PowerLoop

power loop image

A simplified version of Launch Loop technology can be used to store global-scale energy. Peak load power production and transmission on an international scale will pay for the development and optimization of loop technology, while financing the expansion of life into the solar system. A shared global power storage system will move power around the Atlantic and Pacific oceans, moving unused power around the world to peak loads in eastern Asia, North America, and Europe. Later, power loops will connect South America with Australia and Africa, and Africa with India and Australia.

The illustration shows one of many power loops, routed west of the Phillipines and through the Indonesian archipelago, encircling rather than crossing into the Phillipines tectonic plate. It may be easier to route this loop west of the Phillipines, crossing two more plate boundaries but running in deeper water. Power for Indonesia, Indochina, and Australia could be tapped perhaps 100km south of Palau.

As Buckminster Fuller pointed out, a globally shared power grid is a powerful incentive for peace. If 50% of your country's peak load energy comes from other countries, it is stupid to attack them, immediately crippling your domestic economy. Nations are capable of great stupidity, and war is one of the stupidest things they do, so a global power economy will not ensure world peace. But it can help make citizens wealthy and cosmopolitan enough to resist the calls of the demagogues. Here's hoping!

Hundreds or thousands of power loops may be constructed on paths along the lower continental shelf, with emergency rotor dump zones sited in lifeless portions of the deep ocean. Prudent "design for failure" will minimize risk to human and animal life. Indeed, a dumped rotor may stir up bottom sediments, providing nutrients for plankton, attracting fish and fishermen to these dump sites, subjecting them to the risk of future rotor dumps. Paradoxically, increasing the abundance of life can lead to more death. But increasing experience and improved designs will reduce these expensive accidents over time.

Eventually, when rotor and magnetic deflection technology matures, and hyper-automated production of power loops drives costs to unimaginable lows, power loop technology will evolve into launch loops. Power loops will be the way we move power from mid-oceanic space power receiving antennas, and to mid-oceanic launch loops.

Scaling Power Loops

Smaller power loops will look like a racetrack oval. The radius of the D shaped ambits on the end will depend on the velocity squared, the magnetic field strength, and the width of the magnet poles. With the right geometries of coils and permanent magnets, the field strength can approach the saturation flux of the rotor iron, applied over many strips along the surface of a curved (or tubular) rotor. The spacing can be small - a millimeter or so - as long as variations in the spacing can be measured within a tiny fraction of that. A working rule of thumb derived from the launch loop, for a combination of permanent and copper coil magnet, is that the radius is proportional to the velocity squared divided by 14km/sec2.

Thus, a 1000 meter per second rotor will need a 70 meter radius, 140 meter diameter ambit. If the whole oval is 500 meters end to end, then the total length of the rotor is 1160 meters. If the rotor weighs 3 kilograms per meter, then it stores 1.5MJ per meter of kinetic energy, and the whole rotor stores 1.74GJ of energy - about 480 kilowatt hours.

If we double the speed to 2km/s, then the ambit diameter becomes 560 meters, 4 times the size. If we increase the oval length proportionally to 2000 meters, then a 3 kilogram per meter rotor stores 6MJ/m, and the whole rotor stores 27.8GJ, or 7.7 megawatt hours, 16 times the power of the previous example.

For "low" velocity loops, the energy goes up as the square of the linear dimensions, and presumably the square of the cost. Put differently, the cost goes up as the square root of the stored energy, at least until the velocity creates other problems.

There is some loss associated with length. We must hold the rotor up against gravity. However, gravitational support forces are much smaller than ambit forces, and the magnets will be correspondingly weaker and cheaper. Simpler as well, we do not need to build complex geometries to achieve the desired field strength, nor do we need to anchor against very high forces.. Rather than 14,000 meters per second squared, we must make 10 meters per second squared, and the cost per length of the magnets will be at least 140 times smaller. Let's assume that a meter of straight-away costs 100 times less than our ambits.

Thus, for our two examples above, the cost of the straightaway is 5% of the cost of the ambits, yet they store 5 times as much ballistic energy. Obviously, an optimal loop storage system should have very long straightaways. However, with a simple oval, the land cost will also go up with the straightaway cost. We can assume that the power loop is buried in tunnels for safety in case of failure, but access will still require an expensive easement.

Q-tip tracks

We can reduce the cost of the easement by turning the ambits somewhat more, into a "Q tip" shape. If we add an additional 45 degrees of turn, then 45 degrees of straightening out, then our easement will fit in about ten times the radius squared, with a long straight section of narrow easement in between. On land, that easement may fit under a straight railroad right-of-way. Finding two large patches of land next two a railroad right-of-way is probably not too difficult. The tunnels can be small bore - perhaps 50 centimeters - and dug with the same slant-drilling equipment used for fractured-shale gas fields. The tunnels around the end magnets will probably be much larger.

