installation, as the depth, which is measured from the water surface, will vary during tidal cycles, while the elevation, which is measured from the seabed, will not. Another past approach utilized with some success is a fixed suspension from a bridge or piling or some other structural means of support. This fixed arrangement fails to satisfy the desired requirement for maximum efficiency due to its inability to maintain a perpendicular relationship to the water's direction. A fixed system precludes the elevation adjustment necessary in an open water channel. As water velocity and surface level varies due to seasonal or tidal change—a fixed system can not adjust. Fixed suspension also precludes the realization of an optimum maximum device capacity factor (ratio of actual kilowatt-hours generated—for the time considered, to the kilowatt-hours that could have been generated at continuous full power operation during the same time period). The vertical freedom of movement for any open channel energy conversion device is acutely necessary to realize a maximum generation capacity factor. What is needed is a tethered, submerged power generating device which is free to traverse up and down in elevation and yaw to orient the turbine propellers perpendicular to water flow in an environment with reversing water flow conditions.

[0005] The invention is a tethered, water velocity seeking tidal generator. The device will actively dive when the water velocity is too high for generation or ascend to seek water velocities in higher elevations. The device uses water and air ballast and drag to adjust pitch, roll and elevation. It will also remain buoyant and actively yaw 180 degrees in slack tide in order to face the approaching and receding tidal waters.

[0006] A typical tidal power generation plant achieves a capacity factor of 44% annually. This invention is capable of achieving a capacity factor of 50% or more due to its ability to seek water velocity suitable for generation.

[0011] FIG. 1 depicts the submerged generating device. Included items:

• [0012] Item 1—the restraining anchor
• [0013] Item 2—the tether
• [0014] Item 3—the power and controls cable
• [0015] Item 4—the front chamber containing but not showing the switchgear
• [0016] Item 5—the switchgear
• [0017] Item 6—the air compressor
• [0018] Item 7—one of two water turbine propellers
• [0019] Item 8—the two back chambers, each containing a shaft and bearings
• [0020] Item 9—shaft and bearings
• [0021] Item 10—speed increasing gear
• [0022] Item 11—a generator
• [0023] Item 12—ballast chamber
• [0024] Item 13—consists of a frame which ties chambers (2) 8, and 4 together and provides structural rigidity to the power generating device
• [0025] Item 14—is the air hose through which air is supplied to the compressor
• [0026] Item 15—the buoy marking the location of the generating device, supporting the air hose and providing an air inlet as well as a local interface to the device.

[0027] FIG. 2 depicts a plan view of the device in FIG. 1. Visible are the doors for maintenance access of the device.

[0028] FIG. 3 depicts a side elevation view of the device in FIG. 1. Included in the switchgear 5 are the sensors which record operating characteristics of the device and relay them to local control. The power and control cable 3 provides an interface between local control and shore control, which allows for remote operation. Minimum and maximum water velocities are set.

[0029] The device will be at maximum elevation, which is controlled by the length of the tether 2 attached to the restraining anchor 1, during slack tide, or when water velocities are approaching zero. The device senses water velocity by means of a velocity sensor as part of the switchgear. When a minimum velocity is reached the device begins to generate power.

[0030] In order to generate power, water flows over the turbine propeller (2) 7, inducing rotation at a relatively slow rotational speed. The slow rotational speed of the propeller is increased to the synchronous speed of the generators (2) 11 by means of shafts and bearings (2) 9 coupled to speed increasing gears (2) 10. Once a tachometer in the switchgear detects that synchronous speed has been reached, the switchgear activates the generator, and power is output via the power and control cable.

[0031] As the water velocity continues to increase with the tidal action, drag forces on the two turbine propellers and three chambers force the device to a greater depth. In a water channel, the water velocity is parabolic, that is, the greatest water velocities are at a depth that is approximately ten to twenty-five percent of the total depth. The maximum elevation, controlled by the tether, is somewhat below the maximum channel velocity allowing for vessel traffic, and for ice formation in cold climates. As the device is forced down by drag, the water velocity of the channel which the device experiences decreases. The device itself always remains positively buoyant, and acts to force the device upward. If the balance of drag forces and device buoyancy bring the device to a depth in which water velocities are still above optimal levels, the device descends by taking on water ballast. Water ballast is added by pumping water from the channel into the ballast chambers. Should the descent of the device come to some predetermined minimum elevation, sensed by a depth sounder in the switchgear, the device ceases descent. If water velocities at the minimum elevation are still above predetermined maximums, the device issues a shutdown command, in which it ceases generating and activates rotor brakes. After the increase in water velocity caused by tidal action peaks, and the water velocity begins to slow, the device ascends to seek optimal water velocity. This ascension occurs either by the alleviation of drag forces through the reduction in water velocity alone, or through a combination of reduction of drag and expulsion of water ballast by compressed air from the air compressor 6, which is supplied by the air hose 14. After the device has ascended to the maximum elevation, and the water velocity has decreased below the minimum velocity, the device invokes the shutdown command, ceases generating, and the turbine propeller is braked.

[0032] As the tidal velocity continues to decrease and eventually changes direction, the device begins to yaw due to drag. The yawing action allows the device to begin to generate once the tidal velocity increases above some predetermined minimal level in the new direction. The yawing is assisted by air or water propulsion systems mounted on the rear chambers. The air or water propulsion systems are also used to eliminate cable twist. The yaw of the device is recorded using a yaw sensor in the switchgear, and if yaw is continually detected in one direction, the air or water propulsion systems allow the twist to be alleviated by forcing the device to yaw in the direction opposite the detected twist.

[0033] During operation, instabilities caused by turbulent currents or various other factors may induce roll and/or pitch in the device. This roll and/or pitch are sensed by a roll/pitch sensor in the switchgear. The device moves air or water ballast to alleviate the roll and/or pitch condition. That is, if the device is experiencing positive pitch, the front chamber will take on water ballast, and the rear chambers will force water ballast out by using compressed air. Accordingly, if the device is experiencing negative pitch, the front chamber will expel water ballast using compressed air, and the rear chambers will take on water ballast. Those skilled in the art will understand that the same rationale will be used to alleviate roll.

[0034] Power transmission and control cable 3, extend to the seabed along the restraining cable 2, and can be buried in or fixed to the seabed and extend to either other units or a control and power station either at some point in the water channel or at shore.

[0035] FIG. 4 depicts a rear elevation view of the device in FIG. 1, and shows the rotational directions of the turbine propellers 7.