1.2.1.2 Efficiency and Cost

Theoretical maximum efficiency is (Twarm-Tcold)/Twarm

This is called the Carnot Efficiency

Theoretical MAXIMUM 7.5% to 8% efficiency

Some is lost to heat, friction, etc

Practical Maximum gross 3.5% to 4.0%

25 to 30% of gross power production is needed to operate the plant

Net electric energy available is about 2.5% and 3%

1.2.1.1 Closed Cycle

Most likely uses Ammonia as a working fluid

Warm surface water enters a boiler/evaporator that contains liquid ammonia

Liquid Ammonia boils and produces a vapor pressure of 9.3 atm

Vapor expands and drives turbine to produce electricity

Vapor then enters a condenser at a pressure of 6.1 atm

Ammonia condenses and liquid is pumped back into evaporator

Same as RANKINE cycle in steam engines, but different fluid and lower temps and pressure

Opposite of a commercial refrigerator

Any common refrigerant fluids (freons) can be used in OTEC

Thus, studies on refrigeration and cryogenic systems can be applicable to OTEC

1.2.1 Power Systems

CLOSED cycle vs OPEN cycle

Open Cycle:

Working fluid is water

Warm surface water brought under vacuum, pressure lowered, water boils at lower temperature

Steam passes through turbine and is condensed into liquid and then discharged. Alternatively, the vapor can be passed through a heat exchanger cooled by cold water resulting in a source of FRESH WATER

Mini-OTEC tested by Lockheed Martin in Hawaii in 1979 produced an gross output of 50kWe. The cold water pipe dimensions were .71m diameter, 670 m long.

OTEC-1 produced 1MWe in Hawaii. The cold water pipe dimensions were 2.55m diameter and 670 m long. (Castellano, 1981)

1.2 Design Reqs

Major Subsystems:

1. POWER PLANT

2. WATER DUCTS

3. ENERGY TRANSFER

4. POSITION CONTROL

5. PLATFORM

1.1 The OTEC Resource

This is the OTEC resource:

Solar energy captured by ocean is a layer 100-300 ft deep
Tropical Oceans are 15 deg N and 15 deg South, have water temps near 82 deg F
Constant day and night, month to month
Temp varies from 80 - 85 deg F
Deeper about 2500 - 3000 ft you have 40 deg F water
Cold water starts below 3000ft
Water accumulated from polar ice melts, flows along bottom across oceans unmixed
Creates 2 layer temperature difference of 40-45 deg F

OTEC uses this resource to produce electric power
Can operate continuously without significant environment impacts if power generated is 0.5 MWe per square mile of ocean surface
This amount would convert 0.07% of the solar energy to electricity

10Million MWe potential from OTEC vs 165,000 MWe Total US Electricity produced in 1987

Ocean Energy Launch

Natural Energy Laboratory of Hawaii Authority (NELHA)

http://www.nelha.org/index.asp

Unique Resources
Many Advantages In a Single Location

• THE LAND on which NELHA is situated consists of 870 acres with a steep offshore bathymetry for easy access to the ocean depths and what may become Hawaii's most valuable natural resource: deep ocean water.

• COLD DEEP SEAWATER (DSW) is delivered onshore at a chilly 6ºC (43ºF) from a 2,000-foot depth.

• WARM SURFACE SEAWATER (SSW) from a source rated Class AA pure, is at comfortably warm temperatures within the narrow range of 24.5º to 27.5ºC (76º to 82ºF) year 'round.

• PURITY OF NELHA'S SEAWATER SUPPLY makes it ideal as a growth medium for marine plants and animals. (Click here to view seawater quality data)

• POTENTIAL ENERGY from a natural temperature difference ("delta T") of about 20ºC between the cold and warm seawaters is available for use year 'round.

• ANNUAL SOLAR INSOLATION at NELHA is the highest of any location in the coastal United States.

• LOW RAINFALL, less than 15 inches per year, means more clear, sunny days to naturally maximize both marine and terrestrial plant photosynthesis and growth with no added expense of artificial lighting or heating, and virtually eliminates concern for unwanted dilution of critical salinities in open pond aquaculture.

• A WINTERLESS CLIMATE makes NELHA ideal for year 'round cultivation of a variety of organisms dependent on plant-based food resources.

• PROXIMITY TO KONA INTERNATIONAL AIRPORT at Keahole puts NELHA at the center of the two largest markets in the world, Asia and North America. Direct flights from Kona to the East and West create opportunities to get fresh products to market fast.

• HAWAII ENTERPRISE ZONE benefits apply to qualifying businesses located at NELHA's Keahole facilities, providing significant savings to them.

• A FRIENDLY COMMUNITY where the "Aloha Spirit" is alive and well, and a stable political climate provide the setting for all ventures at NELHA.


Application of Resources
NELHA offers unique opportunities for new industry development:

• LOW COST COOLING for air conditioning and industrial cooling is extremely cost-effective using cold deep seawater to replace traditional coolants. NELHA has been saving up to $4,000 per month since it switched its 3 buildings to deep seawater-based cooling.

• A WIDE RANGE OF TEMPERATURE REGIMES can be easily created to maintain suitable environments for a wide variety of marine plants and animals as well as terrestrial flora and fauna.

deep sea water air conditioning system
This small deep seawater (DSW) air conditioning system provides cooling for NELHA's water quality laboratory, tenant laboratory space, and public meeting rooms totaling 67,200 cubic feet in two adjacent Research Compound buildings.


• ALTERNATIVE ENERGY PRODUCTION from renewable resources such as the "ocean thermal energy conversion" (OTEC) process has been the focus of energy research at NELHA, the world's leading facility for this area of research and development.

• SOLAR ENERGY from ample sunshine is available year 'round for testing and applying solar energy-based technologies.

• AQUACULTURE takes advantage of the abundant resources at NELHA to create optimum growing conditions for a wide range of marine organisms.

• MARINE BIOTECHNOLOGY optimizes large-scale production of marine microorganisms with vast pharmaceutical and nutraceutical market potential. NELHA is a prime location for the development of this new multimillion-dollar industry.

• COLDWATER AGRICULTURE chills the soil using cold deep seawater to improve on nature, dramatically increasing yields for land-based crops.

• RESEARCH THAT FOSTERS INNOVATION using the unique complement of resources at NELHA is creating the industries of tomorrow... today.