Ocean Energy,tidal Energy And Geothermal Energy 6g183m
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UNIT -7 Tidal Power: Ocean Thermal Energy Conversion , Geothermal Energy Conversion • Tidal Power: Tides and waves as energy suppliers and their mechanics; fundamental characteristics of tidal power, harnessing tidal energy, limitations.
• Ocean Thermal Energy Conversion: Principle of working, Rankine cycle, problems associated with OTEC. • Geothermal Energy Conversion: Principle of working, types of geothermal station with schematic diagram, problems associated with geothermal conversion, scope of geothermal energy.
Outline • Renewable – Hydro Power – Wind Energy
– Oceanic Energy – Solar Power – Geothermal – Biomass
2
Sources of New Energy
3 Boyle, Renewable Energy, Oxford University Press (2004)
Tidal Energy
Energy from the moon • Tides generated by the combination of the moon and sun’s gravitational forces • Greatest affect in spring when moon and sun combine forces • Bays and inlets amplify the height of the tide • In order to be practical for energy production, the height difference needs to be at least 5 meters • Only 40 sites around the world of this magnitude • Overall potential of 3000 gigawatts from movement of tides
• The tidal power is generated by the gravitational pull of the Moon on water. Due to these gravitational forces the water level follows a periodic high and low. The height of the tide produced at a given location is the result of the changing positions of the Moon and Sun relative to the Earth coupled with the effects of Earth rotation and the local shape of the sea floor. • The tidal energy generator uses this phenomenon to generate energy. The higher the height of the tide the more promising it is to harness tidal energy.
The monthly tidal cycle (29½ days) • About every 7 days, Earth alternates between: – Spring tide • Alignment of Earth-Moon-Sun system (syzygy) • Lunar and solar bulges constructively interfere • Large tidal range
– Neap tide • Earth-Moon-Sun system at right angles (quadrature) • Lunar and solar bulges destructively interfere • Small tidal range
Earth-Moon-Sun positions and the monthly tidal cycle Spring Tide Highest high tide and lowest low tide
Neap Tide Moderate tidal range
Natural Tidal Bottlenecks
11 Boyle, Renewable Energy, Oxford University Press (2004)
How it works • First generation, barrage-style tidal power plants • Works by building Barrage to contain water after high tide, then water has to through a turbine to return to low tide • Sites in (La Rance), Canada (Annapolis), and Russia
Tidal power types Tidal power can be classified into two main types: • Tidal stream systems make use of the kinetic energy from the moving water currents to power turbines, in a similar way to wind mills use moving air. This method is gaining in popularity because of the lower cost and lower ecological impact. • Barrages make use of the potential energy from the difference in height between high and low tides. Barrages suffer from the problems of very high civil infrastructure costs, few viable sites globally and environmental issues.
Second-generation tidal power plants
• Barrage not need, limiting total costs • Two types- vertical axis and horizontal axis • Davis Hydro turbine….. Successfully tested in St. Lawrence Seaway • Harness the energy of tidal streams • More efficient because they allow for energy production on both the ebbing and surging tides • One site has potential to equal the generating power of 3 nuclear power plants
Deeper Water Current Turbine
15 Boyle, Renewable Energy, Oxford University Press (2004)
TIDAL ENERGY
Advantages: • Tidal power is completely independent of the precipitation
(rain) and its uncertainty, besides being inexhaustible. • Large area of valuable land is not required. • When a tidal power plant works in combination with thermal or hydro-electric system, peak power demand can be effectively met with.
• Tidal power generation is free from pollution.
Disadvantages: • Due to variation in tidal range the output is not
uniform. •Since the turbines have to work on a wide range of
head variation (due to variable tide range) the plant efficiency is affected.
•There is a fear of machinery being corroded due to corrosive sea water.
•It is difficult to carry out construction in sea.
disadvantages • Presently costly – Expensive to build and maintain – A 1085MW facility could cost as much as 1.2 billion dollars to construct and run
• Connection to the grid • Technology is not fully developed • Barrage style only produces energy for about 10 hours out of the day • Barrage style has environmental affects – Such as fish and plant migration – Silt deposits – Local tides change- affects still under study
Advantages • No pollution • Renewable resource • More efficient than wind because of the density of water • Predictable source of energy vs. wind and solar • Second generation has very few disadvantages – Does not affect wildlife – Does not affect silt deposits – Less costly – both in building and maintenance
Wave Power
Wave Facts:
•
•
• •
Waves are caused by a number of forces, i.e. wind, gravitational pull from the sun and moon, changes in atmospheric pressure, earthquakes etc. Waves created by wind are the most common waves. Unequal heating of the Earth’s surface generates wind, and wind blowing over water generates waves. This energy transfer results in a concentration of the energy involved: the initial solar power level of about 1 kW/m2 is concentrated to an average wave power level of 70kW/m of crest length. This figure rises to an average of 170 kW/m of crest length during the winter, and to more than 1 MW/m during storms. Wave energy performance measures are characterized by diffuse energy, enormous forces during storms, and variation over wide range in wave size, length, period, and direction. Wave energy is an irregular and oscillating low-frequency energy source that must be converted to a 60-Hertz frequency before it can be added to the electric utility grid.
