An Introduction to Wave and Tidal Energy Renewable
An Introduction to Wave and Tidal Energy Renewable Energy in (and above) the Oceans Frank R. Leslie, BSEE, MS Space Technology 5/25/2002, Rev. 1. 7 fleslie @fit. edu; (321) 674 -7377 www. fit. edu/~fleslie f. leslie @ieee. org; (321) 768 -6629 “It is pleasant, when the sea is high and the winds are dashing the waves about, to watch from shore the struggles of another. ” Lucretius, 99 -55 B. C.
Overview of Ocean Energy z Ocean energy is replenished by the sun and through tidal influences of the moon and sun gravitational forces z Near-surface winds induce wave action and cause windblown currents at about 3% of the wind speed z Tides cause strong currents into and out of coastal basins and rivers z Ocean surface heating by some 70% of the incoming sunlight adds to the surface water thermal energy, causing expansion and flow z Wind energy is stronger over the ocean due to less drag, although technically, only seabreezes are from ocean energy 1. 0 020402
What’s renewable energy? z Renewable energy systems transform incoming solar energy and its alternate forms (wind and river flow, etc. ), usually without pollutioncausing combustion z This energy is “renewed” by the sun and is “sustainable” z Renewable energy is sustainable indefinitely, unlike long-stored, depleting energy from fossil fuels z Renewable energy from wind, solar, and water power emits no pollution or carbon dioxide z 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) 1. 1 020302
Renewable Energy (Continued) z 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 z Biomass combustion is also renewable, but emits CO 2 and pollutants y Biomass can be heated with water under pressure to create synthetic fuel gas; but burning biomass creates pollution and CO 2 z Nonrenewable energy comes from fossil fuels and nuclear radioactivity (process of fossilization still occurring but trivial) y Nuclear energy is not renewable, but sometimes is treated as though it were because of the long depletion period 1. 1 020402
The eventual decline of fossil fuels z 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 z Coal may last 250 to 400 years; estimates vary greatly; not as useful for transportation due to losses in converting to liquid “synfuel” z We can conserve energy by reducing loads and through increased efficiency in generating, transmitting, and using energy z Efficiency and conservation will delay an energy crisis, but will not prevent it 1. 1 020402
Available Energy z Potential Energy: PE = mh z Kinetic Energy: KE = ½ mv 2 or ½ mu 2 z Wave energy is proportional to wave length times wave height squared (LH 2)per wave length per unit of crest length y A four-foot (1. 2 m), ten-second wave striking a coast expends more than 35, 000 HP per mile of coast [Kotch, p. 247] z Maximum Tidal Energy, E = 2 HQ x 353/(778 x 3413) = 266 x 10 -6 HQ k. Wh/yr, where H is the tidal range (ft) and Q is the tidal flow (lbs of seawater) z E = 2 HQ ft-lb/lunar day (2 tides) or E = 416 x 10 -4 HV k. Wh, where V is cubic feet of flow 1. 2 020412
Economics z z z z 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 z Environmental Impact Statements (EIS) require early funding to justify permitting 1. 3 020402
Ocean Energy z The tidal forces and thermal storage of the ocean provide a major energy source z Wave action adds to the extractable surface energy z Major ocean currents (like the Gulf Stream) may be exploited to extract energy with underwater rotors (turbines) z The oceans are the World’s largest solar collectors (71% of surface) z Thermal differences between surface and deep waters can drive heat engines z Over or in proximity to the ocean surface, the wind moves at higher speeds over water than over land roughness 2. 0 020329
Wave Energy z Energy of interchanging potential and kinetic energy in the wave z Cycloidal motion of wave particles carries energy forward without much current z Typical periodicities are one to thirty seconds, thus there are low-energy periods between high-energy points z In 1799, Girard & son of Paris proposed using wave power for powering pumps and saws z California coast could generate 7 to 17 MW per mile [Smith, p. 91] 2. 0 020402
