RENEWABLE SOURCES OF MECHANICAL ENERGY

SC 208 Our Energy FutureApril 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 TURBINECONDUIT 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, 2005http://hydropower.inl.gov/

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

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 (225-260º 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