Alternatives to storing electric energy

[mozirry]

How else can we store electric energy, other than wasteful and bulky Li and Ni based batteries?

I'm not a battery, but I can retain a static electric charge quite easily.

 

[bobsmith1492]

Capacitors are what you would think of when you say static charge; all a capacitor is is a pair of huge, flat surfaces that store electric charge (rolled up into a nice package). However, they cannot store nearly as much energy for their weight and volume as you can in chemical storage (batteries).

Chemical storage is, as far as I know, the best way; most everything is stored that way.

Batteries are based on chemical reactions and directly produce electricity. Indirectly, hydrogen, oil products, fissile material (nuclear) and any heat source can all be used to store electric energy; it just has to be converted back from its current energy form to a useful form.

Anything besides chemical/nuclear storage and capacitors, anyone? I reckon compressed air could store energy to drive a turbine to spin a generator. A flywheel or pendulum could store kinetic energy to convert back to electric, but friction and size make those pretty useless.

 

[Talcite]

I remember watching a documentary on how hydrogen fuel cells would replace batteries, allow us to use renewable energy sources, and change the political landscape.

 

[mozirry]

Do hydrogen cells store electric energy? I thought that was just a kind of fuel like gasoline

 

[CTho9305]

I'm not a battery, but I can retain a static electric charge quite easily.

You're actually storing very very little energy, and very poorly (any humidity and you lose it all to the air). Capacitors can be used for electricity storage, but currently the energy density still isn't as high as batteries.

 

[Mark R]

This is quite a large electrical energy storage project: Text

You can also store compressed air in large underground caverns, and use it to turn a turbine when rquired (in practice this is very inefficient - the the compressed air is used to run a gas turbine with the compressor segment removed).

You can also get flywheels. Text - these were often used as UPS systems before electronic systems were advanced enough to make good inverters.

 

[BrownTown]

I think he was more talking about cars which kinda narrows it down since you can't build pumped storage into a car. In terms of large scale energy storage pumped hydro blows everything else away in terms of capacity and price. However for a car you are pretty much stuck with batteries or capacitors (which right now are alot WORSE than batteries).

 

[f95toli]

Originally posted by: mozirry
Do hydrogen cells store electric energy? I thought that was just a kind of fuel like gasoline

They store energy which can be easily converted into "electric energy"; in the same way as batteries store chemical energy which can be used to drive a current.
It is so easy to generate electricity from a fuel cell (once you have the fuel) that for all practical purposes you can think of it as a battery; there is a good reason why you soon will be able to buy laptops and mobile phones which use fuel cells instead of conventional batteries.

 

[Matthias99]

Anything besides chemical/nuclear storage and capacitors, anyone? I reckon compressed air could store energy to drive a turbine to spin a generator. A flywheel or pendulum could store kinetic energy to convert back to electric, but friction and size make those pretty useless.

Compressed air (or other gases) works alright, but the power density really isn't that great when you take into account that the tanks have to be very strong (and heavy) to contain high pressures safely. And while compressed air (or nitrogen/CO2) isn't flammable, failure of a high-pressure gas tank (as in a car crash) can still be quite dangerous.

Some people have worked on using magnetically-suspended flywheels (in near-vacuum) to store potentially large amounts of energy in a small space. This (mostly) eliminates friction during storage, but getting the energy in and out with high efficiency can be an issue. Also, if you want to move it (or, rather, accelerate it) while it is spinning, gyroscopic effects can be a problem. Also, to have a good power density/volume, you either need the material to be very dense (read: heavy), or it has to spin really fast (which means super-strong and super-expensive materials, and a mechanical failure could be catastrophic at high RPM), or both.

Hydrogen fuel cells seem like a more practical solution in the near term. You get out a constant voltage, and the power density is extremely good (since hydrogen can be compressed to very high densities). Problems include cost and the fact that hydrogen is extremely flammable. Large-scale distribution can be a problem, and if you are installing large fuel cells in cars, they'll likely need to be very sturdily constructed/armored so that they don't rupture easily in a crash (similar to what is done for the fuel tanks in NASCAR vehicles).

 

[f95toli]

Originally posted by: Matthias99

Some people have worked on using magnetically-suspended flywheels (in near-vacuum) to store potentially large amounts of energy in a small space. This (mostly) eliminates friction during storage, but getting the energy in and out with high efficiency can be an issue.

