An Introduction to Ocean and Sea Breeze Wind Energy

Frank R. Leslie, BSEE, MS Space Technology

5/25/2002, Rev. 1.7

f.leslie@ieee.org; (321) 768-6629

Renewable Energy from Ocean Winds

Overview of Ocean Energy

Ocean energy is replenished by the sun and through tidal influences of the moon and sun gravitational forces

Near-surface winds induce wave action and cause wind-blown currents at about 3% of the wind speed

Tides cause strong currents into and out of coastal basins and rivers

Ocean surface heating by some 70% of the incoming sunlight adds to the surface water thermal energy, causing expansion and flow

Wind energy is stronger over the ocean due to less drag, although technically, only seabreezes are from ocean energy

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What’s renewable energy?

Renewable energy systems transform incoming solar energy and its alternate forms (wind and river flow, etc.), usually without pollution-causing combustion

This energy is “renewed” by the sun and is “sustainable” Renewable energy is sustainable indefinitely, unlike long-stored,

depleting energy from fossil fuels Renewable energy from wind, solar, and water power emits no

pollution or carbon dioxide Renewable energy is “nonpolluting” since no combustion occurs

(although the building of the components does in making steel, etc., for conversion machines does pollute during manufacture)

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Renewable Energy (Continued)

Fuel combustion produces “greenhouse gases” that are believed to lead to climate change (global warming), thus combustion of biomass is not as desirable as other forms

Biomass combustion is also renewable, but emits CO2 and pollutants Biomass can be heated with water under pressure to create

synthetic fuel gas; but burning biomass creates pollution and CO2

Nonrenewable energy comes from fossil fuels and nuclear radioactivity (process of fossilization still occurring but trivial) Nuclear energy is not renewable, but sometimes is treated as

though it were because of the long depletion period

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The eventual declineof fossil fuels

Millions of years of incoming solar energy were captured in the form of coal, oil, and natural gas; current usage thus exceeds the rate of original production

Coal may last 250 to 400 years; estimates vary greatly; not as useful for transportation due to losses in converting to liquid “synfuel”

We can conserve energy by reducing loads and through increased efficiency in generating, transmitting, and using energy

Efficiency and conservation will delay an energy crisis, but will not prevent it

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Available Energy

Potential Energy: PE = mh Kinetic Energy: KE = ½ mv2 or ½ mu2

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Economics

Cost of installation, operation, removal and restoration Compare cost/watt & cost/watt-hour vs. other sources Relative total costs compared to other sources Externality costs aren’t included in most assessments Cost of money (inflation) must be included (2 to 5%/year) Life of energy plant varies and treated as linear depreciation to zero Tax incentives or credits offset the hidden subsidies to fossil fuel

and nuclear industry Environmental Impact Statements (EIS) require early funding to

justify permitting

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Ocean Wind Energy

Over or in proximity to the ocean surface, the wind moves at higher speeds over water than over land roughness

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Ocean Wind Energy

Wind energy results from uneven heating of the atmosphere Wind resources vary greatly worldwide; strong over oceans Power is proportional to the cube of the wind speed

Ref.: www.freefoto.com/pictures/general/ windfarm/index.asp?i=2

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Ocean Wind Energy (continued)

Long fetch (distance) of unhindered wind increases speed and available energy beyond land installations

Offshore wind turbines diminish public outcry against wind turbines (low visibility, monopod supports)

Turbines are typically placed on concrete supports in groups; rotors are often 80 m in diameter

Turbines are also placed along a coast on the foreshore area to intercept the prevailing wind from over the ocean

Must avoid bird migration routes; turbine ~20 to 30 rpm

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Ocean Wind Energy (continued)

Present and planned offshore wind energy plants will supply significant consumer demand and reduce need for coal- and oil-fired plants and resultant pollution Middlegrunden near Denmark Oil-drilling platforms

Small auxiliary turbinePlatform design can be modified to support large

wind turbine

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Wind Energy Equations(also applies to water turbines)

Assume a “tube” of air the diameter, D, of the rotor A = π D2/4

A length, L, of air moves through the turbine in t seconds L = u·t, where u is the wind speed

The tube volume is V = A·L = A·u·t Air density, ρ, is 1.225 kg/m3 (water density ~1000

kg/m3) Mass, m = ρ·V = ρ·A·u·t, where V is volume Kinetic energy = KE = ½ mu2

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Wind Energy Equations (continued)

