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RENEWABLE SOURCES OF MECHANICAL ENERGY SC 208 Our Energy Future April 14, 2005 John Bush WIND, WATER, THERMAL GRADIENTS Hydroelectric Tidal and Ocean/River Currents Wave Wind Geothermal Ocean thermal COMMON FEATURES With minor exceptions they all provide electricity exclusively

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wind water thermal gradients
WIND, WATER, THERMAL GRADIENTS
  • Hydroelectric
  • Tidal and Ocean/River Currents
  • Wave
  • Wind
  • Geothermal
  • Ocean thermal
common features
COMMON FEATURES
  • With minor exceptions they all provide

electricity exclusively

  • They have very specific site

requirements

  • They all have environmental or aesthetic

negatives

  • Until recently only hydroelectric and

geothermal were commercially useful

the case of hawaii
THE CASE OF HAWAII
  • Now almost totally dependent (90%) on imported oil for its energy
  • Has an increasing need for fresh water
  • Has access to ample renewable resources
    • Intense sunlight
    • Fast growing crops, particularly sugarcane
    • Strong, steady winds
    • Fast flowing streams
    • Ocean currents
    • Warm and cold ocean waters
  • Renewables represent a great opportunity for Hawaii but what about for the rest of the United States?
hydroelectric power
HYDROELECTRIC POWER
  • Electricity generated by using gravitational potential energy to power a turbine-generator
  • Two utility applications
    • Conventional hydroelectric generation
    • Energy storage by pumping water to upper reservoir during electric surplus and releasing it through a turbine-generator when needed
  • Two approaches for conventional hydro
    • Dams create a reservoir
    • Run of river depends on diverting river flow
large scale conventional hydroelectric generation
LARGE SCALE CONVENTIONAL HYDROELECTRIC GENERATION
  • Output depends on time of year and precipitation
  • Future sites in the US are limited to none because of strong public resistance
  • Impacts
    • Water resources: stream flows, water temp.
    • Effects on fish migrations
    • Damage to archaeological/historic sites
    • Loss of scenic/wilderness resources
    • Upstream deposition (silting) & downstream erosion
    • Increased landslide potential
    • Gain in recreation resources
  • DOE forecast a net decline in hydro generation (see chart following)
future of minihydro
FUTURE OF MINIHYDRO?
  • Small, low impact units: 1-2 MWe
  • Advanced controls permit integration into a distributed network
  • May reactivate some sites abandoned in the 1960s
  • Active in Japan and the Phillipines
  • Net impact in the US probably low
hydroelectricity in california
HYDROELECTRICITY IN CALIFORNIA
  • About 15% of California’s in-state generation is from hydroelectric (vs. 7% nationally)
  • Substantial imports of hydropower from the Pacific Northwest sensitive to precipitation and salmon migrations
  • Total of 386 hydroplants with 14,116 MWe capacity
  • Future large installations in California are unlikely
power from tides and currents
POWER FROM TIDES AND CURRENTS
  • Technical approaches
    • Tidal dams (barrages)
    • Tidal fences
    • Turbine fields
  • Common features
    • Depend on water driven fans/turbines
    • Low operating costs if can avoid biofouling and storm damage
    • High construction costs
    • Known or suspected negative impacts on marine environment
tidal barrages
TIDAL BARRAGES
  • Dams across estuaries with gates and turbines
  • Tidal differences must be more than 16 feet—there are about 40 such sites in the world
  • Gates are opened when tide is high enough allowing water to flow through hydroturbines
  • La Rance a 240 MWe facility in France has operated reliably for many years
  • No facilities in the US—possibilities in the Pacific Northwest and the Atlantic Northeast
  • Cause silting, destroy wetlands and interfere with fish migrations
  • Probably limited potential for the US
tidal fences
TIDAL FENCES
  • Look like giant turnstiles
  • Span channels and spin in tidal currents
  • Current must be at least 5 to 8 knots
  • Density of sea water permits extracting much more energy from these than from corresponding wind mills
axial flow tidal turbines
AXIAL FLOW TIDAL TURBINES
  • Arrayed in rows like wind farms
  • Look like wind turbines
  • Ideally close to shore in water depths of 60-100 ft.
  • Estimated costs of 5 MWe free-flow turbine installation (2005 dollars)
    • Capital cost $4300/KWe
    • Operating cost $.07-.09/KWH
    • Deployable 2010-2012
cross flow turbines
CROSS FLOW TURBINES
  • Like those for tidal gates
  • Use conduits to concentrate the tidal flow
  • Raised during incoming tide
  • Lowered to generate power during tidal ebb
potential for tidal turbines in us
POTENTIAL FOR TIDAL TURBINES IN US
  • Tidal locations (120): 1200 MWe
  • Riverine locations: 12,500-170,000 MWe
  • Gulf Stream: 685,000 MWe
  • Fragmented industry with no major industrial firms
  • Demonstration in 2006: Manhattan’s East River, 6 turbines, 35 rpm, 200 KWe by Verdant Power
  • For discussion see:

