A Power Grid for the Hydrogen
June 26, 2006 Paul M. Grant, Chauncey
Starr and Thomas J. Overbye sciam.com
Cryogenic, superconducting conduits could be
connected into a "SuperGrid" that would simultaneously
deliver electrical power and hydrogen fuel
On the afternoon of August 14, 2003, electricity failed
to arrive in New York City, plunging the eight million
inhabitants of the Big Apple--along with 40 million
other people throughout the northeastern U.S. and
Ontario--into a tense night of darkness. After one
power plant in Ohio had shut down, elevated power
loads overheated high-voltage lines, which sagged
into trees and short-circuited. Like toppling dominoes,
the failures cascaded through the electrical grid,
knocking 265 power plants offline and darkening 24,000
That incident--and an even more extensive blackout
that affected 56 million people in Italy and Switzerland
a month later--called attention to pervasive problems
with modern civilization's vital equivalent of a biological
circulatory system, its interconnected electrical
networks. In North America the electrical grid has
evolved in piecemeal fashion over the past 100 years.
Today the more than $1-trillion infrastructure spans
the continent with millions of kilometers of wire
operating at up to 765,000 volts. Despite its importance,
no single organization has control over the operation,
maintenance or protection of the grid; the same is
true in Europe. Dozens of utilities must cooperate
even as they compete to generate and deliver, every
second, exactly as much power as customers demand--and
no more. The 2003 blackouts raised calls for greater
government oversight and spurred the industry to move
more quickly, through its Intelli-Grid Consortium
and the Grid-Wise program of the U.S. Department of
Energy, to create self-healing systems for the grid
that may prevent some kinds of outages from cascading.
But reliability is not the only challenge--and arguably
not even the most important challenge--that the grid
faces in the decades ahead.
A more fundamental limitation of the 20th-century
grid is that it is poorly suited to handle two 21st-century
trends: the relentless growth in demand for electrical
energy and the coming transition from fossil-fueled
power stations and vehicles to cleaner sources of
electricity and transportation fuels. Utilities cannot
simply pump more power through existing high-voltage
lines by ramping up the voltages and currents. At
about one million volts, the electric fields tear
insulation off the wires, causing arcs and short circuits.
And higher currents will heat the lines, which could
then sag dangerously close to trees and structures.
A hydrogen-filled SuperGrid would serve not only
as a conduit but also as a vast repository of energy.
It is not at all clear, moreover, how well today's
infrastructure could support the rapid adoption of
hybrid vehicles that draw on electricity or hydrogen
for part of their power. And because the power system
must continuously match electricity consumption with
generation, it cannot easily accept a large increase
in the unpredictable and intermittent power produced
from renewable wind, ocean and solar resources.
We are part of a growing group of engineers and physicists
who have begun developing designs for a new energy
delivery system we call the Continental SuperGrid.
We envision the SuperGrid evolving gradually alongside
the current grid, strengthening its capacity and reliability.
Over the course of decades, the SuperGrid would put
in place the means to generate and deliver not only
plentiful, reliable, inexpensive and "clean" electricity
but also hydrogen for energy storage and personal
Engineering studies of the design have concluded
that no further fundamental scientific discoveries
are needed to realize this vision. Existing nuclear,
hydrogen and superconducting technologies, supplemented
by selected renewable energy, provide all the technical
ingredients required to create a SuperGrid. Mustering
the social and national resolve to create it may be
a challenge, as will be some of the engineering. But
the benefits would be considerable, too.
Superconducting lines, which transmit electricity
with almost perfect efficiency, would allow distant
generators to compensate for local outages. They would
allow power plants in different climate regions to
bolster those struggling to meet peak demand. And
they would allow utilities to construct new generating
stations on less controversial sites far from population
For moving tens of gigawatts over hundreds of
kilometers, perfect conductors are a perfect fit.
SuperGrid connections to these new power plants would
provide both a source of hydrogen and a way to distribute
it widely, through pipes that surround and cool the
superconducting wires. A hydrogen-filled SuperGrid
would serve not only as a conduit but also as a vast
repository of energy, establishing the buffer needed
to enable much more extensive use of wind, solar and
other renewable power sources. And it would build
the core infrastructure that is a prerequisite if
rich economies are to move away from greenhouse-gas-emitting
power plants and vehicles.
