Ocean Thermal Energy Conversion
Ocean Thermal Energy Conversion (OTEC) is a process that can produce electricity by using the temperature difference between deep cold ocean water and warm tropical surface waters. OTEC plants pump large quantities of deep cold seawater and surface seawater to run a power cycle and produce electricity. OTEC is firm power (24/7), a clean energy source, environmentally sustainable and capable of providing massive levels of energy.
Recently, higher electricity costs, increased concerns for global warming, and a political commitment to energy security have made initial OTEC commercialization economically attractive in tropical island communities where a high percentage of electricity production is oil based. Even within the US, this island market is very large; globally it is many times larger. As OTEC technology matures, it should become economically attractive in the southeast US.
What is being done at the OERC?
OTEC Power Plant Operation
Makai added a 100-kW turbine generator to the OERC in August 2015. This is currently the largest grid-connected OTEC plant in the world. This fully functioning OTEC power plant provides several benefits:
1. Development of OTEC power control and automation systems
2. Measure the actual versus predicted power output
3. Use long-term operational data to improve future commercial OTEC plant designs and cost projections
OTEC and Marine Heat Exchanger Testing
A basic closed-cycle OTEC plant is shown in the figure above. Warm seawater passes through an evaporator and vaporizes the working fluid, ammonia. The ammonia vapor passes through a turbine which turns a generator making electricity. The lower pressure vapor leaves the turbine and condenses in the condenser connected to a flow of deep cold seawater. The liquid ammonia leaves the condenser and is pumped to the evaporator to repeat the cycle.
The Ocean Energy Research Center (OERC) is an essential tool for the development and testing of candidate OTEC heat exchangers. Heat Exchangers will be the single most expensive component in a commercial offshore OTEC plant and thus optimizing their cost, longevity and performance are critical for OTEC’s economic success. The operating conditions of OTEC heat exchangers are unique, and an optimal design has yet to be developed.
The OERC enables OTEC engineers to rapidly design, build, and test OTEC heat exchangers on an operational land-based OTEC plant, providing the feedback that is necessary for optimization. Makai uses a unique OTEC plant analysis software to design heat exchangers which accounts for lifespan, performance (heat transfer and pumping efficiencies), and cost (fabrication and effect on platform), to enable true optimization. Makai is in the process of scaling up a design for a low-cost, compact, corrosion-resistant design that could revolutionize OTEC heat exchangers. In addition, Makai provides objective performance testing services to other OTEC engineering firms for multiple heat exchangers simultaneously.
What is the future of the OERC?
Makai’s Ocean Energy Research Center will continue to serve as the premier testbed for OTEC technology and a platform for collaboration with the international OTEC community. Makai is an engineering services provider, and thus we work with multiple OTEC project developers to provide objective technical guidance at all levels, from engineering and economic feasibility to component design. Finally, the operation of a landbased OTEC plant by Makai will provide invaluable knowledge and expertise for the next step in OTEC commercialization: the construction of a large-scale pilot plant.
Benefits and Opportunities of OTEC
OTEC is in many ways a very attractive solution to US energy issues (Energy Security, Price Volatility, Unsustainable Supply, Climate Change, and Environmental Risks):
· Immense Resource: OTEC is solar power, using the oceans as a thermal storage system for 24-hour production. Unlike other renewable energies, the maximum available energy from OTEC is not limited by land, shorelines, water, environmental impact, human impact, etc.
· Baseload Power: OTEC produces electricity continuously, 24 hours a day throughout the entire year. Intermittent renewable energy sources are not baseload and often require storage of their energy during peak production hours for later consumption. Large, baseload OTEC plants could actually start to replace fossil-fuel-fired power plants without compromising grid stability.
· Dispatchable Power: OTEC is dispatchable, meaning that its power can be ramped up and down quickly (in a matter of seconds) to compensate for fluctuating power demand or supply from intermittent renewables. For this reason, OTEC is complementary to other renewables like solar and wind, and could enable further penetration on the grid while helping to maintain its stability.
· Security: OTEC offers the opportunity of tapping an immense energy resource that is not controlled by other nations.
· Renewable: OTEC is conservatively believed to be sustainable at four or more times man’s current total electrical energy production.
· Clean Energy: OTEC has the potential of being a very clean alternative energy – unique for a firm power source capable of providing massive energy needs. The environmental risk with OTEC is very low.
· Offshore: OTEC production occurs offshore. Land resources are not needed other than for on-shore landing. OTEC is not competing for other vital resources such as food and fresh water.
· Low Risk: Conventional Closed Cycle OTEC is a low-risk
The problem with this remarkable renewable energy is cost. At present, OTEC plants can be built that will be economically attractive to Hawaii, Puerto Rico and Guam (at electrical rates just above twenty cents per kWh range without energy credits). Makai Ocean Engineering performed a study for Office of Naval Research looking at an offshore OTEC industry providing energy to the continental US via ammonia as an energy carrier. These future OTEC prices are slightly high, but close to competing with other renewables and with overlapping margins of error.
The winners: Island communities, U. S. Department of Defense (who have been strong supporters of OTEC and want smaller OTEC plants for base locations), and the U.S. Public. A mature and well developed OTEC industry (which will exist after building dozens of OTEC plants just to provide the US tropical islands) is a tremendous backup technology, as the US is backing into an energy corner and becomes more dependent upon nuclear and clean coal to fulfill our non-oil needs. Those technologies come with enormous environmental risk. Biomass, Wind and Solar can in some instances provide lower cost energy, but these are limited in the total quantity of energy delivered. Having OTEC as a viable and cost competitive alternative would be a very healthy position for the US.