Substituting ρ·A·u·t for mass, and A = π D2/4 , KE = ½·π/4·ρ·D2·u3·t

Theoretical power, Pt = ½·π/4·ρ·D2·u3·t/t = 0.3927·ρa·D2·u3, ρ (rho) is the density, D is the diameter swept by the rotor blades, and u is the speed parallel to the rotor axis

Betz Law shows 59.3% of power can be extracted

Pe = Pt·59.3%·ήr·ήt·ήg, where Pe is the extracted power, ήr is rotor efficiency, ήt is transmission efficiency, and ήg is generator efficiency

For example, 59.3%·90%·98%·80% = 42% extraction of theoretical power

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Generic Trades in Energy

Energy trade-offs required to make rational decisions

PV is expensive ($4 to 5 per watt for hardware + $5 per watt for shipping and installation = $10 per watt) compared to wind energy ($1.5 per watt for hardware + $5 per watt for installation = $6 per watt total)

Are Compact Fluorescent Lamps (CFLs) always better to use than incandescent?

Ref.: www.freefoto.com/pictures/general/ windfarm/index.asp?i=2

Ref.: http://www.energy.ca.gov/education/story/story-

images/solar.jpeg

Photo of FPL’s Cape Canaveral Plant by F. Leslie, 2001 7.1 020315

Energy Storage

Renewable energy is often intermittent, and storage allows alignment with time of use.

Compressed air, flywheels, weight-shifting (pumped water storage at Niagara Falls)

Batteries are traditional for small systems and electric vehicles; first cars (1908) were electric

www.strawbilt.org/systems/ details.solar_electric.html

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Hydrogen can be made by electrolysis Energy is best stored as a financial credit

through “net metering” Net metering requires a utility to bill at the

same rate for buying or selling energy

EnergyTransmission

Electricity and hydrogen are energy carriers, not natural fuels Electric transmission lines lose energy in heat (~2% to 5%); trades

loss vs. cost Line flow directional analysis can show where new energy plants are

required to reduce energy transmission Hydrogen is made by electrolysis of water, cracking of natural gas,

or from bacterial action (lab experiment level) Oil and gas pipelines carry storable energy

Pipelines (36” or larger) can transport hydrogen without appreciable energy loss due to low density and viscosity

More efficient than 500 kV transmission line and is out of view

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Legal aspects and other complications

PURPA: Public Utility Regulatory Policy Act of 1978. Utility purchase from and sale of power to qualified facilities; avoided costs offsetting basis of purchases

Energy Policy Act of 1992 leads to deregulation “NIMBYs” rally to shrilly insist “Not In My Backyard”! Investment taxes and subsidies favor fossil and nuclear power High initial cost dissuades potential users; future is uncertain Lack of uniform state-level net metering hinders offsetting costs Environmental Impact Statements (EIS) require extensive and

expensive research and trade studies Numerous “public interest” advocacy groups are well-funded and

ready to sue to stop projects

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Conclusion

Renewable energy offers a long-term approach to the World’s energy needs

Economics drives the energy selection process and short-term (first cost) thinking leads to disregard of long-term, overall cost

Increasing oil, gas, and coal prices will ensure that the transition to renewable energy occurs

Offshore and shoreline wind energy plants offer a logical approach to part of future energy supplies

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References: Books, etc. General:

Sørensen, Bent. Renewable Energy, Second Edition. San Diego: Academic Press, 2000, 911 pp. ISBN 0-12-656152-4.

Henry, J. Glenn and Gary W. Heinke. Environmental Science and Engineering. Englewood Cliffs: Prentice-Hall, 728pp., 1989. 0-13-283177-5, TD146.H45, 620.8-dc19

Brower, Michael. Cool Energy. Cambridge MA: The MIT Press, 1992. 0-262-02349-0, TJ807.9.U6B76, 333.79’4’0973.

Di Lavore, Philip. Energy: Insights from Physics. NY: John Wiley & Sons, 414pp., 1984. 0-471-89683-7l, TJ163.2.D54, 621.042.