Flywheels with superconducting bearings in a good vacuum is a surprisingly efficient method to store energy and the "energy density" is very high (higher than in chemical batteries). I have been to a few conferences where whole sections have been dedicated to this idea, as far as I understand the main application would be powering satellites.

 

[dkozloski]

I read a paper that stated the case that for input/output efficiency it's hard to beat a wound up rubber band. Busses have been operated in Germany for years that use a huge flywheel under the floor for energy storage. The bus stops at a recharge station and uses electrical energy to spin up the flywheel so you could make the claim you are storing electricity with at least the same veracity as the guy with batteries.

 

[Mark R]

Originally posted by: dkozloski
I read a paper that stated that for input/output efficiency it's hard to beat a wound up rubber band. Busses have been operated in Germany for years that use a huge flywheel under the floor for energy storage. The bus stops at a recharge station and uses electrical energy to spin up the flywheel so you could make the claim you are storing electricity with at least the same veracity as the guy with batteries.

Would this not have, erm, issues with going round corners?

 

[Matthias99]

Originally posted by: Mark R

Originally posted by: dkozloski
I read a paper that stated that for input/output efficiency it's hard to beat a wound up rubber band. Busses have been operated in Germany for years that use a huge flywheel under the floor for energy storage. The bus stops at a recharge station and uses electrical energy to spin up the flywheel so you could make the claim you are storing electricity with at least the same veracity as the guy with batteries.

Would this not have, erm, issues with going round corners?

Most buses weigh a *lot*. Yeah, the flywheel adds rotational inertia (like a gyroscope), but it's probably not that big compared to the mass of the bus to begin with. It also depends on how much range you need; if it only has enough charge to go, say, 10 or 20 miles, that cuts down on how much power you need. Plus you lose the weight of the fuel tanks and gas/diesel, so overall the effective inertia of the vehicle might not change much (and could potentially be lower if the range is limited.)

 

[BrownTown]

But, in order to go very far the rotational inertia would have to be very since even to get the bus to move 1 mm you have to overcome the buses inertia with the inertia in the flywheel. However cornering I don't think is too much of a problem since you are ratating along the axis of the flywheel, so you aren't really forcing it to change direction, just speed up or slow down a tiny amount on each turn. However, if they flywheel was up-down and you tried to turn than i can see serious problems.

 

[bobsmith1492]

Originally posted by: BrownTown
But, in order to go very far the rotational inertia would have to be very since even to get the bus to move 1 mm you have to overcome the buses inertia with the inertia in the flywheel. However cornering I don't think is too much of a problem since you are ratating along the axis of the flywheel, so you aren't really forcing it to change direction, just speed up or slow down a tiny amount on each turn. However, if they flywheel was up-down and you tried to turn than i can see serious problems.

Some guys at work told me about a friend who put a massive flywheel in his car; he spun it up at night and drove it to work and back during the day. I can't remember what they said the effects on the car's handling were...

Even if the flywheel's axis was perpindicular to the plane of travel, what if you went up a hill? Would that just bottom out your suspension in the front while forcing the wheel to move? Could it make the back of your car lift off the ground to keep the car level?

 

[BrownTown]

I'll need to look into the numbers on these, the fact that a flywheel could power a car for a decent amount of time seems kinda amazing to me given the speeds and mass required to store that much energy in a flywheel. In my experience a flywheel is used to ride-through of short term losses of power, smoothing out inconsistant power sources etc, kinda like the mechanical version of a capacitor. The fact that a flywheel could be a good source of energy and not jsut a good source of power in news to me.

 

[f95toli]

Originally posted by: Mark R

Originally posted by: dkozloski
I read a paper that stated that for input/output efficiency it's hard to beat a wound up rubber band. Busses have been operated in Germany for years that use a huge flywheel under the floor for energy storage. The bus stops at a recharge station and uses electrical energy to spin up the flywheel so you could make the claim you are storing electricity with at least the same veracity as the guy with batteries.

Would this not have, erm, issues with going round corners?

Why not just use two flywheels rotating in the same plane but in opposite directions?

