Feature ArticleWave Catcher Provides Momentum For Alternative Energy
By Donald Gehring
The Wave Catcher Barges can be installed in shallow to ultradeepwater, as stand-alone generators for small communities with relatively low power needs or in large power farms taking advantage of the economies of scale. In a large power farm, each barge can export its power through draped, flexible power cables to other barges, to a seabed power collection system and then, finally, to an inverter-transformer-control hub platform, which could be a fixed or floating offshore platform. The hub platform will be very important because of the value of the power going through it. It will most likely house personnel who can be quickly dispatched to fix problems on the barges and maintain continuous power output. The hub platform will invert the power if needed, transform the power, control the farm and export the power by an efficient, high-voltage power cable to its end-user.
This barge overcomes significant challenges that have faced the marine energy industry for years. The capture, conversion and transmission of significant marine power is as economically efficient as onshore wind. The barge is low cost and low risk, with quick installation and removal. Safe offshore, above-water maintenance and replacement of almost all mechanical components, minimal environmental impact and minimal visual pollution make the barge reliable. Service lasts for 15 years or more, until hull repainting is needed. It has the robustness to survive extreme, more than 100-year return period storms.
Waves apply cyclic prying forces between the barge and the seabed. The waves lift the barge up, and the barge's mooring belts try and pull the barge back down. After going over a series of large-diameter pulleys, the waves apply a large turning force to the flywheel that turns the generators. The larger the barge's bottom area and the higher the waves, the higher the mooring belts' vertical lift. The higher the forces, the more power is produced. All of this results in wave energy being transferred to the barge, then to the mooring belts and finally the generators, which convert the energy to electric power. The energy conversion efficiency should be more than 80 percent.
The articulated pulley, the first pulley the mooring line belt goes over, is housed in a wet room on the barge. The articulated pulley is aligned with the long axis of the barge and normally will not significantly change its angle if the bow of the barge remains headed into the waves. However, if the barge has a fixed heading, the waves will sometimes hit the barge from the side, and the articulated pulley will change angle as the mooring legs incline to the side. The second pulley that the mooring line belt goes over is a unidirectional pulley with a recoil spring, like the pulleys and recoil springs on a lawn mower starter. The unidirectional pulley keeps the mooring leg belt applying torque to the generator in the same direction. The recoil spring in the unidirectional pulley rewinds the mooring leg belt back onto the unidirectional pulley when the barge enters the wave trough. The unidirectional pulley is turned by its mooring belt each time the wave crest lifts the barge, and the unidirectional pulley turns the large flywheel. The flywheel then turns the generator. The flywheel temporarily stores wave energy in the form of momentum and keeps turning when the barge enters the wave trough. All mooring legs' belts do the same thing with their pulleys, flywheels and generators. Many of these separate components may someday be combined into one component, saving weight, space and costs.
The Wave Catcher Barge can use many types of moorings systems depending on variables like water depth, environmental conditions, desired efficiency, etc. The mooring legs are long enough to allow the barge to ride the 100-year storm waves. The bow has a long, gradual taper to the horizontal, which causes both horizontal and vertical wave forces to lift the barge as high as possible under normal sea conditions. The bow's shape diverts extremely high storm waves and winds, laterally minimizing horizontal loading.
Barges are the lowest-cost floating offshore structures and can be sized for normal waves to produce enough upward force for the vertical mooring lines to turn four large wind turbine generators. The result is significant power generation from one barge.
A conceptual design has been carried out for a possible barge in normal, 2-meter significant waves. The costs would be similar to onshore wind power when using the costs of known components, like a typical deck barge, high output wind turbine generators, direct seabed mooring systems and typical offshore installation costs. To continue this article please click here.
Donald Gehring has worked for more than 38 years designing, fabricating and installing offshore projects all over the world. This work includes hundreds of fixed offshore platforms, five TLPs, eight FPSOs, three FPSs, two FSOs and seven very large topside floatovers. He holds eight patents.