Flywheel energy storage

1.    Introduction

When electricity production exceeds electricity consumption, energy storage becomes necessary. The current total worldwide energy production exceeds 3400 GW while storage capacity is only 90 GW.2 Electrical utilities commonly store the energy during non-peak hours in the form of hydroelectric storage by pumping water uphill when electricity is cheap and storing it in a reservoir. This water can then be discharged to spin a turbine and generate electricity during peak hours. The main disadvantage of this method is that the process is only 66% efficient, meaning two-thirds of the total electrical energy is lost in the process. Flywheels on the other hand offer a means of storing energy in a rotating disk with efficiencies higher than 90%.3

A more efficient way of storing energy would also allow for the expansion of renewable energy generating systems such as wind and solar. For example, wind turbines have great fluctuation and are not predictable. By storing the renewable energy, the energy will be made predictable because it can be used during peak hours. Also, a local supply of energy storage would be “compensating for load variations [that] would make it possible to operate transmission, subtransmission, and distribution networks with lighter designs”.2 In contrast to renewable energy, fossil fuel and nuclear plants run nearly 100% of the time at full throttle making them very predictable. These types of plants account for the base load, which is 45% of peak load. Intermediate load generators include older and less efficient generators that only operate during the day to meet demand. Peak load generators allow for peak consumption to be met with gas turbines or diesel engines.2 If the energy can be effectively stored using flywheels, the less efficient peak load generators would be obsolete since less predictable renewable energy can be stored for peak use. For this reason, electric utilities would want 5 MWh storage capacities. This is the “largest that can be factory-assembled and truck-mounted for delivery to substations or energy storage facilities”.4

Besides grid energy storage for electrical utilities, there is also application for energy storage in space onboard satellites that receive energy by solar power, where flywheels can be used for energy storage as well as attitude control instead of batteries. Flywheels can also be used in hybrid-electric cars and trains coupled with regenerative breaking. Another application of flywheels is uninterruptible power supplies for semiconductor fabrication factories and computer data centers. The goals of this study will be to explain how flywheels work, the advantages and disadvantages of flywheel energy storage, as well as technical and economic criteria that will ensure the flywheel’s success.

 

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2. Background

Flywheels consist of a rotating mass, a vacuum containment structure, bearings, and an electrical device that can function as a motor or generator. Energy is supplied to the flywheel when the device functions as a motor, and energy is discharged when the device functions as a generator.

Kinetic energy is given by

(Eq. 1)

where KE is the kinetic energy,  is the moment of inertia, and  is the angular velocity of the flywheel.

A solid cylinder will have a moment of inertia equal to

(Eq. 2)

Where r is the radius, a is the length of the cylinder, m is the mass, and  is the density.

Figure 1 – University of Texas at Austin Composite Flywheel.5

A composite flywheel, such as the one shown in Figure 1, is usually a hollow circular cylinder, which can be approximated by a composite rim attached to the shaft via a web. In this case, the moment of inertia is given by

(Eq. 3)

Where  is the outside radius of the hoop, and  is the inside radius of the hoop.6 Because kinetic energy is proportional to the square of angular speed, but only linearly proportional to mass, the best way to increase the kinetic energy is to increase the angular speed.       

The tensile strength of the material is what limits the maximum speed. The hoop stress σθ is given by

(Eq. 4)

Where v is the poisson ratio.6

The figure of merit for flywheels is the maximum specific energy density Esp, given by

(Eq. 5)

where Ks is the shape factor, σm is the maximum tensile strength.5 Thus the specific energy density is inversely proportional to the density of the material and linearly proportional to the tensile strength. Composites are thus the ideal flywheel material because they possess very high specific energy densities due to their low densities and high tensile strengths. As shown in Figure 2, the composite material T-1000 graphite has a specific energy density about 16 times that of steel.

Figure 2: Specific energy density chart for different flywheel materials.5

 

Now that the workings and materials selection of flywheels is established, several applications will be discussed.