A New Grid for a New Era
A continental supergrid may sound like a futuristic
idea, but the concept has a long history. In 1967
IBM physicists Richard L. Garwin and Juri Matisoo
published a design for a 1,000-kilometer transmission
cable made of niobium tin, which superconducts at
high currents. Extraordinary amounts of direct current
(DC) can pass resistance-free through such a superconductor
when the metal is chilled by liquid helium to a few
degrees above absolute zero. The scientists proposed
a DC cable with two conductors (made of superconducting
wire or tape) that together would carry 100 gigawatts--roughly
the output of 50 nuclear power plants.
Garwin and Matisoo were exploring what might be possible,
not what would be practical. It would not make sense
to inject that much power into one point of the grid,
and liquid helium is a cumbersome coolant. But their
ideas inspired others. In the following decades, short
superconducting cables were built and tested to carry
alternating current (AC) in Brookhaven, N.Y., and
near Graz, Austria, with the latter operating connected
to the local grid for several years.
Ten years after the discovery of high-temperature
superconductivity, a technical study by the Electric
Power Research Institute (EPRI) concluded that with
liquid nitrogen as a coolant, a five-gigawatt DC "electricity
pipe" could compete economically with a gas pipeline
or conventional overhead lines for transmission distances
of 800 kilometers or more. Two of us (Grant and Starr)
developed the idea further in papers that explored
how ultracold hydrogen--either liquid or supercritical
gas--might both chill the superconducting wires and
deliver energy in chemical form within a continental-scale
system. In 2002 and 2004 the third author (Overbye)
organized workshops at which dozens of experts detailed
a plan for a 100-meter pilot segment, precursor to
a 50-kilometer intertie between existing regional
It is important to develop prototypes soon, because
existing electrical grids are increasingly reaching
the point of maximum loading--and, as the blackouts
indicate, occasionally exceeding it. As total generating
capacity in the U.S. has risen by almost a quarter
in the past five years, the high-voltage transmission
grid has grown in size by just 3.3 percent. Yet society's
appetite for energy continues to grow rapidly: the
U.S. Energy Information Administration forecasts that
by 2025 annual energy use in the U.S. will hit 134
trillion megajoules (127 quadrillion BTUs), over a
quarter greater than it was in 2005.
The rising demand poses two problems: where to get
this new energy and how to distribute it. Fossil fuels
will probably still supply a large fraction of our
energy 20 years from now. But global competition for
limited petroleum and natural gas resources is intense,
and even mild production shortages can send prices
skyrocketing, as we have seen in the past few months.
Concern over greenhouse warming is leading to other
If we have an opportunity to move away from our
dependence on fossil fuels, clearly we should take
it. But fully exploiting nonfossil energy sources,
including wind, solar, agricultural biomass and in
particular advanced nuclear power, will require a
new grid for this new era. To distribute trillions
of kilowatt-hours of extra electricity every year,
the U.S. grid will have to handle roughly 400 gigawatts
more power than it does today.
The current infrastructure can be enhanced only so
far. New carbon-core aluminum wires can be stretched
more tautly than conventional copper wires and so
can carry perhaps three times as much current before
sagging below safe heights. And U.S. utilities will
take advantage of provisions in the 2005 Energy Act
that make it easier to open new transmission corridors.
But high-voltage lines are already approaching the
million-volt limit on insulators and the operating
limits of semiconductor devices that control DC lines.
AC lines become inefficient at distances around 1,200
kilometers, because they begin to radiate the 60-hertz
power they carry like a giant antenna. Engineers will
thus need to augment the transmission system with
new technologies to transport hundreds more gigawatts
from remote generators to major cities.
One of our goals in designing the SuperGrid has been
to ensure that it can accept inputs from a wide variety
of generators, from the smallest rooftop solar panel
and farmyard wind turbine to the largest assemblage
of nuclear reactors. The largest facilities constrain
many basic design decisions, however. And the renewables
still face tremendous challenges in offering the enormous
additional capacity required for the next 20 years.
So we built our concept on a foundation of fourth-generation
The 2005 Energy Act directed $60 million toward development
of "generation IV" high-temperature, gas-cooled reactors.
Unlike most current nuclear plants, which are water-cooled
and so usually built near large bodies of water--typically
near population centers--the next-generation reactors
expel their excess heat directly into the air or earth.
In newer designs, the nuclear reactions slow down
as the temperature rises above a normal operating
range. They are thus inherently resistant to the coolant
loss and overheating that occurred at Chernobyl in
Ukraine and Three Mile Island in Pennsylvania [see
"Next-Generation Nuclear Power," by James A. Lake,
Ralph G. Bennett and John F. Kotek; Scientific
American, January 2002].
