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Flywheel home energy storage

Constructing a windmill is not very hard[1] The big problem with wind energy is the number of batteries. The wind doesn't blow all of the time after all.

I find the following example[2]:

"A 1 foot diameter flywheel, one foot in length, weighing 23 pounds spinning at 100,000 rpm will store 3 kWh of energy. However at this rotational speed the surface speed at the rim of the flywheel will be 3570 mph."

This is the typical description one finds. The speed is very unrealistic but the weight seems to be an even stranger figure. In stead of using only 10 kg we can quite easily use 1000 kg or 5000. Weight doesn't seem to be a problem of resources. To give the number a crude swing 3570 / 500 = 7.14 mph This doesn't seem to be a lot.

A vacuum isn't really nesasary, we pay for the losses in wind after all. When we move the mass to the rim of the wheel it seems possible to float such flywheel in a ditch in the back yard.

Storing 1 kwh using batteries costs between 250-500 $

Batteries have very limited life span and it's hard to step down the charging voltage. It seems far easier to use a motor to dump the wind into a rotating mass. The flywheel could be huge but digging a hole in the ground doesn't cost much space at all.

A 10 ton block could be "disapeared" into the ground quite easily. The energy density of flyweels can be 2 times as high as that of high tech batteries.[3] When we loose some of that edge though cheap engineering it would still equate to 20 tons worth of battery packs. Keep in mind, a big propeller is also relatively cheap.[1]

I'm trying to get an idea how fast such flywheel would run down. A smooth surface spinning in water. What kind of drag does that produce? I think it could take a lot of days for it to run down.

a note:
Applied physics would look good on your resume, there could be some serious money in this if you want to help. I'm a honest guy :-) The world needs saving, going off-grid is just to expensive. The debunkers pretend return on investment is poor but they seem all to happy to ignore the dwindeling curency and the sky rocketing energy prices. Compare the mortage rates with 30 years ago. The demand for batteries isn't going to come down either, this will most likely will drive up the prices before production can match it. The green bottle neck is the energy storage technology. Generating power isn't much of an issue. Storage is just way to expensive, unreliable and hard to mass produce.

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wind, energy