One application of flywheels is in space. Flywheels can be used in satellites because power is generated by solar panels only during the day, so energy needs to be stored when the satellite is in a dark orbit. For the International Space Station in particular, nickel-hydrogen batteries are currently being used with a rating of 38,000 cycles and 6.5 year lifetime.7 A flywheel can be used with the same space and weight, but the flywheel would last 3-10 times longer. The cost savings is estimated by NASA to be $200 million. The flywheel would be 93.7% efficient. Flywheels can also be used for 3-axis attitude control by creating a torque as the flywheel is charged or discharged. The US Airforce is leading the attitude control research that could also make its way to space applications. Current targets are a specific energy of 150 kJ/kg, and a torque at least 50 Nm on each axis.8

Flywheels can also be used for hybrid electric vehicles. The engine can be designed to always run at an optimized rpm and a constant speed. Sudden bursts of power needed to accelerate can come from a flywheel, which can be recharged by the engine. Regenerative breaking can also be used to recharge the flywheel instead of dissipating the braking energy to waste heat by friction.8 One example of flywheels being implemented in cars is the Porsche GT3 R Hybrid. A flywheel can deliver 120 kW (161 hp) in 8 seconds to two electric motors connected to the front wheels for a very powerful boost. Because it also has regenerative breaking, the GT3 is able to make fewer pit stops and win more races.9 A schematic of the flywheel implementation in the GT3 is shown in Figure 3.

Figure 3: Porsche GT3 R Hybrid.9

Another application of flywheels is for semiconductor fabrication facilities and computer data centers. AMD’s Dresden Germany semiconductor fabrication facility has a 30 MW flywheel that can absorb 5 MW for 5 seconds. The 5 second storage interval allows the AMD plant to switch from one power source to the next uninterrupted. Internet data centers also need a form of energy storage for power interruptions. Since 80% of power line disturbances last for less than a second, flywheels can be used to store energy for the next generation cloud computing server farms.8 For large internet companies like Google, “the cost of a power interruption can exceed $1 million per minute.” 10 With this in mind, flywheels may offer a cost-effective solution.

3.   Analysis

3.1         Advantages

One of the primary advantages of flywheels is the long lifetime of 15 to 20 years. This is evidenced by the fact that a composite flywheel has 90,000 cycles even high speeds of 48,000 rpm with no evident degradation.8 Unlike batteries, flywheels exhibit no depth of discharge effects as shown in Figure 4. Depth of discharge means that the useable energy in a battery degrades over time. Laptop and cell-phone users are often victims of this effect. Flywheels also have the advantage that they can deliver large amounts of energy in a short span of time, and require little to no maintenance over their lifetime. They are also highly scalable, and have fewer environmental impacts compared to batteries.

Figure 4: Efficiency vs Lifetime at 80% Depth of Discharge.2

3.2         Disadvantages

The primary disadvantages of flywheels are that they are often more than 10 times expensive than pumped hydroelectric and generally more expensive than compressed air energy storage, as seen in Figure 5.

Figure 5 – Capital Cost per Cycle of various energy storage methods.2

Another disadvantage of flywheels is that they have both low volumetric and weight energy densities compared to traditional batteries as seen in Figure 6.

 

Figure 6: Weight Energy Density vs Volume Energy Density.2

Lastly, poor flywheel containment design can lead to dangerous situations, since composite flywheels can fly apart at very high speeds.

3.3         Obstacles

The main obstacle to widespread flywheel usage is the low energy density that is currently achievable. This limitation can possibly be overcome in the future with a better choice of composite flywheel materials. US Flywheel Systems predicts that with better composites, specific energies of 200 Wh/kg (10 times higher than current specific energy density) and specific power of 30 kW/kg will be possible.11

Another obstacle that needs to be overcome is the frictional losses that flywheels incur over time. In order to reduce losses to viscous friction, flywheels can be housed in a high vacuum, low pressure containment. Magnetic bearings have come to be used over lubricated shafts to reduce friction. Magnetic bearing flywheels have high frictional losses of 1% per hour, however high temperature superconductor bearing flywheels have energy losses of 0.1% per hour because the superconductors stabilize the load well since they are perfect diamagnets.4 Boeing is currently working on a compact 250 kW flywheel as shown in Figure 7, but these types of flywheels remain in the research phase, and may prove to be ineffective because energy needs to be supplied to provide for cooling.12

Figure 7: Boeing flywheel with high temperature superconducting bearings. 12

The last obstacle to flywheels is cost. At the present time, flywheels are simply not economically competitive with pumped hydroelectric storage. A good example of this is the 20 MW flywheel storage system recently built by Beacon Power. The private company would have been unable to build the plant had it not received a $43 million Department of Energy loan guarantee.13

3.4         Technical Objectives for Success

The objectives for commercial success of flywheels are overcoming the obstacles described in the previous section, namely higher energy density, fewer losses to friction, and a lower cost.

