Is Gravimetric Energy Storage a Viable Alternative to Batteries for Solar Power?

[Jasongreat]

Lately I have seen a lot of people switching over to solar panels, they have basically 2 choices of what to do with the extra energy as far as I know.
1- Batteries
2- Return the extra power to the grid for a credit on their power bill
It got me to thinking and I need some input as to how viable or insane my idea is.

I was wondering if I built a large pole that had a set amount of weight surrounding it and if I used the extra power to lift the weight to the top of the pole, when I needed it could I let the weight fall and recover the power? To gain a further advantage, could I use pullies or some other way to gain leverage say at a 1:4 ratio so that I would have 4 times the power used to raise the weight available to me when I let it fall? I am just beginning on my physics journey so I am sure I am overlooking something, any suggestions will be greatly appreciated.

 

[fatra2]

Hi there,

You can certainly imagine a pole of sometype, with weights attached to it. Therefore, you will need a very big pole, and very big weight to store energy. Gravitational potential energy is not the most "efficient" way of storing energy, unless you do like the hydro power, and store immense amount of water behind a damn.

For you idea of pulley, you need to understand and follow the golden rule of mechanics: Whatever you gain in strength, you will lose in distance. Don't forget that we are talking about storing energy and not strength. So if you use a pulley system to gain on strenght, you will need to move your weights more to get the same energy stored.

Cheers

By the way, some companies have already tought of something like this. I live in Switzerland, where we have a lot of mountains, so a lot of stored hydro power. Some electric companies buy cheap electricity (overnight) to pump water back up the damns. They open the valves when the electricity reaches higher prices (around 5pm). Its a very good way of making profits.

 

[Danger]

In some ways, using black collector pipes and a hot water storage system is more efficent, but it depends upon your needs.
If you are already established with photovoltaic cells, a large flywheel would yield essentially the same results as your tower idea, but with a lot less complexity and climatic concerns. As Fatra pointed out, there's no way around the 2nd Law. You will not extract nearly as much energy as you store; it simply isn't physically possible.

 

[Jasongreat]

Hi there,

You can certainly imagine a pole of sometype, with weights attached to it. Therefore, you will need a very big pole, and very big weight to store energy. Gravitational potential energy is not the most "efficient" way of storing energy, unless you do like the hydro power, and store immense amount of water behind a damn.

For you idea of pulley, you need to understand and follow the golden rule of mechanics: Whatever you gain in strength, you will lose in distance. Don't forget that we are talking about storing energy and not strength. So if you use a pulley system to gain on strenght, you will need to move your weights more to get the same energy stored.

Cheers

By the way, some companies have already tought of something like this. I live in Switzerland, where we have a lot of mountains, so a lot of stored hydro power. Some electric companies buy cheap electricity (overnight) to pump water back up the damns. They open the valves when the electricity reaches higher prices (around 5pm). Its a very good way of making profits.

Thanks for your reply I had a feeling I was overlooking something simple. I was thinking that once the weight was at the top I could change pullies and cables to a 1:1 ratio to get more power out on the way down. Now I see that if I get a 1:4 strength advantage going up I will only get 4:1 distance on the way down, so if it takes 25w for a hour to get the weight up I would get 100w out but for only 15 min on the way down? Thanks for setting me straight.

 

[ank_gl]

By the way, some companies have already tought of something like this. I live in Switzerland, where we have a lot of mountains, so a lot of stored hydro power. Some electric companies buy cheap electricity (overnight) to pump water back up the damns. They open the valves when the electricity reaches higher prices (around 5pm). Its a very good way of making profits.

This is done all over the world(i guess).

Generally the base load is taken up by steam plants, & steam plants are not very efficient at part loads, so at night, when load decreases, instead of operating the plant at poorer efficiency, power is sold to hydro plants at cheaper rate. The math works out to be profitable for both HEP & the steam plants. Such hydro plants are termed as pumped storage hydro electric scheme.

 

[Integral]

Frankly, to me the pulley and pole system sounds like a mechanical nightmare and an accident waiting to happen. If you really want to store energy mechanically you may want to research a flywheel.

Currently batteries may be the best storage system available.

 

[Bob S]

When Fairbanks Alaska wanted a large electrical energy storage system, they chose Ni-cad batteries:
"The battery-electric storage system (BESS) passed a critical benchmarking test in December 2003 when it produced 27 MW for 24 minutes, exceeding the guarantee of 27 MW for 15 minutes. By March 2005, the system had passed another benchmark. When GVEA first contracted to have the BESS designed, the agreement included an 18-month availability guarantee. The guarantee required that the BESS maintain 98 percent or better availability during its first 18 months of operation. During the 18-month availability guarantee period, the BESS provided a 99.2 percent availability, meaning it was available to pick up load 99.2 percent of the time."
Their first choice might have been pumped water, but it often freezes in Fairbanks.

from http://pepei.pennnet.com/display_article/246701/6/ARTCL/none/none/1/World%E2%80%99s-Largest-Battery-Storage-System-Marks-Second-Year-of-Operation/

Bob S.

 

[russ_watters]

I was wondering if I built a large pole that had a set amount of weight surrounding it and if I used the extra power to lift the weight to the top of the pole, when I needed it could I let the weight fall and recover the power?

We get this question a lot. Many people when first thinking of it just don't realize how much power our electrical devices require to operate. A practical example:

How many 1 kg weights would you have lower from a 10m pole per hour to to power a standard 100w light bulb? (assuming 100% efficiency)

1w = 1 J/s
100W = 360,000 J/h

P.E. = mgh = 1 * 10 * 10 = 100 J per 1 kg weight

360,000 / 100 = 3,600

So in order to power a light bulb, you would need to lower 3,600 1kg weights a distance of 10 m, every hour.

 

[dr dodge]

in my opinion, compressed air has a lot of potential. I don't mean shop air, I am talking about 3 to 6 stage slow compression, to eventually store ambient air at 10K psi. I currently am working on, what probably will be, the worlds slowest compressor. one stroke/day from solar. I know the heat losses can be problematic, but if the system does not leak, the storage life is indefinant, and even with any loses, its still free. little "mini bottles" at ~1800 to run the weed eater, car, mover, etc. use storage batteries as short term storage (2-3 day house load) and run a alternator for the charging off of compressed air. and it could all be buried, so the wife doesn't have to look at my tank farm...lol

russ, thanks for the math, you just helped me scrub another idea before I invested any time

dr

 

[Dadface]

In some ways, using black collector pipes and a hot water storage system is more efficent, but it depends upon your needs.
If you are already established with photovoltaic cells, a large flywheel would yield essentially the same results as your tower idea, but with a lot less complexity and climatic concerns. As Fatra pointed out, there's no way around the 2nd Law. You will not extract nearly as much energy as you store; it simply isn't physically possible.

I also think that a hot water storage system is far more efficient and will become increasingly more so as fuel prices rise.We use a lot of fuel just to heat water,even in hot climates where hot water is used for things such as showers.

 

[Topher925]

Gravimetric storage may sound impractical when dealing with weights and such but it can be very effective when use with fluids, like water towers for example. Hydroelectric plants store energy using this method every day.