Flywheels store electricity - cheap enough

[Enthalpy]

Hello everybody!

 

Flywheels have been used for long to store energy. Doing it at the scale of the power grid or even a fraction of it isn't common, and they want to:

http://www.popularme...ry/4337758.html

but their wheel of carbon fibre is (too) expensive, and I suggest steel instead - very strong steel.

 

Maraging steel is too expensive, but a disk of dirt-cheap S960MC could rotate at 412m/s+20%.

Better yet: spring steel. Cheap silicon makes it martensitic (the aim of quenching) at any thickness. At 1200MPa only, a cylinder can rotate at 555m/s and a tore at 492m/s, storing much energy.

 

Because spring steel stays martensitic it can't be machined in a softer austenitic condition and quenched thereafter.

The Ovako 477solves it with a very long annealing that precipitates much carbon, leaving a softer matrix for machining; then a short annealing dissolves the carbon to harden.

Alternately, I imagine a turning machine could be installed at the forge, and machine the flywheel right after forging, when it's still hot - present tools do like hot chips.

 

Marc Schaefer, aka Enthalpy

 

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This subject was posted there beginning Wed Nov 25, 2009 , but it's messy:

http://saposjoint.ne...php?f=66&t=1974

here it shall be clearer and shorter. More to come.

 

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The procurement cost of flywheels makes them very seducing, even when compared to power plants consuming fossil energy, provided my estimate is sensible.

 

A 1300MW peak power plant costs about 2€/W or 2.6G€ (gas less, nuclear more), but only produces a mean 1000MW over a day, because demand peaks for <4h, and drops down to 700MW for <4h. Storing only 300MW * 4h energy lets build a 1000MW plant instead of 1300MW, or rather 10 plants instead of 13, and also run the plants near full power where efficiency improves.

 

As an example, I take small flywheels of 80t, or D=2.4m L=2.25m cylinders of spring steel, still movable on roads: usual truck size, more tyres. A pair costs 240k€ and, at 555m/s, stores 12GJ. One common alternator-motor and electronics for 850kW *4h shall cost 200k€. Four hydrodynamic bearings are estimated at 50k€. A concrete pit houses the unit for 30k€ and contains the wheels if the bearings fail - excellent idea though not mine. Transport and installation are to cost 60k€. Summing to 570k€, the flywheel storage costs 0.7€/W - far less than the production plant.

 

Few units smooth the consumption of a factory, a hospital... At a big power plant, 300MW fluctuation would need 350 of the small flywheel units; on a 10m*5m pattern they take only 50m*150m, less than the plant itself, and the pits' surface can have other uses. For such a big storage, the flywheels would be forged, turned and ground on the site, so they're bigger, and more wheels couple with one alternator-motor: cheaper.

 

Earth's rotation creates a tiny gyroscopic moment allowing any flywheel orientation. A vertical axis would simplify the bearings, but a horizontal axis makes seism-proof design easier and is expandable.

 

In times when peak demand exceeds the available supply (Japan now), the flywheels limit blackouts.

Full operation immediately after a seism would make the flywheels a praised emergency supply.

For railways and underground, a bigger alternator-motor would provide more power over a shorter time - classical use.

 

Marc Schaefer, aka Enthalpy

 

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The Iwate-Miyagi earthquake reached 4.36g (single component).

http://en.wikipedia....ble_earthquakes

No huge and expensive dampers to mitigate the tremor: I prefer oversized bearings (here only a symbolic representation) and a stiff construction, where the flywheel, the motor-alternator, and all bearings move together.

 

 

A pit (not my idea, but a good one) is to hold the shrapnel in bad cases; it also anchors well the aggregate in the soil.

 

Marc Schaefer, aka Enthalpy

 

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Edited August 21, 2011 by Enthalpy

[Enthalpy]

Plain or hydrodynamic bearings would dissipate much. Computed after Dubbel, Taschenbuch für den Maschinenbau, chapter Gleitlagerungen, pages G97 and G187.

