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# Solid gravity storage slides

attached to hillsides and tall buildings, of course in a closed pipe
 (+3, -2) [vote for, against]

[edited name (After Hippo's MFD)] from Gravity storage slides to Solid gravity storage slides.

[edited for clarity]For low cost energy storage at low peak hours and retreival at high peak hours. All thats needed is a rope, a generator/motor and a heavy weight - used lead acid batteries or bags of building materials mostly cement .

An enclosed "slide" has a weight or many weights pulled up with low cost electricity. During the day, they are released in a controlled way, and pulling the rope cause a dynamo to release electricity.

Im sure its cheaper than batteries. For the side of a wind tower or even for a 10 kw turbine it would be great.

Force = weight * 9.8 = ~ 10 x weight.
kWh = Force/3600/1000.

So I would need to raise 3 tons (1000 kg's) up 100 meters (30 stories high) to get 1 kw. That's a tiny truck. Not too much of a problem, and probably not that expensive.

 — pashute, Apr 03 2011

Dilbert http://dilbertblog....ravity-battery.html
Broken link back to halfbakery. It seems there once was an Energy/Storage/Gravity category [pashute, Apr 03 2011]

Very much baked, and widely known to exist - [marked-for-deletion] http://en.wikipedia...ge_hydroelectricity
[hippo, Apr 05 2011]

[MechE, Apr 05 2011]

There is a lot of water up there already...
 — 4whom, Apr 04 2011

 Are my numbers correct?

 A gravity storage system could easily be stored uphill for example, if you have a hill 100 meters high nearby.

 Of course there would be energy loss - friction, control, handling etc. Still, the loss would be marginal.

 My calculations are that for the equivalent of 1 kw of electricity for one hour, I need to raise 3 tons 100 meters high, or 1 ton 300 meters high.

Can anyone verify or discard my calculation?
 — pashute, Apr 04 2011

//Can anyone verify or discard my calculation?// Yes, and both, funnelly enough...
 — 4whom, Apr 04 2011

 4whom please follow up. What is wrong with my numbers. Are they wrong, or do you for some reason think this is impossible or not practical?

 There are low cost ropes available that could hold that kind of weight at those distances. If it is lead or even tin, it would catch 10 to 20 times less space than water, will not evaporate, and most of the energy can easily be recovered (and invested).

As I proposed you could use old batteries (enclosed of course for safety) for this. So it's also a useful system for waste recovery.
 — pashute, Apr 04 2011

A better low cost energy storage would be a plant that fischer-tropsched CO2 into octane during nonpeak hours. The octane is indefinitely stable, portable, salable. Not to mention fungible and frangible. Plus you should be able to generate carbon credits.
 — bungston, Apr 04 2011

 OK, so you want to use gravitational potential energy, and convert it to kinetic energy -> electrical energy, to serve high demand times. You want to do this by using low cost non-peak energy to move "stuff" (I use the term loosely) up an energy gradient. First point, if everyone did this there would be no low demand cycle. Secondly, completely ignoring losses on getting low demand energy to your system, the losses in dragging a small truck of old lead acid accumulators up a hill, or some such garbage, would negate the entire process. Just because it is low demand doesn't mean it is free...or, rather, without cost.

 I can verify that your idea is correct. Store gravitational potential energy at an elevation. See hydroelectric power. See water towers. They both negate peak power demands (in their spheres of reference).

 I can, equally, discard your calculations by dividing the energy held by everything you lift up by a factor of two, to be optimistically cautious. This would be due to frictional losses, heat losses, noise losses (etc, if you want the truelly macabre).

Funnelly, (I know same joke different implementation) there is quite a lot of water, you know that heavy stuff (weighs about a ton per cubic meter) up there courtesy of evaporation. Much better idea, oh wait we have already mentioned hydro...
 — 4whom, Apr 04 2011

 Hi bungston, long time no (United Mediterranean) see! In Hebrew we say: The enemy of a good idea is a better idea...