Like all fission generators, however, generation
IV units will produce some radioactive waste. So it
will be least expensive and easiest politically to
build them in "nuclear clusters," far from urban areas.
Each cluster could produce on the order of 10 gigawatts.
Remote siting will make it easier to secure the
reactors as well as to build them. But we will need
a new transmission technology--a Super-Cable--that
can drastically reduce the cost of moving energy over
For the electricity part of the Super-Grid, where
we need to move tens of gigawatts over hundreds of
kilometers, perfect conductors are a perfect fit.
Although superconducting materials were discovered
in 1911 and were fashioned into experimental devices
decades ago, it is only quite recently that the refrigeration
needed to keep them ultracold has become simple enough
for industrial use. Super-conductors are now moving
beyond magnetic resonance imaging scanners and particle
accelerators and into commercial power systems.
For example, the DOE has joined with power equipment
manufacturers and utilities to produce prototypes
of superconducting transformers, motors, generators,
fault-current limiters and transmission cables. Other
governments--notably Japan, the European Union, China
and South Korea--have similar development programs.
Three pilot projects now under way in the U.S. are
demonstrating superconducting cables in New York State
on Long Island and in Albany and in Columbus, Ohio.
These cables use copper oxide-based superconducting
tape cooled by liquid nitrogen at 77 kelvins (-196
degrees Celsius). Using liquid hydrogen for coolant
would drop the temperature to 20 kelvins, into the
superconducting range of new compounds such as magnesium
diboride [see "Low-Temperature Superconductivity Is
Warming Up," by Paul C. Canfield and Sergey L. Bud'ko;
Scientific American, April 2005].
All demonstrations of superconducting cables so
far have used AC power, even though only DC electricity
can travel without resistance. Even so, at the frequencies
used on the current grid, superconductors offer about
one two-hundredth the electrical resistance of copper
at the same temperature.
The Super-Cable we have designed includes a pair
of DC superconducting wires, one at plus 50,000 volts,
the other at minus 50,000 volts, and both carrying
50,000 amps--a current far higher than any conventional
wire could sustain. Such a cable could transmit about
five gigawatts for several hundred kilometers at nearly
zero resistance and line loss. (Today about a tenth
of all electrical energy produced by power plants
is lost during transmission.)
A five-gigawatt Super-Cable is certainly technically
feasible. Its scale would rival the 3.1-gigawatt Pacific
Intertie, an existing 500-kilovolt DC overhead line
that moves power between northern Oregon and southern
California. Just four Super-Cables would provide sufficient
capacity to transmit all the power generated by the
giant Three Gorges Dam hydroelectric facility in China.
Because a Super-Cable would use hydrogen as its cryogenic
coolant, it would transport energy in chemical as
well as electrical form. Next-generation nuclear plants
can produce either electricity or hydrogen with almost
equal thermal efficiency. So the operators of nuclear
clusters could continually adjust the proportions
of electricity and "hydricity" that they pump into
the Super-Grid to keep up with the electricity demand
while maintaining a flow of hydrogen sufficient to
keep the wires superconducting.
Electricity and Hydricity
The ability to choose among alternative forms of power
and to store electricity in chemical form opens up
a world of possibilities. The Super-Grid could dramatically
reduce fuel costs for electric- and hydrogen-powered
hybrid vehicles, for example.
Existing hybrids run on gasoline or diesel but use
batteries to recover energy that otherwise would go
to waste. "Plug-in" hybrids that debuted last year
use electricity as well as gas [see "Hybrid Vehicles,"
by Joseph J. Romm and Andrew A. Frank; Scientific
American, April]. BMW, Mazda and others have demonstrated
hydrogen hybrids that have two fuel tanks and engines
that burn hydrogen when it is available and gasoline
when it is not. Many automakers are also developing
vehicles that use onboard fuel cells to turn hydrogen
back into electricity by combining it with oxygen.
Even the most efficient automobiles today convert
only 30 to 35 percent of their fuel energy into motion.
Hydrogen fuel-cell hybrids could do significantly
better, reaching 50 percent efficiencies with relative
ease and eventually achieving 60 to 65 percent fuel
Replacing even a modest percentage of petroleum-based
transportation fuels would require enormous amounts
of both hydrogen and electricity, as well as a pervasive
and efficient delivery infrastructure. The Super-Grid
offers one way to realize this vision. Within each
nuclear cluster, some reactors could produce electricity
while others made hydrogen--without emitting any greenhouse
By transporting the two together, the grid would
serve both as a pipeline and as an energy store. For
example, every 70-kilometer section of Super-Cable
containing 40-centimeter-diameter pipes filled with
liquid hydrogen would store 32 gigawatt-hours of energy.
