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Can you approach the energy density by charging up capacitors at a useful voltage?

How about high mass flywheels motor generator sets?

LarryC

It all comes down to $, in the end. All the battery/kinetic, etc. solutions have the problem of weight. For a vehicle; ship, plane or car, weight = money.
The Europositron battery, if it can be made commercially, still stores only 10% of the energy per pound of gasoline*.

Flywheel problem ditto. No known material is able to withstand the huge hoop stresses needed, [ say 2 million psi ] to achieve comparable storage capacity kWh/lb. And a flywheel containing the energy of 10 gallons of gas in a crash would probably take out 2 blocks if it burst!

* The person who really unlocks a practical way of using Aluminum/hydrogen/WHY for vehicles will be made:
Europositron, 2065 btu/lb = 0.6kWh/lb
Gas, 23000 btu/lb = 6.7kWh/lb
Al.[to Al(OH)3] 22000 btu/lb = 6.4kWh/lb
H2 [to H2O] 60000 btu/lb = 17.5kWh/lb

We ain't there yet!

Alan

LarryC, after my hasty last post, I did a few calcs on 'flywheel' energy storage, with some interesting and positively 'hat-eating' results.

Let's look at a plain steel-disc flywheel.
For ease of calculation, let diameter be 24" and thickness 1".
Weight 131 lb. Mean diameter, [c. of gyration, all forces assumed to act at ], = 17".
Let rpm = 24000.

Mean V; 24000/60[secs] x 2pi x 17"/12 = 3560ft/sec.

Kinetic energy; 131x3560x3560/64.4[2g] = 25780149ft.lb. giving 582.6 kWh

In a plain disc flywheel, stress is at maximum at the center, reducing toward the rim. But a flywheel can be contoured progressively, [thinning rimward], to show equal hoop and radial stresses at every point while rotating. This contouring also increases the energy stored per pound of weight. The above flywheel, same approx weight and centre of gyration diameter, but contoured, would have hoop and radial stress of about 50 tons/sq. inch throughout.
Alloy steels can be made to achieve the above as working stresses, but not in large 'ruling sections'*, [ and here I am thinking of big ship-mounted flywheels transporting hydro-power].
[* This is for practical heat-treatment reasons ].
Large wheels could, however, be laminated from thin plates and / or by the use of composite materials such as carbon fibre. There are technical manufacturing difficulties here, not least the need for perfect balance and getting big wheels to run and stay true for a long useful life.

OK, let's build a machine round our shiny new 24" contoured flywheel. If the shaft, casing etc. weigh 70 lb. = 201 lb total, [ and I'm assuming here we go gaga with someone else's money and build a 'vaccuum casing' and special low-friction bearings to reduce our drag losses]. Our machine performs 582/201 = 2.9kWh/lb.
Only 43% that of gasoline but more than 3 times Europositron's claims. And this is today's technology for the investors to risk their capital on, no 'ifs' or 'buts'. Our machine, properly built and maintained, could do much better than 3000 cycles, and with no pollution. However, note that our losses will be time dependant- eventually friction will dissipate all the stored energy, so rapid transport and use is necessary for a viable scheme.

Now, although 'shaft' or 'electrical power' is often expressed or compared with 'heat units', they are not the same! Heat energy in a gas is chaotic, the motion of the molecules is in all directions. The primary purpose of a heat-engine, [ turbine, piston engine, etc.], is to [ what I like to call ] "tidy up the energy and arrange it in straight lines". In doing so a heat-engine incurs unavoidable thermodynamic losses- [ Google; Carnot's Cycle ]. 75% loss in a gasoline engine, 60% in a diesel. But flywheel energy is already 'straightened', [ as is electrical energy, BTW ]. Gasoline may have 2.3 times the kWh of our flywheel per pound, but put it through a piston engine to get shaft power and it only gives 60% as much!

So, the Big Ship sails on the Allyally-oo on the 1st day of September, and on board are a bunch of flywheels humming expectantly with stored energy. On arrival in NY or Liverpool, we couple and run generators to extract the power and run it to the Grid.
One design possibility might be to have a motor-generator permanently in-line with each flywheel, simplifying layout and charge/discharge to the operation of a simple clutch once speeds are synchronised. Electrical output will vary with the gradual loss of speed on discharge of course, but this is not a problem with solid-state devices creating the sinusoidal power output to the grid.

Larry, this shows some promise!

Now, where's my Fedora sandwich?

Alan

So all we need is lossless conversion into and out of the flywheels, lossless storage, and suitable transmission facilities at both ends. Patent office here I come!!!

Magnetic bearings for the rotating assemblies. Vacuum housings to remove windage losses. Superconductor motor generators. Plus the ship doesn't rock and roll so much.

LarryC

Brought this thread back out of the mothballs.