Ocean Energy: Wave Energy z Wave energy potential varies greatly worldwide Figures in k. W/m Source: Wave Energy paper. IMech. E, 1991 and European Directory of Renewable Energy (Suppliers and Services) 1991 2. 0 20329
Concepts of Wave Energy Conversion z Change of water level by tide or wave can move or raise a float, producing linear motion from sinusoidal motion z Water current can turn a turbine to yield rotational mechanical energy to drive a pump or generator y Slow rotation speed of approximately one revolution per second to one revolution per minute less likely to harm marine life y Turbine reduces energy downstream and could protect shoreline z Archimedes Wave Swing is a Dutch device [Smith, p. 91] 2. 1 020402
Salter “Ducks” z Scottish physicist Prof. Stephen Salter invented “Nodding Duck” energy converter in 1970 z Salter “ducks” rock up and down as the wave passes beneath it. This oscillating mechanical energy is converted to electrical energy z Destroyed by storm z A floating two-tank version drives hydraulic rams that send pressurized oil to a hydraulic motor that drives a generator, and a cable conducts electricity to shore http: //acre. murdoch. edu. au/ago/ocean/wave. html Ref. : www. fujita. com/archive-frr/ Tidal. Power. html © 1996 Ramage 2. 2. 1 020402
Fluid-Driven Wave Turbines z Waves can be funneled and channeled into a rising chute to charge a reservoir over a weir or through a swing-gate y Water passes through waterwheel or turbine back to the ocean y Algerian V-channel [Kotch, p. 228] z Wave forces require an extremely strong structure and mechanism to preclude damage z The Ocean Power Delivery wave energy converter Pelamis has articulated sections that stream from an anchor towards the shore y Waves passing overhead produce hydraulic pressure in rams between sections y This pressure drives hydraulic motors that spin generators, and power is conducted to shore by cable y 750 k. W produced by a group 150 m long and 3. 5 m diameter 2. 2. 2. 1 020402
Fluid-Driven Wave Turbines z Davis Hydraulic Turbines since 1981 y. Most tests done in Canada y 4 k. W turbine tested in Gulf Stream z Blue Energy of Canada developing two 250 k. W turbines for British Columbia z Also proposed Brothers Island tidal fence in San Francisco Bay, California 1000 ft long by 80 ft deep to produce 15 – 25 MW z Australian Port Kembla (south of Sydney) to produce 500 k. W 2. 2. 2. 1 020402
Air-Driven Wave Turbines (Con’t) z A floating buoy can compress trapped air similar to a whistle buoy z The oscillating water column (OWC) in a long pipe under the buoy will lag behind the buoy motion due to inertia of the water column z The compressed air spins a turbine/alternator to generate electricity at $0. 09/k. Wh The Japanese “Mighty Whale” has an air channel to capture wave energy. Width is 30 m and length is 50 m. There are two 30 k. W and one 50 k. W turbine/generators http: //www. earthsci. org/esa/energy/wavpwr/wavepwr. html 2. 2 020402
Air-Driven Wave Turbines z British invention uses an air-driven Wells turbine with symmetrical blades z Incoming waves pressurize air within a heavy concrete box, and trapped air rushes upward through pipe connecting the turbine z A Wavegen™, wave-driven, air compressor or oscillating water column (OWC) spins a two-way Wells turbine to produce electricity z Wells turbine is spun to starting speed by external electrical power and spins the same direction regardless of air flow direction z Energy estimated at 65 megawatts per mile Photo by Wavegen http: //www. bfi. org/Trimtab/summer 01/ocean. Wave. htm 2. 2 020402
Ocean Energy: Tidal Energy z Tides are produced by gravitational forces of the moon and sun and the Earth’s rotation z Existing and possible sites: y. France: 1966 La Rance river estuary 240 MW station x Tidal ranges of 8. 5 m to 13. 5 m; 10 reversible turbines y. England: Severn River y. Canada: Passamaquoddy in the Bay of Fundy (1935 attempt failed) y. California: high potential along the northern coast z Environmental, economic, and esthetic aspects have delayed implementation z Power is asynchronous with load cycle 3. 1 020402