 

Two horizontal bearings have L=0.3m, D=0.3m+0.5mm, oil is 9mPa*s thin. Having given the 80t flywheel the form of a slower D=5m tore helps, but the bearings dissipate 30kW together, or in 10h 18% of the stored energy.

 

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In June 2011, as Japan lacks peak capacity for electricity production, a first storage plant using batteries has been decided, to receive excess electricity at night and release it during day peak. Flywheels would be several times cheaper than the battery gross prices I found.

 

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This hydrostatic bearing with vertical axis improves losses. The 80t toroid has OD=5m ID=3.8m h=1.2m, whose slow 392m/s = 174rd/s = 27,8Hz also reduce losses.

 

 

The axial bearing is at the centreline and the piston and cylinder have no sealing ring. 700b on tiny D=120mm (not drawn to scale!) lift the wheel; a nonreturn valve allows for vertical overload during a seism and gentle landing on an emergency bearing (not represented).

 

If the piston is centred by the adjusted lower roll bearing, 30µm radius clearance over 40mm hydraulic fitting, combined with 55mPa*s oil, lose 3kW in the leak and 3kW in the torque, or over 10h 3.5% of the stored energy.

 

On the right figure, a smaller clearance permits lighter oil, which reduces losses. For that:

A surrounding chamber equalizes the pressure on the inner cylinder so it deforms little;

The hydrostatic bearing can follow the shaft's lateral movements. 12 vertical parallel rods of d=12mm L=300mm pull it and allow 50µm to the sides with some 100N force;

Sensors (maybe capacitive) can detect the relative position and (maybe piezoelectric) lateral actuators centre the cylinder around the axle.

Now 10µm radius clearance over 5mm fitting and 39mPa*s oil lose 800W in the leak and 800W in the torque, or over 10h 0.9% of the stored energy.

 

I prefer this hydrostatic bearing to the usable magnetic bearing I described elsewhere.

 

Marc Schaefer, aka Enthalpy

 

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Roll bearings must be oversized to live long, but losses of usual parts are already good . Here I don't apply the standard life expectancy model that varies like load power 10/3, but use instead the "wear limit load" given by SKF and compute losses with their applet:

http://www.skf.com/s...d=&action=Calc5

 

One NNCF 5048 CV per side lifts 390kN each. Maximum 1000rpm impose a wheel of D=8.4m, undesired, and no fair play. With an oil viscosity of 6.6mm²/s, loss is 27N*m or 2.8kW per bearing, the pair summing over 10h 3.3% of the stored energy.

 

Better: several smaller bearings at each shaft end accept more rmp and reduce the loss torque. This wins the 5m wheel back at identical power loss. It needs added hardware to align the bearings and share the load, like spherical caps working similarly to bogies.

 

And now, running the shaft on a big roller shall reduce losses further - it can even be a cascade, as on the right sketch.

Advantages: passive and strong; easy to assemble and service; a shaft line can couple many wheels with one motor-alternator.

 

 

How much does this dissipate? From contact mechanics computations, we can keep the shaft's diametre from roll bearings

http://en.wikipedia....h_parallel_axes

so the shaft is around 6.4 times larger than the usual rolls. The contact line is around sqrt(6.3) or 2.5 times wider, and the equivalent length of rolling resistance shall do the same at most. Then, as the big roller is supported by its smaller shaft, this loss occurs once, instead of twice at a roll bearing. The main improvement comes from the radius increased 6.4 times over the rolls. The combination cuts loss by 5.

This shall bring rolling losses over 10h under 1% of the stored energy.

 

Roll bearings need a long contact line, so the big roller would be longer than a roll bearing, and the shaft accordingly narrower - the shaft's diameter has margin and this reduces loss. Elastic bending at the shaft may become a limit, but the roller can be inclined and grinded slightly non-cylindrical.

 

Marc Schaefer, aka Enthalpy

 

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If these flywheels rotate bare in air, aerodynamic loss is huge and prohibitive. The common answer is vacuum, but feel the big chamber too expensive and unreliable, so here's the solution.

