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A greener approach to energy storage
  • I saw the talk on Ted and found my way to your your site. I really like what you're doing, and hopefully will have a plot of land to try and implement some of these things eventually.

    I noticed that one of the components of the GVCS is building batteries. I had this idea one day while sitting around being lazy... after a little bit of research I found that the idea is very old and already implemented in large installations.

    Essentially, you have an inground pool and an above ground pool. Pump the water up when you have excess power, let it run down through a generator during times of need.

    Currently this method is used to store night-time energy from nuclear power for the purpose of bolstering peak usage time during the day, but on a smaller scale, it would do a good job of storing solar energy for night-time use. The size of the water reservoirs needed for this would depend on the power needed at night and the efficiency of the generator. Completely enclosing the reservoirs in plastic would diminish or prevent any water loss due to evaporation, or alternatively could be funneled up and into a catch for distilled clean water.

    And most importantly, it is a lot cleaner and safer for the environment than large lead-acid batteries (or any other type of chemical battery).

    It goes without saying that a water well would need to be available beforehand, else it would take a long time to fill the reservoir to a useful level using rainwater only.
  • 35 Comments sorted by
  • Both novel and practical.
  • what about emulating photosynthesis
  • In 5-10 years we might.
  • @ CyberCod - I agree that chemical batteries are a problem on many fronts. They are hard to justify except in portable applications.

    I also have put a lot of thought into this very thing. I feel a hydraulic system would be a better choice. It's basically the same as your suggestion except it can be made much more compact. You see I would use a very heavy weight on a tower instead of water in large pools. You pump up the weight to 30 or 40 feet and release the pressure into a hydraulic motor driving a generator.

    Totally closed system that just runs and runs. This would be perfect in a tidal system. You could tie it into a floating dock for instance.

    One day, I will build one of these.

    The Dawg
  • A weight based system was actually my first thought, though using pullies rather than hydraulics. I'm not all that familiar with hydraulics, so it tends to be a blind spot in my thinking.

    I switched to a water based concept after my wife told me she'd be afraid to let our child play unattended if she knew there was a five ton weight suspended 30 feet off the ground somewhere nearby. Admittedly there are drowning dangers associated with the water system, but our child is plump enough that he'd float without much effort. ;)

    I just think the idea of using stored chemical energy is a little short-sighted. Converting to potential energy makes so much more sense.
  • Potential energy is
    U = mgh, where m is the mass in kg, g is the gravitational acceleration, h is the height in meters, and U is the potential energy in joules
    so m = U/(gh)

    20 kWh = 72 million joules = U
    g = 9.8 m/s^2
    h = 50 meters (for example)

    that means m = 146938 kg of water which is 147 cubic meters of water

    So we're talking a 15ftx15ftx15f box of water at a height of 150 ft up for 20 kWh of electricity, which is only enough to power the average home for 2 hours. Inefficiencies in the system will likely be around 50%, so we're talking more like 10 kWh, or a single hour for an average, non-industrial home.

    So in conclusion, unless you've got natural land features that allow this type of storage, it isn't feasible.
  • @ Jason - Good info. How about calculating this. How much energy is in a 20,000 pound load on a 50 foot tower?

    The Dawg
  • @Dawg

    Well, that's simple enough:

    20,000 lbs = 9,072 kg
    50 ft = 15.2 m
    g = 9.8 m/s^2

    m*g*h =
    9072 * 9.8 * 15.2 = 1,351,365 joules

    1,351,365 joules = 0.375 kWh

    This isn't really surprising because gravity is the weakest force in nature, by many orders of magnitude.

    Note: using google makes the conversions and calculations really easy, for example, convertion lbs to kg:,000+lbs+in+kg&aq=f&aqi=&aql=&oq=&pbx=1&bav=on.2,or.r_gc.r_pw.&fp=6af0f014ae16db6c

    Heck, you can even do the whole equation in google and it will convert all the units automatically! And it won't work if you don't type in the units right.,000+lbs+*+9.8+m/s^2+*+50+ft+in+kWh&aq=f&aqi=&aql=&oq=&pbx=1&bav=on.2,or.r_gc.r_pw.&fp=6af0f014ae16db6c
  • @ Jason: While I admit you've made the idea look like an idiotic pipe dream, keep in mind that this isn't meant for the average energy-sucking home. Its meant for an efficient home. Also, its only meant for use a few hours after the sun goes down. If a lot of the heavy lifting for heating and cooling, hot water, and cooking are done via other green methods, whats the energy consumption then?
  • lets assume we cant build a platform and we dont have any natural advantageous formations, so everything has to be done at ground level.