 -----

 Thanks [4whom]. I was asking about the numbers, which you did not confirm. They are what would define and determine the cost benefit. Not everyone has rights to use a hill or tower, and there's not THAT MUCH that can be stored and then recycled in that space. And space is one of the main restricting factors here. So its not "if everyone" - first point.

 A friend from Kibbutz Tzora made calculations that a water reservoir uphill, recycling treated sewage water would be extremely profitable. But he didn't get the permit to build the reservoir, because the hill is public land.

 Calculation: 0.15 NIS per kWh for large scale industrial off-peak electric use. 0.45 NIS per kWh for regular home use. 1.05 NIS for industrial peak hour use (which is what the Kibbutz uses). That's over a 70% difference for peak hours.

 ~100 homes, 30 offices, 3 large industrial factories.

 Lets say the pulling is done with electric power. Supposedly electric motors can reach efficiency of 85% and more. Generators (Dynamo) can do the same if power received directly from mechanical pull. Heated water, cooling the motor and generator, possibly the exact same unit, can be used for industrial processes.

 So losses can be 20 to 30 percent, while gain (in money) are 70%, leaves you with 40% earnings before tax.

 Better yet, if the kibbutz - or building, buys the solution, they pay no tax. They just lower their electric bill.

Lead: 207g/mol. Water 18.01g/mol. (If it's correct that I should figure 1 mol of Oxygen and not half a mol).
 — pashute, Apr 05 2011

 So, 15% losses on the motor, 15% losses on the generator. That's a 28% loss right there. Add in transmission losses to and away from your site, figure 6% each way, so you're down to 63%. Add in another 10% loss in your bearings and wheels. Don't forget gearing, let's say another 5% loss, and you're down below 55%. I'm sure I missed some other factors, but that's probably pretty close.

 A lead-acid battery has a net efficiency of about 85% and can be sited at point of supply or demand, giving a net storage of ~76%. It takes up less total space for a given power (since it's stationary) and is something like 97% recyclable, so the waste is minimal. You can buy a bank of lead acid batteries for a couple hundred or couple thousand bucks. You're going to have that much cost in the steel rails for your weight, let alone a heavy duty gearhead motor/generator, the cabling and the weight itself (not sure what an old rail box car costs, let alone transportation to your site, but that's about the cheapest option I can think of). Not sure I see the advantage here.

The actual best option is demand shifting, figuring out which of the industrial or high load processes can be shifted to off peak hours, but that's another story.
 — MechE, Apr 05 2011

 Thanks [Meche] but no need for steel rails. Wheels don't cost that much.

 Much higher efficiencies can be achieved in both parts. I was talking minimum. There is no 70% efficiency in the full cycle of storage and retrieval from lead acid. Where did you get that number.

 Initial cost is extremely low.

 PLEASE PLEASE! Can someone confirm my original numbers: Force = weight * 9.8 = ~ 10 x weight. kWh = Force/3600/1000. So I would need to raise 3 tons (1000 kg's) up 100 meters (30 stories high) to get 1 hour of one kw energy (if I could retrieve 100% of it).

To tow a single 3 ton truck costs much less than buying 5 kWh worth of new lead acid batteries, let alone a bank of batteries giving 200 kWh or megawatts. And then I'm waiting to find a lead acid battery with a warranty of over a year.
 — pashute, Apr 05 2011

//Can someone confirm my original numbers//
You might want to look at...
// 3 tons (1000 kg's)//
 — FlyingToaster, Apr 05 2011

 Using PE=mgh

 with m=3000, h=100, g=10

 I get PE=3 million joules; 3 million joules = 0.84kWh

 It's not a whole lot of energy storage. To put this into perspective you could power one 80W street light for one night.

My preferred energy storage idea is flywheels.
 — xaviergisz, Apr 05 2011

[+] but not because it would work well though: it'd be like one of those evaporative-nodding-bird thingies: more art than science.
 — FlyingToaster, Apr 05 2011

 If you don't have steel rails and wheels, drop that rolling efficiency number down from 90% to something more like 50-60%.