4.   Conclusion

Energy storage is necessary when electricity production exceeds consumption. Flywheel energy storage offers a convenient method of small-scale storage which can help expand the unpredictable renewable wind and solar power generation. Flywheel energy storage also has application in space onboard satellites, hybrid electric cars, and semiconductor factories and internet data centers. Composite flywheels have proven to last 90,000 cycles with no degradation, and operate at speeds of 48,000 rpm.  But due to their inherently low energy densities, new composite materials must be developed to make flywheels competitive with batteries. Lastly, high temperature superconducting bearings are currently in the research phase, and may offer a means of reducing frictional losses by a factor of 10.

5.   References

 

  1. Werfel, F.N., U. Floegel-Delor, T. Riedel, R. Rothfeld, D. Wippich, B. Goebel, G. Reiner, and N. Wehlau. “A Compact HTS 5 KWh/250 KW Flywheel Energy Storage System.” IEEE Transactions on Applied Superconductivity 17.2 (2007): 2138-141.
  2. Ibrahim, H., A. Ilinca, and J. Perron. “Energy Storage Systems—Characteristics and Comparisons.”Renewable and Sustainable Energy Reviews 12.5 (2008): 1221-250.
  3. Kirk, J. “Flywheel Energy Storage – I.” Int. J. Mech. Sci 19 (1977): 223-31.
  4. Hull, J., T. Mulcahp, K. Uherka, R. Erck, and R. Abboud. “Flywheel Energy Storage Using Superconducting Magnetic Bearings.” Applied Superconductivity 2.7-8 (1994): 449-55.
  5. Liu, H., and J. Jiang. “Flywheel Energy Storage—An Upswing Technology for Energy Sustainability.” Energy and Buildings 39.5 (2007): 599-604.
  6. Bolund, B., H. Bernhoff, and M. Leijon. “Flywheel Energy and Power Storage Systems.”Renewable and Sustainable Energy Reviews 11.2 (2007): 235-58.
  7. http://www.grc.nasa.gov/WWW/RT/RT1999/5000/5420miller.html
  8. Hebner, R., J. Beno, and A. Walls. “Flywheel Batteries Come Around Again.” IEEE Spectrum(2002): 46-51.
  9. http://www.porsche.com/usa/aboutporsche/pressreleases/pag/?id=2010-02-11&pool=international-de
  10. http://www.wired.com/wired/archive/8.05/flywheel.html?pg=4&topic=&topic_set=
  11. Bitterly, J. “Flywheel Technology – Past, Present, and 21st Century Projections.” IEEE AES Systems Magazine (1998): 13-16.
  12. Strasik, M., J. Hull, J. Mittleider, J. Gonder, P. Johnson, K. McCrary, and C. McIver. “An Overview of Boeing flywheel Energy Storage Systems with High-temperature Superconducting Bearings.” Superconductor Science and Technology 23 (2010): 1-5.
  13. http://news.cnet.com/8301-11128_3-20067886-54.html?part=rss&subj=news&tag=2547-1_3-0-20

Still not convinced flywheels are amazing? You can still dislike flywheels here.

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Energy Storage

Electrical Energy Storage – enables alternative energy and management of the grid. Also allows for less dependence on imported energy.

Analogies: Power density – acceleration for an automobile, energy density – how far the car will travel

Sodium sulfer batteries are $1000/W produced by NGK in Japan

Lithium ion batteries in laptops are also $1000/W.

Lithium ion batteries came out in the 1970s. In the 1990s Sony put lithium ion batteries into their electronics for lighter products. There are no US manufacturers of lithium ion batteries. In 2010, lithium batteries are a 10 billion dollars industry.

How do lithium ion batteries work?

Positive electrode made of graphite (not lithium to reduce possibility of an explosion), and a negative electrode made of lithium cobalt oxide. The ions in the electrolyte transfer electrons. Process of intercalation: Lithium ions transfer the electrons between electrodes.

Specific capacity of cathode materials is theoretically about 200 mAh/g

iPhone has a packaged energy density of about 60 mAh/g. The packaging includes safety aspects and extra weight components.

All battery technology has leveled off. Ni/MH and Ni/Cd has already leveled off. We don’t know if lithium ion has leveled off for energy density since 2005.

Using a silicon anode can give a density more than 10 times of typical lithium batteries. But the problem is stability with volume expansion problems.

