Ocean Renewable Energy Hybrid Power Generation

Combining wave and wind energy in a hybrid power generation system appears to be economically and technically feasible. Waves are a more steady energy source than wind. Wave power is predictable at 90% accuracy up to 48 hours in advance, and up to 50% accuracy five days in advance. This makes it more attractive to utilities as a power source. When the wind suddenly drops the waves keep on surging past. Moreover wave power is even more complementary to wind power - in high winds the wind turbines have to brake or stop to avoid breaking. However that is usually when the wave power is strongest, so power generation from the hybrid system is maintained. A discussion on hybrid power is maintained here.

Wave power is the obvious hybrid with wind. But solar power and Ocean Thermal Energy Conversion power could also be added to platforms depending on their locations.

With a platform fixed in the ocean there are a variety of ways to convert wave energy into renewable power. The Company has proposed Oscillating Water Columns built into the legs of the platform. This appears to be the simplest way to make some wave power. However the power in not that significant, less than 10% of the expected wind power. This is because the platform legs do not have significant cross-section to the waves, in fact it is desirable to make the legs as this as possible to decrease wave loads on them.

Wave-driven pistons are another means to convert wave energy to power on a fixed structure. An Israeli company has demonstrated such devices. Use of waves and pistons to drive air turbines is claimed in an invention, "Ocean Wave Air Piston", US Patent 7,468,563, Joseph J Torch; (Towaco, NJ). Click to enlarge this image provided with permission of the inventor.

Offshore Renewable Energy and the Capacity Problem

Wind and wave energy are intermittent. Sometimes they just stop. This is not good for power customers who need steady power. Very large wind/wave projects must either transmit power into a regional grid that can quickly balance changes in power, or they must include a power source that can be brought online quickly to make up the power loss when the wind quits.

Natural gas, in pipeline or Liquid Natural Gas (LNG) form, is adequate as an energy source to balance intermittent wind and wave energy. LNG terminals located offshore are already under construction in the Gulf of Mexico and proposed in California, New England and New Jersey. Such terminals can provide fuel to natural gas turbine generators installed on offshore wind turbine platforms. When the wind drops the gas power plant increases its output so the total power is always maintained near maximum. Here is a good presentation (PDF) about the concept. Integration of a gas power plant into an offshore wind farm has been pioneered by Eclipse Energy in its Ormonde Project (picture below).

The mobile jack-up platform proposed by the Company is suitable to support a complete LNG power plant offshore as follows:

At each wind/wave farm, there is a platform with a substation that gathers the power from all the other platforms and packages it for transmission to the shore station. On this platform could be installed a large LNG-powered generator with up to 500 MW capacity (the platform will need to be larger than the "normal" platform, of course). LNG storage tanks are installed on the sea bottom under the platform, between the legs, below the waves. The legs are about 150 feet apart and typically in 100 feet or more of water depth. The tank can thus be 140 feet in diameter and at least 50 feet high. If the tank is integrated with the legs then the entire platform becomes much more stable. Tankers with LNG anchor near the platform and offload the LNG into the tank. When the wind and waves are low the LNG power plant fires up and delivers power to the customers.

This offers several significant advantages:

Power delivery reliability and stability
System can deliver much more power, the project rated power is the wind/wave PLUS the LNG power plant rated power.
Makes offshore LNG delivery needed for large demand much more economical and acceptable.

The Company is not proposing a LNG combination at this time. However the benefits of a combined technology solution are obvious.

Offshore Renewable Energy and Aquaculture

Given a fixed platform in the ocean, there are several ways to use it for aquaculture:

Elevator Fish Pens: A fish pen can be suspended between the legs of the platform. The pen is attached to elevator lifts on the legs. Normally the pen is up near the surface for light and food. When a storm approaches that would destroy a floating fish pen, the elevator in lowered down close to the sea bottom where it is safe from the waves. Then it is raised back up when the waves die down. This handily solves the biggest problem of offshore aquaculture, the destruction of pens and mooring systems in storms. The platform above is large enough that it could even hold a fish processing facility.

Shellfish Cage Elevators: Large racks can be placed on elevator tracks along the legs and seeded with shellfish such as oysters and mussels. These normally are placed below the waves and only raised up for harvesting.

Any wave power devices attached to the platform will affect its structural loads and requires sound engineering based on the devices and also the local wave regime. The Company will offer its offshore platforms to wave power and aquaculture technology developers to test their systems.