of Airborne-Mass by Height (update and review)
Sept. 6,m 2014 Dave Santos
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
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
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!
|Sept. 8, 2014 Dave Santos
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,
|Setpt. 8, 2014 Joe
Cents per kWhr
DennisS' 10 cents seems to be a good figure for rough calculations for the USA.
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
Japanese giant backs 'energy storage tower' pioneer with 110m
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.