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2	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
3	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)
4	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
5	The eventual decline of 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
6	Available Energy Potential Energy: PE = mh Kinetic Energy: KE = ½ mv² or ½ mu²
7	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
8	Ocean Wind Energy Over or in proximity to the ocean surface, the wind moves at higher speeds over water than over land roughness
9	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
10	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
11	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 turbine Platform design can be modified to support large wind turbine
12	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
13	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, P_t = ½·π/4·ρ·D²·u³·t/t = 0.3927·ρ_a·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 P_e = P_t·59.3%·ή_r·ή_t·ή_g, where P_e is the extracted power, ή_r is rotor efficiency, ή_t is transmission efficiency, and ή_g is generator efficiency For example, 59.3%·90%·98%·80% = 42% extraction of theoretical power
14	Generic Trades in Energy
15	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
16	Energy Transmission 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
17	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
18	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
19	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.
20	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
21	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
22	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
23	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: P_a = 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 = gQ_mh/ή_p W, where g=9.81 N/kg, Q_m is mass capacity in kg/s, h is head in m, and ή_p is pump mechanical efficiency