What about using lithium for the anode. If carbon is replaced with metallic lithium, the energy density is 3829 mAh/g. Problem: a solid electrolyte interface forms, which leads to dendrites forming, and the dendrites go from the anode to cathode and short the circuit. One solution is to use a protective coating that prevents dendrites from forming.

Aerogels used as electrochemical materials – have a high surface area, low density, and high porosity. Aerogels made by sol-gel chemistry with supercritical drying of solvent. Specific capacity is a few times higher than lithium cobalt.

Vanadium Oxide gels – can intercalate lithium reversibly.

 

Capacitive Energy Storage –

Supercapacitors – Been around since 1950s. Charge is stored by ions in electrolyte adsorbing onto a high surface area electrode. High surface areas allow for a high capacitance. Charge is stored in the double layer.More than a million life cycles. The process is highly reversible since there are no chemical or phase changes. Each electrode behaves as a single capacitor. Power is related to distance between electrodes. High power density, but lower energy densities. The ions are absorbed and desorbed under an electric field. Energy is stored in the double layer.

Two tyupes of Supercapacitors

  • EC Double Layer Capacitor – no transfer of charge so there is no redox reaction. The electrode is a high surface area carbon.
  • Pseudocapacitors – charge transfers through the surface. The energy storage per unit area is much higher because there is a redox reaction. The electrode can be metal oxides and conducting polymers.

RuO2 – oxide that is conductive like a metal. Good ionic conductor at the surface. Can get over 1000 F/g energy density. Ru metal is more expensive than platinum, which makes it very expensive.

Energy Storage – Necessary because the electricity load fluctuates over time.

Power produced by renewable energy such as wind, solar, and wave energy, fluctuates even more.

Pumped Hydroelectric Energy Storage – water energy is stored in the form of potential energy. Pumped Hydroelectric energy storage is the most widespread energy storage in the world, about over 90 GW. Discharge times ranges from a few hours to a few days.

Advantages: Many cycles, low cost per cycle, long lifetime, and high efficiency (70-85%).

Disadvantages: Requires large area for supper and lower reservoirs. Has to be large (>1000 MW) to be economical. Takes long time to construct dam, and has a high capital cost.

 

Compressed Air Energy Storage – Use off-peak electricity to compress air into an underground reservoir. When you need electricity, release air from the reservoir, and passes through turbines which drive a generator and again produce electricity. Commercialized in Germany in 1978 with a 290 MW unit. 110 MW plant in McIntosh, Alabama in 1991, which comes up within 14 minutes.Third plant in Ohio for 2700 MW.

Flywheel Energy Storage – storing energy in kinetic  energy. Flywheel charged by using electricity to power a motor to spin the wheel through a system of gears. The discharge, the flywheel delivers kinetic energy to spin an electric generator. Magnetic bearings used to minimize friction. Also vacuum used to reduce air drag. Can be optimized by increasing mass, which causes a linear increase in kinetic energy. Or by increasing angular speed. Flywheels with magnetic bearings and high vacuum can maintain 97% of the mechanical efficiency for 2 hours. Can spin at speeds of 20,000 to over 50,000 rpm.

Advantages: low tech, low maintenance, high power output, long life (20 years), numerous charge/discharge cycles, and high efficiencies.

Disadvantages: Doesn’t store a lot of energy, magnetic bearings are expensive, vacuum containment vessel expensive.

 

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Hydrogen Fuel Cells

Energy contained in 1 kg of H2 is equivalent to 1 gallon of gasoline

Fuel cells are more efficient than internal combustion engines, and require 5-8 kg of hydrogen on board.

H2 is an energy carrier and not a fuel

H2 has a low volumetric energy density

Hydrogen reacts explosively with oxygen above the ignition temperature of 450 oC at atmospheric pressure.

 

How to store hydrogen

  • Compressed hydrogen gas
  • Liquid hydrogen (cryogenic, 20 K at atmospheric pressure)
  • Hollow glass microspheres
  • Metal hybrides

Know the 2015 DOE targets in red

 

DOE 2015 targets

  • Gravimetric energy density should be larger than 9 wt% or 10.8 MJ/kg
  • Volumetric energy density should be larger 81 g of H2/L or 9.72 MJ/L
  • Refueling time of hydrogen tanks as short as refueling with current fuels such as diesel or gasoline. 2.5 minutes for 5 kgof h@
  • Autonomy of 300 miles without refueling.