World Wave Power Resources
• • • • •
World Energy Council 2001 Survey stated the "potential exploitable wave energy" resources worldwide to be 2 TW. For European waters the resource was estimated to be able to cover more than 50% of the total power consumption. The wave market is estimated at $32 billion in the United Kingdom and $800 billion worldwide. The United States has exhibited weak effort compared to overseas projects in Norway, Denmark, Japan and the United Kingdom. As of 1995, 685 kilowatts (kW) of grid-connected wave generating capacity was operating worldwide. This capacity comes from eight demonstration plants ranging in size from 350 kW to 20 kW. Until recently the commercial use of wave power has been limited to small systems of tens to hundreds of watts aboard generate power
Wave Concentration Effects
24 Boyle, Renewable Energy, Oxford University Press (2004)
Wave Energy Where does wave energy originate? – Differential warming of the earth causes pressure differences in the atmosphere, which generate winds – As winds move across the surface of open bodies of water, they transfer some of their energy to the water and create waves
Wave Energy The amount of energy transferred and the size of the resulting wave depend on – the wind speed – the length of time for which the wind blows – the distance over which the wind blows, or fetch Therefore, coasts that have exposure to the prevailing wind direction and that face long expanses of open ocean have the greatest wave energy levels.
How do we harness wave energy? • In order to extract this energy, wave energy conversion devices must create a system of reacting forces, in which two or more bodies move relative to each other, while at least one body interacts with the waves. • There are many ways that such a system could be configured.
Wave Energy Technologies • Waves retain energy differently depending on water depth – Lose energy slowly in deep water – Lose energy quickly as water becomes shallower because of friction between the moving water particles and the sea bed • Wave energy conversion devices are designed for optimal operation at a particular depth range
Wave Energy Technologies Therefore, devices can be characterized in of their placement or location. – At the shoreline – Near the shoreline – Off-shore
One wave energy conversion system that has proven successful at each of these locations is the OSCILLATING WATER COLUMN.
• Oscillating Water Columns (OWC) These devices generate electricity from the wave-driven rise and fall of water in a cylindrical shaft. The rising and falling water column drives air into and out of the top of the shaft, powering an air-driven turbine. • Floats or Pitching Devices These devices generate electricity from the bobbing or pitching action of a floating object. The object can be mounted to a floating raft or to a device fixed on the ocean floor. • Wave Surge or Focusing Devices These shoreline devices, also called "tapered channel" systems, rely on a shore-mounted structure to channel and concentrate the waves, driving them into an elevated reservoir. These focusing surge devices are sizable barriers that channel large waves to increase wave height for redirection into elevated reservoirs.
Oscillating Water Column • An Oscillating Water Column (OWC) consists of a partially submerged structure that opens to the ocean below the water surface. This structure is called a wave collector. • This design creates a water column in the central chamber of the collector, with a volume of air trapped above it.
Oscillating Water Column • As a wave enters the collector, the surface of the water column rises and compresses the volume of air above it. • The compressed air is forced into an aperture at the top of the chamber, moving past a turbine. • As the wave retreats, the air is drawn back through the turbine due to the reduced pressure in the chamber.
Oscillating Water Column
The turning of the turbine drives a generator, producing electricity!
Oscillating Water Column • The type of turbine used is a key element to the conversion efficiency of an OWC. • Traditional turbines function by gas or liquid flowing in one direction and at a constant velocity. When the flow is not always from the same direction or at a constant velocity – such as in the OWC – traditional turbines become ineffective.
Wave Power Designs Although many wave energy devices have been invented, only a small proportion have been tested and evaluated. Only a few of these have been tested at sea, in ocean waves, rather than in artificial wave tanks. Large scale offshore devices and small scale shoreline devices have been ocean tested. The total power of waves breaking on the world's coastlines is estimated at 2 to 3 million megawatts. In favorable locations, wave energy density can average 65 megawatts per mile of coastline.
Wave Energy Oceanlinx
Oscillating Column Cross-Section
37 Boyle, Renewable Energy, Oxford University Press (2004)
Floating Devices
•
•
The Salter Duck, Clam, Archimedes wave swing, and other floating wave energy devices generate electricity through the harmonic motion of the floating part of the device. In these systems, the devices rise and fall according to the motion of the wave and electricity is generated through their motion. The Salter Duck is able to produce energy very efficiently, however its development was stalled during the 1980s due to a miscalculation in the cost of energy production by a factor of 10 and it has only been in recent years when the technology was reassessed and the error identified.
Tapered Channel Wave Power
These shoreline systems consist of a tapered channel which feeds into a reservoir constructed on a cliff. The narrowing of the channel causes the waves to increase their amplitude (wave height) as they move towards the cliff face which eventually spills over the walls of the channel and into the reservoir which is positioned several meters above mean sea level. The kinetic energy of the moving wave is converted into potential energy as the water is stored in the reservoir. The water then es through hydroelectric turbines on the way back to sea level thus generating electricity.
Tapered Channel (Tapchan)
40 http://www.eia.doe.gov/kids/energyfacts/sources/renewable/ocean.html
Turbines for Wave Energy
Turbine used in Mighty Whale
41
Wave Energy Power Distribution
42 Boyle, Renewable Energy, Oxford University Press (2004)
Advantages: •It is relatively pollution free. •It is a free and renewable energy source. •After removal of power, the waves are in placed state. •Wave-power devices do not require large land masses. •Whenever there is a large wave activity, a string of devices have to be used. The system not only produces
electricity but also protects coast lines from the destructive action of large waves, minimises erosion and help create artificial harbour.
Disadvantages: Lack of dependability. Relative scarcity of accessible sites of large wave activity. The construction of conversion devices is relatively complicated.
There are unfavourable economic factors such as large capital investment and costs of repair, replacement and maintenance.
Problems associated with wave energy
collection : The collection of wave energy entails the following problems: •The variation of frequency and amplitude makes it an unsteady source.
•Devices, installed to collect and to transfer wave energy from far off oceans, will have to with stand adverse weather conditions.