Proceedings of the Hydrokinetic and Wave Energy Technologies Technical and Environmental Issues Workshop Oct. 26-28, 2005

http://hydropower.inl.gov/

wave energy technical approaches
WAVE ENERGYTECHNICAL APPROACHES
  • Floats or pitching devices: wave action moves two or more bodies relative to one another—various devices generate power; energy storage in supercapacitors since voltage/current are wildly erratic
  • Oscillating water columns: wave action drives air in and out of column—power is generated by an air turbine in the column
  • Wave surge or focusing devices: wave action drives water up a channel into a reservoir—power is generated by hydro turbines during outflow from reservoir
wave energy potential
WAVE ENERGY POTENTIAL
  • Designs range from distributed generation to large scale power plants
  • Susceptibility to storm damage and biofouling are issues
  • Power conditioning and grid connection are also issues
  • EPRI estimate: at 60 m off US coast the average wave power is 2100TWH/Year
  • Could generate 7% of current US electricity demand by capturing 20% of the total wave energy at 50% efficiency.
problems preventing realization of potential
PROBLEMS PREVENTING REALIZATION OF POTENTIAL
  • Both wave and tide technologies are largely unproven
  • DOE has no R&D capacity for them
  • The firms involved are small and undercapitalized
  • The regulatory structure is poorly defined
  • There are no tax credits for wave/tide power
wind power
WIND POWER
  • The most promising near term renewable resource
  • Issue: what will happen when the subsidies vanish?
  • US installed capacity growing at about 25% per year
  • Intermittent, irregular supply:
    • Value depends on installed capacity, site specific capacity factor, and timing of generation (e.g. summer generation is usually more valuable than winter generation)
    • At greater than 20% of a grid’s supply, managing the grid becomes difficult and expensive
some general attributes
SOME GENERAL ATTRIBUTES
  • Best sited where there is a reliable strong wind: the US midwest and southwest
  • Adaptable to either centralized (wind farm) or decentralized siting
  • Used by utilities to save fuel—not reliable baseload generation
  • Siting issues: Long Island, Nantucket/Martha’s Vineyard
    • Aesthetics/visibility: NIMBY
    • Noise
    • Electromagnetic interference
    • Banned within 1.5 miles of shipping or ferry lanes
  • Wild life fatalities: California, West Virginia
    • Low flying, migratory song birds (Altamount Pass)
    • Bats
technologies
TECHNOLOGIES
  • Horizontal axis fans are the best proven technologies
  • Windmills have been in use in the West since the Middle Ages
  • New designs are proliferating
  • Technical issues
    • Mechanisms are complex and expensive to maintain
    • Large blades for efficient units are expensive to make and transport
    • Power conditioning and grid connection issues seem to be resolved
vertical shaft turbines
VERTICAL SHAFT TURBINES
  • Compared to horizontal axis turbines
    • Greater efficiency: 45% vs. 25-40%
    • Operate in higher winds: 70 mph vs. 50 mph maximum
    • Quieter and less visibly intrusive
    • More readily scaled up in size: to 10 MWe vs. 5MWe maximum
  • Unproven technology at large scale
wind power examples
WIND POWER: EXAMPLES
  • Upstate New York: Maple Ridge
    • Leeward of Lake Ontario
    • Largest project east of the Mississippi: 195 turbines, 320 ft high, 320 MWe (peak)
    • Generate lease payments to landowners: $5000-$10,000 per turbine annually
    • Cost ~$1700 per KWe (peak) [2005 dollars]
    • Financed by Goldman Sachs
    • Subsidized by surcharge on utility bills
  • US installed capacity (2004) 6740 MWe (peak)
windpower potential for the united states
WINDPOWER POTENTIAL FOR THE UNITED STATES
  • Battelle estimated that with constraints wind can provide 20% of US electricity demand
  • DOE goal 6% of US demand by 2020
  • Unconstrained estimate is that the US potential is equivalent to operating ~1500 1000 MWe nuclear or coal plants
  • Of the 50 states North Dakota has the greatest potential followed by Texas, Kansas, South Dakota, Montana and Nebraska—California is 17th
  • North Dakota could supply 25% of the current US electricity demand but would require a major growth of electricity transmission capacity.
windpower prospects
WINDPOWER PROSPECTS
  • A big potential market: worldwide capacity is growing at 30% per year
  • Annual equipment sales ~ $2Billion in 2005
  • Project financing for renewables in 2005
    • Windpower $3.5 Billion
    • Solar Photovoltaic $2.2 Billion
    • All Other $1.25 Billion
    • Growing at 25% per year
  • Major companies are involved
    • General Electric
    • British Petroleum
    • Goldman Sachs
    • J P Morgan Chase
    • Siemens AG
geothermal power
GEOTHERMAL POWER
  • Employs geothermal heat directly (buildings, greenhouses, etc.) or to generate electricity
  • Electricity generation requires source temperatures > 300º F
  • Three basic plant designs
    • Dry steam: uses steam directly from reservoir w/o recycling: cost $.04-.06 per KWH
    • Flash steam: partially flashes superheated water (> 360º F) to steam and recycles the rest
    • Binary cycle: Reservoir fluid and working fluid kept separate—able to use lower temperature fluids (225-260º F): cost $.05-.08 per KWH
some site specific reservoir characeristics
SOME SITE SPECIFIC RESERVOIR CHARACERISTICS
  • Fluid temperature and production rate
  • Corrosive nature of fluids
  • Co-production of noxious gases
  • Difficulty of drilling reservoir rock
  • Rate of replenishment of fluids and heat
  • Reservoir plugging due to mineralization or rock deformation
  • Access to maintenance and electric transmission
resources actual and potential
RESOURCES: ACTUAL AND POTENTIAL
  • Geothermal wells/springs (> 130º F) are widely distributed in the Western US (see map)
  • US currently generates 3000 MWe and uses 570 MWt from geothermal sources
  • Research efforts
    • Resource characterization
    • Plant efficiencies
    • Geothermal field development
resources actual and potential51
RESOURCES: ACTUAL AND POTENTIAL
  • Potential resource > 50,000 times that of oil and gas if could engineer systems that tap
    • Hot dry rock reservoirs
    • Magma reservoirs
  • Engineered systems have thus far not proved to be feasible
    • Low permeability of dry rock reservoirs
    • Closing of reservoirs when fluids injected
    • Difficulty of drilling to great depths in very hot rock
  • Research effort on engineered systems was greatly reduced after failures at Valle Caldera New Mexico in the 1970s and 80s
resources california
RESOURCES: CALIFORNIA
  • Forty one plants are currently operating: Imperial Valley; Salton Sea; Geysers; Lassen, Inyo, Mono Counties
  • There are 14 known resource areas with temperatures over 300 ºF
  • Sites of hot dry rock (Clear Lake) and magma (Long Valley Caldera) are known
  • California Energy Commission Geothermal Program
    • Since 1992 funds r&d and commercialization
    • In 2006 $ 3.4 Million is available
ocean thermal power
OCEAN THERMAL POWER
  • Depends on temperature differences between sea surface and sea depths--requires about a 36º F difference
  • Three types of cycles