Compressed Hydrogen – hydrogen is in the gas phase at a pressure of 10,000 psi. The gravimetric density of hydrogen is 143 MJ/kg, and the Volumetric density is 5.6 MJ/L at 700 bar. Advantages: simple, few losses, up to 700 bar. The disadvantages are that there is a high compression cost (up to 20% of the stored energy).

Hydrogen embrittlement – metals become brittle and fracture when they are exposed to hydrogen. In high temperatures, hydrogen diffuses in the metal, and leads to crack development and propagation. High strength steels and nickel and titanium alloys are the most susceptible. As hydrogen diffuses through steel, it reacts with carbon and forms methane, which initiates cracks in the steel.

Aluminum compressed hydrogen tanks have a maximum pressure of 175 bar. Steel tank can have a maximum pressure of 200 bar. Carbon reinforced composites with a polymer liner can have up to 700 bar of maximum pressure. The polymer liner disallows hydrogen from diffusing.

 

Liquid Hydrogen – requires cryogenic storage at 20 K, with super thermal insulation. Gravimetric density is 5.22 MJ/kg, and volumetric is 22.9 MJ/L. Advantages: increase energy storage density. Cost of Dewar decreases exponentially with volume. Disadvantages: high compression and cooling cost (40%). Heat transfer during long-term storage.

 

Ammonia H2 storage – second most commonly produced chemical in the world. Ammonia is toxic at standard temperature and pressure. The infrastructure for making and transporting it is already in place.

 

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Photobiological Hydrogen Production

Photobiological Hydrogen Production –  uses microorganisms to convert solar energy into hydrogen.

Advantages of hydrogen:

  • Hydrogen is the most abundant element in the Universe, but not in the form of H2.
  • Hydrogen also has a large gravimetric energy density (higher than methane and oil)
  • Does not emit CO2.
  • PEM (Proton Exchange Membrane) fuel cells are 40-60% efficient.

 

Disadvantages of hydrogen:

  • Storing hydrogen is very expensive
  • Hydrogen needs to be compressed.
  • fuel cells have high expenses and are not reliable.

 

 

Hydrogen is produced from: 48% natural gas reforming, 30% from oil refining, 18% from coal refining, and 4% from water electrolysis.

 

Photobiological Hydrogen Production eats up CO2, and the only products are O2 and biomass. So it is renewable and sustainable. Maximum theoretical light to H2 conversion efficiency is 41% efficient using hydrogenase enzymes, and economically viable at 10%.
Disadvantages of Photobiological Hydrogen Production

  • needs water
  • Low efficiency due to low amounts of sunlight, presence of oxygen (needs to be removed), presence of nitrogen, and large partial pressures of hydrogen.
  • Difficulty in scaling up.

There are 4 different species of microorganisms: green algae, cyanobacteria, purple non-sulfur bacteria, and dark fermentative bacteria.

ATP (Adenosine-5’-triphosphate) – energy source in the cell

NADP+ – coenzyme used in lipid synthesis.

Photosynthesis – converts CO2 into organic compounds. First step: light dependent reaction – converts sunlight into chemical energy (ATP and NADPH). Second step: Dark reactions convert CO2 and H2O into organic compounds.

Enzyme – protein that catalyze chemical reactions

Nitrogenase – converts N2 into NH3. The turn over rate is 10 reactions /s.

 

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Coal Power Generation

Clean Coal – Coal takes millions of years to form. Comes from swamps.

Heating value = energy released as heat when a compound undergoes complete combustion with oxygen under standard conditions.

Higher heating value = determined by bringing all the products of combustion back to the original pre-combustion temperature

Lower heating value = determined by subtracting the heat of vaporization of the water vapor from the higher heating value.

Higher heating values

  • Hydrogen: 142 MJ/kg
  • Gasoline: 47 MJ/kg
  • Ethanol: 30 MJ/kg
  • Coal – 15-27 MJ/kg.

4 different types of coal

  • Anthracite
    • Contains 86-97% of carbon.
    • Contains highest heating value
    • Not common in the US
    • Bituminous coal
      • Contains 45-86% carbon
      • Most common coal found in US
      • Used to generate electricity, and to make steel.
      • Subbutuminous coal
        • Contains 35-45% coal
        • 36% of coal in the US is of this type
        • Lignite
          • Contains 25-35% carbon
          • Lowest rank of coal with lowest energy content
          • Has high moisture content
          • 7% of US coal is of this type.

