these kinds of developments are essential if we are really serious about increasing renewable energy to 15% of total generating capacity by 2020 (the current target). great work, and nice to see the UK leading rather lagging for once in cutting-edge tech.

Smaller supercapacitor-battery combo may also be a very good solution as Hybrid-PHEV-BEV ESSUs, specially to capture the maximum decelleration-breaking energy and to supply the large short energy burst required for quick accellerations.

It makes you wonder why it's not on the market allready. Didn't an Australian Co. do it combined with a standard sealed Lead Battery? It should work with different battery technologies?

Any recent news on the ESStor ESSU?

This reminds me of altairnano's deal with AES to use their batteries in a way that reduces the need for spare capacity on the grid. What ever became of that deal?

if devices could be cheap enough and have a long enough life span, small businesses could install batteries at communities to make them "off peak". Specific power and energy be damned. Such a business would buy off peak power in bulk at say .05c/kW/hr and sell it to residents at $.10c/kW/h.

Blah blah blah with the supercapatteries - I'm tired of this kind of hype. What is really interesting is UNDERSEA AIRBAGS. It sounds simple enough, but there are a lot of variables that need to be explored - ie. how deep? what kind of material for the bag? What is the energy input to fill the bag vs. energy output upon release at the sea floor as it floats to the surface? What are the potential implications on sea life?

The best way to store renewable energy is to use it to compress natural gas into vehicles during the night...the vehicles then run during the day. Perfect solution, 25% lower CO2 than petrol vehicles, no waste of energy.

Reference:

off shore wind mill

http://www.cnn.com/2008/TECH/science/03/31/windpower/index.html?section=cnn_latest

Excerpt:

At a depth of around 600 meters, Professor Garvey calculates that the bags would be able to store 25 megajoules of energy for every meter cubed. The deep water is essential. "Only in deep water, where the pressure is greatest, are the bags a good economic proposition," Garvey explained.

At 15/lbs sq in for every 10 meters of water depth that is

(600/10)(15) = 900 lbs/sq in air pressure

Professor Garvey wants to put the air compressor in the blades of the wind mill. I can’t see how that can create the 900 lbs pressure needed. I see a high pressure compressor in the central housing connected to the central hub to do that.

I could be wrong here. If falling weights in the wind mill blades solution can be made to work, it is an elegant solution.

Also the undersea storage bags should be piped to an on shore power generator that converts the compressed air to electric power.

This is a peak energy producer. These floating wind mills can meet peak demand and their air storage should be reserved for that purpose.

There is no limit to the size of the air storage that can be implemented.

Another advantage here is that water pressure can reduce the strength and quality of the material needed (plastic) to contain the air pressure both in the bag and the undersea pipeline (until it emerges from the sea to shallow depth).

However, it will take some engineering to keep the air bags secured at the proper depth.

Another advantage is the elimination of the use of copper in the mill and undersea cables. At $4/lb that is a lot of money. Use only concrete, steel, and plastic in the construction.

The compressed air mill is simpler and more reliable than standard wind mill construction. This is very important in the offshore environment because of the difficulty of repair out at sea.

anther off shore wind mill story

http://www.bbc.co.uk/nottingham/content/articles/2007/10/12/wind_turbine_invention_feature.shtml

While the under sea air bags are an interesting alternative towards the very real need of a dispatchable storage device the batteries could hold a double reward. With all the various battery types out there Altairnano’s seem to hold the most promise with the ultra fast charge and discharge rates combined with a long lifespan if only the price was something that was affordable. Once again as with all the other promising hopefuls they are in a chicken or the egg situation. If only someone with deep pockets would buy a few million cells the rest of us could hop on for the ride. For all those types out there who like to legislate change, a simple requirement for the Wind Turbine folks “whose pockets are extremely deep” to store the energy up and provide it at a controlled rate could go along way towards providing power system stability and open the door for even more wind energy than is currently planned due to the limitations of the power system to regulate. And if they happened to use a proven technology as was demonstrated by AES and Altair then the rest of us just might be able to afford a few for our transportation needs. As far as the need to regulate wind farms it can’t be understated as I recently watched a 70 million watt wind farm oscillate between 40mw and 70mw as the wind gusted with an 8 second period and could see the frequency bouncing along with it. Nothing in the power system moves that fast not even hydro.

