Another way to store electricity

Capt'n Midnight

You take a gas turbine powerstation.
You compress air in an abandoned mine off peak using the generator.
To extract the energy you bypass the air intake compressor , you still burn fuel but you can get up three times as much energy out with the same size turbine.

Air can be stored for many months at about 75bar.

http://www.doc.ic.ac.uk/~mpj01/ise2grp/energystorage_report/node7.html

In a normal gas turbine, as much as two thirds of the energy produced by the power turbine is consumed by the compressor. This means that a 300 MW plant actually produces 100 MW of net output while 200 MW is consumed by the compressor. If compression is carried out at a different time to when power generation is needed, that is, by CAES, the peak power which the gas turbine can generate is increased by this amount. Hence additional power production capacity is not required.

The turbine work that conventionally would drive the compressor in a combustion turbine is directed to the generator, increasing the output. In fact the power output from each turbine shaft will be nearly three times the capacity of a comparable simple cycle combustion turbine.
...

CAES systems can be used on very large scales. Unlike other systems considered large-scale, CAES is ready to be used with entire power plants. Apart from the hydro-pump, no other storage method has a storage capacity as high as CAES. Typical capacities for a CAES system are around 50-300 MW. The storage period is also the longest due to the fact that its losses are very small. A CAES system can be used to store energy for more than a year.

Fast start-up is also an advantage of CAES. A CAES plant can provide a start-up time of about 9 minutes for an emergency start, and about 12 minutes under normal conditions. By comparison, conventional combustion turbine peaking plants typically require 20 to 30 minutes for a normal start-up.

Possibly you could use a large underwater bladder too if a suitable mine could not be found. Pressure would have to be lower 10m depth per bar. But you'd have to go a long way off Erris head to get water deeper than 200m. Then again you could use wind power to supply compressed air instead of electricity, saving a lot of copper.

using compressed air as a large UPS
http://powerelectronics.com/mag/power_leveraging_thermal_compressed/

http://www.sandia.gov/media/NewsRel/NR2001/norton.htm

“During electric generation, some natural gas will be burned to super-expand the compressed air,” Bauer says. “When at its full production stage of 2,700 megawatts, it will produce the same amount of emissions as a 600-megawatt gas-powered combustion turbine power plant.”

air

How efficient is it though? IE for every unit of power that you use for compressing the air how much do you get back? There doesnt seem to be any info on that in those articles.
The other disadvantage is that it relies on exploiting naturally occuring geological features to circumvent huge civils costs - a feature it shares with pumped storage.
Still, it would compliment pumped storage nicely and diversity in a generation network is generally going to be a positive feature.

democrates

And how about using wave energy to compress the air in that undersea bladder? Fully mechanical with no electrical supply required...
Also wind power could similarly pump water up to a hydro dam through a syphon.
Or visa versa with the wind-sea, wave-hydro.

Surely cheaper to build and run storage solutions primarily mechanically than using pricey generators and electric pumps? Anyone aware of any such experiments?

Edit: And while I'm at it solar or geothermal producing steam for a steam engine driving a pump. Steam is mental.
Edit2: Or alternatively to an undersea bladder an abandoned oil field. Would need to be near the shore, though there are oilfields on land too, maybe that's no different to using abandoned mines.
Edit3: And what about lifting a weight at a massive mechanichal advantage, say I stick a big fan up out the back and over a few hours it has to mechanically lift a sack of rocks up the side of the house to the roof apex, they start coming down driving a generator depending on power demand and meanwhile the turbines energy is switched to rock-sack 2, or, the weights and gennie could be integrated into the fan tower, a lead acid battery could be part of the weight if it's still required, or the fan tower could store compressed air so we could take batteries out of the equation, and do I hear cheap street lighting not to mention roundabouts with those war of the worlds lamp clusters...

silverharp

http://news.bbc.co.uk/2/hi/europe/2281011.stm

What about this, an powered car

Foxwood

silverharp wrote:

http://news.bbc.co.uk/2/hi/europe/2281011.stm

What about this, an powered car

"Wednesday, 25 September, 2002, 14:43 GMT 15:43"

It sounds interesting, but the report is almost 4 years old. Does anyone know who killed the compressed air car?

silverharp

Foxwood wrote:

"Wednesday, 25 September, 2002, 14:43 GMT 15:43"

It sounds interesting, but the report is almost 4 years old. Does anyone know who killed the compressed air car?

I dont know much more about it, wikipedia have an entry about it, and the company is still going, if you think about it though you just can't launch it on the market and expect it to be a sucess, you would need the local authorities to buy into it, and provide facilities etc. maybe when fuel is 2euro ltr these will be seen as cool.
there should be a market for lightweight city cars, the compressed air idea seems great, top up at night when usage is low etc.

Sarsfield

Foxwood wrote:

"Wednesday, 25 September, 2002, 14:43 GMT 15:43"

It sounds interesting, but the report is almost 4 years old. Does anyone know who killed the compressed air car?

http://www.theaircar.com/

Reports of it's death may be exaggerated.

Here's a few other options besides compressed air & pumped storage

http://www.mpoweruk.com/alternatives.htm

Capt'n Midnight

democrates wrote:

Edit: And while I'm at it solar or geothermal producing steam for a steam engine driving a pump. Steam is mental.

