Mechanical storage of energy.

[HardDrive]

I am aware that there have been efforts to create cars that use some sort of flywheel system to store energy. But what about systems for use in homes or business?

I have to assume that there would be a great deal of loss due to mechanical inefficiency in the process of storing energy from a power source (wind, solar, etc).

I guess what I had in mind would be some sort of large weight that gets raised using solar power, then is used to drive a generator at night to power lights and such. I suppose one could also pump water, compress air, etc....

I'm just ranting here, but I know there are some folks with the engineering chops here that could illuminate the subject. Do tell.

[widebody911]

Look up "gererator"

[red-beard]

Originally Posted by HardDrive

I am aware that there have been efforts to create cars that use some sort of flywheel system to store energy. But what about systems for use in homes or business?

I have to assume that there would be a great deal of loss due to mechanical inefficiency in the process of storing energy from a power source (wind, solar, etc).

I guess what I had in mind would be some sort of large weight that gets raised using solar power, then is used to drive a generator at night to power lights and such. I suppose one could also pump water, compress air, etc....

I'm just ranting here, but I know there are some folks with the engineering chops here that could illuminate the subject. Do tell.

The only thing that is done that is somewhat cost effective is pump hydro. You buy cheap power at night from plants that cannot easily reduce load (Nuclear and Coal fired big plants), and pump water into an upper resevoir. During the day, you make power during peak. The price difference between night time base and day-time peak is significant.

But lets do a small one for your house! So, lets pump some water and see how this works.

Energy is m*g*h, assuming the water is still before and after. If you use 3000 kWh per month, then you are using 100 kWh per day.

Assuming you have a water tank ~30 feet off the ground, how big does the tank need to be to support your 50 kWh (night time) usage?

h = 10 meter height (close enough!)
g = 9.81 m/s^2
m = kg
water is 1 liter per kg

50 kWh = 180 000 000 joules (kg * m^2 / s^2)

e = m*g*h

m = e/(g*h)

180,000,000/(9.81*10)=1,834,862 kg of water = 1,834,862 liters of water

or about 416,552 gallons

With efficiency issues, call it 1/2 million gallons for your house. The OBVIOUS solution is to increase the height. The pump-hydro I visited 20+ years ago had I think 1500 feet between the upper and lower ponds. If you had that, you could cut the tank to something like 10000 gallons. However, your piping and pump system would need to be able to handle upwards of 750 psi!

[Amail]

A buddy of mine had thought thermal mass was best way to store energy. His thought was to store a large cistern of water under the house. Heat exchangers would provide air conditioning throughout the day, and at night the warmed water could heat the house.

[daepp]

Remember Rosen Motors?

[masraum]

If possible, I'd think that geothermal would be best, but I think that's really only for heating/cooling.

[HardDrive]

Let see, a 416,552 gallon tank 30 feet above my house. I'm not real good with numbers, is that going to be expensive to build?

[Don Plumley]

Flywheel Energy Storage - idea that you power a large flywheel with grid (solar/wind) power during the day, then during sags, at night, etc., the flywheel delivers power to the grid by running the motor in reverse (that's a generator). The flywheel spins really, really fast - like 20K RPM. I'm familiar with a project that uses superconducting magnetic bearings to reduce rotational losses in the storage system and enable rpm's not really feasible with mechanical bearings.

[red-beard]

You also need to hope it doesn't leak.

It would need to be about 62,500 cu feet, or a cube about 40 feet on a side. I'm sure the HOA would have no problem with that.

[Hugh R]

One of my neighbors works for a company that makes flywheell UPS systems for computers. They run them in a vacuum.

[sammyg2]

I worked on an interesting project in the 80's.
It was based on energy absorbtion during phase change (from a liquid to a solid or versa visa).
The product they were using was a special salt/water solution with a freezing point around 45 degrees.
it was contained in thousands of plastic bottles that were stacked in a something that looked like an enclosed swimming pool.

It's been a long time so the details are a little foggy but if I remember right, at night cooling tower pumps circulated water through the cooling towers which dropped the temperature significantly through evaporation and convection. Then the cold water was circulated around the plastic bottles. Eventually they would get cold enough to freeze.
During the day when it started getting hot, they reversed the flow of coolnig water from the bottles to heat exchangers in the HVAC system, which cooled the large industrial building.

The salt solution would freeze at 45 degrees but because of the phase change characteristics it wouldn't melt until it got to almost 50 and it would absorb a great deal of energy in the process.
It was actually very efficient except when it was humid or extremely hot outside. then it wouldn't get cold enough to freeze the salt at night. We installed one system in Palm Springs, another in the Ventura city building, and a couple others scattered around.
I worked for them on the side but make good $$$$.

[NICKG]

what you are looking for is what the basis and design of the william f1 KERS system is doing ....google it, they use flywheels to store energy

[jyl]

What is the advantage of countless small energy storage systems at each individual home, compared to a few large energy storage systems on the area's grid? Unless you find an energy storage technology that is becomes efficient as you scale it down.

[island911]

Entropy happens.

Seriously, HD, nothing new here. Engineers have been forever looking for cost effective capacitance solutions everywhere.

Of course our electrical grid would be much more efficient if we had more electrical capacitance ...as long as it doesn't cost more than is saves. Then there are car engines. once again, having good capacitance would allow the optimization of IC engines for fuel efficiencies . ...again, so long as the cost (entropy and otherwise) doesn't exceed the savings.

It's just that pesky entropy always getting in the way.

[HardDrive]

I guess I was thinking beyond the grid here. What about little villages in India where the grid sucks (or doesn't reach them at all) and sunshine is plentiful.

Entropy happens, but if your storing power that is 100% solar or wind, why do we need to fixate so much on efficiency? Even if I lose 80% of the power going into the system, if its 100% free energy from the sun.....what exactly did I lose there?

I realize none of this makes sense from a cost perspective.....

[Jim Sims]

Boeing and the U.S. Department of Energy have been working in this area for some time (see below link for a report); with HTS magnetic bearings and other loss reducing measures they are obtaining rundown times comparable with battery natural discharge times. The technology may be useful for diurnal energy storage (solar and wind). I don't seeing it going low-tech enough for the third world for some time, but who knows. Fragment shielding could perhaps be more economically done by placing the units in pits or behind earthen berms.

http://www.osti.gov/bridge/purl.cover.jsp;jsessionid=EB55CF130E64F579D9AAF302 6F0594CA?purl=/909279-2BXgX2/

[cgarr]

I just tap in before the meter.

[red-beard]

Originally Posted by Jim Sims

Boeing and the U.S. Department of Energy have been working in this area for some time (see below link for a report); with HTS magnetic bearings and other loss reducing measures they are obtaining rundown times comparable with battery natural discharge times. The technology may be useful for diurnal energy storage (solar and wind). I don't seeing it going low-tech enough for the third world for some time, but who knows. Fragment shielding could perhaps be more economically done by placing the units in pits or behind earthen berms.

http://www.osti.gov/bridge/purl.cover.jsp;jsessionid=EB55CF130E64F579D9AAF302 6F0594CA?purl=/909279-2BXgX2/

Scary!

[Crowbob]

Diurnal energy storage. That's what happens when da line to the restroom is too long.

[Zeke]

My meter wouldn't know the time of day. Literally. The only way I can save money is to make it go backwards. Now, I could do that during the day with solar. Or, if I wanted to be sly, I'd store it and sell it back when I don't need it, nor do they.

Sounds like a lot of trouble and expense on which I'd never see a positive return.