 

Turbulent flow lets force and torque increase as the square of speed differences or even faster. By adding rotating separators in the flow, like the disks in the sketch below, I divide the flow in cells where speed differences are smaller, and this reduces the loss torque.

 

 

At the wheel's outer face, concentric cylinders ("can close" at the sketch) can split the speed gap into smaller steps. A cylinder and a disks pair can't be one single part, for access inside; maybe the cylinders can be sewn at the disks.

 

Here's a loss estimate with my flow calmer. For a wheel of OD=5m ID=3.8m L=1.11m that rotates at 28Hz = 1680/min = 177rd/s, or 440m/s at the external radius, I add per side 70 disks spaced by 5mm air. That's many disks, but composite material are cheap. Now, speed drop across the 5mm is 6.3m/s only. Air viscosity of 15mm²/s and 18.6µPa*s gives a Reynolds number Re = 2100, meaning a laminar flow. Shear constraint is then 23mPa at R=2.5m; combine with 19.6m2 and an integral coefficient of 0.5 to get a torque of 0.57N*m only. Tripling it for the other side and for the cylindrical face, the power loss is 305W, or over 10h 0.2% of the stored energy, nice. 70*5mm are in fact an exaggeration.

 

Some bearings must hold the disks. They can run slowly between adjacent disks. In a flywheel, they would differ from the main bearings.

 

The disks and cylinders at the flow calmer rotate fast and must resist the same centrifugal acceleration as the flywheel itself. Fibre composites, especially graphite fibres, are even better than steel at fast rotation and can produce the big thin parts rather easily. The performance gap over steel permits to use fabric or crossed unidirectional layers laid down and overlapped. A stronger product would result from filament winding, which can even leave a hole at the centre but lose no strength. A sandwich, or a non-flat shape, can increase the parts' stiffness. And aerodynamic skis, with some elasticity, might hold the distance between the calmer's layers.

 

I consider holding the cylinders by the disks. A circumferential rope or thin rod made of present-day fibres holds easily the centrifugal acceleration that is difficult for steel; such a rope could pass many times through the ends of a disk and a cylinder alternately, a bit like if sewing. It can be opened within a reasonable time. When producing the disks and cylinders, handles can be made for the rope, and filament winding maintains full strength there.

 

Anyway, I don't imagine a reliable prediction of the collective stability of the flow calmer, which should be experimented early in the development.

 

The same losses plague many rotating objects beyond flywheels, like centrifugal turbines, compressors, pumps, alternators, motors... These disks and cylinders at intermediate speed look useful there as well.

 

Marc Schaefer, aka Enthalpy

Edited August 22, 2011 by Enthalpy

[Enthalpy]

Graphite filament winding is simple but it may stay expensive just because it's space technology, so here are alternative materials for the flow calmer.

 

Chromium and electroless nickel plating can be very hard. Provided some compositions aren't brittle, they could make the disks and the cylinders including stiffening corrugations.

 

Cold-worked austenitic steel is the material I trust best. 5m wide sheets shall be hammered from an existing width, maybe 2.5m. Hammers, as long as the sheet (for instance 5m), make an affordable machine:

 

 

Reducing steel from 1mm thickness and 1500MPa to 0.5mm and 2000MPa+ on 5m*3mm surface may need some 20kJ, or at 5m/s, 2 hammers of 800kg each, or a tapered section of just 0.1m*0.3m - the 0.3m shall maintain a straight impact area, which is seriously hardened.

 

One impact per second makes a sheet in 20min; a second pass, crossed, can make the sheet more uniform. 20min at +200°C improve both the yield strength and the toughness. And I'd make a sandwich with two sheets over some balsa or foam, sure.

 

Marc Schaefer, aka Enthalpy

Edited August 25, 2011 by Enthalpy

[Enthalpy]

The thin sheets of hard material than make the flow calmer can't make strong weld seams, that's why I wanted to obtain big single-part sheets, but they can be soldered together - even stainless steel if nickel-plated - or glued. So sheets of commercially available size fit the task, including as skins for a sandwich, or as stiffeners.

[studiot]

Have you considered fluid flywheels?