    if u build two same volume water storages, dig a hole in the ground, and then, next to it built some retaining walls for above ground storage.

    how big a hole and how high a wall would you have to have to get the same .375 kWh?

    what reasonable limits should we place on depth and height?
    can we optimize it for the least amount of dirt that needs to be moved?

    does the math change being at ground level?
  • Storing any appreciable amount of power via pumped hydro is probably not practical. That being said, it does make a good way of buffering power for a few minutes or of powering much smaller devices off a generator that would be way more than what is necessary to run them. A water tower holding a few cubic meters of water would have enough power to run a computer for quite a while. This would allow you to run the power cube motor or a solar->steam->water pump to fill up the tower quickly and then power the computer for 6 hours, then another short burst of power before the sun sets and the computer works well into the night. This allows you to make better use of the useful output done by the generation equipment as it can be run at a constant rate where the equipment is most efficient and then the consumption of the power can happen at whatever rate is needed. As long as the long term average of the power consumption is maintained you can always run at the peak efficiency (minus the lossess from converting some of the load to/from water, but this can be lower than the increase from generation efficiency allowing for an overall gain).
  • @CyberCod

    Without heating or cooling, and using efficient lighting, your power would drop by a lot. But look at it this way - then your storage needs would drop a lot too. For example, I just found a 12 V battery online for $150, with a capacity of 90 Ah. How much power is that?*+90+Amp*hr+in+kWh&aq=f&aqi=&aql=&oq=&pbx=1&bav=on.2,or.r_gc.r_pw.&fp=6af0f014ae16db6c

    Its 1 kWh. So for only $150, you can have the same capacity stored under your desk, no pumps or conversions or anything, as a 60,000 lb weight suspended 50 ft in the air.
  • >> 20 kWh of electricity, which is only enough to power the average home for 2 hours.
    Houses do not use 10kW.

    >> Inefficiencies in the system will likely be around 50%
    I think you could do much better than that. These two sites say efficiencies range from 70-85% -
  • @ Jason - This is great info. One thing I like about the hydraulic tower idea is it's a mechanical system that can be self made and serviced. It has no leakage so once the weight is up there you can come back a year later and it's still there ready to go. Also, once built, a system like that could theoretically last many decades before needing major repairs. At the very least it would make a great dump load for a battery charge controller.

    Chemical batteries on the other hand have leakage currents that can be quite significant. They will go dead just sitting on the shelf, especially in the cold. They are not 100% efficient either, especially when fast charged. In the case of a liquid electrolyte lead acid battery, you charge at 14.3 volts but the float voltage settles down to 12.6. Also, you can only discharge a well designed deep cycle battery to no more than about half it's amp hour rating or you will shorten it's life considerably. So your 1 KWh is actually .5 KWh. Combine the relatively short lifespan of a battery (6-10 years) and the environmental issues associated with its makeup and you can see why some less efficient ideas might not be so bad when looking at the big picture.

    We're not going to get rid of batteries any time soon. But it would be nice to explore how we might make other technologies actually work in some useful manner.

    Keep the ideas flowing.

    The Dawg
  • @Conor

    I'm assuming pretty much any energy storage mechanism will be around 50%, when you factor in all the losses. So I'm not trying to ding this specific technology due to losses, just trying to provide a realistic scenario of what someone should expect and budget for.

    Although I will say, to be fair, that you'd be hard-pressed to get any type of efficient hydroelectric conversion without at least a couple hundred feet of head pressure to work with. So while I'm not dinging the technology in principle for efficiency, below 200 ft of drop is a tough problem in and of itself.


    I completely agree with you, 100%. I've had many batteries go dead, and much money wasted. What I'd be interested in investigating is what it would take to simply melt the lead acid batteries down after they die and cast new ones. Then the old sulphuric acid could either be reused, or be neutralized and new acid produced. Perhaps someone who is familiar with lead acid batteries can tell me why this is or isn't feasible.

    For energy storage, I've always wondered, why not just efficiently use electrolysis to break down H2O into hydrogen and oxygen gas? Is it because it is difficult to store hydrogen gas?
  • @ Jason - So, 60,000 lbs is only 30 Tons. In the hydraulic world this is still very doable. I used to operate a 100 Ton press. The cylinder was only about 8 inches in diameter. So here's my idea:

    Try to imaging a round structure mounted at ground level that was made up of 5 pie shaped pieces of concrete. These weights would be thin on the outer rim and thick near the center. Think a rather flat truncated cone cut into 5 slices. Ideally, each slice would weigh approximately 100 tons. They would pivot upwards about 10 feet lets say. The pivots would be near the outer rim. So because we would be lifting only one end we might only have 80 Tons in the center.