Coal emits the most CO2 per kWh.

Coal is extracted through underground mining (1000 feet deep), and surface mining (less than 200 feet deep). 2/3 of coal production is surface mining.

Large Bucket Wheel Excavator – cost $100 million, weighs 14,000 tons, took 5 years to assemble. Can extract 240,000 m3 of coal per day.

Once coal is extracted, the coal is then processed and cleaned. Rocks and dirt, ash, and sulfur are removed to increase the heating value.

The US has 406 coal fired power plants, each of about 500 MW.

3000 miners die in China every year.

Miners get asthma, pneumoconiosis (lung disease), and heart attacks.

Coal also has air pollution problems: emits CO2, Sox, Nox, and particulate matter.

Surface mining causes contamination of water.

Read about the future of coal here.

Clean Coal –

  • Hypercoal – use higher quality coal without ashes
    • 45% thermal efficiency
    • 13% reduction in CO2.
    • Carbon capture and sequestration
      • CO2 from coal power plant is processed and stored underground.
      • Coal gasification
        • Burn coal, add oxygen, then CO2 is injected in a well. Purified syngas (hydrogen) goes through the gas turbine (Brayton cycle).
        • Coal liquefaction
          • Use the Fischer-Tropsch process to convert CO+H2 into oil. Needs a catalyst, so it can be expensive.

Solubility of CO2 as a function of temperature: solubility increases as temperature decreases.

 

 

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Harvesting Energy from the Ocean

Ocean Energy – There is a potential 13 GW of ocean energy available in the US, whereas 35 GW of wind power already exists in the US. One problem with ocean energy is that many of the most optimal sites are in Alaska, which is far away from any densely populated areas.

US Department of Energy estimates that 2 TW of electricity can be provided by ocean waves alone.

Tidal power is more limited in its potential because only 40 places in the world have a large enough difference between the high and low tides to make electricity generation practical.

Ocean Energy

A wave energy buoy typically has 40 KW, and the new generation is 150 kW. A 40 kW buoy is energy for 40 households. The surface area would be about 30 acres for a 10 MW wave power station.

Advantages of ocean energy

  • No carbon emissions
  • No fuel required

Disadvantages

  • Variable energy production
  • High initial construction and maintenance costs
  • Environmental impact such as noise and disruption to marine life
  • Possible threat to navigation from collisions
  • May degrade scenic ocean front views
  • Loss of potential boating and swimming sites
  • Requires government subsidies.

Technical challenges – must be able to withstand strong ocean currents. Must be able to withstand rough weather conditions. Materials are costly because they have to be strong and resistant to corrosion.

World Energy Council estimates market potential as 2000-4000 TWh per year.

Wave energy – waves formed by winds. The amount of energy in waves depends on their height and period.

Wave energy is largest between October to April

Types of devices

  • Oscillating water column – on the shore. The waves enters a water column which compresses air contained inside, which compresses air and drives a turbine. Implemented in Australia.
  • Ocean Swell Powered Renewable Energy  – first commercial sea based energy machine. Located in Scotland.
  • Attenuator – multi-segment floating structure oriented parallel to the direction of the waves. About 180m long with 4 segments.
  • Pelamis wave power generator – uses a water hammer effect to create pressure.
  • Overtopping Device – reservoir filled by incoming wave. Gravity returns water to the ocean. As it returns back to the ocean it drives a turbine.
  • Point absorber – capture the up and down motion of the wave.

 

Tidal stream energy – the rise and fall of the tides (happens twice a day). Similar to wind power extraction, but water is denser than air. Thus the same amount of energy can be produced as with using a wind turbine, but with a smaller area footprint.

  • More predictable than wind or wave, but comes at a high cost, and limited availability of sites.
  • Tidal Barrage Power Plant – built in France 1966. 240 MW. Costs $0.17/kWh.
  • Tidal stream generator – uses axial flow pitch controlled rotors. Can achieve over 48% efficiency over a broad range of current velocities.

 

Salinity Gradient Energy

  • Pressure Retarded Osmosis – seawater and freshwater is separated by a membrane. The difference in salt concentration between seawater and freshwater creates a difference in pressure.
  • Reverse Electrodialysis – two membranes: one permeable to positive ions, and one permeable to negative ions. Salt water separated from freshwater by membranes loses both positive ions and negative ions. One side is charged more than the other, so you have a voltage.