[Enthalpy]

I did, and came to nothing interesting - which is no argument against other people trying.

 

Kinetic energy demands a high speed, which seemingly a rotation attains best. Then the possible kinetic energy is a question of surviving the centrifugal force. A quickly rotating liquid would need a strong container, and is worse than rotating the container alone.

 

I also checked if the unwanted moving air around a solid wheel could provide a dynamic bearing, but it seems worse than a standard bearing of small diameter hence small torque. Similar conclusions with liquid bearings.

 

Well, it's all a matter of cost. if a contained can be cheap (immobile concrete walls in the soil?) and the fluid doesn't loose its speed, fine.

[Enthalpy]

Toroids are to spin quickly to store energy, but shall please stay dynamically stable. That is, if some locations move slightly outwards and others inwards, the centrifugal force tends to exaggerate this, but the stiffness must suffice to prevent a runaway. The stability conditions must be known, but not having my books here, I've recomputed it.

The toroids here a mean radius R and a rectangular section of height h and radial thickness e. Just as in Euler's theory, I fourierize the arbitrary deformation and observe that higher harmonics are less critical as they need more elastic energy, so I keep only the second one since the first is meaningless: U*sin(2*alpha), where alpha is the geometric angle.

For this small arbitrary amplitude U, I evaluate and compare the elastic and centrifugal energies.

The stiffness would increase a bit if e<<h. The bending is per length unit R*d(alpha). The kinetic energy is a difference with U=0. Then I introduce the longitudinal sound velocity and get a simple expression.



Flexural sound speed gives the same result. From
EI*k⁴ = µ*w²
where I is the bending moment, k*2pi*R makes two phase turns, µ is the mass per length unit, and w is 2pi*F, I obtain that the toroid must rotate slower than the lowest bending mode propagates - quite similar to the dynamic stability of shafts.

For steel, 5140m/s and 400m/s +20% margin demand e/R>0,081.

Marc Schaefer, aka Enthalpy

[Enthalpy]

Transporting a flywheel limits its size. Forging and turning it in situ needs huge tools that would serve for few parts. Alternately, we could transport steel coils and wind the band in situ as bigger toroids. A assembled shape can define the toroid's inner diameter and be removed after winding.

Below few mm, the band is light enough that the glue between the turns (hot glue, epoxy...) holds the external turn of the spiral. The toroid holds the centrifugal force by themselves; a few tilted bands hold the much smaller toroid's weight only. They cross the azimutal bands many times, for instance where these end, and are nearly radial, overlapping an other around the shaft.



Cold work can harden some steels (duplex, austenitic stainless, and more) to 2000MPa and keep them resilient. This permits 419m/s with 20% speed margin but rolling mills seem to limit the bands' width to h=0.7m; then e=1m and R=9m (the size of Itaipú's alternators, just faster) store 3h*2.5MW, that is, a 1000MW power plant could use 120 flywheels to absorb 300MW at night and restore them during peak consumption.

Heat treatment achieves only 1500MPa hence 364m/s for cheap resilient alloys, but hot rolling permits h=1.5m and possibly more. Then e=2m and R=24m store 3h*22MW in 3550t, so just 14 flywheels smoothen out the 1000MW consumption.

Can we increase h (and then e)? Maybe if the bands make helices rather than a spiral, but the ends' behaviour isn't clear; leading the bands there towards the shaft may improve. I prefer some narrower bands so the edges at successive turns don't overlap, here sketched with one single narrower width and without the tilted bands.



Now a 3550t toroid doesn't take R=24m any more, but just R=6m h=5.2m e=2.3m. Other proportions may enable a horizontal shaft.

One shaft can also carry several toroids with separate tilted bands; I doubt one can interleave the tilted bands.

Magnetic levitation may save the tilted bands altogether.

Marc Schaefer, aka Enthalpy

[Enthalpy]

A toroid of material density rho used at tensile stress sigma attains the azimutal speed U

and stores in its volume V the kinetic energy


A disk leads to the same conclusions and even the same figures as a toroid within few per-cents:

• Unless the speed or the mass are constrained, only the strength and the cost per volume unit count.
• Steel is as strong as carbon fibre and much cheaper at identical volume.
• Ballast (concrete, water...) added to the strong material stores the same energy at a lower speed.
• Running water, balls, rolls in a racetrack stores the energy defined again by the track's strength and volume.

