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elevated weight as storage for generator?
By dsc, Section Storage Posted on Thu Sep 15, 2005 at 05:13:10 PM MST
Would this work?

Maybe a simple-minded question, but, after reading about flywheel energy storage, the thought came to me of an even easier way to store energy:
Use a motor, powered by solar/wind/water to store excess energy as potential energy by raising a large weight (maybe properly sized concrete blocks or a big chunk of granite?) Then, when energy is needed, (again, properly sized) gears let the weight descend, which powers a generator.
What am I missing here?
(thanks for all the great posts!)
Doug

elevated weight as storage for generator? | 26 comments (26 topical)

Re: elevated weight as storage for generator? (3.00 / 0) (#1)
by Phil Timmons on Thu Sep 15, 2005 at 11:31:06 AM MST

I guess the three big considerations with storage are starting hardware cost, maintenace costs/lifetime, and return of energy in v. energy recovered.

I am no great fan of batteries -- for those three reasons -- so I enjoy creative ideas along your lines.

The nearest existing model that comes to my mind is elevated water storage. It is pumped uphill to storage during surplus times, and allowed to return downhill through a turbine to recover the energy. I have heard quotes of 90 to 95% efficency in those models. There is a huge one at Ludington, Michigan. Water is pumped up hill from a Nuke at night (low use time on the grid) and recovered during the day.

I think I recall someone on here that actually pumped water uphill on their own property using purchased grid electricity -- in Virginia seems to come to mind. Anyway, they had an offset time billing so electricity was cheaper at night for them. They would recover it during the day, when electricity cost more. By gaming the ulitity, they were actually making money.

I am guessing you are thinking more mechanically? You will have to look out for high entry costs, and mechanical losses. I would think we could reasonably design a mechanical system with very low maintenance, and very long lifetiem.

But if you would like to brainstorm it a bit, I am game.

Re: elevated weight as storage for generator? (3.00 / 0) (#6)
by nanotech on Thu Sep 15, 2005 at 05:39:00 PM MST

Grand Coulee Dam in Eastern Washington state does this also. When they have an abundance of water, they pump it from the main resevoir up into the coulee. When the river starts dropping and they lose a little of headway on their resevoir, they let the water stored in the coulee plummet back down, turning the pumps into generators in the process!! :)
__________________________________________
My ship finally came in, but it was the Kobayashi Maru!
[ Parent ]

Re: elevated weight as storage for generator? (3.00 / 0) (#2)
by drdongle on Thu Sep 15, 2005 at 12:05:16 PM MST

Just remember it takes energy to lift that weight, wind the spring or pump water to a tank. If you have a surplus available to do that great. If not then your better of not doing it.
Carpe Vigor, Dr.D

Re: elevated weight as storage for generator? (3.00 / 0) (#3)
by ghurd on Thu Sep 15, 2005 at 03:38:45 PM MST

Norm had a few ideas about a weight.

Re: elevated weight as storage for generator? (3.00 / 0) (#4)
by richhagen on Thu Sep 15, 2005 at 04:28:20 PM MST

For a very small system it should be doable, however, I would think that water would make a better storage media for that potential energy if you plan on powering your cabin. Otherwise the weight becomes unmanagably large, or the required height unmanagably tall. Equipment to move water uphill, reasonably efficient pumps ect., are readily available. For a solid weight, one would likely have to design a custom set of gears and screw to match an alternator design. Rich
'A Joule saved is a Joule made'

Re: elevated weight as storage for generator? (3.00 / 0) (#5)
by georgeodjungle on Thu Sep 15, 2005 at 04:57:27 PM MST

like a big grand father clock.
a realy realy realy big one.
how high can you go?

Re: elevated weight as storage for generator? (3.00 / 0) (#7)
by Phil Timmons on Thu Sep 15, 2005 at 08:07:56 PM MST

Well, since this is sort of brainstorming, still, and not yet ready to reduce to practice . . . I suppose a rather large weight we might have available to work with is a given house, building, or barn -- or whatever is being powered, itself.

But I am thinking about lifting hydraulic rather than "gears and pullies." As it is pumped upward, the energy is stored in the elevation of the tons of weight of the building. To recover the energy the pump is reversed, and the building lowers.

Be handy if a flood is coming. :) :)

Re: elevated weight as storage for generator? (3.00 / 0) (#17)
by georgeodjungle on Fri Sep 16, 2005 at 05:29:36 PM MST

i thought of that to: with gears or pullies
i have towers that the gennys are on.
sooooo.
one lil extra thing was i thought about is
changing the cog ratio.like tork up and hp down.
just a thought.

[ Parent ]

Re: elevated weight as storage for generator? (3.00 / 0) (#8)
by thunderhead on Fri Sep 16, 2005 at 12:55:12 AM MST

If you're going to use weights and gravity as a storage, as many people have pointed out the best solution is water. A pelton wheel will deliver near 100% conversion of falling water into shaft power, and a force pump will deliver near 100% conversion of shaft power into lifted water.