With Steam Turbines you can convert 40-50% of the thermal energy. The lower figure is routine, the upper is with special materials for very high temperatures. The waste heat can be used too if you have a CHP system. Steam turbines may be cheaper than photovoltic solar panels - perhaps a you could have a combined power station that uses renewable/fossil fuel at night and bad weather and sunlight in good weather to produce the steam. A bit like the way many older power stations were converted to gas.

Flywheels and trickle charging of UPS batteries takes about 1% of average load in addition to conversion ineffiencies.

Electric cars like the prius have very poor regernerative braking efficiencies, because it's mech to elec to chem to chem to elec to mech and you are loosing at each stage. For buses and trucks a pair of large nitrogen tank and turnbine is probably a better store of braking energy.

Capt'n Midnight

http://socialwork.arts.unsw.edu.au/tsw/D92.RE.Ch.7.Storing.html

Compressed air storage.

Storage of energy in the form of compressed air is claimed to be much more energy efficient than storage as hydrogen. Sorensen (2000, p. 568,552) gives two figures; 40-50%, and 65%. Hansen (2004) says 75% of the energy used to compress the air is retrievable, without the use of added heat. (He says that if gas is used to add heat the energy return on the total air plus gas input energy can be 85%.)

yes the major problem is finding a big hole in the ground. Maybe we and the UK can use depleted gas fields, and possibly a few % more gas could be extracted this way too.

CO2 can be liquified under pressure and the Norweigeans are pumping it into old wells offshore as a carbon sink - maybe they could have tanks to allow some of it to exand back for when they need more power. We will all be interconnected someway so efficiencies in one part of Europe will benefit us all,

http://www.mpoweruk.com/alternatives.htm.

A 1 foot diameter flywheel, one foot in length, weighing 23 pounds spinning at 100,000 rpm will store 3 kWh of energy. However at this rotational speed the surface speed at the rim of the flywheel will be 3570 mph. or 4.8 times the speed of sound and the centrifugal force on particles at the rim is equivalent to 1.7 million G. The tensile strength of material used for the flywheel rim must be over 500,000 psi to stop the rotor from flying apart.

23 pounds - 10Kg
3KWh =3000w * 3600s = 10,800,000joules
= 9.8 * 10 * 100 * 1,102 (mgh)
Or in other words a 10Kg Flywheel from an ultracentrigue has the same energy (kenetic) as 110 tonnes of water with a 10m head (potential). This is why flywheels are fequently proposed as a way of powering cars of the future. The main problem is if there is an accident the flywheel will go through any thing in it's path.

For street lights a 100Kg weight lifted 10m would store 9,800 joules, which would keep a 150watt light going for just over a minute. this is why hydro needs so tall dams and a lot of water

Takeshi_Kovacs

Flywheels are a great way to store energy, but i dunno how good they would be for powering cars. I can barely imagine the destruction one would cause if ever there was an accident, and the flywheel with tens of kilowatts of power, came loose. You would need a very heavy and sturdy enclosure to contain it.

Also wouldn't the large gyroscopic forces mess with the handling of the car,. Take for example, if you have a external harddrive, pick it up and twist and move it around in your hand. You will feel the significant force as you turn the hardrive around due to the platter inside spinning at high rpm. I think it is called precession, (which keeps bicycle wheels in motion,upright..)

air

You're right Takeshi, put three of them orthogonal to one another and the car would be resistant to acceleration in any direction
The handheld video cameras that you see cameramen with at soccer matches etc use Kenyon gyros for just this purpose. They're battery powered heavy weights spinning inside enclosures.

Takeshi_Kovacs

Interesting stuff on using gyros to stabilise tv cameras.. no wonder they are so expensive!!
I was just thinking, if you had two flywheels instead of one, and mounted them so that they were in line with each other, and had them rotating in opposite directions, then this would cancel out the gyro effects...?

Capt'n Midnight

The first car had a horizontal flywheel because they were worried about gyroscopic effects.

Anyway you would put the flywheel on gimbols and use motor/generator to transfer the power. might help smooth out some of the potholes too

The problems with energy storage are that high energy density storage is dangerous if the energy is released by accident/incident but low energy density means you need huge things to store it in.

air

Takeshi, I dont think it would, I think the induced stability is more to do with the axis of rotation than the direction of rotation.
Captn - Mounting the flywheel on gimbals might make it a lot more difficult to transfer power to it, unless it was electrically driven or its degree of freedom was quite restricted.

Capt'n Midnight

air wrote:

Captn - Mounting the flywheel on gimbals might make it a lot more difficult to transfer power to it, unless it was electrically driven or its degree of freedom was quite restricted.

Capt'n Midnight wrote:

Anyway you would put the flywheel on gimbols and use motor/generator to transfer the power. might help smooth out some of the potholes too .

There are chemical systems where you can replace the electrolyte so you'd have a battery,not a fuel cell and two tanks , or one tank with flexable barrier /bladder to store the fresh and spent liquid. Unlike a petrol pump you'd have a return pipe to collect the spent electrolyte to refresh it. No idea if how you measure how used it is - in a normal car battery you can use density as a measure. The energny density is a lot lower than petrol.

democrates

Folks, you might find this thread interesting.