An idea for mechanically storing energy

[JoeKing]

BLUF: We already make a lot of power, but have no efficient way to store that energy for use when we need it.

I've been editing and adding to this post as I work the idea out in my head, so some of my quotes in posts by others will not be exactly the same as in this post. I'm not trying to win any arguments, I'm just throwing an idea out there to see if it'll work. I'll italicize or make note of my edits and additions. Seriously, thanks guys for helping with this exercise in thought!


So I came up with an idea to store some of that excess power we produce for use during peak hours. I know we use dams to store potential energy but what about those places where large reservoirs of water with elevation are not feasible?

So I present to you....

The JoeKing underground energy storage system!!!!

During off peak hours excess power would be shunted to the main motor(s) to pull the weights up. During peak hours the weights would be released to slowly move down the tracks converting the motor into a generator thus creating power.

The grade of the tracks would be very gradual just enough to take advantage of gravity. Multiple weights would be used on several tracks to increase or decrease power generation. Braking rods would well.... brake the weights.

The system when networked with the power grid should require very little maintenance.

System can be scaled up or down for different situations. I know mag rails would also work well, but I'm trying to keep the system simple and sweet with well established technology. But that's not to say you couldn't marry my system with newer techs that use renewable naturally occurring sources for energy production. However my system should not solely rely on that energy source. Why not put it close to a nuke plant and a solar farm?



So has this already been thought up? Is it feasible? I figure you could use this system around deserts, foothills, and maybe even under farm land. You could even use this as an power relay station. I think the main flaw in my system is the motor/generator. Do we have/can we build a purely electrical engine(s) that will work this way on this scale?

====edit w/ copy paste of content from one of my responses below====

In my system I seriously envision something spanning many miles upwards of 20-100+ all underground. We could use the same boring machines they used for projects like the chunnel from England to France and the Big Dig done in Boston. If we pick geologically stable sites whats to say these systems couldn't last hundreds of years?

The project(s) would be on a massive scale with massive investments. But simultaneously we would be employing huge numbers of people that should not require too much technical skill.

I really wish I had the math skill set to calculate all of this but I don't... any math wizards out there bored enough to work this system out to see if it's really viable?

And I really like the flywheel idea, maybe it can be incorporated into my system to help regulate power output, or to more efficiently convert the energy from the weights to electricity. But again my concern is upkeep and reliability of flywheels. I'm really adverse to fast moving components in this system. Faster = more wear and tear I want my system to move as slow as feasible.

 

[Mark R]

It's an issue of size.

A typical pumped-storage hydro unit would lift 10 million tonnes of water a height of 300-2000 feet, and when releasing the energy, would be done by releasing 500 tonnes per second at 100 mph.

It's simply not practical, nor cost effective, to use material, except water, as your weights. Similarly, drilling pipes through mountains is relatively straightforward and cheap compared to laying rails which can hold weights that make freight trains look like kids' toys.

 

[Modelworks]

It isn't really a new idea to mechanically store energy, actually it is really really old. Springs are the best example. You wind a spring to store the energy that is slowly released over time.

 

[CycloWizard]

There are efforts underway to use flywheels to mechanically store energy. As long as the friction in the wheel is low, it's very efficient because you can simply hook it directly to the dynamo to recover the mechanical energy as electricity. When you want to store energy, you just use the dynamo as a motor to spin up the wheel. I can't recall the name of the company here working on it off the top of my head, but the idea has its own Wikipedia article.

 

[wuliheron]

If you're actually going to be moving something it might as well be used for transportation as well as energy storage. Freight trains with regenerative breaks have been explored, but the breaks on trains are spread over the cars making it less desirable. A space elevator using linear motors is a definite possibility. During peak production hours you could load it up with passengers and freight destined for orbit and shift the balance of the weight during off peak hours to sending things down from orbit.

 

[Aluvus]

It seems easier to use compressed air, not that that is a perfect solution either.

 

[wuliheron]

It seems easier to use compressed air, not that that is a perfect solution either.