OTEC-OCEAN THERMAL ENERGY CONVERSION
OTEC Process 5. Heat extraction from cold-water sink to condense the working fluid in the condenser.
Cycle begins again Return to step 2
1. Power input to pumps to start process
4. Expanding vapor drive the turbine, and electricity is created by a generator
2. Fluid pump pressurizes and pushes working fluid to evaporator
3. Heat addition from the hotwater source used to evaporate the working fluid within the heat exchanger (Evaporator)
47
Open cycle or Claude Cycle Or Steam Cycle
Closed Rankine cycle or vapour cycle or Anderson cycle
Hybrid cycle
Advantages 1. OTEC uses clean, renewable, natural resources. Warm surface seawater and cold water from the ocean depths replace fossil fuels to produce electricity. 2. Suitably designed OTEC plants will produce little or no carbon dioxide or other polluting chemicals.
3. OTEC systems can produce fresh water as well as electricity. This is a significant advantage in island areas where fresh water is limited. 4. There is enough solar energy received and stored in the warm tropical ocean surface layer to provide most, if not all, of present human energy needs. 5. The use of OTEC as a source of electricity will help reduce the state's almost complete dependence on imported fossil fuels.
Disadvantages 1. OTEC-produced electricity at present would cost more than electricity generated from fossil fuels at their current costs. 2. OTEC plants must be located where a difference of about 20º C occurs year round. Ocean depths must be available fairly close to shore-based facilities for economic operation. 3. No energy company will put money in this project because it only had been tested in a very small scale. 4. Construction of OTEC plants and lying of pipes in coastal waters may cause localized damage to reefs and near-shore marine ecosystems.
5. Construction of floating power plants is difficult. 6. Plant size is limited to about 100 MW due to large size of components. 7. Very heavy investment is required.
Geothermal Energy
AGENDA – Geothermal Energy • • • • •
Geothermal Overview Extracting Geothermal Energy Environmental Implications Economic Considerations Geothermal Installations – Examples
Geothermal Overview
Geothermal in Context Energy Source
2000
2001
2002
2003
2004P
Total a
98.961
96.464
97.952
98.714
100.278
Fossil Fuels
84.965
83.176
84.070
84.889
86.186
Coal
22.580
21.952
21.980
22.713
22.918
0.065
0.029
0.061
0.051
0.138
Natural Gasb
23.916
22.861
23.628
23.069
23.000
Petroleumc
38.404
38.333
38.401
39.047
40.130
Electricity Net Imports
0.115
0.075
0.078
0.022
0.039
Nuclear Electric Power
7.862
8.033
8.143
7.959
8.232
Renewable Energy
6.158
5.328
5.835
6.082
6.117
Conventional Hydroelectric
2.811
2.242
2.689
2.825
2.725
Geothermal Energy
0.317
0.311
0.328
0.339
0.340
Biomassd
2.907
2.640
2.648
2.740
2.845
Solar Energy
0.066
0.065
0.064
0.064
0.063
Wind Energy
0.057
0.070
0.105
0.115
0.143
Coal Coke Net Imports
U.S. Energy Consumption by Energy Source, 2000-2004 (Quadrillion Btu) http://www.eia.doe.gov/cneaf/solar.renewables/page/geothermal/geothermal.html
Advantages of Geothermal
http://www.earthsci.org/mineral/energy/geother/geother.htm
Heat from the Earth’s Center • Earth's core maintains temperatures in excess of 5000°C – Heat radual radioactive decay of elements
• Heat energy continuously flows from hot core – Conductive heat flow – Convective flows of molten mantle beneath the crust.
• Mean heat flux at earth's surface – 16 kilowatts of heat energy per square kilometer – Dissipates to the atmosphere and space. – Tends to be strongest along tectonic plate boundaries
• Volcanic activity transports hot material to near the surface – Only a small fraction of molten rock actually reaches surface. – Most is left at depths of 5-20 km beneath the surface,
• Hydrological convection forms high temperature geothermal systems at shallow depths of 500-3000m.
Earth Temperature Gradient
http://www.geothermal.ch/eng/vision.html
Geysers Clepsydra Geyser in Yellowstone
http://en.wikipedia.org/wiki/Geyser
Hot Springs
Hot springs in Steamboat Springs area. http://www.eia.doe.gov/cneaf/solar.renewables/page/geothermal/geothermal.html
Fumaroles Clay Diablo Fumarole (CA)
http://lvo.wr.usgs.gov/cdf_main.htm
White Island Fumarole New Zealand
http://volcano.und.edu/vwdocs/volc_images/img_white_island_fumerole.html
Extracting Geothermal Energy
• Hydro thermal convective systems. These are again sub classified as: – (a) Vapour-dominated or dry steam fields. – (b) Liquid-dominated system or wet steam fields, and
• • • •
Geopressure resources. Petro-thermal or Hot dry rocks (HDR). Magma resources. Valcanoes.