8 km/sec rotors

An interesting thing happens when the rotor speed is the same as orbital velocity - the rotor no longer needs to be supported against gravity. Earthquakes still pose a risk - we may need to move the rotor as much as 1 gee, both up and down and side to side, to match the Earth's movement, but the important point here is that earthquakes have limited duration - the coils and magnets need be energized only for a few seconds, or minutes for "500 year" earthquakes. The magnet controllers might heat up more than normal, but they do not normally consume much standing power.

Being able to run the rotor at near ballistic velocities of around 8 km per second means that we can go large distances with only second-order correction forces. Assume that the rotor velocity ranges between 9km/sec (full store) and 6 km/sec (empty store). Assume a straight section, under a railroad right-of-way, of 500 km, hopefully along a very straight right-of-way in the desert. The ambit radius is 5.8km, and the area of the easements is 330 square kilometers - large, but remember that we can sublet the easement for other uses, such as wheat fields or cattle ranching.

Such a large system may accomodate many rotors and tubes, perhaps packed together into a triangular array for most of their journey. A 1 meter diameter tunnel might carry 100 kilograms per meter of rotor. The available energy per meter is 0.5*100kg/m*(90002-60002 m/s) or 2.25 GJ/m. The whole system stores 2.25 Petajoules of available energy, or 625 Gigawatt hours. This can power the electrical grid of North America for one hour.

Assume the rotor is cylinders of structured iron, surrounded by a few percent by weight of strength-oriented carbon (pyrolitic? diamondoid? graphene?) to minimize the effects of hypervelocity spalling. Iron is about 140 dollars per ton - assume our mass produced cylinders are 1000 dollars per ton, one dollar per kilogram. One kilogram can store 225 megajoules of accessable energy, or 62.5 kilowatt-hours; at 6.5 cents per kWh industrial rates, that is \$4 of electricity per kilogram, stored per cycle.

If the tunnel, track, and rotor cost 1000/meter, and store \$400/meter worth of electricity, then we can pay for the storage system in a few power cycles - days or possibly weeks. Of course, the way the system will make money is on the differences between spot market lows and highs. If the spot market fluctuates daily between 4 cents/kWh and and 8 cents per kWh, and we can level that to between 5 cents and 6.6 cents on a national scale, then our profit is \$$100 per meter per day. We can pay for the storage system in a couple of weeks.

Large batteries may someday cost \$200/kWh (they are more expensive now). Batteries corrode, have a limited lifetime, and can be as subject to catastrophic failure as power loop. Flywheels are more expensive (\$300/kWh) but have longer service life. Pumped hydro can be as cheap as \$10/kWh, but it is inefficient and sites are few and distant. Compare these to power loop at \$$1.60 per kWh for the regional facility described above. International ocean scale storage will be far cheaper.

Efficiency

We will lose power with drag, magnet losses, and motor losses. Both magnet and motor losses are proportional to force, and only indirectly to velocity. Motor drive power is proportional to force times velocity - the faster we go, the smaller the ratio of motor loss to motor power. The bigger the loop, the less often we need to force the rotor to turn, relative to the time we are traveling mostly ballistically. The larger the diameter of the rotor, the less surface area exposed to residual gas. So very big loops, moving very fast around gentle turns, will be highly efficient, perhaps less than 1% loss per week, and less than 1% loss per input/output cycle. We can efficiently transport power around the globe, instead of losing 40% per 1000km (CHECK THIS) in HVDC intertie systems.

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The Pacific Loop

Much larger systems are possible. Perhaps 4 billion people live around the Pacific rim, with a circumference of more than 30,000 kilometers. If the rotor and tube is deep underwater, far out on the edge of the continental shelf, the water can provide safety shielding. A system weighing 1000 kilograms per meter, and moving at 6 to 9 km/s, provides 187.5 Terawatt-hours of energy storage. At 10kW per person (first world consumption for all energy sources), this system will store almost 20 hours of power. More importantly, the power can be added or removed anywhere along the loop. It is 12 time zones across, permitting very large spreading of peak load.

Similar loops could store power in all the oceans of the world - Indian, North and South Atlantic, Artic, and circum-Antarctic.

Many systems can coexist on similar tracks, perhaps separated by a kilometer or two (except at crossings), reducing the possibility of common mode failure and fratricide. It is conceivable that 10 such systems of loops could load-level the planet over an entire week. Of course, by that time we suffer many failures, and learn how to make the power loops very robust and safe. A 700 terawatt-day system, providing week-long power storage for 10 billion people using 10 kilowatts each, is conceivable by the end of this century.

This can load-level any source of energy, from steady-state nuclear plants to wind and solar systems with week-scale weather patterns. While space energy should be the long term goal (relieving the earth of damaging "green" energy harvesting systems), in the short term this will make any energy source more adaptable to daily, weekly, and hemispheric demand fluctuations.

If we use 10% of that power ( 10 TW ) for space launch, with 40% efficient launch loops to high orbits, we can launch 4000 metric tonnes per minute, or 840 million tons per year into space. This is about 10% of global ocean shipping, or about 4 times global air cargo. We can provide far more power with energy beamed from space, collected by mid-ocean receivers in one part of the world and sent to mid-ocean launchloops halfway around the globe.

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