Powerpro:

Reference:

storage ring

If it can be upscaled, A storage ring may be a better solution to the wind farm problem you saw.

Olde world domestic and small workshop battery chargers were constant current, constant voltage. Add a resistor and the voltage rises with state of charge, a simple improvement. More advanced versions allowed the option of fast charge.
Serious chargers started to become available with more voltage and current control, but it was up to the serviceman to manually match the output for the purpose in mind.
Trickle charge or in a stationary battery a 10* C thrash charge for a while to stir the electrolyte and discourage sulphation, and bridging, a good shake etc . This enabled the recovery of ailing batteries and improved the lifespan of others.
Meanwhile the consumer market had to wait for second generation Nicads , Alkaline alkaline, NiMh and laptop computers with auto sensing ,a"interrogative" smart chargers to have this in common everyday appliances.
There was no user adjustment possible, everything is performed by the "smarts"
The smarts could increasingly monitor or interrogate the type of battery, state of charge, heat, condition and set in place appropriate charging strategy.
In a laptop, similar strategies apply to the discharge side.
When the battery technology changes within the same family this system becomes challenged as there are now effectively as many strategies as manufactures and products.
Along came the idea that building some of the smarts into the battery ie capacitor will be a great help to battery manufacturer optimise their product on both charge and discharge cycles.
Windmill manufacturers are on the ball with smarts built in to some degree.
With this technology it should be possible to maximise the performance and reliability of battery technology.
Apparently the reported benefits(without knowing the extent of conditioning ) are meeting expectation.

The undersea airbag technology is actually closer than we think. Firefighters already use high pressure lifting bags capable of exerting (withstanding) tons of force. There could be banks and banks of these high pressure bags placed in deep-sea locations anchored to the sea floor with massive concrete blocks. There wouldn't need to be very many high-pressure lines leading to the bag assemblies. The pumps & specialized linkages could be located in the mill towers somewhere and be pretty much completely automated.

http://www.savatrade.com/hpliftbags.htm
http://www.google.com/search?hl=en&q=%22rescue%22%22lifting+bags%22

The energy losses will be to the usual friction losses as include the internal friction of the expansion, within wall of the piping. As the pipe expands the stretching will generate heat. At the pressures envisioned, heating of he conducting fluid(air?) will occur. Heat (pumping) losses and friction losses at these pressures need looking at.

John,very good point.
Its also cooler at night so elecrical resistances are lower, cooling requirements lower, and the gas is denser so volumetric efficiency is improved - the compressor looks bigger at night.
Diurnal now thats a nice word.
But while the larger expansion conraction frequency may be dayly, a microimpulse will occour at the frequency of the compressor.
Please read The WORKING fluid, to previous comment.

John,very good point.
Its also cooler at night so elecrical resistances are lower, cooling requirements lower, and the gas is denser so volumetric efficiency is improved - the compressor looks bigger at night.
Diurnal now thats a nice word.
But while the larger expansion conraction frequency may be dayly, a microimpulse will occour at the frequency of the compressor.
Please read The WORKING fluid, to previous comment.

the undersea bag idea is brilliant, one air line going down to the bags would be enough for storing power and releasing it. The compressed air would lose energy as it cools, and it is cold downthere.. ambient air, compressed to 900psi and then cooled to whatever temperature you have downthere. Can anyone calculate the energy losses?.. then again it is cheap storage, essentially free.. kind of the reverse of pumping water up to a reservoir and then releasing it to generate electricity when needed.