 

[dkozloski]

Originally posted by: f95toli

Originally posted by: Mark R

Originally posted by: dkozloski
I read a paper that stated that for input/output efficiency it's hard to beat a wound up rubber band. Busses have been operated in Germany for years that use a huge flywheel under the floor for energy storage. The bus stops at a recharge station and uses electrical energy to spin up the flywheel so you could make the claim you are storing electricity with at least the same veracity as the guy with batteries.

Would this not have, erm, issues with going round corners?

Why not just use two flywheels rotating in the same plane but in opposite directions?

The flywheels were flat under the floor of the bus and drove a device that was similar to a starter generator in a turbine engine. The device could be switched to be used as a motor to spin up the flywheel or converted to a generator to supply power for a prime mover to power the bus. There was a small aux generator for use if the bus got stuck in traffic and the flywheel slowed to much. It seems to me these are used in Germany. The routes and the bus are designed so that the bus can get all the way around the route easily.

 

[Matthias99]

Originally posted by: dkozloski

Originally posted by: f95toli

Originally posted by: Mark R

Originally posted by: dkozloski
I read a paper that stated that for input/output efficiency it's hard to beat a wound up rubber band. Busses have been operated in Germany for years that use a huge flywheel under the floor for energy storage. The bus stops at a recharge station and uses electrical energy to spin up the flywheel so you could make the claim you are storing electricity with at least the same veracity as the guy with batteries.

Would this not have, erm, issues with going round corners?

Why not just use two flywheels rotating in the same plane but in opposite directions?

The flywheels were flat under the floor of the bus and drove a device that was similar to a starter generator in a turbine engine. The device could be switched to be used as a motor to spin up the flywheel or converted to a generator to supply power for a prime mover to power the bus. There was a small aux generator for use if the bus got stuck in traffic and the flywheel slowed to much. It seems to me these are used in Germany. The routes and the bus are designed so that the bus can get all the way around the route easily.

These seem to have been built by a company named 'CCM'. Some general info on the specs of the buses (and some other vehicles they built): http://www.ccm.nl/pdf/FLW-Tech-160204.pdf

The buses had a flywheel that could output 200kW (~150HP), and had an energy capcity of 2kWH (so it can output ~150HP for about 40 seconds if fully wound up, assuming I'm reading this right.) Their newer systems have about double the capacity and 50% more power output.

 

[BrownTown]

OK, so I was right, there only really can source power on the seconds to minutes range? Seems pretty darn useless for any real world applications.

 

[Matthias99]

Originally posted by: BrownTown
OK, so I was right, there only really can source power on the seconds to minutes range? Seems pretty darn useless for any real world applications.

Well, the ones in those buses, at least. Obviously you'd need to scale it up or have more of them if you wanted to use them as the sole power source for a vehicle.

Likely that would be impractical due to either size/weight or cost right now, much like making a car powered fully by chemical batteries. In brief searching I couldn't find exact numbers on the dimensions/weight of these things; it may be competitive with Li-Ion batteries in terms of power density for all I know. But being able to output 150HP, even for a short period, is pretty impressive in terms of power output.

 

[Mark R]

Originally posted by: BrownTown
OK, so I was right, there only really can source power on the seconds to minutes range? Seems pretty darn useless for any real world applications.

It depends what you want the power storage for.

For transport applications, the use of such a short term store are limited.

However, for power grid management, these stores can be useful. The vast majority of power quality problems are of short duration (transient voltage sags due to sudden short term loads - e.g. large motor start-up, or a 10s disconnect due to a breaker tripping, then auto resetting). The problem is once power to one area has been lost, it could cause cascading failures, or require a managed restart. Short term power stores (e.g. flywheels, but occasionally battery, or experimentally superconducting magnetic storage) are starting to be deployed by power companies in problem areas.

 

[dkozloski]

Critical RADAR sets at Anderson AFB in Guam were protected by a "No Break" power storage systems that consisted of spinning flywheels weighing many tons that stored enough energy to keep things going until standby generators could be started to keep service unintterupted in the event of a power failure.

 

[Born2bwire]

Potatoes. Lots and lots of potatoes.

 

[QuantumPion]

Here are the following ways you can store energy:
gravity (waterfall, pendulum)
chemical bonds (gasoline)
nuclear binding energy (fission)
electric fields (capacitors, batteries)
magnetic fields (inductors, conductive fluid)
kinetic (flywheel, high pressure gas)

I think that's everything.