The Soviets experimented with using low radiation atomic bombs to create hermetically sealed underground chambers for storing oil. You'd need to wait a couple of years for the radiation to die down, but they created chambers around 100 meters or so in diameter with ten foot thick glass walls capable of something like 86 atmospheres. How cost effective that might be is another issue.

 

[imagoon]

There are efforts underway to use flywheels to mechanically store energy. As long as the friction in the wheel is low, it's very efficient because you can simply hook it directly to the dynamo to recover the mechanical energy as electricity. When you want to store energy, you just use the dynamo as a motor to spin up the wheel. I can't recall the name of the company here working on it off the top of my head, but the idea has its own Wikipedia article.

Already used in datacenters to provide power during the UPS and Gen Set switch overs / load balancing. The magnetic bearing ones are pretty cool also.

 

[JoeKing]

but think of those areas where a large reservoir of water is not possible. Yes I conceded that the initial investment will be massive for a large scale system, but once it's constructed and working the project should reap dividends for generations... not even counting efficiencies in motors and generators over time. Also the number of weights can vary according to design specs. You can even have several hundred weights attached to a generator to reduce the size of each weight. Of course the addition of parts becomes a multiple for maintenance and efficiency.

It's an issue of size.

A typical pumped-storage hydro unit would lift 10 million tonnes of water a height of 300-2000 feet, and when releasing the energy, would be done by releasing 500 tonnes per second at 100 mph.

It's simply not practical, nor cost effective, to use material, except water, as your weights. Similarly, drilling pipes through mountains is relatively straightforward and cheap compared to laying rails which can hold weights that make freight trains look like kids' toys.

I actually started thinking about ways to mechanically store energy after watching someone reset a cuckoo clock in Austria.

It isn't really a new idea to mechanically store energy, actually it is really really old. Springs are the best example. You wind a spring to store the energy that is slowly released over time.

 

[JoeKing]

that's my problem with most solutions I see out there. Trying to do too many things when one good solution will work great. Example... you know those multi-function printers, scanners, faxing machines out there built by companies like HP, Lexmark, Canon, ect. 9/10 times you get horrible integration, bulky design, poor implementation. The essence of the product looses direction. Yeah it does everything... but with mediocrity.

If you try to do too many things with a system that should just be for energy storage, you throw an unnecessary cog into the mix. I say let the massive underground power storage machinery do their one and only task, well! And let the gear down the line decide what to do with all that excess cheap power later.

If you're actually going to be moving something it might as well be used for transportation as well as energy storage. Freight trains with regenerative breaks have been explored, but the breaks on trains are spread over the cars making it less desirable. A space elevator using linear motors is a definite possibility. During peak production hours you could load it up with passengers and freight destined for orbit and shift the balance of the weight during off peak hours to sending things down from orbit.

 

[wuliheron]

that's my problem with most solutions I see out there. Trying to do too many things when one good solution will work great. Example... you know those multi-function printers, scanners, faxing machines out there built by companies like HP, Lexmark, Canon, ect. 9/10 times you get horrible integration, bulky design, poor implementation. The essence of the product looses direction. Yeah it does everything... but with mediocrity.

If you try to do too many things with a system that should just be for energy storage, you throw an unnecessary cog into the mix. I say let the massive underground power storage machinery do their one and only task, well! And let the gear down the line decide what to do with all that excess cheap power later.

I'm not talking about making a swiss army knife that also stores power. Transportation and power storage are merely two complimentary functions just as our sex organs also serve to eliminate waste and windows commonly allow in air as well as light.

 

[wirednuts]

for transportation, having a flywheel that ramps up to say 20krpm or so would be pretty cool. you would have basically unlimited acceleration, and when you brake you can directly spin the wheel back up to speed. of course this wont keep the wheel spinning its fastest, so a small electric motor would do that, but it would be very efficient and simple. as long as you use air bearings or something, and have a perfectly balanced and sealed flywheel.

for houses, i think its much more useful to have underground heat storage. a large underground brine tank that you can heat up via parabolic mirrors focused onto a pipeline filled with oil. pump the hot oil through the water underground and store the heat for later use- either for showers, cleaning or heating the house in the winter.

that alone would take care of most of your energy needs without any special technology. a windmill and photovoltaic solar panel could address the direct electric needs...

