Loop power storage Re: Ground solar storage

[Keith Lofstrom]

The CC list has grown and no doubt needs pruning, but my
task list is long before an wee-AM Friday flight.

Power storage loops will be the enabling technology
for launch loop ... someday. Someday there will be
megatonne-past-GEO/year markets that will justify
building enough launch loops for failover capacity,
but until then, similar technology can work out the
bugs and the manufacturing and the training of the
design and maintenance and sales and legal cadres that
will do this, and the management cadres who will hinder
development enough so that ordinary folk can pretend to
stay informed about what's happening.

So, let's talk off-topic power storage, of a form that
builds towards on-topic launch technology.

The simplest model of a embryonic launch loop is a
magnetically-suspended and -deflected circular ring.
The system is constrained by B²/2μ₀ pressure, with the
side constraint that superconductor level magnetic B
fields evaporate when your coolant does, leading to
energetic disassembly and dewar shrapnel embedded in
walls, floor, ceiling, graduate students.

If the ring itself has huge kinetic energy, then graduate
students in other buildings and perhaps on distant campuses
will also experience shrapnel.

Huge kinetic energy? "Reliable" superconducting magnetic
field storage is a few Tesla (5T?). Higher numbers are
possible, but when cryogens are required, costs go up
and reliability drops. For the ENORMOUS energy storage
ring systems I will describe, reliability matters far more
than energy density. Give me less than 1e-9 failures per
year per square meter of superconducting magnet surface,
and I will consider superconductors (my graduate thesis
topic).

Anyway, the deflection pressure is limited by B²/2μ₀.
A wider cross-section ring can support more P x W force
per circumferential force, but needs a wider containment
and more containment mass.

For a 2T field, the B²/2μ₀ deflection pressure is
approximately 400 kPa (approximately 4 atmosphere).
Not a lot, but enabling a nearly friction-free bearing
for a flywheel-ring energy storage system.

This is preface to discussing scaling of magnetically
deflected energy storage rings. Really Really BIG
energy storage rings, evolving from smaller rings.
Perhaps evolving from an experimental ring that would
fit would in a circular trench in my 27-meter-wide
back yard, and scare-empty the bowels of my neighbors
if I told them what was going in the trench ...

Imagine a circular ring of iron with rectangular cross
section, for ease of calculation rather than engineering
optimization. Assume a narrow gap between rotating ring
and stationary magnet poles. Assume a magnetic-north pole
above, and a magnetic-south pole below (1)

Scale - assume a 5 cm tall iron rotor ring, 2 cm thick,
with a 2 Tesla field between moving rotor and nearby 2 cm
stationary magnet pole rings above and below. Assume a
a 2 mm gap from pole to ring, and exquisitely good active
spacing control maintaining that spacing (for now, magic,
for real a 100 page essay resulting from years of work).

Anyway, the attractive magnetic pressure in the gap is
400 KPa, or 8000 newtons per rotor meter per pole,
16000 newtons for both poles per rotor meter. Iron
density is approximately 8000 kg per cubic meter, so
the rotor mass is 8000 kg/m³ × 0.05m × 0.02m or 8 kg/m.
The magnetic field can deflect the rotor with 1000 m/s²
of centripedal acceleration.

For a 10m radius ring (3 meters of tall hedges hide my
dangerous experiment from the neighbors, the ring trench
lined with concrete is explained as a circular swimming
pool lane) v² = a r = 10m × 1000 m/s², so v = 100 m/s .
The ring mass m is 2πrρ = 2 × π × 10m × 8kg/m or 500kg.
and the kinetic energy stored is ½ × 500kg × (100 m/s)²
or 2.5 megajoules. Me on my bicycle screaming down a
mountainside at 90 mph (don't ask, I was young and
stupid. AND screaming).

What if we increase the ring radius to 20 meters?
The cost approximately doubles. How much energy can
the ring store, at the same magnetic pressure?

The mass doubles. The magnetic pressure is the same,
the centrifugal acceleration is the same, so for the
same mass DENSITY PER METER, doubling the radius allows
v² = a r to double. Thus mv² stored system energy
increases by a factor of 2×2 or 4 for a doubled
system cost.

*******************************************************
Economic optimization says "make the ring REALLY REALLY
BIG to store a VAST AMOUNT OF ENERGY."
*******************************************************

Tort liability says keep this less-than-100% reliable
giant ring buried DEEP UNDER A LOT OF MASS and FAR from
people. Deep is expensive, but ocean mass is probably
easier to tunnel through than rock mass.

Especially here in western Oregon, over the Cascadia
subduction zone, where the rock mass shifts 30 meters west
about three times per thousand years. The last shift was
January 26, 1700, at 9 in the evening, which killed almost
all the natives, leaving Oregon "safe" for settlers moving
west from the early United States. We know the exact
"when" because the Japanese timed the arrival of the
resultant "ghost" killer tsunami.

Loops buried under ocean water, far from land and
earthquake faults, can be ENORMOUS with VERY VERY HIGH
rotor velocities inside a good vacuum. A good vacuum
like the Large Hadron Collider, where protons circulate
for weeks, mostly by inertia alone.

An under-ocean failure will make a vast amount of rusty
incandescent steam, but it probably won't damage ships
overhead, which are scattered over a vastly larger area of
ocean. They are more at risk of Amelia Erhart wannabees
hitting the deck from above.

A Modest Proposal illustrated here:
http://launchloop.com/PowerLoop

That is NOT a circular ring, the diagram intentionally
shows high-radius "kinks". It is shown near continental
margins of North America, Asia, and Australia, and the
populous Indonesian archipelago, moving terawatts between
them. Other "rings" in the Indian and Atlantic Oceans can
also be useful. The most important aspect of this
hypothetical ring is that it spans MANY time zones and
also spans winter and summer in the northern and southern
hemisphere, moving power surplus to deficit over vast
distances and months of time.

----

Sadly, the political/behavioral problems are more difficult
to solve than the technical problems. People can be nasty,
and will eagerly inflict their nastiness at national scale
on the infrastructure of so-called peaceful nations.
Breaking one of these loops will make a LOT of rusty steam.

That said, the enriched "ring nations" may finally have big
enough incentives to pacify crazy nations with education,
inclusion, and abundant wealth. It never happened before,
but there is a first time for everything, maybe even world
peace and plenty. BEHAVE, or we shall MARRY THE HELL out
of your sons and daughters, and educate our shared
grandchildren. But I digress. Again. And again.

Note that similar vulnerabilities apply to GEO. It is
3.6 km/s easier to loft a cloud of gravel to apogee at a
GEO asset then to loft and circularize more GEO assets.
"Kesslering GEO" is MY nightmare. GEO power density
assets are more difficult to share across 120 degrees
of latitude and longitude.

Keith L.

--
Keith Lofstrom kei...@keithl.com