Methods of Heat Extraction
http://www.geothermal.ch/eng/vision.html
Dry Steam Power Plants • “Dry” steam extracted from natural reservoir – 180-225 ºC ( 356-437 ºF) – 4-8 MPa (580-1160 psi) – 200+ km/hr (100+ mph)
• Steam is used to drive a turbo-generator • Steam is condensed and pumped back into the ground • Can achieve 1 kWh per 6.5 kg of steam – A 55 MW plant requires 100 kg/s of steam
Boyle, Renewable Energy, 2nd edition, 2004
Dry Steam Schematic
Boyle, Renewable Energy, 2nd edition, 2004
Single Flash Steam Power Plants • Steam with water extracted from ground • Pressure of mixture drops at surface and more water “flashes” to steam • Steam separated from water • Steam drives a turbine • Turbine drives an electric generator • Generate between 5 and 100 MW • Use 6 to 9 tonnes of steam per hour
Single Flash Steam Schematic
Boyle, Renewable Energy, 2nd edition, 2004
Binary Cycle Power Plants • Low temps – 100o and 150oC • Use heat to vaporize organic liquid – E.g., iso-butane, iso-pentane
• Use vapor to drive turbine – Causes vapor to condense – Recycle continuously
• Typically 7 to 12 % efficient • 0.1 – 40 MW units common http://www.worldenergy.org/wec-geis/publications/reports/ser/geo/geo.asp
Binary Cycle Schematic
Boyle, Renewable Energy, 2nd edition, 2004
Double Flash Power Plants • Similar to single flash operation • Unflashed liquid flows to low-pressure tank – flashes to steam • Steam drives a second-stage turbine – Also uses exhaust from first turbine
• Increases output 20-25% for 5% increase in plant costs
Double Flash Schematic
Boyle, Renewable Energy, 2nd edition, 2004
Hot Dry Rock Technology • Wells drilled 3-6 km into crust – Hot crystalline rock formations
• Water pumped into formations • Water flows through natural fissures picking up heat • Hot water/steam returns to surface • Steam used to generate power http://www.ees4.lanl.gov/hdr/
Hot Dry Rock Technology
Fenton Hill plant http://www.ees4.lanl.gov/hdr/
Soultz Hot Fractured Rock
Boyle, Renewable Energy, 2nd edition, 2004
Geothermal Heat Pump
http://www.worldenergy.org/wec-geis/publications/reports/ser/geo/geo.asp
Technological Issues • Geothermal fluids can be corrosive – Contain gases such as hydrogen sulphide – Corrosion, scaling
• Requires careful selection of materials and diligent operating procedures • Typical capacity factors of 85-95%
http://www.worldbank.org/html/fpd/energy/geothermal/technology.htm
Technology vs. Temperature Reservoir Temperature
Reservoir Fluid
Common Use
High Temperature >220oC (>430oF).
Water or Steam
Power Generation
Water
Low Temperature 50-150oC (120-300oF).
Water
http://www.worldbank.org/html/fpd/energy/geothermal/technology.htm
• • • • •
Flash Steam Combined (Flash and Binary) Cycle Direct Fluid Use Heat Exchangers Heat Pumps
Power Generation Direct Use • • • •
Binary Cycle Direct Fluid Use Heat Exchangers Heat Pumps
Direct Use
Intermediate Temperature 100-220oC (212 - 390oF).
Technology commonly chosen
Direct Use • •
Direct Fluid Use Heat Exchangers
Geothermal Performance
Boyle, Renewable Energy, 2nd edition, 2004
Environmental Implications
Environmental Impacts • Land – Vegetation loss – Soil erosion – Landslides
• Air – Slight air heating – Local fogging
http://www.worldbank.org/html/fpd/energy/geothermal/assessment.htm
• Water – – – – –
Watershed impact Damming streams Hydrothermal eruptions Lower water table Subsidence
• Noise
Renewable? • Heat depleted as ground cools • Not steady-state – Earth’s core does not replenish heat to crust quickly enough
• Example: – Iceland's geothermal energy could provide 1700 MW for over 100 years, compared to the current production of 140 MW
http://en.wikipedia.org/wiki/Geothermal
Economics of Geothermal
Cost Factors • • • • • • •
Temperature and depth of resource Type of resource (steam, liquid, mix) Available volume of resource Chemistry of resource Permeability of rock formations Size and technology of plant Infrastructure (roads, transmission lines)
http://www.worldbank.org/html/fpd/energy/geothermal/cost_factor.htm
Costs of Geothermal Energy • Costs highly variable by site – Dependent on many cost factors
• High exploration costs • High initial capital, low operating costs – Fuel is “free”
• Significant exploration & operating risk – Adds to overall capital costs – “Risk ” http://www.worldbank.org/html/fpd/energy/geothermal/
Geothermal Installations Examples
Geothermal Power Examples
Boyle, Renewable Energy, 2nd edition, 2004
Geothermal Power Generation • World production of 8 GW – 2.7 GW in US
• The Geyers (US) is world’s largest site – Produces 2 GW
• Other attractive sites – Rift region of Kenya, Iceland, Italy, , New Zealand, Mexico, Nicaragua, Russia, Phillippines, Indonesia, Japan http://en.wikipedia.org/wiki/Geothermal
Geothermal Energy Plant
Geothermal energy plant in Iceland http://www.wateryear2003.org/en/
Geothermal Well Testing
Geothermal well testing, Zunil, Guatemala http://www.geothermex.com/es_resen.html
Heber Geothermal Power Station
52kW electrical generating capacity
http://www.ece.umr.edu/links/power/geotherm1.htm
Geysers Geothermal Plant The Geysers is the largest producer of geothermal power in the world.
http://www.ece.umr.edu/links/power/geotherm1.htm
Scope of geothermal •Geothermal heat pumps • Space heating •Greenhouse and covered ground heating •Aquaculture pond and raceway heating • Agricultural crop drying • Industrial process heat
• Snow melting and space cooling • Bathing and swimming
Geothermal Summary
http://www.earthsci.org/mineral/energy/geother/geother.htm
Single Flash Plant Schematic
http://www.worldbank.org/html/fpd/energy/geothermal/technology.htm
http://www.worldbank.org/html/fpd/energy/geothermal/technology.htm
Binary Cycle Power Plant
http://www.worldenergy.org/wec-geis/publications/reports/ser/geo/geo.asp
Flash Steam Power Plant
http://www.worldenergy.org/wec-geis/publications/reports/ser/geo/geo.asp
• Ocean Thermal Energy Conversion: Principle of working, Rankine cycle, problems associated with OTEC. • Geothermal Energy Conversion: Principle of working, types of geothermal station with schematic diagram, problems associated with geothermal conversion, scope of geothermal energy.