    There would be a hydraulic ram for each slice. These cylinders would be connected together to act as one. I'll whip up a model for this eventually.

    So, 80 Tons is 160,000 lbs. There are 5 slices. So we're looking at 800,000 lbs total moving 10 feet. Do your magic!

    Now imagine a system something like this that acts as a base for a tall tower housing a wind turbine generator. Now you're using the real estate twice. Also, being close to the turbine comes in handy when the batteries are full and you need somewhere to dump the excess power being produced.

    I'll try and model this and see if it sparks any ideas from others.

    Thanks for the help.

    The Dawg
  • @Dawg

    All you need to do to quickly calculate these different scenarios is click on this link:,000+lbs+*+9.8+m/s^2+*+10+ft+in+kWh&aq=f&aqi=&aql=&oq=&pbx=1&bav=on.2,or.r_gc.r_pw.&fp=6af0f014ae16db6c

    Then change the search terms to fit whatever model you're thinking of and you've got instant results. (Results for 800k lbs at 10 ft are 3 kWh.)
  • "Although I will say, to be fair, that you'd be hard-pressed to get any type of efficient hydroelectric conversion without at least a couple hundred feet of head pressure to work with. So while I'm not dinging the technology in principle for efficiency, below 200 ft of drop is a tough problem in and of itself."

    Ok, but its a problem that can be thought about.... what if I park a boat in the pool? Would that increase the pressure? Thats an honest question, I'm not trying to be snarky.
  • In Highschool academic team, my team went to state for Future Problem Solving. And I've also had training to do improv comedy. I don't say this to boast, but to explain that I have some effective but strange brainstorm methods.
  • Good to see we have people that can brainstorm here. It really slows things down when people get stuck on some specific detail you write in a huge paragraph and get off topic.

    As far as, say, putting a boat in the water, if that raises the entire water pool by an additional 1 ft due to water displacement, that gives you precisely 1 ft of extra pressure.
  • So, mathematically, if I have one cubic foot of water which is one foot off of the ground, it has the same potential energy as one cubic foot of water sitting (fluidly) on top of another cubic foot of water.   Seems like it'd be handy to live next to an abandoned water tower one could re-purpose. lol

  • I guess the only other idea I have for increasing pressure would be a sort of giant bladder (like a bellows) with weight on the lever, but that's impractical at this scale.   Ah well.  At least it works in the gigantic scale.

  • Here is a very basic example of where I'm going with this Power Cone.  As I was finishing up this design I realized that it's only the top half of what could be made.  Ideally you would start the movement 45 degrees in the downward direction and lift it up to the 45 degree upward position.  More bang for your buck so to speak.  But never the less, this gives the general idea.

    power cone 01.jpg 76K
    power cone 02.jpg 59K
    power cone 03.jpg 46K
  • Vote Up0Vote Down
    October 2011
    I know this is an old thread but maybe we can get a bit more discussion on this. 

    It seems that gravitational potential just doesn't store enough energy at the scales we are talking about. Batteries are very effective but they are expensive and over time they die. What if energy was instead stored in flywheels as mechanical energy. E = (1/2)(Iw^2) With the squared angular velocity, this energy can increase pretty quickly. Also this is still in mechanical form and could still be easy to apply to a generator without too much loss to efficiency. A problem I see right away is the frictional forces of the wheel are both taking energy and heating up. With a good lubricant this wont be too much of a problem especially if this is just an "over-night" kind of energy storage.

    What do you guys think?
  • Vote Up0Vote Down
    October 2011
    The nickel iron battery project on this site looks promising, but I am unable to find a source of low cost nickel sheets. 

    Does anyone know if we could use the American nickel coin in this type of battery?  I know it is nicked but there are many examples of people using nickel plated panels as the electrode plates.
  • A couple thoughts...

    20 kwh of energy would power my computer and all three of its monitors for 2 days.  

    20 kwh of energy would power my rv's comfort electrical systems (such as the heater and lights) for at least a week if not two.  

    If we had 20kwh of battery in our hablab, I would consider it to be well equipped indeed.

    You need no more than 3 feet of head to run a small hydroelectric generator.  Certainly anything on the order of dozens of feet will do you quite nicely.

    Hydraulic accumulators of various sorts

    store some quantity of energy for surge usage.  I agree that using some sort of buffered system with a high recharge rate would be preferable to continually operating a generator, but the nickel iron batteries would probably be entirely adequate for the purpose of household energy storage, and so much better for reliability. 