Bowditch, Nathaniel. American Practical Navigator. Washington:USGPO, H.O. Pub. No. 9. Harder, Edwin L. Fundamentals of Energy Production. NY: John Wiley & Sons, 368pp., 1982. 0-471-08356-9,

TJ163.9.H37, 333.79. Tidal Energy, pp. 111-129. Wind:

Patel, Mukund R. Wind and Solar Power Systems. Boca Raton: CRC Press, 1999, 351 pp. ISBN 0-8493-1605-7, TK1541.P38 1999, 621.31’2136

Gipe, Paul. Wind Energy for Home & Business. White River Junction, VT: Chelsea Green Pub. Co., 1993. 0-930031-64-4, TJ820.G57, 621.4’5

Johnson, Gary L, Wind Energy Systems. Englewood Cliffs NJ: Prentice-Hall, Inc. TK 1541.J64 1985. 621.4’5; 0-13-957754-8.

Waves: Smith, Douglas J. “Big Plans for Ocean Power Hinges on Funding and Additional R&D”. Power Engineering, Nov.

2001, p. 91. Kotch, William J., Rear Admiral, USN, Retired. Weather for the Mariner. Annapolis: Naval Institute Press, 1983.

551.5, QC994.K64, Chap. 11, Wind, Waves, and Swell. Solar:

Duffie, John and William A. Beckman. Solar Engineering of Thermal Processes. NY: John Wiley & Sons, Inc., 920 pp., 1991.

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References: Internet

General: http://www.google.com/search?q=%22renewable+energy+course%22 http://www.ferc.gov/ Federal Energy Regulatory Commission http://solstice.crest.org/ http://dataweb.usbr.gov/html/powerplant_selection.html http://mailto:energyresources@egroups.com http://www.dieoff.org. Site devoted to the decline of energy and effects upon population

Tidal: http://www.unep.or.kr/energy/ocean/oc_intro.htm http://www.bluenergy.com/technology/prototypes.html http://www.iclei.org/efacts/tidal.htm http://zebu.uoregon.edu/1996/ph162/l17b.html

Waves: http://www.env.qld.gov.au/sustainable_energy/publicat/ocean.htm http://www.bfi.org/Trimtab/summer01/oceanWave.htm http://www.oceanpd.com/ http://www.newenergy.org.cn/english/ocean/overview/status.htm http://www.energy.org.uk/EFWave.htm

http://www.earthsci.org/esa/energy/wavpwr/wavepwr.html

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References: Internet

Thermal: http://www.nrel.gov/otec/what.html http://www.hawaii.gov/dbedt/ert/otec_hi.html#anchor349152 on OTEC systems

Wind: http://awea-windnet@yahoogroups.com. Wind Energy elist http://awea-wind-home@yahoogroups.com. Wind energy home powersite elist http://telosnet.com/wind/20th.html

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Units and Constants

Units: Power in watts (joules/second) Energy (power x time) in watt-hours

Constants: 1 m = 0.3048 ft exactly by definition 1 mile = 1.609 km; 1m/s = 2.204 mi/h (mph) 1 mile2 = 27878400 ft2 = 2589988.11 m2

1 ft2 = 0.09290304 m2; 1 m2 = 10.76391042 ft2

1 ft3 = 28.32 L = 7.34 gallon = 0.02832 m3; 1 m3 = 264.17 US gallons 1 m3/s = 15850.32 US gallons/minute g = 32.2 ft/s2 = 9.81 m/s2; 1 kg = 2.2 pounds Air density, ρ (rho), is 1.225 kg/m3 or 0.0158 pounds/ft3 at 20ºC at sea level Solar Constant: 1368 W/m2 exoatmospheric or 342 W/m2 surface (80 to 240

W/m2) 1 HP = 550 ft-lbs/s = 42.42 BTU/min = = 746 W (J/s) 1 BTU = 252 cal = 0.293 Wh = 1.055 kJ 1 atmosphere = 14.696 psi = 33.9 ft water = 101.325 kPa = 76 cm Hg =1013.25

mbar 1 boe (42- gallon barrel of oil equivalent) = 1700 kWh

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Energy Equations

Electricity: E=IR; P=I2 R; P=E2/R, where R is resistance in ohms, E is volts,

I is current in amperes, and P is power in watts Energy = P t, where t is time in hours

Turbines: Pa = ½ ρ A2 u3, where ρ (rho) is the fluid density, A = rotor area

in m2, and u is wind speed in m/s P = R ρ T, where P = pressure (Nm-2 = Pascal) Torque, T = P/ω, in Nm/rad, where P = mechanical power in

watts, ω is angular velocity in rad/sec Pumps:

Pm = gQmh/ήp W, where g=9.81 N/kg, Qm is mass capacity in kg/s, h is head in m, and ήp is pump mechanical efficiency

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