 As far as the rest of the tow efficiencies, the numbers I used are pretty reasonable, except the transmission losses might be a little high for most locations (it's net for the US grid). The motor/generator numbers can be improved, but only if you pay a lot more for the unit, and not more than about 90% max. Most optimistic estimate is ~65% net efficient for steel on steel dropping to something in the ~35-40% range if you go with any other wheels.

 Your energy recovery is going to be directly related to your initial investment, the more you spend on low mechanical loss systems the better you'll do, but you're still looking at maybe 70% as a hard upper limit.

As for the efficiency of lead-acid batteries, any one of a number of different sources, they are rather efficient (see link).
 — MechE, Apr 05 2011

 As far as lead-acid battery cost, a car battery holds somewhere around 1 kWh and costs maybe ~\$100.

I stand by my tiny, efficient, inexpensive battery bank relative to your massive weight.
 — MechE, Apr 05 2011

 It would work, and be worth it.

 Initial costs a 15 ton truckload, vs 5kva x 5. A typical 18 AH 12V lead acid battery goes for 20\$. I need (5000 * .87) / (18 * 12) / 1000 = 20K batteries = \$400K. My truck from the Petach Tikwa factory where they have used batteries to my building in Tel Aviv would cost about 1000 times less.... and I think my system would last longer.

Since a battery weighs 5.5 kg, I would need only 1000 batteries for the same result.
 — pashute, Apr 05 2011

I swear I still don't know what the idea is.
 — FlyingToaster, Apr 05 2011

see my link - that will explain it
 — hippo, Apr 05 2011

 pashute's idear, not yers ya twit. Besides, isn't Israel sorta deserty ? You'd have to dig down a few hundred metres to get to water in the first place. ...

Something about building a sloping driveway in everybody's backyard and during the night the vehicles get pulled up it which gives them a bit of a headstart in the morning ?
 — FlyingToaster, Apr 05 2011

 Please put some units on your numbers. Where does that 5000 come from? 18 Ah at 12V is 216 Wh, so four is .864 kWh, roughly the same as your initial 3 ton weight.

Your fifteen tonne load is only going to do 5 times as much, so 20 batteries, or \$400, the motor for your pulley alone will cost more than that.
 — MechE, Apr 05 2011

 Corrected: I have no idea what I meant with those numbers, written late at night. I think I was discussing a small (single home) example.

 Initial costs are 3 ton truckload + 5kw motor/dynamo + 100 meter kernmantle rope, Large pipe or canopy. vs. batteries capable of 5kva for 5 hours.

 A typical new 18 AH 12V lead acid battery goes for 20\$. Ampere hour * Volts =gives us Watts. So 18 AH * 12V = 216W So for the 5kw I need 5000 / 216 units for each hour = 23 units * 5 : 115 units. Cost: \$2300. Lasts for a year and half (if used continuously). So for 15 years: \$23,000, Not including the charger.

A truckload from the Petach Tikwa factory where they have used batteries to my building in Tel Aviv would cost about 100 times less. With the rope and motor/dynamo it would'nt cost more than \$2300....
 — pashute, Apr 06 2011

And your efficiencies would be somewhere around 40%. That motor and gearing is going to be low efficiency, and the wheels are going to be very inefficient.
 — MechE, Apr 06 2011

 It's got to be much cheaper to use the same motor / generator with a pump / turbine to move water up and down. Water weighs 1 ton per cubic metre.

 A Mercedes 12 ton truck measures 9.2 x 3.6 x 2.5 metres = 82.8 cubic metres = 0.145 ton / cubic metre.

 The truck system needs a 9.2 x 2.5 metre parking space at the top and bottom of the hill, plus a 2.5 metre wide roadway in between.

 The equivalent water system need only a 12 cubic metre tank or pond at the top and bottom of the hill, and a length of pipe in between.

