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wiki/Gravitational_energy

Potential-Energy of Airborne-Mass by Height (update and review)

Sept. 6,m 2014   Dave Santos
The AWES intermittent-wind generation problem could almost disappear if we master the inherent energy storage potential of mass raised to a height. When the wind lulls, system mass could descend while maintaining power output, much like the weights that power a cuckoo-clock. Airborne mass is missing from most discussions of a possible mass-storage tech.

AWES mass at 10km high could last for many hours before depletion. A kilo raised to 100m stores 2.72Whr, which is about 1/2 the charge of a cell-phone. Harvesting cloud water for mass at altitude remains a most synergistic concept, since both energy and clean water (or even cooling ice above summer heat, by going high enough) can be produced. Polymer fog-harvesting mesh is quite light and natural as a kite material.

Current KiteLab Illwaco experiments with toy kites are testing various ideas for safely running the working-mass up-and-down the kiteline, as a kite-messenger. Endless variations are possible, but a basic goal is to use the working-mass to extend kite flight or generate power-out. which requires a clever rig. We know enough about safety to use water-ballast and provide means for the water to disperse if dropped (like open-topped water bags).

What forms and uses of airborne-mass potential-energy may eventually take is an open question. If a massive kite aerotecture civilization emerges, the weight of everything rising and lowering together might ideally cancel intermittency (in complex staged cascades of prioritized lift).

CC 4.x BY SA NC
Sept. 8, 2014      Dennis Stevens
You say “A kilo raised to 100m stores 2.72Whr…”  A Kilo weighs 9.8 Newtons, and when raised 100 M, has potential energy of 980 Newton-Meters.  980 Newton-Meters is the same as 980 Joules, which is the same as 980 Watt-Seconds.  Dividing 980 Watt-Seconds by 3,600 Seconds per Hour yields an energy of 0.272 Watt-Hours.  Your result is too high by a factor of ten.

I thought someone would catch that by now, but they didn’t.
Sep[t. 8, 2014    Dave Santos

Dennis,
We are plagued by order-of-magnitude (and greater) fingers-and-toes arithmetic errors here, so your help catching them is appreciated. In this case, lets adjust the height to 1km, for simplicity, and remember ~3W, for our rule-of-thumb. The corrected formula-

       1kg raised 1km stores 2.72Whr

As most everyone stopped using hand calculators when math programs took over, we lost handiness. I am regressed in keeping a vintage slide rule handy (Aristo MultiLog), "just enough math to be dangerous", as Wayne German likes to put it (enough math for unlimited mistakes, as well),
Sept 8, 2014   Dave Santos

Whoops, "3Whr" that is (for rule-of-thumb).
Sept. 8, 2014   Dennis Stevens

DaveS writes about using the geopotential energy of a kite system as it descends during lulls in the wind.  He speaks of raising one Kilo by 100 Meters, which I say (see below) establishes 0.272 Watt-Hour of potential energy.  Now…let’s see.  What if we raise 1000 Metric Tons by 100 Meters.  Now we have increased potential energy by 272 KWHr.  I have a little Audi TT roadster that weighs about a Metric Ton.  We could use a kite system to tow 1000 of them up a 100 Meter hill, and let them coast down the hill.  If we convert the resultant kinetic energy into electric energy (at 100% efficiency), and if we value a KWHr at 10 cents, then we could sell the energy for $27.20.  HUBBA DUBBA WINGDING!  $27.20, and all we need is the big kite and 1000 roadsters.  Or, maybe we could tow one roadster up the hill 1000 times.  AARG!
Dennis
Sept. 8, 2014   Dave Santos

Dennis,
Obviously, pumped-hydro storage is already an economic mass-by-height energy-storage medium (constrained by a shortage of sites), so your reducto-ab-absurdum argument is moot. Its necessary to imagine the inhuman scale of these ideas at their ultimate engineering and geophysical scales, without reference to quaint human-scale objects like roadsters.

Keep in mind that energy storage often has a premium value: For example, one does not expect a UPS's stored kWhrs to be costed like electric utility kWhrs, but costed according to criticality. Allow that there will be synergistic profits in mass-aloft, from refrigeration (incl cryogenic energy cycling) to civilizational aerotecture.

Concede how improbable your roadster would seem, from a sufficiently primitive perspective,
daveS
Setpt. 8, 2014    Joe Faust

Cents per kWhr

EIA - Electricity Data

 

DennisS'    10 cents seems to be a good figure for rough calculations for the USA.
Sept.8, 2014    Dave Santos

Agreed, 10 cents kWhr is the correct rounded figure for the US currently, but this topic is not about comparing a futuristic energy storage with global market prices (like 20x Antarctica prices ~2.00USD kWhr).

We have no idea yet what the economics will be of future mega-mass aloft. Imagine how expensive an International Space Station battery kWhr must be, but the electrical engineers forged ahead anyway. A robber-baron fantasy energy-market view of AWE is not everything.

I am calculating kite-levitating civilization next, with height as buffer energy-storage, but by wattage and environmental impacts only, since actual costs vary greatly by willful cultural choices to spend whatever necessary to meet deep desirements (as Wubbo observed).
Aug. 16, 2019    Joe Faust

Japanese giant backs 'energy storage tower' pioneer with 110m
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Get mass up; let mass down.
AWES may capitalize on the capability of raising mass to high altitudes for storage of potential energy. Let the mass down to drive electric generators or pumps.