It occurred to me that a larger stationary version of this would be the bee's knees to assist wind power generation with shifting winds and semi-abrupt changes in wind speeds. No need to be portable, could be placed on the DC bus of the inverter to provide a means of limiting the power surges into the inverter, scalable, etc.

Placed at substations and point of use, these could be "charged up" at night to help with base loading.

My question is how would you couple power into and out of the flywheel? Obviously you do not want to use brushes and sliprings or communtators. Can magnets handle the forces needed? How fast can the system speed up and slow down in response to abrupt step changes in power flow?

This a great thread guys, we need more of these here!.
One other thing that is being sold here, quite prolifically so I'm told, is the solar water heater, it is a unit that is totally self-contained and is installed on your roof.
It works on UV light not actually heat from the sun, so even on a cloudly sort of day, you can expect to get a reasonable supply of hot water.
Now considering that Hot water is a large degree of people's electricity bills, would it make sense that solar panels and this thing would make a house a LOT more energy efficient?.

As far as flywheels are concerned for storage of energy in a fixed location, the precision balancing, bearings and construction costs might favor simpler technologies.

Consider a very simple machine, attached to a wind turbine/group of turbines/farm. Simplistically a rope hauls up a weight so arranged to turn an alternator shaft when it is allowed to fall. Such a low-tech device would literally last forever and cost less to build and maintain than a complex flywheel arrangement.
Let us again go mad with someone else's money. Bore a vertical shaft alongside/under the mill, say 40 feet in diameter and 600 feet deep. Let’s say a 2000 ton concrete ‘piston’ 40 feet long were lifted up the shaft 500 feet during times of excess production over demand. The potential is 2240 million ft lb. of energy or c. 850 kW hours.

Consider the production of hydrogen, by electrolysis, at a wind-farm site.
On May 2 1800, Mr W Nicholson and Mr A Carlisle happened to put a drop of water in contact with two wires from an electric battery. They noticed small bubbles of gas forming at the tips of the wires, which were not in contact. They then put the wires into a glass of water and found that gas was evolved from both wires. The gasses were oxygen at the anode and hydrogen at the cathode. The gasses were then mixed and exploded, when the product was found to be water. Two volumes of hydrogen were formed to each volume of oxygen. By Avogados theorum, [1811], the explosion of 3 volumes of ‘electrolytic gas’ produces 2 volumes of steam.
BTW, anyone thinking of copying the above experiment should be aware of the dangers of ‘electrolytic’ or ‘detonating gas’ - it is powerfully explosive.

The hydrogen could be used directly by fuel cells to produce electricity at times of lower wind speeds or peak demands. The electrolysis itself is theoretically 80-94% efficient with modern developments, so overall efficiencies producing electrical power would be lower, perhaps 40-60%. Oxygen production, as a by-product, might be viable to add to the overall earnings from the plant.

Alan

Indeed, hot water is the second greatest energy consumer in the home, after space heating and cooling (food refrigeration is third). Solar hot water is much less expensive than photovoltaics, and is the most cost-effective application of renewable energy there is (other than clotheslines).

If you live in a climate with no hard freezes, the technology is simple and relatively inexpensive. If freezes are frequent or of long duration, system design must include glycol loops, circulator pumps, and heat exchangers, which adds to the complexity and drives up the cost, but even cold climate systems have a favorable payback time compared with electricity.

The most cost effective application of solar hot water is for swimming pools, because the delta T involved is very small and the amount of water to be heated is huge. A typical pool system consists of cheap black plastic tubes and a single circulator pump.

My thought of the stationary flywheel storage system is more for smoothing of the changing output of a large wind generation facility. Since most generators have to be spinning in order to supply power during any lulls, the more unstable any one generation source is, the more "cushion" one needs to absorb any transients.

I believe that Germany has an electric grid stability problem because a significant portion of their generation capacity is wind powered. When a weather front moves through the area, the ouput of the wind driven generation fluctuates significantly. These fluctuations can wreak havoc, especially under extreme load conditions.

Here in the 'colonies', our interconnect grid is so huge that variations in one geographical area can usually be offset by generation outside the affected area. Plus, at this time, wind is not a major generation source.

I agree that H2 generation is a load that doesn't really care about short term variations too much. Along the same lines, most pumped storage plans probably don't care either. However if wind is going to become a significant player in the grid connected generation, I believe that it would be VERY helpful to have it contribute to the stability of the grid, not unsettle it.

I have solar hot water and I live in an area with hard freezes(Maine). The system has been installed since the early 90s and has been running ever since with zero maintenance. 2 -3 by 8 panels, a soft tank, differential controller, bronze pump, heat exchanger and some piping. Its a drain back system and works great. Its pretty much useless in late november, december and january as the sun is pretty low in the sky
but come febuary I can get water as high as 160 degrees f.