OTEC plants pipe in hot and cold seawater and run them through heat exchangers and water condensers, in the process spinning turbines that generate electricity. The concept of OTEC power is enormously appealing. Sunlight is free and renewable every morning. And scientists estimate that OTEC has the potential to generate billions of watts of electricity. Yet only a few, mainly experimental, plants have been built. One of the problems that restrict OTEC is that the necessary thermal gradient is found at sea, but the power it can generate is needed on land.
In this activity, you will examine some of the issues involved in this dilemma by comparing onshore and offshore OTEC facilities. Examine and compare the two diagrams of OTEC facilities. You can click on each diagram to see a larger image. Once you understand how each of the OTECs work, answer the questions below.
OTEC plants built on ships at sea sit right on top of the thermal gradient but face challenges in transmitting the power they produce to shore. Large heat exchangers are required to transfer heat from the seawater to the working fluid, both for evaporation and condensation. At the same time, they have to fulfil high expectations with regard to mechanical strength, weight, size, fouling, corrosion and costs.
The main objective of this research is to analyze and develop the most suitable heat exchanger design for OTEC. The majority of the OTEC resource is best accessible using offshore floating structures. Key technical challenges under investigation are the dynamic behaviour of the floating structure and the cold water pipe, its interface and the power cable.
These offshore systems require detailed research to find technical feasible solutions supported by analytical methods and hydrodynamic modeling of mooring - riser - floating structure configurations. OTEC still is a relatively unexplored renewable energy technology and it will require design and implementation studies to better understand the challenges and risks associated with commercial OTEC facilities.
Also, opportunities for a more synergetic use of the ocean thermal energy resource and infrastructure are part of ongoing studies. Last, taking into consideration the unique characteristics of tropical coastal regions the TU Delft analyzes different implementation strategies for OTEC. Biomass, Wind and Solar can in some instances provide lower cost energy, but these are limited in the total quantity of energy delivered.
Since , increased energy prices, environmental concerns, and new Department of the Navy energy policy led to government and commercial support to improve key OTEC technologies.
This new, state-of-the-art facility features advanced manufacturing equipment to be used in fabrication of entirely new and innovative heat exchanger designs. In addition to serving Ocean thermal energy conversion OTEC power plants, these heat exchanger units can be used in a variety of applications, including:. With an increasingly electrified population and concerns about energy efficiency and carbon footprint increasing worldwide, industrial and military users are looking for ways to make more efficient use of their thermal energy resources.
Makai has a long and intense involvement with OTEC. We have significant programs in heat exchanger design and testing, plume modeling, power module design, plant layout, cold water pipe handling and deployment, a pilot plant design, analyzing the power cable to shore, and bioplume modeling. That study developed a detailed evaluation of short term floating OTEC plants providing electricity to shore and a long term OTEC industry manufacturing an energy carrier for the continental US.
Initial Plant designs and analytical tools were developed that are major design tools being used today in OTEC planning. A development Road Map was created that is now being implemented. The subsequent projects, items , have been a direct consequence of this earlier SBIR work. We were thus able to leverage our enthusiasm, OTEC experience and analytical tools by aligning ourselves with Lockheed Martin Corporation. An OTEC plant of this size has yet to be built.
A smaller pilot plant is shown in the figure above. In an offshore floating OTEC plant, deep, cold seawater is drawn through a vertical fiberglass pipeline from a depth of meters feet. This Cold Water Pipeline would have a 10 meter 33 foot diameter, and its weight in water would be over 2. This pipe is unprecedented in the offshore industry and Lockheed Martin has developed a method of fabricating this fiberglass pipe while on a floating OTEC platform at sea.
A major engineering challenge, however, is how to safely lower this large, flexible and delicate pipeline down into the ocean as it is fabricated section by section on the deck of the platform. These Grippers squeeze on the exterior of the pipe from all sides, and hold the vertical weight of the pipeline through Kevlar reinforced rubber pads using friction.
The two Grippers are identical in structure except that the bottom Gripper moves up and down using hydraulic cylinders and the top Gripper is fixed to the platform. The Grippers lower the pipeline by a handover sequence where the Grippers transfer the weight back and forth; only one Gripper must be squeezed on the pipe at all times. Major concerns considered in the design include crushing the pipe and dropping the pipe. All these concerns were solved with the design developed by Makai.
Energy from the sun heats the surface water of the ocean. In tropical regions, surface water can be much warmer than deep water. This temperature difference can be used to produce electricity and to desalinate ocean water. Warm surface water is pumped through an evaporator containing a working fluid. The vaporized fluid is turned back to a liquid in a condenser cooled with cold ocean water pumped from deeper in the ocean.
OTEC systems using seawater as the working fluid can use the condensed water to produce desalinated water. The laboratory is one of the world's leading test facilities for OTEC technology. This facility became operational in and supplies electricity to the local electricity grid. Other larger OTEC systems are in development or planned in several countries, mostly to supply electricity and desalinated water for island communities.
Hydropower explained Ocean thermal energy conversion. What is energy? Units and calculators.
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