Energy for Future Presidents

Physics for Future Presidents

by Richard Muller, physics professor at UC Berkeley. Cofounder of

Notes inspired by the books.

• [[#CO2adiabatic |

• CO2 runup - don't ignore agriculture

• Liquid methane for aviation

• Power storage Loop

CO2 increase - don't ignore agriculture

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While the ocean contains far more CO2 than the air, there is far more carbon in soil and rock than both.

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220 ppm CO2 is 60 ppm elemental carbon. The air column has a mass of about 10,000 kg/m², so assuming uniform mixing that is about 600 grams of carbon per square meter. If 15% of the earth's surface can grow plants (including most deserts), that is around 4 kilograms of carbon per square meter of growing plants - for an average soil depth of a meter, and an average density of 2000 kg/m³, then an additional 0.2% carbon-by-weight captured in the soil will sequester 220 ppm CO2. Carbon is good for soil - the high carbon terra preta soils in Amazonia are very good for agriculture compared to the low nutrient clay soils nearby.

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Liquid methane for aviation

First things first - before greatly expanding shale gas production, we need to manage water better:

• 1) Full public disclosure on what goes in the wells, and comes out of them 2) Mark individual wells chemically, so we can trace the source of pollution 3) Use seawater, pumped overland, rather than drain aquifers and compete with agriculture for water 4) Regulation to enforce long term responsibility for fractured shale commensurate with long term, boundary crossing effects.

Jet aircraft may be the best transportation use for methane, possibly from fractured shale. Tupolev is designing planes to run on natural gas. Unlike passenger vehicles, aircraft travel between major airports, with fuel systems operated by professionals. Aircraft fuel is stored in huge, easy to insulate tanks. Liquid methane must be kept cryogenically cold, but the heat of evaporation can maintain temperature for the duration of a flight. If the tank and liquid are pressurized, that may require wing redesign, but the pressure can help stiffen the wing, much like the thin tanks on the Atlas rocket. LCH4 is only 60% as dense as normal jet fuel, but the energy per weight is higher and fuel cost and the pollution are lower. This increases fuel economy, lowers takeoff weight, and makes aircraft operation cheaper. This reduces the need for a recooler after the intake compressor in the engine. Under pressure the boiloff displaces air from the ullage above the remaining liquid. Managed correctly, this should prevent air-fuel explosions like TWA Flight 800 in 1996.

Drawbacks: The cryogenic liquid can lead to icing, stuck valves, and mechanical problems in the wings. There may be safety problems while maintenance crews learn new techniques and procedures. Ultracold metal can be more brittle.

Wikipedia paragraph about LNG for aviation

===Power storage Loop ===

Flywheel speeds are limited because the structural mass rotates - even very expensive carbon fiber has a limited strength to mass ratio, so v² is proportional to a&mult;r and S/ρ .

Magnetic levitation is weaker than structural materials, but a magnetic field is massless. The strength of a magnetic field is H²/2 &mu$; for an average 1 Tesla field, that is 800KPa .

Imagine a horizontal rotating ring of iron in vacuum (axis pointed vertically, supported by magnetic levitation, with very strong stationary electromagnets inside the ring providing centripedal acceleration. By Earnshaw's theorem, the magnetic suspension is unstable, but the ring-to-magnet spacing can be controlled by distance measurement (optical, capacitance, ...) and rapid (10s of microseconds) electronic adjustment of the electromagnet current. If the ring has radius R, height H, velocity V, and mass M, then the pressure P_R necessary to counteract centrifugal acceleration is P_R = M V^2 / 2 \pi H R^2^ . The energy E stored in the ring is E = \pi P_R H R^2^ . Unlike a flywheel, a small ring does not store much energy, but a very large ring with large R can move incredibly fast and store a huge amount of energy in ordinary steel, costing perhaps $300/tonne.

If the ring is a meter high, a centimeter thick, and the diameter of an agricultural pivot irrigator (1km), it weighs about m = 80 kg/meter, or 250 tonnes for the ring (the stationary magnets weigh more). the velocity is sqrt{ P_R H R / m } or 2200 m/s , and the energy stored is 6.3e11 joules or 170 MW-h , as much as 6800 Beacon Power flywheels.

This is proportional to R². A ring 12.5 km diameter would use 10 times as much material, 12.5 times as much power for the magnet windings, 12.5 times as much electronics. But it would move sqrt{12.5} times as fast ( 7900 m/s ), store 12.5 times as much energy per meter, and 156 times as much total energy as a 1 km diameter ring, in this case 26 GW-h, more than a million flywheels.

7900 m/s is interesting - it is orbital velocity. If we cut our ring in half, and insert long straight sections between the halves, we add total mass and total energy storage without increasing velocity. The "straight" sections follow the curvature of the earth. Nominally they do not need magnet support - but since we are speeding and slowing the loop to add and subtract energy, and we must move the rotor during earthquake accelerations, we will need about 800 Pa/meter of control magnets - about 0.1% of the magnets needed for the D shaped turnarounds. If we added 180 km of straight section, the energy stored goes up 10X. This loop would store 260 GW-h, perhaps 160 GW-h recoverable from speeds between 4900 and 7900 m/s (slower than that, and we need to put more average power into our straight section magnets to provide lift). The two straight sections could be converged into one track for most of the distance, perhaps under a railroad right-of-way.

7900 meters per second is fast - if the system breaks and throws chunks, they go a long way. This must be deeply buried - but we can use horizontal well drills to make the tunnels, or put it underwater.

If a sand particle gets loose between the moving iron rotor and the stationary magnet track (stator), it may cause a "hypervelocity spalling cascade", with material from the rotor knocking loose material from the stator and vice versa. But we can make the rotor thicker and slower, increasing the mass of the rotor and the straight section magnets while reducing the velocity and the spalling energies. We can also coat the rotor and stator surfaces with diamond (now a common industrial process), which is lighter and stronger - less energy per particle, and more tightly bound surfaces.

Imagine a loop running underwater, following the continental shelf around the Pacific, from China past Alaska to Mexico, and back, a total length of around 30,000 km. This loop could provide 12 terawatt-hours of usable energy storage, while efficiently sharing power between the US and Asia. The loop would be expensive - perhaps 30 billion dollars at 1 thousand dollars per mass-produced meter - but if the cost difference between peak and trough demand prices was 1 cent per kilowatt hour, it would produce 120 million dollars per cycle. With two deep cycles per week, it would pay for itself in 2.5 years. In 2012, the peak-to-trough prices vary a lot more, but a very large system will eliminate most of that variance.

This is all wildly speculative, and will need a lot of development, but the physics is well understood.