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To evaluate the viability of constructing a transoceanic high voltage direct current (HVDC) power line as a means to power to cargo ships with electric motors along shipping routes. The goal of this design is to improve international trade by increasing trade efficiency, reducing costs, and implementing a low carbon means of transportation. We will investigate the economic potential, the HVDC line design and materials, possible low carbon methods of power generation as the only power source for the HVDC line, the environmental ramifications, and the financial viability of such a large scale project.
Like many other countries, the economic strength of the United States is dependent on international trade specifically through sea transportation. Unlike air transportation, sea transportation allows exporters to move large amounts of cargo long distances. According to the U.S. Department of Transportation, Maritime Administration (MARAD), the U.S. exported over 450 billion metric tons of cargo in 2010. This illustrates the huge potential for a Trans-oceanic high voltage direct current (HVDC) line to improve international trade across large distances.
Determining the location and the route of the Transoceanic HVDC is vital to realizing its full potential, and as such, the first route would be best utilized by constructing it between two major trade hubs. According to MARAD, the top recipient of exports in 2009 was China at about 65 billion metric tons. Similarly, Los Angeles, CA was the third largest exporter in the U.S. and the largest export location on the west coast at about 40 billion metric tons. Building the Trans-Pacific HVDC line would create a great economic advantage to increase trade relations with China while developing an inexpensive, efficient and low carbon intensive means of transportation. According to the US Census Bureau’s Foreign Trade Division, China has been the US’s top trade partner for over the past 6 years trading about $250 billion in goods during 2009 alone. This accounts for about an 85 percent increase in trade between the U.S. and China since 2003. Due to China’s growing economic power, easy ocean access and proximity, the best way to fully utilize the HVDC line is to build between Los Angeles and Hong Kong, China.
Total International Exports from the United States in thousands of USD (unadjusted for inflation). Right and left columns represent maximum and minimum range for a designated color, respectively.
There are currently 2 options available; HTS cables, or Elpipe cabling.
HTS (High Temperature Superconducting) cables do not have any internal resistance and therefore produce no heat due to electron collisions and also allows for very high current flow. The downside of HTS cables is the fact that they need to be in a refrigerated environment in order to be super-conductive.
Elpipe cabling does not need to be refrigerated, but it does have internal resistance, causing it to generate heat, and therefore lose power over distance. This can be reduced through cryogenic cooling, similar to the process needed for the HTS cable.
Due to its guarantee of no losses due to resistance, the HTS cabling seems to be the best option. We decided to go with a bismuth based HTS cable with a cryogenic cooling center located every 50-75Km on a suspension buoy.
Figure 5: Elpipe Cable
Figure 6: HTS Cable
Figure 7: HTS System Diagram
Because we are using HTS cables, the cable must have a system to keep these cables around a temperature of -163C. In order to accomplish this, our system will spray liquid nitrogen into the conduit, using the latent heat of vaporization to cool the cables. The liquid nitrogen will pool in the lower half of the cable until the invading heat causes it to vaporize, and then that vapor will be vented out into another pipe and re-cooled every 50-75Km at a cooling station located on one of the suspension buoys.
The cable must be insulated well enough such that the liquid nitrogen cooling system would not freeze the water around it, and such that there is very little or no heat invasion from the surrounding water. The most feasible way to insulate the lines would be through vacuum jacketed piping for the liquid nitrogen itself, and rubber polymer insulation around the conduit, which would reduce the amount of heat invasion, as well as allow for some flexibility in the line.
In order to avoid issues with stresses created by a ship being towed along by a motor on the cable itself, the cable will only provide power to the ship, not tow the ship. To connect the cable to the ship 2 things must be present; a coupling for the secondary cable to connect to a ship, and a connection between that cable to the main cable. The coupling between the secondary cable and the ship must be strong enough to stay connected during normal operation, but must have an emergency release in order for it to be quickly disconnected in case of an emergency, or the ship needs to move away from the main cable to avoid a storm. In the case of disconnection, the secondary line must have a water tight cover on the ship's side in order to protect the connection in the coupling from being damaged by the elements, and to prevent current from flowing into the ocean. The connection between the main cable and secondary cable must also be water tight and allow for a direct connection between the two. There must be one cable connection on each side of the main cable There must be a motorized guide at the connection between the cables so that the cable moves at the same rate the ship is moving, preventing any problems with too much or too little slack in the cable.