    You don't have to get low cost nickel sheets to make it worthwhile you know.  You only have to get sheets that are cheaper than the continual replacement of the batteries, as you need to in lead acid.

  • Going back to the water pumping idea, I think every installation would have to be specifically designed for the users, climate and terrain of where it's installed, but here are some other optimization that could be added:

    1. Collect rainwater.

    2. Use evaporation (solar, etc)

    3. Hook it up to a windmill.

    4. When heating your house or cooking any excess energy could also be used to move the water (through evaporation or some other means).

    5. Is there a low tech way to harness geothermal energy to move water?

    6. Energy from composting? Pressure from gasses or heat from composting process.

    I think the beauty of the water system is that it's very modular. All you care about is getting water into the top container. You may have a whole slue of water movers all pointing to that top container some of them may only move water when it's raining, some may move water very slowly, etc. You can make it as simple or as complicated as you want. Then have a mechanical pump running to make up the difference between the free energy you got and your electrical energy consumption.
  • 1. ok
    2. interesting idea.  A boiler effect could transport both the water in the steam *and* run a pump.  condense it into the upper pool, viola.
    3. good.
    4. probably not worth the trouble
    5. Is drilling a multi-mile hole to get boiling heat low tech?  You could use the ambient coolness near the surface to help condense water.  Thats kind of geothermal.
    6. That could work, if you have a good supply of decomposing biomass.  Getting notable energy this way will require A WHOLE LOT of biomass

    I agree that a large buffer is entirely appropriate for the situation of dealing with both surges of supply and demand.  I don't know that water is the best way of buffering it or not, but its certainly an option to consider the pros and cons of relative to other methods.  Hydraulic storage pressure from a large weight pushing down on a huge piston is particularly attractive because it supplies hydraulic power, which is usable in many shop machines as well as to spin generators.
  • Vote Up0Vote Down
    October 2011
    The biggest problem with the water wheel and pools is that it needs to be so big. Gravitational potential is just so weak that we need to make a giant pool in order to have the same energy storage as a small battery.
  • Vote Up0Vote Down
    October 2011
    I am liking the idea of Dawg's "Power Cone" as a giant hydraulic accumulator for stationary hydraulic shop power.

  • Vote Up0Vote Down
    February 2012
    As some have already pointed out this solution is not scalable easily. Pumped-storage hydroelectric plants are in use all over the world but you need some naturally occurring reservoirs to make it work.

    A olympic-size pool of water pumped 10 meters up gives you less energy than is in 10 liters of gas/diesel. It's just not practical.

    If you're looking for a green and low-tech energy storage I think you should focus on a different form of energy. ;). Flywheels maybe? Quite an engineering challenge to make them practical, but still seams more realistic than pumping water in and out of your garden pool. Compressed air tanks are also considered a viable solution, but again the same olympic-size pool container with air compressed @20 MPa should store less than 5 times more energy than pumped water. You just can't beat good old fuel burning (and these are the levels of energy we are accustomed to in the modern world.).

    If storing energy was easy we would have already switched to renewables.
  • Maybe you could build a large biofuel-algae pool. The surface would be for the algae. The depth would be for pumping water in and out as an energy buffer.
  • We live on a hill in the alps. There is 100m (at least) altitude difference between one end of our property and the other (distance ~500m). We want a pond at the top of the hill ANYWAY, have streams at the bottom and I still decided that pumped water storage was not a practical solution, due to pipe and wire losses etc.

    Flywheel storage? evacuated container and magnetic bearings with integrated motor/generator for a completely non-contact flywheel electric storage. Issues: tensile strength of materials reached quite quickly (low capacity limit) and has to be mounted in line with earths rotational axis to avoid gyroscopic twisting effects on magnetic bearings.

    The guy who made the clockwork radio did a lifted weight thingy in his garden - a bucket of rocks on a rope up a tree. worked quite well if I recall.
  • Vote Up0Vote Down February 2013
    Hi Guys,

    One idea I had for providing some "peak" power when needed is to perhaps store some energy as compressed air. Run through an air engine to drive a generator (or car alternator perhaps) should provide a fairly steady flow of power.
    Obviously you could not scale this up too much, but if you need a lot of energy in a rush, this may just do the trick.

  • Vote Up0Vote Down February 2013
    You can get a lot of energy out of compressed air, check this out

    You could even use compressed air to store/convert wind power or water power without a generator

    So it can be a viable alternative to chemical or other forms of mechanical stored energy.

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