Outline • Renewable – Hydro Power – Wind Energy
– Oceanic Energy – Solar Power – Geothermal – Biomass
2
Sources of New Energy
3 Boyle, Renewable Energy, Oxford University Press (2004)
Tidal Energy
Energy from the moon • Tides generated by the combination of the moon and sun’s gravitational forces • Greatest affect in spring when moon and sun combine forces • Bays and inlets amplify the height of the tide • In order to be practical for energy production, the height difference needs to be at least 5 meters • Only 40 sites around the world of this magnitude • Overall potential of 3000 gigawatts from movement of tides
• The tidal power is generated by the gravitational pull of the Moon on water. Due to these gravitational forces the water level follows a periodic high and low. The height of the tide produced at a given location is the result of the changing positions of the Moon and Sun relative to the Earth coupled with the effects of Earth rotation and the local shape of the sea floor. • The tidal energy generator uses this phenomenon to generate energy. The higher the height of the tide the more promising it is to harness tidal energy.
The monthly tidal cycle (29½ days) • About every 7 days, Earth alternates between: – Spring tide • Alignment of Earth-Moon-Sun system (syzygy) • Lunar and solar bulges constructively interfere • Large tidal range
– Neap tide • Earth-Moon-Sun system at right angles (quadrature) • Lunar and solar bulges destructively interfere • Small tidal range
Earth-Moon-Sun positions and the monthly tidal cycle Spring Tide Highest high tide and lowest low tide
Neap Tide Moderate tidal range
Natural Tidal Bottlenecks
11 Boyle, Renewable Energy, Oxford University Press (2004)
How it works • First generation, barrage-style tidal power plants • Works by building Barrage to contain water after high tide, then water has to through a turbine to return to low tide • Sites in (La Rance), Canada (Annapolis), and Russia
Tidal power types Tidal power can be classified into two main types: • Tidal stream systems make use of the kinetic energy from the moving water currents to power turbines, in a similar way to wind mills use moving air. This method is gaining in popularity because of the lower cost and lower ecological impact. • Barrages make use of the potential energy from the difference in height between high and low tides. Barrages suffer from the problems of very high civil infrastructure costs, few viable sites globally and environmental issues.
Second-generation tidal power plants
• Barrage not need, limiting total costs • Two types- vertical axis and horizontal axis • Davis Hydro turbine….. Successfully tested in St. Lawrence Seaway • Harness the energy of tidal streams • More efficient because they allow for energy production on both the ebbing and surging tides • One site has potential to equal the generating power of 3 nuclear power plants
Deeper Water Current Turbine
15 Boyle, Renewable Energy, Oxford University Press (2004)
TIDAL ENERGY
Advantages: • Tidal power is completely independent of the precipitation
(rain) and its uncertainty, besides being inexhaustible. • Large area of valuable land is not required. • When a tidal power plant works in combination with thermal or hydro-electric system, peak power demand can be effectively met with.
• Tidal power generation is free from pollution.
Disadvantages: • Due to variation in tidal range the output is not
uniform. •Since the turbines have to work on a wide range of
head variation (due to variable tide range) the plant efficiency is affected.
•There is a fear of machinery being corroded due to corrosive sea water.
•It is difficult to carry out construction in sea.
disadvantages • Presently costly – Expensive to build and maintain – A 1085MW facility could cost as much as 1.2 billion dollars to construct and run
• Connection to the grid • Technology is not fully developed • Barrage style only produces energy for about 10 hours out of the day • Barrage style has environmental affects – Such as fish and plant migration – Silt deposits – Local tides change- affects still under study
Advantages • No pollution • Renewable resource • More efficient than wind because of the density of water • Predictable source of energy vs. wind and solar • Second generation has very few disadvantages – Does not affect wildlife – Does not affect silt deposits – Less costly – both in building and maintenance
Wave Power
Wave Facts:
•
•
• •
Waves are caused by a number of forces, i.e. wind, gravitational pull from the sun and moon, changes in atmospheric pressure, earthquakes etc. Waves created by wind are the most common waves. Unequal heating of the Earth’s surface generates wind, and wind blowing over water generates waves. This energy transfer results in a concentration of the energy involved: the initial solar power level of about 1 kW/m2 is concentrated to an average wave power level of 70kW/m of crest length. This figure rises to an average of 170 kW/m of crest length during the winter, and to more than 1 MW/m during storms. Wave energy performance measures are characterized by diffuse energy, enormous forces during storms, and variation over wide range in wave size, length, period, and direction. Wave energy is an irregular and oscillating low-frequency energy source that must be converted to a 60-Hertz frequency before it can be added to the electric utility grid.