-Closed cycle with working fluid such as

ammonia and a conventional turbine

-Open cycle using surface water as the working fluid and a low pressure turbine

-Hybrid cycles

  • Open and hybrid cycles also produce fresh water
hawaiian otec projects
HAWAIIAN OTEC PROJECTS
  • Keahole Point Kona Mini-OTEC (1979): barge mounted, closed cycle, 15 KWe
  • Kawaihae Kona Mini OTEC (1980) : component test facility by USDOE
  • Kahe Point Oahu OTEC-1 (1983): pilot plant designed but never built
  • Keahole Point Kona (1992-1998): shore mounted, open cycle, 103 KWe, 6 gal/min fresh water
other us otec projects
OTHER US OTEC PROJECTS
  • US Congress Ocean Thermal Energy Act (1980) established a licensing program for OTEC plants
  • There have been no applications since
  • Reasons
    • Low cost of fossil fuels
    • Limited application for mainland US: Gulf Coast
    • Siting limitations due to sensitivity of ocean environment
    • High risk both technical and financial
    • Large investment (especially the heat exchangers) with uncertain return
other otec projects
OTHER OTEC PROJECTS
  • French designs
    • Cuba(1930) 22KWe open cycle shore mounted destroyed by wave action
    • Brazil (1935) closed cycle ship mounted destroyed by wave action
    • Abidjan (1956) 3MWe designed but never built
  • Japanese design Nauru (1981): 31 KWe closed cycle used Freon working fluid and exceeded design goals
  • Design studies proposed
    • Okinoshima island
    • Antigua and Barbuda
    • Cayman Islands
summary potential contribution to us energy supply in 2025
SUMMARY: POTENTIAL CONTRIBUTION TO US ENERGY SUPPLY IN 2025
  • Hydroelectric: 7% of US electric supply flat to declining
  • Tidal and ocean/river currents: very little if at all
  • Wave energy: negligible
  • Wind energy: 7-10% of US electric supply
  • Geothermal: Perhaps 5% of electric supply in Western US with some direct use
  • Ocean Thermal: Negligible except perhaps in Hawaii