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Old 04-28-16, 04:37 PM   #1
stevehull
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Default "Pump Storage" using concrete and motors

Don't know if any of you have heard about this. Basically, it is a reversible motor on a small rail road track that is "powered" up a hill and then generates power when it goes down the hill - at about 80+% efficiency.

The advantage of this technology is that it uses concrete (twice as dense as water) and easily hacked DC motors. Scrap steel would be even more dense.

I heard about this a few years ago, but could not find anything on it, but today saw a video.

For those on hills - just think of the possibilities!

Imagine a mass of 2200 lbs (1000 kg). Imagine a hill 100 feet high (33 meters). If I recall, the formula for power = m x 9.8 N/kg x meters. If my quick math is right, this is 323400 N-m/sec or about 323 kW of power (1000 N-m/sec = 1 kW). Allow this to move down the hill over 10 hours and you have about 32 kW per hour. This would be at 100% conversion. Even at 50% efficiency, this would run my heat pump all night.

You don't need a large elevation change when moving tons of mass up a small hill. A 10-20 kW generator is easy to imagine. If you don't have a huge hill, then add in more mass (concrete or better scrap iron or steel).

This unit can be powered by excess PV production during the day and then it would provide power at night.

FAR better than any battery!

Years ago, I worked on a water pump storage peaking system on the Connecticut River in Massachusetts. The Vermont Yankee nuke plant was just up the road and, at night, excess kW (actually mW) were used to pump water from the river up a hill into a detention pond. Then at times of peak electricity need, the water flowed downhill and through a turbine. The net efficiency was on the order of 25-33% - or about 67-75% of the energy was wasted. But it did provide excess capacity at peak use times for the Boston area at 4-8 pm.

Enjoy!

The train goes up, the train goes down: a simple new way to store energy - Vox


Steve

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Last edited by stevehull; 04-28-16 at 04:53 PM.. Reason: typos
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Old 04-28-16, 08:14 PM   #2
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Mechanical energy storage is interesting, but when doing calculations, i was amazed by the weight and height needed to even a couple kilowatt hours of juice. Instead of rail, maybe a vertical pully and cable system would work for those without hills.
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Old 05-04-16, 08:09 AM   #3
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Steve,

I'm sorry, but you mix up energy and power (like many people do).

Reality is far less than what you suppose.

1000 kg dropping 33m gives an energy amount of 1000 * 9.8 * 33 = 323,400 Nm = 323,400 J.

Not Nm/second. That would be the power (in Watts) if you dropped the 1000 kg in one second. So 323.4 kW (but just for one second.....)

for comparison: 1 kWh=1000Wh=3600*1000 Ws or J = 3,600,000J

So if you lift/drop 1000 kg over 33m the amount of stored energy is 323,400/3,600,000=0.09 kWh or almost nothing!

Many people think that lifting mass can store huge amounts of energy.
That's only true if you lift huge masses over huge distances (like in waterpower systems).
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Old 05-06-16, 10:06 PM   #4
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Sailing at night in 20 ft waves and a 7 ton boat, used to calculate the horsepower of the vertical movement to try and keep myself occupied and awake, I too used to think it was a ton of power.
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Old 05-07-16, 09:18 AM   #5
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Youhave to keep in mind: energy=power*time.
So power can be considerable, but for a short time.
Although in 20 ft waves, there can be not only considerable power, but also considerable amount of energy, since many tons of water are moving up and down constantly.

Just for comparison:
Suppose you have a AA-battery of 1.5 V and 1500 mAh=1.5 Ah
The amount of energy stored is 1.5*1.5=2.25 VAh=2.25 Wh=0.00225 kWh
If there were no limits for the max. Amperage, You could draw 100 kW of power from it!
However only for 0.00225/100=0.0000225 hour=0.08 seconds
Or 10 kW of power for 0.8 seconds, or 1 kW of power for 8 seconds or 100 W of power for 80 seconds, etc.
So power itself doesn't tell so much. It's the amount of power over a certain time, that tells you how much energy is stored in it....
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Old 05-07-16, 06:09 PM   #6
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Zwerius - I rechecked my formula: power = m x 9.8 N/kg x meters and I don't see anything wrong with it. I agree that this is power NOT energy. But power over time IS energy.

The power stored and then dissipated by it going down hill over time is energy.

Watts wrong with that?

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Old 05-08-16, 02:04 AM   #7
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Steve- This IS actually your mistake!

The formula you give does NOT represent power, but energy!!
So you have to devide it by time and then get the power...
Look at the units:
mass*9.8 N/kg*meters = kg*N/kg*m=Nm and Nm is just the same as J(oules), so an amount of energy.


Back to your original figures:
1000 kg lifted over 33 m gives an amount of stored energy of 1000*9.8*33=323,400 Nm or J.
If you move this mass down over a periode of 10 hours (=36,000seconds), you get a power of 323,400Nm/36,000sec=8.98 Nm/Sec. And Nm/sec is the same as Watt.
So barely 9 Watts !!!

If the numbers were as you supposed, why do you think the whole world is studying to improve batteries (or other systems) for energy storage? Then the lifted mass system would already have been a much easier and cheaper solution....
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Old 05-08-16, 07:07 AM   #8
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Zwerius,

Let's be realistic. If you are correct - then it would take 9 watts to move the weight of a car up 100 feet in height.

Not realistic . . . .

Let's both review our positions and then recalculate.

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Old 05-08-16, 07:14 AM   #9
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Steve,

This is realistic. You can lift up a car 100 feet with 9 Watts, if you only take enough time. So 10 hours!
It can even be done with 1 Watt, but then it'll take 90 hours.

Don't want to be rude, but please check your science lessons again...
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Old 05-08-16, 09:34 AM   #10
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I'm not a physics professor, but I believe the difference here lies between watts and watt hours. In Zwerius' above example, both solitions require 90 watt hours of work. IIRC, the time does not factor in as to the raw amount of work demanded. The supply side is a different story: most jobs are accomplished faster with a less efficient engine. Think corvair versus corvette. Same work performed, corvette gets there faster but uses more fuel.

This same set of misconceptions is manipulated by the "free energy / over unity power gain" folks. A common example is the flywheel: with a really slick set of bearings, friction is very low. As long as you are adding energy to spin the flywheel, it will spin faster and faster. It will coast for a very, very long time if left alone. Many inventions can be rigged to the wheel to do no work but appear to go something special. But once you try to draw a load from the flywheel, it slows down. TANSTAAFL.


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