Tidal Energy z Tidal mills were used in the Tenth and Eleventh Centuries in England, France, and elsewhere z Millpond water was trapped at high tide by a gate (Difficult working hours for the miller; Why? ) y Rhode Island, USA, 18 th Century, 20 -ton wheel 11 ft in diameter and 26 ft wide y Hamburg, Germany, 1880 “mill” pumped sewage y Slade’s Mill in Chelsea, MA founded 1734, 100 HP, operated until ~1980 y Deben estuary, Woodbridge, Suffolk, England has been operating since 1170 (reminiscent of “the old family axe”; only had three new handles and two new heads!) y Tidal mills were common in USA north of Cape Cod, where a 3 m range exists [Redfield, 1980] y Brooklyn NY had tidal mill in 1636 [? ] 3. 1 020402
Tidal Energy (continued) z Potential energy = S integral from 0 to 2 H (ρgz dz), where S is basin area, H is tidal amplitude, ρ is water density, and g is gravitational constant yielding 2 S ρ g. H 2 z Mean power is 2 S ρ g. H 2/tidal period; semidiurnal better z Tidal Pool Arrangements y Single-pool empties on ebb tide y Single-pool fills on flood tide y Single-pool fills and empties through turbine y Two-pool ebb- and flood-tide system; two ebbs per day; alternating pool use y Two-pool one-way system (high and low pools) (turbine located between pools) 3. 1 020402
Tidal Water Turbines z Current flow converted to rotary motion by tidal current z Turbines placed across Rance River, France z Large Savonius rotors (J. S. Savonius, 1932? ) placed across channel to rotate at slow speed but creating high torque (large current meter) z Horizontal rotors proposed for Gulf Stream placement off Miami, Florida 3. 2 020402
Tidal Flow: Rance River, France z z z z 240 MW plant with 24, 10 MW turbines operated since 1966 Average head is 28 ft Area is approximately 8. 5 square miles Flow approx, 6. 64 billion cubic feet Maximum theoretical energy is 7734 million k. Wh/year; 6% extracted Storage pumping contributes 1. 7% to energy level At neap tides, generates 80, 000 k. Wh/day; at equinoctial spring tide, 1, 450, 000 k. Wh/day (18: 1 ratio!); average ~500 million k. Wh/year z Produces electricity cheaper than oil, coal, or nuclear plants in France 3. 3 020329
Tidal Flow: Passamaquoddy, Lower Bay of Fundy, New Brunswick, Canada z z z z Proposed to be located between Maine (USA) and New Brunswick Average head is 18. 1 ft Flow is approximately 70 billion cubic feet per tidal cycle Area is approximately 142 square miles About 3. 5 % of theoretical maximum would be extracted Two-pool approach greatly lower maximum theoretical energy International Commission studied it 1956 through 1961 and found project uneconomic then z Deferred until economic conditions change [Ref. : Harder] 3. 3 020329
Other Tidal Flow Plants under Study z Annapolis River, Nova Scotia: straight-flow turbines; demonstration plant was to be completed in 1983; 20 MW; tides 29 to 15 feet; Tidal Power Corp. ; ~$74 M z Experimental site at Kislaya Guba on Barents Sea y French 400 k. W unit operated since 1968 y Plant floated into place and sunk: dikes added to close gaps z Sea of Okhotsk (former Sov. Union) under study in 1980 z White Sea, Russia: 1 MW, 1969 z Murmansk, Russia: 0. 4 MW z Kiansghsia in China 3. 3 020402
Other Tidal Flow Plants under Study (continued) z Severn River, Great Britain: range of 47 feet (14. 5 m) calculated output of 2. 4 MWh annually. Proposed at $15 B, but not economic. z Chansey Islands: 20 miles off Saint Malo, France; 34 billion k. Wh per year; not economic; environmental problems; project shelved in 1980 z San Jose, Argentina: potential of 75 billion k. Wh/year; tidal range of 20 feet (6 m) z China built several plants in the 1950 s z Korean potential sites (Garolim Bay) 3. 3 0203402
Hydraulic Pressure Absorbers z Large synthetic rubber bags filled with water could be placed offshore where large waves pass overhead y. Also respond to tides y. A connecting pipe conducts hydraulic pressure to a positive displacement motor that spins a generator y. The motor can turn a generator to make electricity that varies sinusoidally with the pressure http: //www. bfi. org/Trimtab/summer 01/ocean. Wave. htm 4. 0 020402
