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
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
• 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
• 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
• 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?
• 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
• 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
• 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
• 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
•
•
•
•
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
• 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
•
•
•
•
Like those for tidal gates
Use conduits to concentrate the tidal flow
Raised during incoming tide
Lowered to generate power during tidal
ebb
CROSS FLOW TURBINE
CONDUIT PLUS RESERVOIR
TIDAL OR WAVE ENERGY
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
• 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
EUROPEAN DESIGN WAVE ENERGY
CONVERTER
AQUABUOY DESIGN (US)
OSCILLATING COLUMN
OSCILLATING COLUMN
(SCOTLAND)
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
• 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
• 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
• 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
• 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
MECHANISMS OF TURBINES ARE
COMPLEX
LARGER MACHINES ARE MORE
EFFICIENT
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
VERTICAL SHAFT WIND TURBINES
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
• 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
• 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
• 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 (225260º F): cost $.05-.08 per KWH
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
• 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
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
• 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
• 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
• 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
• 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
• 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
• 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