That is equivalent to the capacity of the Raccoon
Mountain reservoir, the largest pumped hydroelectric
facility in the U.S.
By transforming electricity into a less ephemeral
commodity similar to oil or natural gas, the new grid
could allow electricity markets to tolerate rapid
swings in demand more reliably than they do today.
Super-Grid links crossing several time zones and weather
boundaries would allow power plants to tap excess
nighttime capacity to meet the peak electricity needs
of distant cities. By smooth-ing out fluctuations
in demand, the low-loss grid could help reduce the
need for new generation construction.
The Super-Grid could go a long way, too, toward removing
one of the fundamental limitations to the large-scale
use of inconstant energy from wind, tides, waves and
sunlight. Renewable power plants could pump hydrogen
onto the grid, rather than selling electricity. Alternatively,
baseline generators could monitor the rise and fall
in electrical output from these plants and might be
able to use electrolysis to shift their electricity/hydricity
blend to compensate.
No major scientific advances are needed to begin building
the SuperGrid, and the electric utility industry has
already shown its interest in the concept by funding
a SuperGrid project at EPRI which will explore the
numerous engineering challenges that integrating Super-Cables
into the existing power grid will pose. The largest
of these is what to do if a Super-Cable fails.
The grid today remains secure even when a single
device, such as a high-voltage transmission line,
fails. When a line sags into a tree, for example,
circuit breakers open to isolate the line from the
grid, and the power that was flowing on the wire almost
instantaneously shifts to other lines. But we do not
yet have a circuit-breaker design that can cut off
the extraordinary current that would flow over a Super-Cable.
That technology will have to evolve. Grid managers
may need to develop novel techniques for dealing with
the substantial disturbance that loss of such a huge
amount of power would cause on the conventional grid.
A break in a SuperCable would collapse the surrounding
magnetic field, creating a brief but intense voltage
spike at the cut point. The cables will need insulation
strong enough to contain this spike.
Safely transporting large amounts of hydrogen within
the Super-Cable poses another challenge. The petrochemical
industry and space programs have extensive experience
pumping hydrogen, both gaseous and liquid, over kilometer-scale
pipelines. The increasing use of liquefied natural
gas will reinforce that technology base further. The
explosive potential (energy content per unit mass)
of hydrogen is about twice that of the methane in
natural gas. But hydrogen leaks more easily and can
ignite at lower oxygen concentrations, so the hydrogen
distribution and storage infrastructure will need
to be airtight. Work on hydrogen tanks for vehicles
has already produced coatings that can withstand pressures
up to 700 kilograms per square centimeter.
Probably the best way to secure Super-Cables is to
run them through tunnels deep underground. Burial
could significantly reduce public and political opposition
to the construction of new lines.
The costs of tunneling are high, but they have been
falling as underground construction and microtunneling
have made great strides, as demonstrated by New York
City's Water Tunnel Number 3 and the giant storm sewers
in Chicago. Automated boring machines are now digging
a 10.4-kilometer-long, 14.4--meter-diameter hydroelectric
tunnel beside the Niagara River, at a cost of $600
million. Recent studies at Fermilab estimated the
price of an 800-kilometer-long, three-meter-wide,
150-meter-deep tunnel at less than $1,000 a meter.
Super-Cables would carry many times the power of
existing transmission lines, which helps the economic
case for burial. But the potential for further technology
innovation and the limits imposed by the economics
of underground construction need more exploration.
To jump-start the Super-Grid, and to clarify the
costs, participants in the 2004 SuperGrid workshop
proposed constructing a one-kilometer-long Super-Cable
to carry several hundred megawatts. This first segment
would simply test the superconducting components,
using liquid nitrogen to cool them. The project could
be sponsored by the DOE, built at a suitable national
laboratory site, and overseen by a consortium of electric
utilities and regional transmission operators. Success
on that prototype should lead to a 30- to 80-kilometer
demonstration project that relieves real bottlenecks
on today's grid by supplementing chronically congested
interties between adjacent regional grids.
Beyond that, price may largely determine whether
any country will muster the political and social will
to construct a Super-Grid. The investment will undoubtedly
be enormous: perhaps $1 trillion in today's dollars
and in any case beyond the timescale attractive to
private investment. It is difficult to estimate the
cost of a multidecade, multigenerational Super-Grid
effort. But one can judge the ultimate benefits: a
carbonless, ecologically gentle domestic energy infrastructure
yielding economic and physical security.