Ocean Thermal Energy: OTEC (Ocean Thermal Electric Conversion) z French Physicist Jacque D’Arsonval proposed in 1881 z Georges Claude built Matanzos Bay, Cuba 22 k. W plant in 1930 [Smith, p. 94] z Keahole Point, Hawaii has the US 50 k. W research OTEC barge system z OTEC requires some 36 to 40°F temperature difference between the surface and deep waters to extract energy z Open-cycle plants vaporize warm water and condense it using the cold sea water, yielding potable water and electricity from turbines-driven alternators z Closed-cycle units evaporate ammonia at 78°F to drive a turbine and an alternator z Hybrid cycle uses open-cycle steam to vaporize closed-cycle ammonia z China also has experimented with OTEC Ref. : http: //www. nrel. gov/otec/achievements. html 5. 0 020402
Wind Energy Equations (also applies to water turbines) z Assume a “tube” of air the diameter, D, of the rotor y. A = π D 2/4 z A length, L, of air moves through the turbine in t seconds y. L = u·t, where u is the wind speed z The tube volume is V = A·L = A·u·t z Air density, ρ, is 1. 225 kg/m 3 (water density ~1000 kg/m 3) z Mass, m = ρ·V = ρ·A·u·t, where V is volume z Kinetic energy = KE = ½ mu 2 6. 1 020402
Wind Energy Equations (continued) z Substituting ρ·A·u·t for mass, and A = π D 2/4 , KE = ½·π/4·ρ·D 2·u 3·t z Theoretical power, Pt = ½·π/4·ρ·D 2·u 3·t/t = 0. 3927·ρa·D 2·u 3, ρ (rho) is the density, D is the diameter swept by the rotor blades, and u is the speed parallel to the rotor axis z Betz Law shows 59. 3% of power can be extracted z 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 z For example, 59. 3%· 90%· 98%· 80% = 42% extraction of theoretical power 6. 1 020402
Generic Trades in Energy z Energy trade-offs required to make rational decisions z PV is expensive ($4 to 5 per Ref. : www. freefoto. com/ pictures/general/ windfarm/index. asp? i=2 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) z Are Compact Fluorescent Lamps (CFLs) always better to use than incandescent? Ref. : http: //www. energy. ca. gov/ education/storyimages/solar. jpeg Photo of FPL’s Cape Canaveral Plant by F. Leslie, 2001 7. 1 020315
Energy Storage z Renewable energy is often intermittent, and storage allows alignment with time of use. z Compressed air, flywheels, weight-shifting (pumped water storage at Niagara Falls) z Batteries are traditional for small systems and electric vehicles; first cars (1908) were electric z Hydrogen can be made by electrolysis z Energy is best stored as a financial credit through “net metering” y Net metering requires a utility to bill at the same rate for buying or selling energy www. strawbilt. org/systems/ details. solar_electric. html 7. 2 020402
Energy Transmission z Electricity and hydrogen are energy carriers, not natural fuels z Electric transmission lines lose energy in heat (~2% to 5%); trades loss vs. cost z Line flow directional analysis can show where new energy plants are required to reduce energy transmission z Hydrogen is made by electrolysis of water, cracking of natural gas, or from bacterial action (lab experiment level) z Oil and gas pipelines carry storable energy y Pipelines (36” or larger) can transport hydrogen without appreciable energy loss due to low density and viscosity y More efficient than 500 k. V transmission line and is out of view 7. 3 020402
Legal aspects and other complications z PURPA: Public Utility Regulatory Policy Act of 1978. Utility purchase from and sale of power to qualified facilities; avoided costs offsetting basis of purchases z Energy Policy Act of 1992 leads to deregulation z “NIMBYs” rally to shrilly insist “Not In My Backyard”! z Investment taxes and subsidies favor fossil and nuclear power z High initial cost dissuades potential users; future is uncertain z Lack of uniform state-level net metering hinders offsetting costs z Environmental Impact Statements (EIS) require extensive and expensive research and trade studies z Numerous “public interest” advocacy groups are well-funded and ready to sue to stop projects 7. 4 020402
