Topic: Storing elevated water as a battery?

Storing elevated water as a battery? 

I'm probably going to sound a little naiive writing this, but it is an idea that has intrigued me for a bit so here goes...

The idea is to collect water in a holding tank which is elevated as high as possible off the ground, which is filled up by rain water, and also water is pumped to it using wind and solar. Then when the amount of water reaches a certain level, it drops into a secondary tank through mini turbines to create electricity, which effectively creates some power to a house. The elevated water would be acting as a kind of battery.

Now unfortunately I don't really have any idea how much water you'd need to elevate to have any real use, but it is just an interesting idea that I've been pondering. I'm not sure if its more effective to just use the solar and wind to generate power seperately or if it would be more efficient for them to move the water up into the holding tank.

Anyone got any suggestions? Would it be unworthwhile or is there any merit?

Re: Storing elevated water as a battery? 

Sounds doable, you may be able to use a water ram to get the water up to the tank from some stream lower down too (water rams don't require power, so could be handy).
And a siphon mechanism would be an easy way to drain the tank when it reaches the desired level, feeding the siphon into your turbine. I've been thinking of doing something like this to power some garden lights - don't think I'd get enough power to do much more.

Re: Storing elevated water as a battery? 

This is a very good idea. Battery technology is coming along, but it is very complicated and expensive. A way to store energy with something so cheap and simple as this is worth it's weight in....water.

I have been thinking about this concept for a while now. I finally ran into a problem with it about two days ago. *What happens during the winter?* If the temperature gets below freezing, you're toast.

But I still think this idea has potential. Instead of pumping the water, why don't you just lift it? In this case, you could use something heavier than water instead. But I think water would still be the cheapest, easiest, simplest solution.

I'm studying to be a mechanical engineer, and the most important lesson I've learned so far is that simplier is almost always better.

Re: Storing elevated water as a battery? 

If you expend energy pumping the water up to the tank using wind or solar, then at a later stage extract the waters potential energy via a turbine, you are in a net loss situation. Would be more efficient to use the wind or solar energy to directly create power for immediate use, grid tie if necessary and use the grid as a battery.

Re: Storing elevated water as a battery? 

These type of systems have been used for many years around the world, but you need natural landscape for them to work. A high point and massive amount of water storage (both at high level and low level) 1000s of cubic meters and normally a low level natural water source at the top storage point.

Re: Storing elevated water as a battery? 

which is exactly what we already have to generate most of the south islands electricity? isn't it HYDRO

Re: Storing elevated water as a battery? 

Lets see: my little magnetic drive pump draws 20 watts and can pump 900 L/Hr to a tank. So to get say 1000 watts to run a small heater then it has to pump 4500 l over a 10 hour period. Then if the tank is drained through a 100% efficient turbine it would generate 1kw. I reality the pump has losses and the turbine has losses so we may get 700 watts.

Not really practical in ones backyard, think I would prefer to use a small battery, probably cheaper too.

Mike

Re: Storing elevated water as a battery? 

Does anyone have any experience in extracting electricity from a slowly falling heavy weight? I'd think you would get smaller losses this way rather than dropping water through a turbine.

And in order to save on space, which is a very good point--space is at a premium for most people, is there another material that could be used instead of water? It needs to be cheap, heavy, and abundant.

And could anyone tell me how much electricity it would take to charge an average electric car? Whether it's realistic or not, I think it would still be beneficial to know how much mass and how high it must be elevated in order for it to have enough potential energy to match the charging requirements of an electric car. Ball park numbers are all I'm asking for.

I've heard that there is enough solar energy to power us ten times over, but the problem is that it's sporadic and battery technology is not feasibly good enough to collect the excess. The wind has the exact same problem, except in most places it's even more sporadic than the sun. Finding a way to store this energy is key to making sun and wind (and countless others) a realistic replacement for todays methods of generating electricity.

So, I said all that in order to say this. This stupid little idea of picking things up and dropping them again, could potentially change everything.

Re: Storing elevated water as a battery? 

Once it is at the bottom, what energy are you going to use to lift it back up?