The main line of the cable must be deep enough so that there is no chance a ship may collide with it during the worst conditions. To achieve this, the cable must be deeper than the draft of the largest ship that may pass over it, during the lowest point in the largest ocean swell that could occur. Due to the fact that the largest ship in the world currently has a draft (vertical submerged distance) of 97.7ft, and the largest, however uncommon wave is 65ft, the cable must be submerged at least 175ft. plus a safety buffer, which might bring it to around 200ft below sea level.
The best electric propulsion system for this application is currently a 36.5MW High Temperature Superconducting (HTS) motor. These motors use superconductor wiring which is able to carry much more current than conventional copper wiring. This enables less material to be used in each motor, which allows the motor to be around 1/3 the size and 1/2 the weight of current motors of the same torque rating. This fact makes it extremely practical to use in shipping because it will create more room for storage, as well as decrease the weight of the ship. Due to the fact that the average cargo ship needs 80-100 MW of power for propulsion, two of these HTS motors will be needed per ship.
Assuming that the average ship weighs roughly 100,000 Tons, and the average diesel motor for those ships weighs around 2,300 Tons,
Standard Diesel Motor = 2.3% of ships weight
Copper motor = .2% of ships weight
HTS motor = .08% of ships weight
Copper to HTS Comparison
30MW Diesel Motor
Cable suspension buoy and ship electrical connection diagrams.
For the High-Voltage Trans-Pacific DC voltage line, we need to generate 100 MW of power per ship. We are recommending either using offshore wind turbines or tidal stream generators to power them. We are recommending the construction of a 5 GW wind or tidal farm. This will generate enough electricity to support up to 50 ships.
Tidal Stream Generators (Underwater turbines)
Artistic rendition of a tidal stream farm from wikipedia
Tidal stream generators operate like wind mills for wind farms. It is believed that they have next to no impact on the environment due to the fact that they can run at 10-30 RPMs, slow enough that fish won’t get caught in the cavitation generated by the spinning of the turbines. Also, Tidal turbines are less expensive that other forms of tidal energy. For example, a tidal stream generator farm is being built in New York’s East River, the estimated cost is $20 million, producing 200-300 tidal turbines that generate 10 MW of power for 18 hours a day (the remaining 6 hours the currents are too slow). This yields an energy cost of $2 per watt. The carbon cost of tidal stream generators is comparable to wind turbines. A single 24m dia. Tidal turbine can generate 1.35 MW. In order to achieve the power goal of 5 GW we would need
Assuming that tidal stream generators have a capacity factor of 75% with an annual operations and maintenance cost of $25/MWhr
For a 5 GW tidal stream farm the annual O&M is
Offshore Wind Turbines
An offshore wind turbine being installed
A single 116 dia. offshore wind turbine can generate 5MW of power and costs US$25 million. This yields a $5 per watt cost. To achieve a 5GW wind farm we need
Assuming that offshore wind turbines have a capacity factor of ~33% with an operations and maintenance cost of $25 per MWhr the annual operations and maintenance costs would be
For a 5 GW offshore wind farm, the annual O&M cost is
The carbon generated for the lifetime of the tidal power generators is:
The carbon generated from a single ship traveling 1 way is:
Where are your carbon intensities from, and what is the 0.48 for? Where are your references? Why do you not put your answer in units of tons of CO2?
The carbon generated for a single container ship traveling the same distance using bunker fuel is:
Our shipping method reduces the carbon emitted per shipment by a factor of
The total cost of construction of the HVDC line accounts for the majority of the total cost of the project. As seen in Figure 11, the total cost of the project accounts for the materials to construct the line, construction of the power sources, and construction of the ships. However, a portion of the cost depends on what type of power generation will be used. The table below separates the total cost into two scenarios: power generation by wind or tidal power only. Using the costs previously discussed for the materials, estimating the cost of labor to construct the cable, and assuming a ship costs about $200 million per ship with a fleet of 50 ships, the total capital cost is between $55 billion and $70 billion.