Herm, the short answer has to be no.
A feel for the reality may come from the proposed studies. The bag itself, as alluded to in the article and correct observation, is fairly well understood. Pump friction losses with current technologies are quite modelable, and well enough understood by laypersons to sink this idea (at least the extreme proposals) as horribly ineficcient. @200 psi we can pump lead. New ways of doing buisness and new materials not included, either reducing the working pressure or the flow either of wich reduces capacity of the system will be usefull - to workable.
But if efficiency is seen as relative.
Efficiency relative to 0 ( or X ? for the current battery storage methods) can be described as improved over say where a real world efficient system like pumpwater storage 90% +, is unavailable.
Not a magic bullet, possibly a good idea, but again depends on what can be cobbled together with the resources available.
There are similar concepts in wave power generation wich power the compressor directly with movement provided by rocking motion of waves and tidal rise and fall .
The same floating barge could presumably be a patform for wind turbine reducing infrastructure footprint smoothing in still times, carrying shipping hazard lights.
Heck why not go the whole hogg and desalinate then electrolyse a few barrels of H to be picked up by H powered tankers or cargo ships en route?

OOPS! 2,000 psi we can pump lead.

Undersea airbag sounds cheap but may not be that cheap! That is due to the long 600-meter high-pressure corrosion-resistant pipe needed to reach the airbag at that depth, requiring considerable amount of material. The pipe must have large diameter in order to reduce the friction of airflow over such an extended distance. Heat loss from the tubing at that distance of travel and the coldness of the sea depth and the high thermal conductivity of sea water would reduce the efficiency of the CAS (Compressed-Air Storage). Making the airbag thicker for protection agains the Crustaceans snd stingrays (sharp shell and teeth) and more insulation would increase the cost.

Furthermore, anchoring and servicing anything at that depth requires much more than just SCUBA diving gears, adding to the cost, all for merely 900 psi of pressure.

By contrast, a large 900-psi steel tank on the surface serving as the floating base for each off-shore wind turbine, with minimum length of air tubing required, won't be that much more expensive, but much more serviceable. The wind turbine at 100-200 meters above will power an electrical generator, which supplies excess electricity down below to an electric motor powering an air compressor right next to the compressed air tank, which is insulated from heat loss to improve efficiency. This setup is more efficient.

For much higher-capacity of energy storage, the tank can be used to store hydrogen instead, that can store 20 times the energy as when compressed air is used. This would be what required for seasonal energy storage, from a season of high wind but low demand for used in a season with little wind but higher demand.

Reference:

SuperGrid

Fellow GCC contributors let dream big, and go all the way. Instead of batteries and smart grids let’s build the super grid. This grid can store electrical power with zero resistance if the superconductive cables are looped around the continent in a racetrack pattern. Electricity can be fed into this grid in the mid west by wind mills and extracted on the east or west coast without electrical loss. All generation that feeds this grid can stop and the grid will act as a big battery until all the circling electrons are used. The grid can absorb power spikes intermittent power generation and generation failures like a lake can absorb a thunderstorm.

Unlike in the smart grid, no expensive microprocessor controls are needed. Every thing is done by the laws of physics like water in a pipeline and a tank.

This grid uses liquid hydrogen filled pipes to carry massive currents in new iron superconductors at 20k.

Another related dream is super conductive energy storage in cars. A few megawatts can be stored in a coil of 100 miles of iron superconductive wire. Recharge can be done in seconds and liquid hydrogen is used only to cool the superconductor.

When someone discovers a room temperature superconductor the super grid cost will drop from a trillion dollars to a few billon dollars. Then, no hydrogen cooling is required.

Such a discovery will be the equivalent of cold fusion: a game changer.

@ Roger Pham

long 600-meter high-pressure corrosion-resistant pipe needed to reach the airbag at that depth, requiring considerable amount of material

Commercial off the shelf high pressure plastic large diameter pipe is now available.

Making the airbag thicker for protection agains the Crustaceans snd stingrays (sharp shell and teeth) and more insulation would increase the cost.

Commercial fishing net will protect the bags from fish.