The physics is simple: height times weight times gravity equals energy.

The problem is size. Raising 1 ton of water 1 metre stores 9810J, so to store a kWh (3,600,000J) you need to raise 1 ton 367 metres, or 367 tons 1 metre, or 36.7 tons 10 metres, or whatever combination you like. If you think your batteries are big and heavy, wait until you see pumped storage.

A ton of water is 224 Imperial gallons, or about 263 US gallons. A metre is about 39 inches, or three foot three. :-)

Normally if you have the right lay of land to make pumped storage work, you also have the right lay of land to make a conventional hydro system work. Which is why there are so few of them in the world, and why the electricity generators still waste capacity in the wee small hours.

Re: elevated weight as storage for generator? (3.00 / 0) (#9)
by pyrocasto on Fri Sep 16, 2005 at 02:54:19 AM MST

You dont have to have the right land. You could use a small water tower and it should work fine.

[ Parent ]

Re: elevated weight as storage for generator? (3.00 / 0) (#10)
by thunderhead on Fri Sep 16, 2005 at 03:15:40 AM MST

How do you define "small"? If you have a 100,000 gallon water tower that is 150 feet tall, that is about 22 tons of water raised about 46 metres. The total energy is about 2 3/4 kWh - a bit more than two of my 100Ah Sonnenschein AGMs.

My AGMs cost UK13 (about $23) each, off eBay: but even if they'd been new, they'd still have cost a lot less than a 100,000 gallon water tower.

They also weigh about 40kg each, instead of the 40-odd tons that your water tower is going to weigh when it's full.

I suspect your water tower weighs and costs about a thousand times as much as my batteries.

[ Parent ]

Re: elevated weight as storage for generator? (3.00 / 0) (#11)
by Fiddlehead44 on Fri Sep 16, 2005 at 04:26:23 AM MST

Another problem with water storage is winter freeze-up.
Insulated pipes and storage as well as an available supply
during winter. Fiddlehead44

[ Parent ]

Re: elevated weight as storage for generator? (3.00 / 0) (#12)
by Fiddlehead44 on Fri Sep 16, 2005 at 04:28:11 AM MST

Another problem with water storage is winter freeze-up.
Insulated pipes and storage as well as an available supply
during winter. Fiddlehead44

[ Parent ]

Re: elevated weight as storage for generator? (3.00 / 0) (#15)
by pyrocasto on Fri Sep 16, 2005 at 11:22:19 AM MST

Well yes small was not plausable for the average family. I think a block of lead or something of the sort may work better. I for one, do agreee and will stick with batteries.

[ Parent ]

Re: elevated weight as storage for generator? (3.00 / 0) (#18)
by benjamindees on Fri Sep 16, 2005 at 08:19:06 PM MST

Good point. But you're off by an order of magnitude.

100,000 gallons raised an average of 75 ft is:

100,000 * 8.3 lbs * 32 ft/s^2 * 75 ft = 1,992,000,000 lb*ft^2/s^2 = 23.3 kWh

That's equivalent to about 17 220 Ah, 6 volt batteries, which, new, are anywhere from $75-$100 each. Assuming you only discharge them halfway, that makes 35 batteries, which is like $2600, not including shipping.

Your point is still valid but, at the same time, for some people it may really be easier or more beneficial to build a storage tank on top of a hill than to purchase batteries.

[ Parent ]

Re: elevated weight as storage for generator? (3.00 / 0) (#19)
by Norm on Sat Sep 17, 2005 at 03:16:47 PM MST

I'm on your side...what is the potential in one
of your batteries? That is how high and how fast
could it lift 2 tons if hooked up to an electric
motor ant used 10 percent of its capacity...
that ought to get some people to appreciate how
much energy is stored in just one battery!
( :>) Norm.
( :>) Norm
[ Parent ]

Re: elevated weight as storage for generator? (3.00 / 0) (#13)
by jlt on Fri Sep 16, 2005 at 05:38:28 AM MST

I have been thinking about using auto aircondioner compresser mounted on the back of a large genni to store excess power as heat

Re: elevated weight as storage for generator? (3.00 / 0) (#14)
by Norm on Fri Sep 16, 2005 at 08:01:56 AM MST

I have considered using weights to store power.
Now if I can remember, a rope wrapped around a
drum connected to a 50:1 ratio gear box and hooked to a small pm motor...about 10 lbs of water in a milk jug....traveled about 1 inch per
second
Something like 6ft.per minute to keep this 2 white led lit for one minute! About 5 volts...
Now do some math...how much weight it takes
over distance in 8hrs to keep these 2 leds
lit....then compare 4 rechargable AA batteries
will do the same job for 16 hrs. then you might
start to appreciate what an e Norm us job they do!

