The Continental SuperGrid, to deliver the preferred energy carriers, electricity and hydrogen, in an integrated energy pipeline. The fundamental design involves wrapping a superconducting cable around a pipe pumping liquid hydrogen, which provides the cold needed to maintain superconductivity. The SuperGrid would not only transmit electricity but also store and distribute the bulk of the hydrogen ultimately used in fuel-cell vehicles and generators or redesigned internal-combustion engines.
A hypothetical supergrid energy pipe could share a tunnel with high-speed, long-distance trains. The pipe, with liquid hydrogen at its core, would be surrounded by electrical insulation, a superconductor (here magnesium diboride), thermal insulation, and a vacuum. A continental system might cost about $1 trillion, or $10 billion per year for 100 years, to build, operate, and maintain. The long road to the SuperGrid should begin with a compelling demonstration. A start would be in two years, the United States build a flexible 100-m “Supercable”—a 3-cm-diameter pipe for 1-m/s hydrogen flow inside a 10- cm-diameter overall pipe whose superconducting wire carries 5,000 V, 2,000 A, and 10 MW dc, demonstrating constant current under variable load and a low ripple factor.
Technical choices and challenges abound—in cryogenics and vacuums, power-control and cable design, and dielectric materials under simultaneous stress from low temperatures and high fields. Still, within 10 years, we could build and operate a 10–20-km segment that solves an actual transmission bottleneck. And by midcentury, we could have the first SuperGrid consisting of some 40 100-km-long sections integrated with nuclear plants of several thousand megawatts supplying the grid with electricity and hydrogen. Nuclear power fits with the SuperGrid because of its low cost of fuel per kilowatt-hour and operational reliability at a constant power level. High-temperature reactors with coatedparticle or graphite-matrix fuels promise a particularly efficient and scalable route to combined power and hydrogen production. Currently, hydrogen comes mostly from steam reforming of methane. To spare the chores and costs of carbon capture and sequestration, hydrogen must eventually come from splitting water, and the energy to make the hydrogen must also be carbon-free. Large-scale production of carbon-free hydrogen using nuclear energy should begin around 2020. Pebble bed reactors provide high energy density and a small ecological footprint.
The Supergrid enables hydrogen, superconductivity, zero emissions, and small ecological footprint. It would use high-temperature reactors, provide energy storage, security, reliability, and scalability. The Supergrid pipe could carry 5 to 10 times the power of a cable today within the same diameter.