Furthermore, anchoring and servicing anything at that depth requires much more than just SCUBA diving gears, adding to the cost, all for merely 900 psi of pressure.

Raise the mostly empty bags to the surface for repair by wench, then after repair, lower it back down.

By contrast, a large 900-psi steel tank on the surface serving as the floating base…..

IF there is no difference in pressure between the air and the water a very thin plastic can be used for the bag.

Only the large pressure difference on the surface requires steel.

The stress points are at the fastening points for the restraining bands keeping the bag under the water because of the large floatation force. This will require some engineering to minimize the structure and the material used.

The simplicity of the Seamus Garvey's design is what makes it elegant. It is really only a large high pressure bicycle pump in each wind mill rotor blade. There is only one moving part: The falling weight that forces air down through a one way valve.

KISS is the governing design principal.

>>"The stress points are at the fastening points for the restraining bands keeping the bag under the water because of the large floatation force. This will require some engineering to minimize the structure and the material used."

Care to elucidate the magnitude of the flotation force, Axil? Water weighs one tonne per cubic meter! Forget about using a thin bag, since for a bag the size of a medium-size room 3m x 5m x 5m would cause flotation force of ~70 tonnes (148,000 lbs). This the weight of a Boeing 737 at takeoff. You will need a heck of a bag to hold that kind of force, and a heck of an anchor at the sea floor to keep it down. I'd choose a steel tank for CAS, doubled as a flotation platform for the wind turbine, over those super sea bag anytime.

>>"Commercial off the shelf high pressure plastic large diameter pipe is now available."

Large-diameter plastic pipe that can withstand 900 psi for 600 meter long? Must be a heck of a pipe, awfully thick plastic...(read: expensive) or carbon-fiber reinforced (read: more expensive). Steel tank is dirt-cheap, even after having a corrosion-proof coating.

It would not be practical to couple the wind turbine directly to the air pump, since the wind varied greatly in speed, hence the available torque on the turbine shaft. At higher wind speed, it would be difficult to harness the higher torque available from the wind turbine shaft without using a mechanical transmission placed between the compressor and the turbine shaft. Otherwise, wind energy will be wasted. By contrast, an electrical generator can directly absorb the higher torque of the wind turbine at higher wind speed, up to a point, of course, hence can get more energy out of a wind turbine without requiring a mechanical transmission requiring more frequent servicing...Just what you don't need in an off-shore device.

The superconducting powerline sounds good, though, as was once featured in Scientific American. Transporting electricity and H2 all in the same line is tough to beat.

LOL.

From basic thermodynamics of ideal gases, for example from this article:

http://www.efcf.com/reports/E14.pdf

it is obvious that overall efficiency of undersea compressed air energy storage/release cycle is less than 40% theoretical limit, and on practice will be less than 30%.

Currently pumps of energy storage lakes are powered by coal and nuclear power plants, in the future they will be powered by renewable energy.
http://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity
An energy storage lake can store way more energy than a flywheel or a battery and reaches efficiencies of 80%.
There are single pump-turbine-generators with a power rating of 1000 MW. Enough power for over 300 Windturbines during storm conditions.

Transmitting electricity over thousands of miles with little losses is easy and available now:
http://www.abb.com/hvdc

Why wait for fancy solutions, why not just do it?

Realist:

Hydro pumping energy storage is severely limited. Moreover, it is freakishly expensive, and makes economical sense only for daily leveling of peak electricity demand.

Any intermittent electricity generating source, like wind or solar, robs the system from highly valuable maneuverable reserves.

To put it simple, you can have 20% renewable electricity mix in the grid for overall 20 cents per KWh, or you can have coal/nuclear baseload with hydro and hydro pumping leveling for overall 7 cents per Kwh.

This is reality of contemporary electricity grid. Make your choice.

And by the way HVDC has a loss of 3% per 1000 km.

In other words:
South Dakota - Chigaco 3% loss.
South Dakota - San Francisco 5% loss.

http://www.abb.com/hvdc

No need for fancy superconductors, just do it with HVDC available now.