Technical and economic considerations
Where can OTEC power plants operate?
OTEC plants can operate anywhere that large volumes of water are available with average temperature differences of approximately 40 degrees F. This includes a wide band of locations around the world from approximately 20 degrees north to 20 degrees south of the equator, such as the Caribbean region.
Does OTEC generate base load or intermittent power?
Ocean water is the largest and most effective solar collector on earth. In the OTEC equatorial bands, the warm surface temperatures are highly consistent on a daily basis and have high to low season variability of less than 10°F. Accordingly, unlike conventional solar or wind, OTEC can provide base load power 24 hours/day, 365 days/year.
Why is OTEC’s technology more favourable over other renewable energy sources?
OTEC is a base-load energy source fueled by the infinite supply of solar energy stored in the upper most thermal layer of the ocean. OTEC can operate 24 hours a day, 365 days per year.
- Solar and wind renewable energy supplies are intermittent and variable, with lower capacity and power challenges for the grid.
- Geothermal operates at higher capacity, similar to OTEC, but is very site specific, with limited applicability globally.
- Hydroelectric renewable energy is also very site-specific and subject to effects of drought and flood and may have dramatic impact on the local and regional ecosystems.
- Biomass renewable energy requires the use of precious agricultural land and often produces vast amounts of greenhouse gases.
Although OTEC has a higher initial capital cost than other base-load energy projects, its “free” fuel cost and very low operating expenses make it very attractive over the project life cycle. Furthermore, OTEC projects can charge a predictable fixed rate to its utility customers, eliminating the volatility risk of fossil fuel-based systems; and capital cost will decrease as more OTEC Floating Power Plants get built.
How does the platform and piping work?
The patent-pending 6.25MW OTEC Floating Power Plant design uses 2500mm diameter pipe made of high-density polyethylene (HDPE) to draw deep ocean water and return to the ocean used warm surface water cooled in the evaporators and cold deep ocean water warmed in the condensers.
HDPE was chosen because of its excellent physical and chemical properties that enable it to be welded together to form a flexible homogenous pipe of almost any length. The cold water intake pipe will be approximately 8,000 feet (2500 meters) long; the warm and cold water return pipes will be approximately 800 feet (250 meters) long. HDPE pipes are used throughout the world for water systems because of their smooth surfaces; inspection of HDPE pipe that has been in service in the ocean for decades reveal that marine organisms do not easily attach and grow on it.
The HDPE intake and return pipes attach to a manifold anchored to the sea floor directly beneath the OTEC Floating Power Plant (FPP). The patent-pending flexible risers transport the seawater from the manifold to the FPP and back and ensure that the pipes stay connected even in the most severe storm conditions. Remotely operated shut-off valves on the FPP and in the manifold enable individual risers to be isolated for maintenance and repair, if necessary.
Risks and environmental impact
What is the impact on the seawater?
The seawater used in the process will be returned to the ocean. The OTEC process cools the warm water and warms the cool water. Further, the cold water pumped from so deep in the ocean has higher nutrient levels than found in the shallower depth. On release, the two return streams are discharged near 130 meters (425 feet), below the photic zone, and mixed so that they rapidly assimilate with the surrounding ocean, thereby mitigating any adverse impact on the ecosystem for the marine life.
The Cayman OTEC Project includes extensive research into the profile of the currents, water flows and water quality at the proposed site and surrounding areas. Understanding the results from this research, in conjunction with the depth of the returned water, will mitigate any nutrient-caused changes in the environment.
What is the impact to the marine life?
The warm and cold water intakes will have a low impact on marine life. The Cayman OTEC Project will have a secured cold water intake pipe drawing water from about 8 meters above the sea floor at a depth of about 1,340 meters (4,400 feet). There will be a large grate over the pipe opening to prevent large marine vertebrates from swimming into the pipe. The warm water intake, built into the bottom of the hull, will be covered with a fine mesh that will prevent anything larger than 12mm square from passing through, including small fish. The warm water intake and its protective mesh will be regularly maintained in accordance with Cayman OTEC’s operational procedures.
The water quality and impacts on marine flora and fauna will be continually assessed and managed as part of Cayman OTEC’s ongoing responsibility to maintaining the project and the local environment.
What is the impact to the Queen’s Bottom?
The design and location of the floating power plant could impact coral reefs or other elements of the Queen’s Bottom. The total footprint of OTEC FPP on the ocean floor is less than 30,000 square feet, with the largest single component having a footprint of about 6,000 square feet. OTI has committed to install the project to minimize any impact on the Queen’s Bottom and any impact on coral reefs. In the event that endangered coral reefs are impacted, OTI would engage in removal and re-installation of such coral reefs in alternative locations.
How is ammonia used & stored aboard the OTEC power plant to ensure there is no harm to the Cayman Islands environment?
The OTEC process requires vaporising a liquid, to drive turbine-generators that produce the electricity. A low-boiling liquid is needed to facilitate this process and ammonia is a commonly used chemical chosen for this process. Ammonia is used in commercial processes worldwide and is also found in household cleaning products and fertilizers.
Ammonia is contained in a closed loop system aboard the OTEC FPP, and during normal operation no ammonia is ever released into the air. The floating power plant design incorporates numerous safety features including double hull construction and collision zones to protect the ammonia system from damage. While a nominal amount of ammonia will be used in the OTEC process, OTI recognizes that ammonia is a hazardous substance, especially in gaseous form. However, such gaseous ammonia does dissolve easily and quickly in water, and leak detection and alarm activation system along with a water mist and collection system is used wherever the ammonia system exists on the FPP.
Ammonia will be loaded aboard the FPP in the construction yard and transported aboard the floating power plant. The FPP design and operation will adhere to all international requirements for such hazardous substances. The handling of ammonia in compliance with well-established safety standards will be outlined in an independent Emergency Management Plan. The Company will comply with the safety guidelines outlined for the project.
What is the visual impact of the floating platform?
The Cayman OTEC project is reliant upon the use of a Floating Power Platform (FPP). OTI have designed a system that is sympathetic in design to the ocean environment and limits the height of the platform to 16 feet above the surface for the majority of the platform with a small portion rising to 24 feet. The platforms will be located offshore, will be low-profile, have a paint scheme to blend with the ocean and sky, and be relatively unobtrusive from the shoreline.
Rendering of FPP (length of 206ft, width of 140ft) immediately in front of Celebrity EQUINOX (bean of 121ft)
FPP at the GC-1 site as seen from shore
Platform from Over the Edge café