A steady water track could be easier than a rotating toroid and might even use the ground's strength, but I haven't found a convincing setup.

[Enthalpy]

Lifting a weight stores energy as well; a wind turbine at deep sea offers 3km amplitude. Peak 5MWe average to 2MW; providing the 2MW over one calm day needs 173GJ, or 5900t that descend 3km, still feasible.



The cable that lifts the weight needs half the mass of a flywheel, but this storage needs also a weight and a float (D=8m h=116m for 5900t only). Low speed, scaling, sea operations don't help neither. Wherever possible, a flywheel is better.

Marc Schaefer, aka Enthalpy

[Enthalpy]

A pressure vessel accumulates energy as well.

Atmospheric air is compressed in the vessel or expanded out. Exchangers usefully keep the temperature constant in the vessel and at the many-steps compression and expansion. A liquid that enters and exits the vessel, topped there by the pressured gas, is easier but would squander the capacity.

Used between 100 and 200bar, the vessel's volume V resisting the pressure P stores and restitutes nearly 0.5*V at mean 0.75*P; the ideal isothermal process converts Log(150bar/1bar)=5 times these 0.375*PV from and to work, or 1.88*PV. A spherical vessel using its wall material at biaxial stress s needs a wall volume v such sv=1.5*PV, so again the work relates with the amount of strong material:

W=1.25*s*v

 

This is slightly better than the cable of the falling weight and 2.5* better than the flywheel, but the flywheel is far more efficient to convert from and to electricity, and the pressure vessel needs difficult heat exchangers, so a flywheel is better.

Though, I still like prof. Seamus Garvey's underwater bags. As compared with a pressure vessel, they replace the costly walls by free Ocean pressure, and can find colder seawater to cool the compressed air and warmer seawater to warm the expanding air, improving the efficiency.

Marc Schaefer, aka Enthalpy

[Enthalpy]

This discussion too is presently censored, at least from my location.

Inaccessible through Google, through ScienceForums' index, by direct address pasting.

Only through ScienceForums' search engine, maybe because the Internet address differs then.

 

This is seriously tiresome. Even in Europe, speech is said to be free and guaranteed by Law.

I'm fed up that every discussion about an economically interesting invention, or about a topic that doesn't fit a government's policy, gets censored.

[imatfaal]

Enthalpy - I think this is your browser/setup, your network admin, or your imagination. I do not believe this page is being censored or blocked anywhere in Europe.

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Note - I can see this thread in all views when logged on via a German and a Dutch proxy.

[Strange]

Visible in the UK as well. Indexed on the appropriate pages, etc.

And searching for a random sentence from the first post bring this thread up as the 3rd result in Google.

It does look like most comments by posters other then Enthalpy are hidden though.

[Enthalpy]

Thanks for trying!

 

This is definitely not my imagination. As you can expect, I had already tried four different navigators, fully deactivated my firewall and my antivirus - and I have no other network nor admin. The censored pageS (as this has already happened several times with identical pattern) are accessible through Science Forum's search engine, possibly because the Internet address differs a bit then. And after I make the problem public, the page becomes accessible again through its normal address (before you both tried?), as presently from my location.

 

My only explanation presently is censorship. Where and by who remains a bit unclear.

 

By the way, I have already observed other forms of censorship, in a newspaper's blogs. When trying to post under my own name something not pleasant for everyone, the blog's server shut down immediately. This repeated at every attempt and within seconds. But under a different name, exactly the same text passed through. I've observed and documented that already several times. That one is an automatic censorship, the other not necessarily.

[michel123456]

Visible in the UK as well. Indexed on the appropriate pages, etc.

And searching for a random sentence from the first post bring this thread up as the 3rd result in Google.

It does look like most comments by posters other then Enthalpy are hidden though.

From my place, the thread title brings the 5th result in Google.