World Wave Power Resources
• • • • •
World Energy Council 2001 Survey stated the "potential exploitable wave energy" resources worldwide to be 2 TW. For European waters the resource was estimated to be able to cover more than 50% of the total power consumption. The wave market is estimated at $32 billion in the United Kingdom and $800 billion worldwide. The United States has exhibited weak effort compared to overseas projects in Norway, Denmark, Japan and the United Kingdom. As of 1995, 685 kilowatts (kW) of grid-connected wave generating capacity was operating worldwide. This capacity comes from eight demonstration plants ranging in size from 350 kW to 20 kW. Until recently the commercial use of wave power has been limited to small systems of tens to hundreds of watts aboard generate power
Wave Concentration Effects
24 Boyle, Renewable Energy, Oxford University Press (2004)
Wave Energy Where does wave energy originate? – Differential warming of the earth causes pressure differences in the atmosphere, which generate winds – As winds move across the surface of open bodies of water, they transfer some of their energy to the water and create waves
Wave Energy The amount of energy transferred and the size of the resulting wave depend on – the wind speed – the length of time for which the wind blows – the distance over which the wind blows, or fetch Therefore, coasts that have exposure to the prevailing wind direction and that face long expanses of open ocean have the greatest wave energy levels.
How do we harness wave energy? • In order to extract this energy, wave energy conversion devices must create a system of reacting forces, in which two or more bodies move relative to each other, while at least one body interacts with the waves. • There are many ways that such a system could be configured.
Wave Energy Technologies • Waves retain energy differently depending on water depth – Lose energy slowly in deep water – Lose energy quickly as water becomes shallower because of friction between the moving water particles and the sea bed • Wave energy conversion devices are designed for optimal operation at a particular depth range
Wave Energy Technologies Therefore, devices can be characterized in of their placement or location. – At the shoreline – Near the shoreline – Off-shore
One wave energy conversion system that has proven successful at each of these locations is the OSCILLATING WATER COLUMN.
• Oscillating Water Columns (OWC) These devices generate electricity from the wave-driven rise and fall of water in a cylindrical shaft. The rising and falling water column drives air into and out of the top of the shaft, powering an air-driven turbine. • Floats or Pitching Devices These devices generate electricity from the bobbing or pitching action of a floating object. The object can be mounted to a floating raft or to a device fixed on the ocean floor. • Wave Surge or Focusing Devices These shoreline devices, also called "tapered channel" systems, rely on a shore-mounted structure to channel and concentrate the waves, driving them into an elevated reservoir. These focusing surge devices are sizable barriers that channel large waves to increase wave height for redirection into elevated reservoirs.
Oscillating Water Column • An Oscillating Water Column (OWC) consists of a partially submerged structure that opens to the ocean below the water surface. This structure is called a wave collector. • This design creates a water column in the central chamber of the collector, with a volume of air trapped above it.
Oscillating Water Column • As a wave enters the collector, the surface of the water column rises and compresses the volume of air above it. • The compressed air is forced into an aperture at the top of the chamber, moving past a turbine. • As the wave retreats, the air is drawn back through the turbine due to the reduced pressure in the chamber.
Oscillating Water Column
The turning of the turbine drives a generator, producing electricity!
Oscillating Water Column • The type of turbine used is a key element to the conversion efficiency of an OWC. • Traditional turbines function by gas or liquid flowing in one direction and at a constant velocity. When the flow is not always from the same direction or at a constant velocity – such as in the OWC – traditional turbines become ineffective.
Wave Power Designs Although many wave energy devices have been invented, only a small proportion have been tested and evaluated. Only a few of these have been tested at sea, in ocean waves, rather than in artificial wave tanks. Large scale offshore devices and small scale shoreline devices have been ocean tested. The total power of waves breaking on the world's coastlines is estimated at 2 to 3 million megawatts. In favorable locations, wave energy density can average 65 megawatts per mile of coastline.
Wave Energy Oceanlinx
Oscillating Column Cross-Section
37 Boyle, Renewable Energy, Oxford University Press (2004)
Floating Devices
•
•
The Salter Duck, Clam, Archimedes wave swing, and other floating wave energy devices generate electricity through the harmonic motion of the floating part of the device. In these systems, the devices rise and fall according to the motion of the wave and electricity is generated through their motion. The Salter Duck is able to produce energy very efficiently, however its development was stalled during the 1980s due to a miscalculation in the cost of energy production by a factor of 10 and it has only been in recent years when the technology was reassessed and the error identified.
Tapered Channel Wave Power
These shoreline systems consist of a tapered channel which feeds into a reservoir constructed on a cliff. The narrowing of the channel causes the waves to increase their amplitude (wave height) as they move towards the cliff face which eventually spills over the walls of the channel and into the reservoir which is positioned several meters above mean sea level. The kinetic energy of the moving wave is converted into potential energy as the water is stored in the reservoir. The water then es through hydroelectric turbines on the way back to sea level thus generating electricity.
Tapered Channel (Tapchan)
40 http://www.eia.doe.gov/kids/energyfacts/sources/renewable/ocean.html
Turbines for Wave Energy
Turbine used in Mighty Whale
41
Wave Energy Power Distribution
42 Boyle, Renewable Energy, Oxford University Press (2004)
Advantages: •It is relatively pollution free. •It is a free and renewable energy source. •After removal of power, the waves are in placed state. •Wave-power devices do not require large land masses. •Whenever there is a large wave activity, a string of devices have to be used. The system not only produces
electricity but also protects coast lines from the destructive action of large waves, minimises erosion and help create artificial harbour.
Disadvantages: Lack of dependability. Relative scarcity of accessible sites of large wave activity. The construction of conversion devices is relatively complicated.
There are unfavourable economic factors such as large capital investment and costs of repair, replacement and maintenance.
Problems associated with wave energy
collection : The collection of wave energy entails the following problems: •The variation of frequency and amplitude makes it an unsteady source.
•Devices, installed to collect and to transfer wave energy from far off oceans, will have to with stand adverse weather conditions.
OTEC-OCEAN THERMAL ENERGY CONVERSION
OTEC Process 5. Heat extraction from cold-water sink to condense the working fluid in the condenser.