 

[silverpig]

for transportation, having a flywheel that ramps up to say 20krpm or so would be pretty cool. you would have basically unlimited acceleration, and when you brake you can directly spin the wheel back up to speed. of course this wont keep the wheel spinning its fastest, so a small electric motor would do that, but it would be very efficient and simple. as long as you use air bearings or something, and have a perfectly balanced and sealed flywheel.

for houses, i think its much more useful to have underground heat storage. a large underground brine tank that you can heat up via parabolic mirrors focused onto a pipeline filled with oil. pump the hot oil through the water underground and store the heat for later use- either for showers, cleaning or heating the house in the winter.

that alone would take care of most of your energy needs without any special technology. a windmill and photovoltaic solar panel could address the direct electric needs...

I think you can get to 100k rpm easy on one of those. Also, they are typically in vacuum.

We had a few turbopumps in the lab to pump out chambers for putting samples in and unless you let a tiny bit of gas in to let the pump work against to brake it, the thing would spin forever if you just shut it off.

 

[Mark R]

for transportation, having a flywheel that ramps up to say 20krpm or so would be pretty cool. you would have basically unlimited acceleration, and when you brake you can directly spin the wheel back up to speed. of course this wont keep the wheel spinning its fastest, so a small electric motor would do that, but it would be very efficient and simple. as long as you use air bearings or something, and have a perfectly balanced and sealed flywheel.

Electrically driven flywheel motor-generators are already in widespread use in transportation systems, particularly subway and metro rail.

These flywheels are made of extreme-tensile composite materials (e.g. carbon fiber), suspended on magnetic bearings inside vacuum enclosures, and can achieve immense speeds e.g. 20-50 krpm. A flywheel unit the size of a large washing machine can store 25-30 kWh, and can deliver up to 500 kW of power on demand. By attaching a bank of these flywheels to the power grid at major stations, the flywheels are able to absorb electricity from the trains' dynamic brakes that would otherwise end up dumped in resistors, and support the grid when trains accelerate - allowing the train operator to run more trains without upgrading their grid connection, while simultaneously reducing energy consumption by making better use of dynamic braking.

However, at $20k++ for 25 kWh, this is not a cheap option. This type of equipment is not general purpose, but reserved for specialist niches.

 

[wirednuts]

wow mark/silverpig, i didnt know about any of that. even at 20 grand cash though, isnt that still more cost effective then a battery bank? especially over the long run....

whats stopping people from using those instead of batteries in solar power homes and such?

 

[Mark R]

wow mark/silverpig, i didnt know about any of that. even at 20 grand cash though, isnt that still more cost effective then a battery bank? especially over the long run....

whats stopping people from using those instead of batteries in solar power homes and such?

I may be mistaken about the price - it's possible I quoted the price for a small model (e.g. 5 kWh), I don't have my original source to hand any more.

They are an alternative to batteries, in the industrial UPS market - accounting for something like 8% of all new heavy duty (three phase) UPS units.

The flywheels, despite vacuum enclosure and low-loss bearings still do suffer significant frictional losses, and therefore draw a non-negligible idle current and have a very significant 'self discharge' rate (much higher than batteries).

The big benefit is on devices that require short bursts of power, equivalent to discharging the flywheel in 15 minutes or less (3-5 minutes is the normal target market).

Flywheels must be installed in a suitable vault, in case of flywheel failure - which could result in a major explosion. Although batteries also require some care in installation, as hydrogen production is a risk with open lead-acid or NiCd batteries.

Flywheels still require regular maintenance and servicing, even if it is just inspection by an appropriate tech, although the maintenance costs are certainly lower than batteries, which one of the reasons for the popularity of flywheel UPS systems.

Batteries would still be the preferred technology for long-period backups (> 15 minutes) e.g. off-grid use.

 

[Modelworks]

Probably the most widely used storage medium for energy is water towers. There is hundreds of thousands of them that pump water to the top , store the water and let gravity and the force push water to homes that would take a pump much larger than what is used to fill the tanks. A pump also wouldn't work in a power outage. With the water tower setup cities have water pressure even in a power outage .