Total Capital cost in millions of USD
At an interest rate of 8 percent for 40 years of operation, the Capital Recovery Factor of the project can be calculated:
Then, the annual payments at the total present value (PV) for tidal and wind would be:
In addition to the total capital costs, there is an additional operations and maintenance cost for each type of power generation. For tidal power, the annual operations and maintenance cost is $126,000 per year while wind is $361,000 per turbine. Powering 50 ships results in 4200 tidal turbines or 1000 wind turbines for a total operations and maintenance cost of $530 million per year for tidal or $360 million per year for wind.
Revenue will be generated through the transport of goods across the line, but more indirect revenue can also be generated by taxes and tariffs that the government can place on certain goods or for using a port. However, for this analysis, the revenue from shipping goods only will be considered. While the cost to ship varies based on the time of year, type of good, and quantity, according to a recent article by the Journal of Commerce, average price for a 40-foot equivalent container from Hong Kong to Los Angeles is about $2000. If the cargo ship is can hold approximately 7500 containers (the size of an Ultra Large Container Vessel), a single cargo ship can transport about $15 million in one trip. Assuming one shipping between Hong Kong and Los Angeles takes about 20 days (with loading and unloading, according to the ODM Group) and accounting for weekends and holidays, about 15 one way trips can be made per year. Calculating this value,
So, one container vessel can accumulate and astounding $270 million per year. The total annual revenue, therefore, will increase linearly depending on the number of ships in the fleet (until the number of ships outweighs the demand to transport goods). In addition to the goods traded between Hong Kong and Los Angeles, the HVDC could potentially generate more revenue by diverting trade from other cities to the HVDC line, so growth in popularity of the HVDC line could greatly increase the amount of annual revenue.
Financial Model and Return on Investment
The Financial Model is based on using tidal power, which costs less, and looks at a construction time of 15 years and an operation time of 35 years. Since the cost of constructing the line and the power generators makes up the bulk of the total capital costs, the number of ships that you are capable of operating at one time has a small effect on the total cost of construction, but a significant effect on the amount of revenue that can be generated as discussed in the previous sections. The graph below shows the approximate time for the return on investment depending on the number of ships that the line is capable of powering making the same assumptions for revenue (mainly, that each ship can make 15 one way trips per year and the ships will contain the max amount of cargo).
I'm confused as to the shape of the curves. They should be curved the other way, no?
Return on Investment for the HVDC line based on the number of ships in operation.
From the graph above, it is clear that the HVDC line will be a long term investment that will require plenty of capital from the start in order to fund the project in its entirety. In addition, revenue will not be generated from the project until after construction is complete, which is 15 year in this case. In addition, the line will need to support at least 40 ships in order to make this project profitable after 35 years of operation, or 50 years after the start of construction. However, since trade will continue to increase over the 15 year construction period, the employing 40 ships may not be enough to meet demand (especially when the popularity of shipping via the HVDC line increases). It is not an overestimate to think that 60 or 70 ships could be used to transport goods.
International trade by water is still the most practical and inexpensive way of moving large quantities of goods across the globe. As the demands for goods rises, the need for faster and more eco-friendly means of transportation will also increase. The HVDC line, although a financially expensive and risky project, has the potential to generate a large amount of revenue in the long term while significantly reducing the amount of greenhouse gases that are emitted by cargo ships. This project is well within the scope of today’s technology too. Clean energy is available through a combination of tidal and wind power, and the technology and materials to build the line are already available. While there are many engineering challenges yet to overcome, this project has the potential to strengthen the U.S.’s political and economic ties with the rest of the world.
After construction is complete, Tidal power has no greenhouse gas emissions.
There is no fuel used. The power is generated from the currents and the ebb and flow of the tides.
Tidal power is a reliable source of electricity due to the predictability of the tides
Tidal power is cheap to maintain once constructed
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