Conclusion z Renewable energy offers a longterm approach to the World’s energy needs z Economics drives the energy selection process and short-term (first cost) thinking leads to disregard of long-term, overall cost z Wave and tidal energy are more expensive than wind and solar energy, the present leaders z Increasing oil, gas, and coal prices will ensure that the transition to renewable energy occurs z Offshore and shoreline wind energy plants offer a logical approach to part of future energy supplies 8. 0 0201402
References: Books, etc. z z z General: y Sørensen, Bent. Renewable Energy, Second Edition. San Diego: Academic Press, 2000, 911 pp. ISBN 0 -12 -656152 -4. y Henry, J. Glenn and Gary W. Heinke. Environmental Science and Engineering. Englewood Cliffs: Prentice. Hall, 728 pp. , 1989. 0 -13 -283177 -5, TD 146. H 45, 620. 8 -dc 19 y Brower, Michael. Cool Energy. Cambridge MA: The MIT Press, 1992. 0 -262 -02349 -0, TJ 807. 9. U 6 B 76, 333. 79’ 4’ 0973. y Di Lavore, Philip. Energy: Insights from Physics. NY: John Wiley & Sons, 414 pp. , 1984. 0 -471 -89683 -7 l, TJ 163. 2. D 54, 621. 042. y Bowditch, Nathaniel. American Practical Navigator. Washington: USGPO, H. O. Pub. No. 9. y Harder, Edwin L. Fundamentals of Energy Production. NY: John Wiley & Sons, 368 pp. , 1982. 0 -471 -083569, TJ 163. 9. H 37, 333. 79. Tidal Energy, pp. 111 -129. Wind: y Patel, Mukund R. Wind and Solar Power Systems. Boca Raton: CRC Press, 1999, 351 pp. ISBN 0 -84931605 -7, TK 1541. P 38 1999, 621. 31’ 2136 y Gipe, Paul. Wind Energy for Home & Business. White River Junction, VT: Chelsea Green Pub. Co. , 1993. 0 -930031 -64 -4, TJ 820. G 57, 621. 4’ 5 y Johnson, Gary L, Wind Energy Systems. Englewood Cliffs NJ: Prentice-Hall, Inc. TK 1541. J 64 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, QC 994. K 64, Chap. 11, Wind, Waves, and Swell. Solar: y Duffie, John and William A. Beckman. Solar Engineering of Thermal Processes. NY: John Wiley & Sons, Inc. , 920 pp. , 1991. 9. 1 020402
References: Internet z General: y y y http: //www. google. com/search? q=%22 renewable+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 z Tidal: y y 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/ph 162/l 17 b. html z Waves: y http: //www. env. qld. gov. au/sustainable_energy/publicat/ocean. htm y http: //www. bfi. org/Trimtab/summer 01/ocean. Wave. htm y http: //www. oceanpd. com/ y y http: //www. newenergy. org. cn/english/ocean/overview/status. htm http: //www. energy. org. uk/EFWave. htm y http: //www. earthsci. org/esa/energy/wavpwr/wavepwr. html 9. 2 020329
References: Internet z Thermal: y http: //www. nrel. gov/otec/what. html y http: //www. hawaii. gov/dbedt/ert/otec_hi. html#anchor 349152 on OTEC systems z Wind: y http: //awea-windnet@yahoogroups. com. Wind Energy elist y http: //awea-wind-home@yahoogroups. com. Wind energy home powersite elist y http: //telosnet. com/wind/20 th. html 9. 2 020329
Units and Constants z Units: y Power in watts (joules/second) y Energy (power x time) in watt-hours z Constants: y 1 m = 0. 3048 ft exactly by definition y 1 mile = 1. 609 km; 1 m/s = 2. 204 mi/h (mph) y 1 mile 2 = 27878400 ft 2 = 2589988. 11 m 2 y 1 ft 2 = 0. 09290304 m 2; 1 m 2 = 10. 76391042 ft 2 y 1 ft 3 = 28. 32 L = 7. 34 gallon = 0. 02832 m 3; 1 m 3 = 264. 17 US gallons y 1 m 3/s = 15850. 32 US gallons/minute y g = 32. 2 ft/s 2 = 9. 81 m/s 2; 1 kg = 2. 2 pounds y Air density, ρ (rho), is 1. 225 kg/m 3 or 0. 0158 pounds/ft 3 at 20ºC at sea level y Solar Constant: 1368 W/m 2 exoatmospheric or 342 W/m 2 surface (80 to 240 W/m 2) y 1 HP = 550 ft-lbs/s = 42. 42 BTU/min = = 746 W (J/s) y 1 BTU = 252 cal = 0. 293 Wh = 1. 055 k. J y 1 atmosphere = 14. 696 psi = 33. 9 ft water = 101. 325 k. Pa = 76 cm Hg =1013. 25 mbar y 1 boe (42 - gallon barrel of oil equivalent) = 1700 k. Wh 9. 3 020402
Energy Equations z Electricity: y E=IR; P=I 2 R; P=E 2/R, where R is resistance in ohms, E is volts, I is current in amperes, and P is power in watts y Energy = P t, where t is time in hours z Turbines: y Pa = ½ ρ A 2 u 3, where ρ (rho) is the fluid density, A = rotor area in m 2, and u is wind speed in m/s y P = R ρ T, where P = pressure (Nm-2 = Pascal) y Torque, T = P/ω, in Nm/rad, where P = mechanical power in watts, ω is angular velocity in rad/sec z Pumps: y Pm = g. Qmh/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 9. 4 020402
- Slides: 38