Whenever I think of flywheels I think of Stirling engines. They require a flywheel to even work but once started make use of the flywheel as a sort of storage.

Another example of flywheels and cabling is the San Francisco city cable cars. They all are pulled and controlled from one point where the power is generated and uses the hills of the area to return unused energy when going downhill .

 

[silverpig]

Yeah flywheels are great for fairly short-term storage but they do dissipate energy through friction. They probably aren't the best choice for daily smoothing of power demand (ie, not great for solar power stuff), but would work well on the few hour timescale.

 

[wantedSpidy]

The issue has always been efficiency. The energy lost in the conversion will probably be more than the actual energy you're trying to store.

 

[DrPizza]

but think of those areas where a large reservoir of water is not possible. Yes I conceded that the initial investment will be massive for a large scale system, but once it's constructed and working the project should reap dividends for generations... not even counting efficiencies in motors and generators over time. Also the number of weights can vary according to design specs. You can even have several hundred weights attached to a generator to reduce the size of each weight. Of course the addition of parts becomes a multiple for maintenance and efficiency.



I actually started thinking about ways to mechanically store energy after watching someone reset a cuckoo clock in Austria.

Here's an idea: use transmission lines to send the extra energy to some place where it actually is practical to store it using water. Compared to that method and the losses incurred during transmission, I'm skeptical that those losses would ever add up to more than the cost of the system you're proposing, plus it's inherent losses.

 

[wirednuts]

I may be mistaken about the price - it's possible I quoted the price for a small model (e.g. 5 kWh), I don't have my original source to hand any more.

They are an alternative to batteries, in the industrial UPS market - accounting for something like 8% of all new heavy duty (three phase) UPS units.

The flywheels, despite vacuum enclosure and low-loss bearings still do suffer significant frictional losses, and therefore draw a non-negligible idle current and have a very significant 'self discharge' rate (much higher than batteries).

The big benefit is on devices that require short bursts of power, equivalent to discharging the flywheel in 15 minutes or less (3-5 minutes is the normal target market).

Flywheels must be installed in a suitable vault, in case of flywheel failure - which could result in a major explosion. Although batteries also require some care in installation, as hydrogen production is a risk with open lead-acid or NiCd batteries.

Flywheels still require regular maintenance and servicing, even if it is just inspection by an appropriate tech, although the maintenance costs are certainly lower than batteries, which one of the reasons for the popularity of flywheel UPS systems.

Batteries would still be the preferred technology for long-period backups (> 15 minutes) e.g. off-grid use.

sounds like they would be ideal as car "batteries". my dad has built cars as a hobby, and he has been saying a flywheel powered car would be ideal. he wants to drive the wheels directly off the flywheel, saying the acceleration would be like an electric car (instant, full torque at 0rpm). the actual batteries would just be a way to get the flywheel spinning back up to speed when power isnt needed. also, he wanted to directly spin the flywheel back up when braking.... not sure about how he was going to do all that though. i dont think he even knows haha

 

[numeno]

Hi, concerning Flywheels, we used to use them in a few Buses in Germany (more than 6 years ago, probably older) to store energy from braking. The Idea was discarded due to safty problems, a Bus was in an acident and the spinning mass went out of controll.

Bosch-Rexroth developed a hydraulic storage system for Garbage-Trucks,
it saves quite a bit of energy and is silent and actually reduces the noise of these Trucks, and enables them to use smaller motors. From a safty perspektive, probably better than Flywheels (energy disipation less directional, less mass, as long as the cylinder is sufficently mounted and isn't propelled)

Concering JoeKings Idea, I don't understand why you would want to have a low incline, wouldn't that just make the setup larger? Energy is stored over m*g*h so why not use wheights suspended in a shaft? If the shaft is 100m deep it stores as much energy as if you would have a 1km track with 100m incline per km.
For wheights, I think your best option would be water/gravel (from digging the shaft). But the point being you need a lot of mass, and height. In the end its almost a convetional pump storage. (you would be substituting the Water and the pumps throug motors)

I just don't think its cost efficent, use what nature gives us, use pump storage where possible, pressure storage where you find suitable caverns.
Chemical storage could also be an option, but still requires more research.

