Using Gravity to run a Generator

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Sorry if this isn't the place to ask this question (if anyone knows of a
more appropriate one, please let me know)

I'm interested in seeing if a large weight, (several tons, at least)
when raised up to a certain height and hooked up to a portable
generator, could supply a decent amount of
electricity for a decent length of time.

Let's say I raised a 2 ton weight 20 feet above the ground and attached
it (using some kind of pulley system w/gears) to a 3500-5000 watt
portable generator. (sans motor)

Obviously (even to a neophyte like me) there would be a lot of variables
to consider, but I'm just looking for some rough estimates to see if
it's even worth considering.

I'd really appreciate it If someone could give me some idea (an educated
guess) on the amount of time/watts/ per feet I could expect to get.

 

[Chris]

Well, let's see.

1 horsepower is 33,000 lb-ft/min.

2 tons x 20 feet = 80,000 lb-ft.

So, in very round numbers, letting 2 tons fall 20 feet in 1 minute would
generate 2.4 mechanical horsepower for 1 minute. Let's say that, allowing
for efficiency issues, you could generate 2 electrical horsepower from 2.4
mechanical horsepower.

1 horsepower = 746 watts.

So, again in round numbers, lowering 2 tons through a distance of 20 feet
will produce about 1500 watts for 1 minute.

The heck with dropping the thing. Get it spinning somehow.

 

[[email protected]]

So, again in round numbers, lowering 2 tons through a distance of 20 feet
will produce about 1500 watts for 1 minute.

.... minus all the losses along the way

Basically you hauled 40 bags of sand up to the roof, hooked up your
rope, threw them all off and you get 2 slices of free toast.

 

[Paul Hovnanian P.E.]

... minus all the losses along the way

Basically you hauled 40 bags of sand up to the roof, hooked up your
rope, threw them all off and you get 2 slices of free toast.

Forget the generator. I'll give him two slices of toast just to watch.
;-)

 

[TimPerry]

Forget the generator. I'll give him two slices of toast just to watch.
;-)

use the 100 watt toaster from the other thread

 

[JohnR66]

... minus all the losses along the way

Basically you hauled 40 bags of sand up to the roof, hooked up your
rope, threw them all off and you get 2 slices of free toast.

Well, I'll just pay the utility their 10 cents per Kw/h and let them deal
with the sandbags (or however they produce the juice).
John

 

[Bob]

... minus all the losses along the way

Basically you hauled 40 bags of sand up to the roof, hooked up your
rope, threw them all off and you get 2 slices of free toast.

LOL, tha's rich! Thanks for the chuckle.

BTW, only the actual toasting would be free! You still had to buy the
bread.

Forget the math though. How are you going to get your 2 ton weight to
a height of 20 feet in the first place?

The answer is, you will need to exert ENERGY to do it.

How much?

Answer: A little more than you will recover by generating energy from
dropping it! Friction losses, windage losses, heat losses etc.

Energy out = energy in minus losses. There ain't no free lunch.

Our entire world runs off of energy that has fallen onto out planet in
one form or another and has been stored for us up to this point. Most
of it is solar energy either in the form of chemical storage in
billions of plants over millions of years decaying and making oil, or
water being vaporized and falling back down at higher elevations. The
rest is in the form of nuclear (sorry, nucular according to our
fearless leader) energy from elements that became part ofthe planet
back in the big-bang era. No other form of useable energy exists on
this planet as far as we know.

Now if you could put anti-gravity paint on the 2 ton mass prior to
lifting it and peal the paint off just before you drop it, THEN you
would have another source of free energy!

Now where did I leave that can of anti-gravity paint? Oh yeah, right
behind my Tom Swift book collection!

 

[ehsjr]

Isn't that what hydroelectric generation is al about?

Bill

But it makes the toast soggy!

Ed

 

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(Bob) wrote:

" Forget the math though. How are you going to get your 2 ton weight to
a height of 20 feet in the first place? "

I figured there'd be a way of using some type of mechanical advantage.
(e.g. hydraulic jack)

Another option would be to use something that can hold a large amount of
water as the weight. If it was used in an area that got alot of rain,
you'd just need to wait til it rained enough to fill it up or use a
water pump to refill the container. (draining it after it reached the
bottom)

Also, there was a show on TV where a huge dome structure was created by
pouring a cement form over a bladder that was then filled with air to
raise it, and it only took a few pounds of pressure to lift the massive
weight. That might be another possibility.

Or, if the weight were put into a large hole in the ground, then water
(if it could float) or air could be used to bring it up. (or some type
of
mechanical advantage)

Finding a way to raise it didn't really concern me. Whether it would
supply enough energy,
by running a generator, to bother trying did.

Having been through several Hurricanes that caused long periods of power
blackouts, I had hoped this would be viable source of power. (even if it
was for a short period of time)

But it obviously wouldn't be worthwhile if it could only generate enough
electricity to
make two pieces of toast!