Ocean Thermal Energy – A temperature difference of about 20 degrees C exists 1 km below the surface of the ocean.

 

 

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Geothermal Power

Geothermal – energy harvested from underground heat. Geothermal can work anywhere by drilling deep wells, and is not limited to volcanic regions.

Austrailian company Geodynamics plans to drill 90 wells each 5000 meters deep over the 10 years in South Austrailia to harvest the energy from hot rocks. Traditional geothermal uses naturally occurring steam or hot water to generate electricity by running a conventional thermodynamic steam cycle. Most conventional geothermal plants lie along volcanic regions such as in Iceland, where ¼ of Iceland’s electricity is produced through geothermal. Worldwide, geothermal capacity is 10.7 GW.

Engineered geothermal systems (EGS) – work by drilling thousands of meters underground to mimic the design of natural steam or hot-water reservoirs. Cold water is then injected, and subsequently heated to allow for electricity to be generated. Geothermal is clean energy and generates electricity during the night, and is not intermittent like solar and wind.

Even Google has invested over 10 million dollars in two California EGS companies

Hot Dry Rock (HDR) – deep drilling allows for cold water to be injected into a well. The water absorbs heat, and is pumped back to the surface, where it heats up a secondary working fluid in a heat exchanger, and then that fluid undergoes a thermodynamic electricity generating cycle.

The disadvantages of geothermal are high initial cost, and verifying the potential of a site can take a very long time. Conventional Geothermal costs about 10 cents per KWh, making it very cheap, but EGS can cost twice as much because of the high cost of drilling. Most EGS plants can get flow rates of 25 L/s, but geothermal plants can only be profitable at 50-100 L/s flow rates.

Another problem with geothermal is that it can cause earthquakes through fracturing rocks at high pressure.

 

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Peak Oil

Global business travel Association Foundation predicts that oil priced at $125 per barrel would cause a reduction of $5.8 billion or 1.5% of total US business travel spending between 2011-2013. Oil priced at $150 per barrel would cause a reduction of $6.9 billion or 1.8% of total US business travel spending between 2011-2013.

Western oil companies are slowly getting out of the business of turning crude oil into petrol and diesel because of reduced profits. They are selling their assets to state-run companies from Asia and the Middle East. Margins at the high point for oil refining were $4.50 per barrel, but now they are less than 10% of that.

Oil shocks happened with the Arab oil embargo in 1973, Iranian revolution in 1978-79, and Saddam Hussein’s invasion of Kuwait in 1990. Countries in the middle east produce over 1/3 of the world’s oil.

Saudi Arabia has spent $36 billion on ending political unrest in the country.

Goldman Sachs estimates that a 10% price increase in oil trims GDP by 0.2% after one year, and 0.4% after two years.

70% of oil in the US is used for transportation. 64% of that transportation oil is used for light vehicles or passenger cars.

Hugo Chavez in Venezuela has nationalized oil production, and has not invested in new oil production, so Venezuelan oil production is declining. Venezuela sells most of its oil to the United States.

 

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Bio Fuels

Ethanol stores less energy per gallon than gasoline, and also tends to absorb water and is corrosive.

Brazil is a biofuel superpower deriving ethanol from sugar cane. US ethanol (C2H5OH) comes from corn, and is less efficient and produced in distilleries powered by coal. Fermentation feeds on sugar in corn.

 

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Future of Coal for Energy

Demand for coal is strongest in developing countries. China generates more than 70% of its electricity with coal, and plans to build 600 GW of coal-fired plants in the next 25 years. China is the world’s biggest coal producer and now has to import more coal to keep up with its demand. China’s domestic supply is limited because the coal is located in the north and west, which is far away from the coastal cities that are booming. Also, China has old coal mines which are already very deep, making coal extraction very difficult and expensive. China makes up 40% of worldwide coal production. China has the number 2 largest coal reserves with about 187 billion tonnes that can last for about 62 years at 2009 rates of consumption. More than 90% of China’s coal comes from underground mines as far as 1 km deep. Using Hubbert’s peak oil analysis, Tao and Li forecast that China’s coal production will peak by 2025. China doesn’t just use its coal for electricity. Only 80% of China’s coal is used to generate electricity. 16% is used for the steel industry, 5% used for heating, and 28% used in the cement and chemical industries.

Coal is a large contributor to global warming. Stop and dislike global warming now!

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