Energy required to charge an electric car:

From http://en.wikipedia.org/wiki/Mitsubishi_i_MiEV:

The car has a range of 130 kilometres (80 mi) for the 16 kWh lithium-ion pack and 160 kilometres (100 mi) for the 20 kWh pack.

So call it 20kWh a charge. Note that it is unclear whether the battery is one that is designed to fully discharge or designed to be only partially discharged.

Seeker

Re: Storing elevated water as a battery? 

how about storing surplus energy as compressed air?

Its going to take a lot less space and (may) be a lot easier to convert to energy when needed.

Re: Storing elevated water as a battery? 

Here,s some calcs to make it clear that this won't work.

energy potential of raising 1 cubic metre of water 1 metre is

1000 x 1 x 10 = 10000 joules

1 kwhour is equivalent to 3.6MJ.

so

10000J is 0.0027kwh (in other words 2.7 watts for 1 hour).

1000 cubic metres of water at 20 metres would give you 55kWh. That would seem to be about what would be required. Mmmmm

Similarly, for compressed air.

Chris

Re: Storing elevated water as a battery? 

By the way, 1000 cubic metres would need a container measuring is 10 x 10 x 10 metres and would weight 1000 tons. Elevated to 20 metres this would be a significant engineering project and a ridiculous cost....

Buy 55kwh of batteries. That will only set you back 12K it's by far the most cost effective solution.

Chris

Re: Storing elevated water as a battery? 

So, (please correct me if my logic goes astray) if 1000 tons hanging at 20 meters (about 22 yards) will theoretically posses enough energy to charge an electric car, therefore....... 2000 tons hanging at 10 meters should also theoretically be able to do the same thing. A heavier weight lower to the ground might be easier to handle.

Even though these numbers may seem a little impossible, to be honest this is about what I expected. I figured it would have to basically be as powerful as a small bomb.

In order to power it, I'm kind of green lighting on that, and I'm open to any good ideas. It would probably take a solar dish several days to complete the task. If you found a way to hook up a couple excercise bikes to it, I wouldn't be beyond pedalling a little everday. I wanna work out any way. (I apologize if some of these things sound stupid and juvenile, but green lighting and brainstorming is something else I've learned in my engineering classes). Wind is awesomely unrelieable, but it wouldn't hurt to use one or more vertical axis wind turbines.

I like the idea of the compressed air. I'm freaking kicking myself for thinking of that earlier. It would absolutely save on space. I'll do some research and get back to you.

Re: Storing elevated water as a battery? 

You are right, halving the height and doubling the mass will not change the energy. However you will therefore need twice the volume of water through a pipe to get the same flow rate.

2000 tons is about 12 boeing 747-400's! Are you sure you want to build something to hold that much weight 4 stories high? I don't think you would get any change from $1M. Also the storage container and tower would come at a higher environmental footprint that a battery pack.

Re: Storing elevated water as a battery? 

Compressor air cars are already potentially available (in Portugal Iz Think) Compressor air in less efficient, than your water. If you want mechanical potential energy, wind up a rubbber band.

Re: Storing elevated water as a battery? 

Hi danman (glad you posted your username, not many people do...hmm hope *I* have!)

So I recall a solution for this exact scenario. Not the water or weights solution but "Gravel Batteries". There are plans in the UK and I think the US to build large, highly insulated silos containing gravel, at the site of wind turbines.

The idea is that the electrical energy generated during non-peak times (when such generated energy is at its most "useless") can be converted to heat and that heat stored in the gravel, which as we know from using other materials as thermal-mass storage (concrete slabs for example) can store heat for long periods. Each silo is then highly insulated maintaining a decent temperature for days at a time to convert back to electricity again when required and when the wind doesn't seem to be blowing.

Yes there are losses involved, even through the insulation and of course heat-loss during conversion, but I think the companies involved have done the calcs and are building large-scale prototypes.

Here's the link I read some months ago on this: http://www.guardian.co.uk/environment/2010/apr/26/gravel-batteries-renewable-energy-storage

Cheers
Russ