[Spyman]

While individual sites certainly can block specific persons, I hardly think there is a worldwide censorship against Enthalpy.

 

Googling the phrase: "Flywheels store electricity" gives me these three links on top:

(Oh, and I live in Northern Europe if that makes any difference.)

 

1. https://www.physicsforums.com/threads/flywheels-store-electricity.517812/

2. http://www.scienceforums.net/topic/59338-flywheels-store-electricity-cheap-enough/

3. http://lofi.forum.physorg.com/Flywheels-Store-Electricity_29531.html

 

They are all threads made by Enthalpy, but on three different science forums.

(The middle link is to this thread.)

Edited April 17, 2015 by Spyman

[Sensei]

Here, searching Google for "Flywheels store electricity"

gives couple links to Wikipedia English,

http://en.wikipedia.org/wiki/Flywheel_energy_storage(what a surprise)

then 30+ links,

and Enthalpy ScienceForums.net thread (this one) is at 34 position (4th page)..

 

after extending keyword to "Flywheels store electricity - cheap enough"

it's at 5th position (1st page).

 

I would like to note that position in search engine is related to how many somebody from Internet linked that website.

If there are many references (either dynamic = cheating search engine, or real one, by real interested people), then obviously it'll go up in rank.

Edited April 18, 2015 by Sensei

[imatfaal]

Here, searching Google for "Flywheels store electricity"

gives couple links to Wikipedia English,

http://en.wikipedia.org/wiki/Flywheel_energy_storage(what a surprise)

then 30+ links,

and Enthalpy ScienceForums.net thread (this one) is at 34 position (4th page)..

 

after extending keyword to "Flywheels store electricity - cheap enough"

it's at 5th position (1st page).

 

I would like to note that position in search engine is related to how many somebody from Internet linked that website.

If there are many references (either dynamic = cheating search engine, or real one, by real interested people), then obviously it'll go up in rank.

 

I think maybe your google-fu needs updating - if a poster mentions googling for "this keyword or phrase" I would guess it means they have included the quotation marks. This changes google's parameters - putting words in quotation marks makes google prefer results with those words in that exact order. Googling on "Flywheels store electricity" with the quotes does return the results as Spyman noted.

 

If you get a result from a simple toolbar search - you can look to right hand side of the screen and there will be a settings cog icon; this accesses advance search and you can both quickly interpret how google is parsing your enquiry and construct more "insightful" enquiries

[Danijel Gorupec]

Today I read a short article about record-breaking maglev train... got me thinking if another kind of flywheel energy storage is possible:

 

- a very large torus tube made of steel, well supported by concrete... say torus diameter 1000 - 2000 meters, tube diameter 2.5 - 4 meters (somewhat similar to a particle accelerator)

- partial vacuum air or maybe hydrogen (just above air pressure) filled

- passive maglev rails on the outer inner side of the torus ('inductrack')

- ring-shaped (ringular, lol) heavyweight 'train' inside running at speeds of >150m/s... overall train mass, say, 10 - 50 million kg. The 'train' does not have to be a rigid ring.

 

Any sense in this?

[pzkpfw]

How about using the LHC for that once it's obsolete?

 

I figure (not very seriously), fill it with water. Use turbines to get the water moving around the ring. Let the water drive the turbines to get the energy back out. i.e. the water is the flywheel. There'd be plenty of friction, but it'd be simple.

[Enthalpy]

Well, I suggest that you put figures on your proposal. How much energy, which mass and speed, how strong a centrifugal force, and so on.

 

For steel flywheels, I could convince myself that the stored energy is significant at the scale of the grid, that losses at conversion and over half a day or few days are excellent, and that we can afford them.

For the underwater bags, conversion efficiency must not be brilliant but storage is, and the cost per (big) stored energy unit looks good.