 So the water system takes up less space = better chance of installing it in an urban area, or where planning regulations are an issue.

It is for good reason that hydro electric schemes pump water rather than lifting rocks or other heavy things.
 — Twizz, Apr 06 2011

 No, it's not the truck you send up and down. That's just the initial cost to bring the batteries . It's a storage of used batteries. And they can be spread out when on top

 - and also, with a good rope system, spread about the building, mechanically connected and running to a single motor.

 The problem with a hillside pond is a real one I described three times here. So batteries still win in this case.

You're correct though about the pond in a high riser. (Would dampen planes crashing into them next time around, not that it would help against gasoline fire). Lead weighs almost 50 times water for the same volume.
 — pashute, Apr 11 2011

 You were talking about using a hill, what is rolling up and down the hill?

 If you are using a vertical system, then you have a huge space inside or against your building, and a serious structural reinforcement to do it.

As already mentioned, this is expensive and less efficient than a bank of lead-acid batteries tucked in your basement.
 — MechE, Apr 11 2011

 //You're correct though about the pond in a high riser.//

 Just call it a swimming pool and you'll get the planning permission, and say "the filter system" is in the basement, for easier maintenance...

 But be sure to put a grid over the outflow. Saying that people still seem to get injured from outflows even with grids....

 Assuming this idea is in Israel...something cunning with the water flow to the Dead Sea, or just sunlight to evaporate water up a tube, where it gets condensed and stored.

I think the reason water seems to be so popular is that, unless you're using hundreds of m3 the worst that happens when the system breaks is someone gets wet feet. "...and also, with a good rope system, spread about the building" what happens when the rope breaks?
 — not_morrison_rm, Apr 11 2011

 ... and then there's the part where you can use the water too, ie: build a swimming pool big enough to handle the daily requirements of the kibbutz, and refill it nightly when pumping costs are cheap. [edit: posted]

 If everybody uses air conditioning then a small tank of water can be chilled electrically at night (when it's the best time both for heat-exchange and for electricity rates), then provide cooling for the house/building during the day.

And if the water company chills the water prior to pumping (used to inhibit the proliferation of bacteria that may be lodged in the pipes) that can also be used to partially chill the A/C tank (since household usage rarely if ever requires cold water).
 — FlyingToaster, Apr 11 2011

Hey FlyingToaster shouldn't we have worked out a joint consultancy fee first? Damn!
 — not_morrison_rm, Apr 11 2011

Well, you already had your foot in the door with the safety aspect, but I don't think a couple weeks all-expenses-paid vacation in Tel Aviv or somewhere close by and very similar in climate would be out of the question... we may even have grateful friends there.
 — FlyingToaster, Apr 11 2011

 somebody had proposed this idea, but in houses

 I calculated it out in the comments and for a weight-and-pulley system it comes out to like a \$1 million facility on a mountain to store just \$30 of electricity

the only feasible one is pumped-water gravity-energy storage
 — EdwinBakery, Apr 12 2011

does anyone have the link for the same idea that someone posted a few months back?
 — EdwinBakery, Apr 12 2011

[EB] [Spidermother] and myself were going on about pulleys if that helps.
 — FlyingToaster, Apr 12 2011

I can't find it either.
 — spidermother, Apr 13 2011

 //couple weeks all-expenses-paid vacation in Tel Aviv or somewhere close by and very similar in climate would be out of the question//

 I couldn't agree more, I'd settle for Netanya, good pizza and quieter than Tel Aviv.

 Finally remembered what I was going to have added, steam engines. If you want water to go up, then I was thinking use a steam engine to burn whatever you have lying around and make electricity or whatever. The steam will rise anyway, preferably in an insulated tube, then on the roof have a condenser, water hit the cold bit, falls into rooftop tank and can then be cycled back down through a hydro-electric generator.

Do I get the room with a view of the beach for this?
 — not_morrison_rm, Apr 15 2011

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