http://www.otherpower.com/images/scimages/22/TEST.JPG
( :>) Norm
( :>) Norm

Re: elevated weight as storage for generator? (3.00 / 0) (#16)
by upny on Fri Sep 16, 2005 at 11:53:15 AM MST

How about using batteries for weight? Around here a "rack and pinion"-type of lift is used on building sites. The tower is put together in sections. Load one of those full of batteries, add electronics that start lifting when the batteries are fully charged. Here´s a link to the local building equipment rental so you all know what i´m writing about.. http://www.ramirent.com/www/page.php?id=125
This will smack two flies in one hit ;-)

Uffe

Re: elevated weight as storage for generator? (3.00 / 0) (#20)
by Bullsup on Tue Oct 25, 2005 at 05:49:42 PM MST

I found this site by accident doing some research for a biofuel project but found it rather appropriate.

I live 10 metres from the sea about 5 metres above sea level. At the top of the field behind my house is an empty WWII fuel storage tank that I reckon holds 50,000 tons at about 110 metres above sea level.

So I calculate that 105 ( metres) x 50,000 (tons) x 9810 ( joules) = 51,000 MJ is the potential storage. How many Kwh is that ?
Colin Bull

Re: elevated weight as storage for generator? (3.00 / 0) (#21)
by benjamindees on Tue Oct 25, 2005 at 07:41:38 PM MST

Welcome to the site! That's quite a setup you've got! 50,000 tons is almost 13 million gallons of water!

I don't understand your calculation, but you came to the right answer, which is all that's important. You can convert between any of these units at www.convertit.com. I get about 12974 kWh. Of course you will have conversion losses in making use of this energy, and water turbine efficiencies can range from 30%-90%. But even at 30% efficiency, that's enough storage to power an average home for 7.5 months! Good luck and I hope you keep us updated!

[ Parent ]

Re: elevated weight as storage for generator? (3.00 / 0) (#22)
by Neo I on Mon Nov 14, 2005 at 11:30:40 AM MST

What about compressed air?

I've been thinking of creating a micro-hydro undershoot wheel that runs a mechanical air pump that feeds into a tank. I then use the air power to run a basement sump pump.

Typical Sump:
2 meter lift
average 400 liters per day
(800 liter/meters per day)

Typical Stream Flow: 1 liters/second (min=0 max=25 L/sec)
Stream Head Drop: 20 cm

/20 liter/cm per second
*(1/20) liter/cm per minute
*60*(1/20) liter/cm per hour
*60*60*(1/20) liter/cm per day
*60*60*(1/100) liter/meters per day
*0.001 liter/meters per day
liter/meters per day

Make sense?

Re: elevated weight as storage for generator? (3.00 / 0) (#23)
by thunderhead on Wed Nov 23, 2005 at 03:11:51 AM MST

The problem with compressing air is that you'll lose a good percentage of your energy heating up the air. When you compress cold air you end up with compressed hot air - which then cools down and wastes your energy. When you expand it, you end up with expanded cold air - which heats up, and wastes your energy.

Could you figure out a way to get a shaft from the microhydro to the basement pump? After all, the high rainfall that'll flood your basement is also the high rainfall that'll speed up your stream.

[ Parent ]

Re: elevated weight as storage for generator? (3.00 / 0) (#24)
by theTinker on Tue Jan 17, 2006 at 11:30:06 AM MST

as a small experiment for an average urban household with a small garden, how would collecting rain water in a container at about 3 meters(top of a garden shed?)
to maximise the collection area i was thinking along the lines of sheeting like an upside down umbrella which can be moved easily and is easy to make, this would obviously have the container which stores water in the middle so gravity does everything.

-------------------------------------
I dont like being used by people so when I grow up I want to be a renewable energy resource :)
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Re: elevated weight as storage for generator? (3.00 / 0) (#25)
by nimble on Tue Jul 04, 2006 at 10:07:16 PM MST

I've thought a lot about using gravity for energy storage, water is good if you have the land needed, but water doesn't weigh very much. Lead is better. The suggestion to lift lead-acid batteries is not a bad idea, but the weight must be massive to hold any significant amount of energy. My most promising idea was to build a house out of concrete, and raise the entire house to store the solar power. This seems very appropriate for New Orleans, or other hurricane prone areas where the massive weight of the house makes it safe from the wind. but it would be very expensive for a single-family home, however it would last a very long time, both the house and the "battery" it would be.
A simple addition to multiply the storage is to add springs that hold it down, but springs do wear out eventually over time and break, so it would require maintaince.
Jack

Re: elevated weight as storage for generator? (3.00 / 0) (#26)
by thunderhead on Sat Aug 26, 2006 at 05:00:11 AM MST

If your house weighs 100 tons, and you lift it a metre into the air, you store 100,000 x 1 x 10 = 1,000,000 joules.

That's about 1/3 of a kWh.

[ Parent ]

elevated weight as storage for generator? | 26 comments (26 topical)

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