[...] thinking if another kind of flywheel energy storage is possible:

 

- a very large torus tube made of steel, well supported by concrete... say torus diameter 1000 - 2000 meters, tube diameter 2.5 - 4 meters (somewhat similar to a particle accelerator)

- partial vacuum air or maybe hydrogen (just above air pressure) filled

- passive maglev rails on the outer inner side of the torus ('inductrack')

- ring-shaped (ringular, lol) heavyweight 'train' inside running at speeds of >150m/s... overall train mass, say, 10 - 50 million kg. The 'train' does not have to be a rigid ring.

 

Whether spokes (or a disk) hold a rotating mass (including just themselves), or the rotating mass is a ring, OR the circling mass is held by a track, you need to hold against the centrifugal force, and for some reason all the good shapes are nearly identical in requiring (nearly) s*V=E where s is the material's working stress, V its volume, E the stored energy.

 

If running a mass in a track, then the track must resist the force, but it's simpler for the mobile mass much flatter than one radius. Then you can search for track materials less costly at identical s*V than steel is: concrete, the ground... I only intuit it would be difficult but have no hard argument against, so just try!

 

If storing 300MW*3h, you even out the demand at a 1300MW power plant, hence can build a 1000MW one instead, or build fewer ones, saving >300M€, so a D=2km installation can be affordable. A metal tube, not necessarily, if it must resist vacuum or the centrifugal force.

 

Imagine your 10,000t well spread over the D=2km ring. At 150m/s they store 113GJ=10MW*3h (less than we need for one wind turbine) but push 225MN over 6283m circumference, or 36kN/m (only 3.6t/m). If nothing helps the tube, it must resist by its tensile strength in azimutal (track) direction to 35.8MN, and this over costly 6.3km - and the 36kN/m need material too. Same s*V as a flywheel.

 

But if free soil replaces paid steel, fine! It just needs credible ideas.

[Enthalpy]

Tesla Motors has just announced a lithium battery called Powerwall, derived from their technology for electric cars, and meant to even out the home production of renewable electricity.
http://www.teslamotors.com/powerwall

As Mankind needs newewables obviously and quickly, and storage is a condition, I'm happy that efficient people decide to solve it. Thank you.

The excellent surprise is the 92% round-trip efficiency. From other battery chemistry, I had 70% in mind, which would have been an obstacle. As a comparison, I expect the flywheels to lose energy too quickly at home sizes.

Batteries are known to sustain a limited number of cycles, so the extensible 10 years warranty addresses this worry. The size, 130 cm x 86 cm x 18 cm meant for wall mount, is also a nice improvement by lithium chemistry.

Still costly: 3,500 usd for 10kWh. But compare with a 1300MW fossil fuel power plant that produces 700MW during the night and 1000MW as a mean: storing 300,000kW during the night's worst 4h and restoring them during the day's worst 4h needs 1.2*10⁶kWh or 120,000 Powerwalls costing 420M usd. This already equals the purchase of a 1,300MW plant instead of a 1,000MW one.

Yes, a power plant lasts longer than 10 or 20 years, and 8% losses are a drawback (here my flywheels should be better), but the cost of lithium batteries also drops with the size *10⁵.

Does Mankind have enough lithium for batteries at world scale? I didn't check. Time to further improve the relations with the compañero Evo... More deposits will be found if the demand increases. One Japanese university tries to replace lithium with the abundant sodium.

[CasualKilla]

I have always found it strange than humanity hasn't really found a good way to store electricity. Chemical batteries, how primitive. Now we are proposing equally primitive rotating masses to do the job (no offence). Is there corporate interest to suppress energy storage technologies? The automotive industry does come to mind, good energy storage would make electric cars very viable.

 

This does seem like a very cheap solution, but don't we also need to consider that we need generators attached to the wheels, which too have losses, and then we need circuitry to produce a fixed frequency and voltage power from what I assume would be a varying frequency voltage and current produced by the generators depending on the flywheel speed. Chemical cells still have the advantage that they don't need a middleman to convert to electrical energy.

[John Cuthber]

I have always found it strange than humanity hasn't really found a good way to store electricity.

You might not have, the rest of us know how to store electricity

http://en.wikipedia.org/wiki/Capacitor

 

But there's not much demand to store electricity since you can generally store the energy from which the electrical power is derived..