Cycle begins again Return to step 2
1. Power input to pumps to start process
4. Expanding vapor drive the turbine, and electricity is created by a generator
2. Fluid pump pressurizes and pushes working fluid to evaporator
3. Heat addition from the hotwater source used to evaporate the working fluid within the heat exchanger (Evaporator)
47
Open cycle or Claude Cycle Or Steam Cycle
Closed Rankine cycle or vapour cycle or Anderson cycle
Hybrid cycle
Advantages 1. OTEC uses clean, renewable, natural resources. Warm surface seawater and cold water from the ocean depths replace fossil fuels to produce electricity. 2. Suitably designed OTEC plants will produce little or no carbon dioxide or other polluting chemicals.
3. OTEC systems can produce fresh water as well as electricity. This is a significant advantage in island areas where fresh water is limited. 4. There is enough solar energy received and stored in the warm tropical ocean surface layer to provide most, if not all, of present human energy needs. 5. The use of OTEC as a source of electricity will help reduce the state's almost complete dependence on imported fossil fuels.
Disadvantages 1. OTEC-produced electricity at present would cost more than electricity generated from fossil fuels at their current costs. 2. OTEC plants must be located where a difference of about 20º C occurs year round. Ocean depths must be available fairly close to shore-based facilities for economic operation. 3. No energy company will put money in this project because it only had been tested in a very small scale. 4. Construction of OTEC plants and lying of pipes in coastal waters may cause localized damage to reefs and near-shore marine ecosystems.
5. Construction of floating power plants is difficult. 6. Plant size is limited to about 100 MW due to large size of components. 7. Very heavy investment is required.
Geothermal Energy
AGENDA – Geothermal Energy • • • • •
Geothermal Overview Extracting Geothermal Energy Environmental Implications Economic Considerations Geothermal Installations – Examples
Geothermal Overview
Geothermal in Context Energy Source
2000
2001
2002
2003
2004P
Total a
98.961
96.464
97.952
98.714
100.278
Fossil Fuels
84.965
83.176
84.070
84.889
86.186
Coal
22.580
21.952
21.980
22.713
22.918
0.065
0.029
0.061
0.051
0.138
Natural Gasb
23.916
22.861
23.628
23.069
23.000
Petroleumc
38.404
38.333
38.401
39.047
40.130
Electricity Net Imports
0.115
0.075
0.078
0.022
0.039
Nuclear Electric Power
7.862
8.033
8.143
7.959
8.232
Renewable Energy
6.158
5.328
5.835
6.082
6.117
Conventional Hydroelectric
2.811
2.242
2.689
2.825
2.725
Geothermal Energy
0.317
0.311
0.328
0.339
0.340
Biomassd
2.907
2.640
2.648
2.740
2.845
Solar Energy
0.066
0.065
0.064
0.064
0.063
Wind Energy
0.057
0.070
0.105
0.115
0.143
Coal Coke Net Imports
U.S. Energy Consumption by Energy Source, 2000-2004 (Quadrillion Btu) http://www.eia.doe.gov/cneaf/solar.renewables/page/geothermal/geothermal.html
Advantages of Geothermal
http://www.earthsci.org/mineral/energy/geother/geother.htm
Heat from the Earth’s Center • Earth's core maintains temperatures in excess of 5000°C – Heat radual radioactive decay of elements
• Heat energy continuously flows from hot core – Conductive heat flow – Convective flows of molten mantle beneath the crust.
• Mean heat flux at earth's surface – 16 kilowatts of heat energy per square kilometer – Dissipates to the atmosphere and space. – Tends to be strongest along tectonic plate boundaries
• Volcanic activity transports hot material to near the surface – Only a small fraction of molten rock actually reaches surface. – Most is left at depths of 5-20 km beneath the surface,
• Hydrological convection forms high temperature geothermal systems at shallow depths of 500-3000m.
Earth Temperature Gradient
http://www.geothermal.ch/eng/vision.html
Geysers Clepsydra Geyser in Yellowstone
http://en.wikipedia.org/wiki/Geyser
Hot Springs
Hot springs in Steamboat Springs area. http://www.eia.doe.gov/cneaf/solar.renewables/page/geothermal/geothermal.html
Fumaroles Clay Diablo Fumarole (CA)
http://lvo.wr.usgs.gov/cdf_main.htm
White Island Fumarole New Zealand
http://volcano.und.edu/vwdocs/volc_images/img_white_island_fumerole.html
Extracting Geothermal Energy
• Hydro thermal convective systems. These are again sub classified as: – (a) Vapour-dominated or dry steam fields. – (b) Liquid-dominated system or wet steam fields, and
• • • •
Geopressure resources. Petro-thermal or Hot dry rocks (HDR). Magma resources. Valcanoes.
