Friday, February 1, 2013
High-temperature Superconductors (HTS) Change the Game
Our HTS cables are presently getting twenty percent of possible. Change that up and reduce costs in half and we have our new grid. These look to be achievable.
It has taken twenty five years from original discovery and there is another decade here at least. A reminder of just how long it take to make nature work out. Of course, we have been tracking a range of developing technologies and this is no surprise. Yet I am still impatient.
As posted before, this is a pending industrial revolution.
High-temperature superconductors change the game
By Arthur L. Robinson
A quarter century after the Nobel-prize-winning discovery in 1986 of the ﬁrst “high-temperature superconductors” (HTS), the once heady prospect of transforming the electrical power industry with lossless superconductors operating at liquid nitrogen temperature is no longer a dream. Years of materials research and a suite of highly successful demonstration projects have put HTS not only on the doorstep of the electric power grid but of facilitating its entry into the 21st century, including the increasingly mandatory shift to green, renewable energy.
The US National Academy of Engineering describes the vast networks of electriﬁcation known as the grid as “the greatest engineering achievement of the 20th century.” But the future demands better: a grid that is not fragmented but truly national in scope; where large amounts of power can be transported over vast distances in a ﬂash by underground cables from wherever generated to wherever needed; where networks are redundant to back up outages; where overloads, short-circuits, losses, and ﬂuctuations can be instantly compensated; where ﬂeets of electric cars can be plugged into the grid to recharge without overloading it; and where the frequency and voltage of the power are reliably maintained (increasingly essential for the digital society).
Many think the grid is not up to the demands of the 21st century without a serious effort to upgrade. A 2010 report titled “Science for Energy Technology” from the US Department of Energy’s (DOE’s) Ofﬁ ce of Basic Energy Sciences offers an entrée for high-temperature superconductor power equipment, [but] “to achieve competitive cost-performance, signiﬁcant improvements over existing wire performance are still required.”
Surveying current major HTS challenges, the DOE report says, “chief among these [is] a major increase (at least a factor of two) in high-temperature superconducting current-carrying capability under operating conditions.”
Superconductors are best known for the lossless transmission of dc electric currents when cooled below their transition temperatures. In service, however,superconductors contain arrays of nanosized, quantized, “ﬂux tubes” or vortices of supercurrent circulating around non-superconducting cores. Vortices are no problem when pinned at structural defects like dislocations or impurities in the superconductor, but at a critical current, they break free, dissipating energy as they move, thereby introducing a resistance. In practice, incorporating pinning defects designed to block vortex motion raises the critical current to levels that are useful, but there is much room for improvement.
Determining the maximum critical current that could be obtained by introducing the “ideal”distribution of defects awaits the ability to understand the behavior of large arrays of vortices in a ﬁeld of pin sites. In large arrays, the best critical currents are only ~20% of the theoretical critical current, but why is not known. “There’s some theory but still lots of empiricism,” said Drew Hazelton of SuperPower, Inc., a major HTS wire maker.
The availability of HTS conductors will be an industry gamechanger said Steve Eckroad of the Electric Power Research Institute (EPRI). Up until now, utilities have relied on a high voltage, low-current network based on copper for generators, transformers, and urban underground cables (rural overhead lines are usually aluminum). Superconductors with no dc and only small ac losses plus high current density change the equation to lower voltage and higher current. HTS cables have ﬁve times the capacity in the same cross-sectional area as conventional copper cables.
One way to exploit this capability is by combining HTS with renewable energy sources for a truly green grid in which remotely generated power from renewable sources could travel to distant consumers over what wind and solar power advocates call “green power superhighways.” However, long-distance transmission is not yet a near-term prospect for HTS, owing to the huge capital investment costs and an unproven track record of beneﬁts.
Here is where the ongoing materials research could pay off.
Eckroad said, “Our studies suggest that reducing the present cost of the superconductor by a factor of two would bring the cost of 10-GW, 1200-mile-long, superconducting cables to within range of that of conventional overhead lines. Since underground dc cables also offer substantial environmental, siting, and aesthetic beneﬁ ts over conventional overhead transmission lines, they may become an attractive alternative option in some situations.”
Whether cable or something else, every HTS power applicaHigh-temperature superconductors change the game
By Arthur L. Robinson
Feature Editor James Misewich
Are high-temperature superconductors ready to take on the grid?
James Misewich, Brookhaven National Laboratory
Arthur L. Robinson, firstname.lastname@example.org