Superconductor Electricity Pipelines FAQs


1.  What are superconductors?

Superconductors are materials that conduct electricity with very high efficiency (zero electrical resistance to the flow of Direct Current, or “DC”) when cooled to cryogenic temperatures.  They also have the capability to conduct much higher electrical currents compared with common conductors such as copper or aluminum.  American Superconductor (“AMSC”) manufactures superconductor wire that is able to carry approximately 150 times more electricity than a copper wire of the same dimensions.  These wires can be used in various applications, including Superconductor Electricity Pipelines.

2.  How proven is superconductor cable technology?

Superconductor power cables have been developed and demonstrated numerous times over the past dozen years.  These cable systems have been deployed in the commercial U.S. power grid several times in recent years and other cable projects are now ongoing globally in countries such as China, Japan and Korea.

3.  How does the cost of a 5 GW Superconductor Electricity Pipeline compare to AC overhead power lines?

Superconductor Electricity Pipelines are very cost competitive with AC overhead lines for long-haul transmission.  Superconductor DC cables have lower life cycle costs because of their efficiency advantage.

4.  How does the cost of a 5 GW Superconductor Electricity Pipeline compare to ultra-high voltage DC overhead power lines?

The cable and associated infrastructure of Superconductor Electricity Pipelines are more expensive than DC overhead power lines. Cost allocation of transmission lines that serve multiple regions, right of way costs, avoidance of permitting problems, lower losses and ability to have multiple terminals for uploading or downloading green power at various points along a transmission corridor can in many cases outweigh the tower and line cost advantage of DC overhead.

5.  How much wire would a mile of Superconductor Electricity Pipeline require?

A 5 GW pipeline would require approximately 200,000 meters of superconductor wire per mile.

6.  How much more efficient are Superconductor Electricity Pipelines than AC overhead lines?

Superconductor Electricity Pipelines are the most efficient option for long-haul transmission.  They are able to cut power losses by two to three times when compared with conventional transmission options.  This results in improved return-on-investment and reduced carbon emissions.

7.  Aren’t DC superconductor cables 100% efficient? Why are there power losses?

It is correct that DC superconductor cables are perfectly efficient electrically, regardless of how much power they carry.  However some power loss occurs in the power converters required to switch between AC and DC, and then DC to AC.  A small amount of power is also consumed by the cryogenic cooling system.  Taking this all into account, the power loss is less than 3% for a 1,000-mile electricity pipeline.

8.  What advantages do Superconductor Electricity Pipelines have over conventional DC cables?

Superconductor Electricity Pipelines are capable of carrying significantly greater amounts (5-10 gigawatts) of power over long distances (800 -1000 miles) while conventional DC cables are capable of carrying less than 2 gigawatts (GW) (limited by their current ratings) and are usually considered for short length (<200 miles) applications such as submarine installations.  Conventional underground DC cables also have greater power losses because they employ copper or aluminum wire rather than superconductor wire.

9.  What advantages do Superconductor Electricity Pipelines have over conventional DC overhead lines?

Given their location underground, Superconductor Electricity Pipelines are easier to site, are more secure and have no aesthetic impact on the surrounding land.  They avoid significant permitting issues faced by ultra-high voltage overhead lines and require a right of way only 25 feet wide rather than hundreds of feet.  Also, unlike conventional high voltage DC lines, which are point-to-point solutions, Superconductor Electricity Pipelines accommodate multiple power on and off ramps for electricity. Superconductor Electricity Pipelines also are more efficient and have no real power limitation.

10.  How much would a 5 GW Superconductor Electricity Pipeline cost per mile?

For a 1,000 mile cable system, the cost would be $8 - $13 million per mile fully installed.  The low end of this estimate is based on a single 5 GW pipeline while the upper end is based on a fully redundant 5 GW system that would transmit a total of 10 GW of electricity.  That is in the same general ballpark as a 765 kV AC overhead transmission line designed to carry 5 GW for 1,000 miles.

11.  Are superconductor cables limited to 5GW?

No. The 5 GW rating is often cited as a value in conjunction with moving renewable energy and allows for simpler comparison with other alternatives. The BP Titan wind farm project in North Dakota is a 5 GW wind farm. T. Boone Pickens is planning a 4 GW wind farm in West Texas and the Chinese government is now installing 10 GW wind farms in China.  There is no reason that a superconductor cable can’t be manufactured with a 10 GW capacity or more.

12.  How do you cool the cable?  How often does the refrigerant have to be replenished and how costly is this?

Superconductor cables operating in commercial grids in the U.S. and around the world are cooled with liquid nitrogen. Nitrogen is normally a gas and makes up about 79 percent of air.  When compressed and cooled sufficiently, it turns into a very useful liquid. For example, McDonald’s uses it to flash freeze hamburgers.  In a superconductor cable, liquid nitrogen is re-circulated through the cable in a closed-loop system with intermediate refrigeration systems being used to extract any heat that leaks into the cable from the surroundings. Only small amounts of liquid nitrogen are needed to replenish the pressure control circuits.

13.  What is the maximum distance between cooling stations?

You would need a cooling station approximately every 14 miles.

14.  If one cooling station goes down, what happens to the cable system?

Superconductor cable systems are designed to have a redundant refrigeration system, so a second refrigerator takes over the load should one refrigerator fail.

15.  Can these cables be used in conjunction with overhead power lines?

Yes.  Superconductor Electricity Pipelines can and will be used in conjunction with AC overhead lines that operate at various voltages, including 765 kV AC overhead lines.  In fact, a 1,000-mile Superconductor Electricity Pipeline would be connected via on-ramps and off-ramps in several locations with AC lines or cables distributing the power locally. 



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