Methods of Heat Extraction
http://www.geothermal.ch/eng/vision.html
Dry Steam Power Plants • “Dry” steam extracted from natural reservoir – 180-225 ºC ( 356-437 ºF) – 4-8 MPa (580-1160 psi) – 200+ km/hr (100+ mph)
• Steam is used to drive a turbo-generator • Steam is condensed and pumped back into the ground • Can achieve 1 kWh per 6.5 kg of steam – A 55 MW plant requires 100 kg/s of steam
Boyle, Renewable Energy, 2nd edition, 2004
Dry Steam Schematic
Boyle, Renewable Energy, 2nd edition, 2004
Single Flash Steam Power Plants • Steam with water extracted from ground • Pressure of mixture drops at surface and more water “flashes” to steam • Steam separated from water • Steam drives a turbine • Turbine drives an electric generator • Generate between 5 and 100 MW • Use 6 to 9 tonnes of steam per hour
Single Flash Steam Schematic
Boyle, Renewable Energy, 2nd edition, 2004
Binary Cycle Power Plants • Low temps – 100o and 150oC • Use heat to vaporize organic liquid – E.g., iso-butane, iso-pentane
• Use vapor to drive turbine – Causes vapor to condense – Recycle continuously
• Typically 7 to 12 % efficient • 0.1 – 40 MW units common http://www.worldenergy.org/wec-geis/publications/reports/ser/geo/geo.asp
Binary Cycle Schematic
Boyle, Renewable Energy, 2nd edition, 2004
Double Flash Power Plants • Similar to single flash operation • Unflashed liquid flows to low-pressure tank – flashes to steam • Steam drives a second-stage turbine – Also uses exhaust from first turbine
• Increases output 20-25% for 5% increase in plant costs
Double Flash Schematic
Boyle, Renewable Energy, 2nd edition, 2004
Hot Dry Rock Technology • Wells drilled 3-6 km into crust – Hot crystalline rock formations
• Water pumped into formations • Water flows through natural fissures picking up heat • Hot water/steam returns to surface • Steam used to generate power http://www.ees4.lanl.gov/hdr/
Hot Dry Rock Technology
Fenton Hill plant http://www.ees4.lanl.gov/hdr/
Soultz Hot Fractured Rock
Boyle, Renewable Energy, 2nd edition, 2004
Geothermal Heat Pump
http://www.worldenergy.org/wec-geis/publications/reports/ser/geo/geo.asp
Technological Issues • Geothermal fluids can be corrosive – Contain gases such as hydrogen sulphide – Corrosion, scaling
• Requires careful selection of materials and diligent operating procedures • Typical capacity factors of 85-95%
http://www.worldbank.org/html/fpd/energy/geothermal/technology.htm
Technology vs. Temperature Reservoir Temperature
Reservoir Fluid
Common Use
High Temperature >220oC (>430oF).
Water or Steam
Power Generation
Water
Low Temperature 50-150oC (120-300oF).
Water
http://www.worldbank.org/html/fpd/energy/geothermal/technology.htm
• • • • •
Flash Steam Combined (Flash and Binary) Cycle Direct Fluid Use Heat Exchangers Heat Pumps
Power Generation Direct Use • • • •
Binary Cycle Direct Fluid Use Heat Exchangers Heat Pumps
Direct Use
Intermediate Temperature 100-220oC (212 - 390oF).
Technology commonly chosen
Direct Use • •
Direct Fluid Use Heat Exchangers
Geothermal Performance
Boyle, Renewable Energy, 2nd edition, 2004
Environmental Implications
Environmental Impacts • Land – Vegetation loss – Soil erosion – Landslides
• Air – Slight air heating – Local fogging
http://www.worldbank.org/html/fpd/energy/geothermal/assessment.htm
• Water – – – – –
Watershed impact Damming streams Hydrothermal eruptions Lower water table Subsidence
• Noise
Renewable? • Heat depleted as ground cools • Not steady-state – Earth’s core does not replenish heat to crust quickly enough
• Example: – Iceland's geothermal energy could provide 1700 MW for over 100 years, compared to the current production of 140 MW
http://en.wikipedia.org/wiki/Geothermal
Economics of Geothermal
Cost Factors • • • • • • •
Temperature and depth of resource Type of resource (steam, liquid, mix) Available volume of resource Chemistry of resource Permeability of rock formations Size and technology of plant Infrastructure (roads, transmission lines)
http://www.worldbank.org/html/fpd/energy/geothermal/cost_factor.htm
Costs of Geothermal Energy • Costs highly variable by site – Dependent on many cost factors
• High exploration costs • High initial capital, low operating costs – Fuel is “free”
• Significant exploration & operating risk – Adds to overall capital costs – “Risk ” http://www.worldbank.org/html/fpd/energy/geothermal/
Geothermal Installations Examples
Geothermal Power Examples
Boyle, Renewable Energy, 2nd edition, 2004
Geothermal Power Generation • World production of 8 GW – 2.7 GW in US
• The Geyers (US) is world’s largest site – Produces 2 GW
• Other attractive sites – Rift region of Kenya, Iceland, Italy, , New Zealand, Mexico, Nicaragua, Russia, Phillippines, Indonesia, Japan http://en.wikipedia.org/wiki/Geothermal
Geothermal Energy Plant
Geothermal energy plant in Iceland http://www.wateryear2003.org/en/
Geothermal Well Testing
Geothermal well testing, Zunil, Guatemala http://www.geothermex.com/es_resen.html
Heber Geothermal Power Station
52kW electrical generating capacity
http://www.ece.umr.edu/links/power/geotherm1.htm
Geysers Geothermal Plant The Geysers is the largest producer of geothermal power in the world.
http://www.ece.umr.edu/links/power/geotherm1.htm
Scope of geothermal •Geothermal heat pumps • Space heating •Greenhouse and covered ground heating •Aquaculture pond and raceway heating • Agricultural crop drying • Industrial process heat
• Snow melting and space cooling • Bathing and swimming
Geothermal Summary
http://www.earthsci.org/mineral/energy/geother/geother.htm
Single Flash Plant Schematic
http://www.worldbank.org/html/fpd/energy/geothermal/technology.htm
http://www.worldbank.org/html/fpd/energy/geothermal/technology.htm
Binary Cycle Power Plant
http://www.worldenergy.org/wec-geis/publications/reports/ser/geo/geo.asp
Flash Steam Power Plant
http://www.worldenergy.org/wec-geis/publications/reports/ser/geo/geo.asp
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