 

[JoeKing]

numeno,

I chose long gradual incline in order to cut down on maintenance and increase reliability. My problems with the shaft idea is that

1. Probability for failure or catastrophic accident is much higher. While yes energy can be stored and accessed using the full effect of gravity more efficiently, the chances for failure increase as you place the entire mass of the weight on either the track/cabling system or on the braking system.

2. The "Elevator" (I use the term elevator now because no one doubts Shaft) system would require more maintenance. In order to overcome gravity to bring the weights straight up, larger, many more motors would be needed. More harder working motors means more break down means more costs means less efficiency.

3. The Elevator method would require more initial work during installation? The deeper you dig the hotter and harder it is to work. And again the increased heat and pressure would wear the machinery down. My system with a long gradual grade should last years if not decades without much maintenance. And more people can work on the project through the entire process whereas with the elevator less people will be willing/able to work at those depths.

==break==

In my system I seriously envision something spanning many miles upwards of 20-100+ all underground. We could use the same boring machines they used for projects like the chunnel from England to France and the Big Dig done in Boston. If we pick geologically stable sites whats to say these systems couldn't last hundreds of years?

The project(s) would be on a massive scale with massive investments. But simultaneously we would be employing huge numbers of people that should not require too much technical skill.

I really wish I had the math skill set to calculate all of this but I don't... any math wizards out there bored enough to work this system out to see if it's really viable?

And I really like the flywheel idea, maybe it can be incorporated into my system to help regulate power output, or to more efficiently convert the energy from the weights to electricity. But again my concern is upkeep and reliability of flywheels. I'm really adverse to fast moving components in this system. Faster = more wear and tear I want my system to move as slow as feasible.

 

[daRkKon]

what about...

different tracks with metal balls following straight lines, on the bottom on each side (imagine a teeter totter)
there will be a simultaneous spring that stretches across all metal tracks for the metal balls.
the metal balls will be off set to not only keep the balls rolling without any extra added energy it would
work purely off of the springs, weight of the balls and timing of the metal balls in order to keep
moving back and forth such as a teeter totter, when the spring is compressed it can create energy the more
weight that is on the spring forces more joules of work to be stored..

OR imagine it almost like pistons in an engine, when the metal balls roll down the tracks they push down huge
pistons filled with water that forces the water out of the tanks and into something else creating energy as well through pressure.

 

[DrPizza]

I think you overlooked my post. Before investing billions of dollars in your storage system, it would be far more economical to simply use existing transmission lines to send the power to some place where it would be much more feasible to use the natural terrain.

I'll run some numbers for you though:
http://en.wikipedia.org/wiki/Raccoon_Mountain_Pumped-Storage_Plant
http://www.tva.gov/sites/pdf/raccoonmtn.pdf

Or rather, I don't think we really need to run too many numbers - look at it this way - the reservoir is 528 acres. Think about what volume of water they're dealing with. They excavated 10 million cubic yards for the lake. Whatever the mass is that you're pushing up an incline... do you know how much 10 million cubic yards of water weighs? (Actually, I'm not sure what the water capacity of the lake is though.) The density of steel is about 8 times that of water. The density of concrete is less than 3 times that of water. Can your system lift 1 million cubic yards of steel to a height of nearly 1000 feet? (990 feet at Raccoon Mountain.) 1 cubic yard is 13000 pounds. You need to lift a MILLION cubic yards. Do you have any idea how large a hunk of solid steel that is? Or, another easier way to think about it is that you'd need to lift a solid block of steel 1000 feet; the block would be about one eighth the size of the capacity of that lake - 66 acres and 200 feet thick.

I think your tunnel would be woefully inadequate. Not to mention, water is pretty cheap vs. a shitton (a million shit tons) of steel.

Another point to make is that you want a shallower angle, rather than lifting vertically. A shallower angle is going to result in more frictional losses than lifting vertically.