No...not indefinitely...unless disconnected from circuit

The main problem is energy density, capacitors have a very low energy density, just a fraction of a battery...

Yes, where have you been?

Have you looked here?

Capacitor - Wikipedia, the free encyclopedia

Note that there are still losses. Nothing is perfect.

I tried to read and understand the article but couldn't. I want to know in simple terms. Is there a device (apart from a battery) that could store electrical energy produced by a solar PV panel, of say 100 watts for 7 hours, making a total of 700 watts, which could be drawn @ 25 watts per hour in a day ?

"

• A standard alkaline AA battery holds about 2.8 amp-hours.
• That means that a AA battery can produce 2.8 amps for an hour at 1.5 volts (about 4.2 watt-hours -- a AA battery can light a 4-watt bulb for a little more than an hour).
• Let's call it 1 volt to make the math easier. To store one AA battery's energy in a capacitor, you would need 3,600 * 2.8 = 10,080 farads to hold it, because an amp-hour is 3,600 amp-seconds.

If it takes something the size of a can of tuna to hold a farad, then 10,080 farads is going to take up a LOT more space than a single AA battery! Obviously, it's impractical to use capacitors to store any significant amount of power unless you do it at a high voltage."

http://electronics.howstuffworks.com/capacitor2.htm

http://www.marathon-power.com/EN/UPSProducts/SupercapacitorUPS/SupercapacitorUPS.html

Your units are incorrect, making the question not meaningful.

Batteries are good for hours to several days of storage, but not generally for long term. Flywheels can also store energy; I'm not sure, but I think for times between those for capacitors and batteries. Pumped water storage can be long term.

Meaningless units.

Lyn & Solareagle said it, not much to add. Although Capacitors loose their charges quicker than batteries, one can convert the electric energy to other forms of energy but every conversion losses are incurred.

Energy at affordable price is the present need of our society. Energy, in the formn of sunlight, wind etc., is available in plenty at some locations, but its transport when converted to electricity to the place of need is the costlier part. Off shore wind power installation is a prime example.

If a ship, call it power-ship, is designed to carry stored electrical energy from such places of abundance (It would be similar to the gigantic crude petroleum bulk carriers), they could roam round the world delivering power. Unfortunately, the weight to storage ratio of a lead acid battery is not conducive for such ships. If a lighter weight mechanism is available, perhaps the energy problem would be permanently solved.

This might be possible one day...Great strides are being made in this field, but still to soon to tell when this will happen....

http://www.technologyreview.com/energy/37519/

The simplest way is like Tornado says, when for example you have a solar farm and the power usage is low, you could use that extra (excess) power to pump water to a higher water storage and when more power is needed it could be released to drive a generator.

Ah...there is a better way.

He could have the power company replace his meter with one of their solar grid tie meters.

Now the power company is storing your electricity free of charge.

If the power company has that option, where the thread owner lives.

Power companies can accept a small increase or decrease in the energy inputs. But if every one wants to send energy to the power companies and they do not have an outlet for it, then the situation would become like a bank only accepting deposits and not able to give advances. They will drown themselves in the surplus cash. So will the power companies with excess power.

The point in question is, whether for the power companies or individuals, how electrical energy could be stored and retrieved at will, with minimal losses, apart from the ubiquitous battery, which through convenient, is expensive in terms of short storage life and also the lower efficiencies of conversion, from electrical to chemical and back.

Members may please suggest possible atrenatives. The only plausible alternative is pumped storage of water, which I have already suggested.

If anyone really knew an answer to your question, they would NOT divulge it here until their patent attorneys had it well tied down. That answer would be worth $trillions!

If all these comments are true, then why does a Cathode Ray Tube (CRT) hold a dangerous amount of power for so long? And also how is it that you can ground the CRT to work on it and have it recharge to dangerous levels on its own? Im wondering if there is a simple explanation and I am just not educated enough to see it.

The CRT doesn't really hold that much power. It doesn't take much power to kill at high voltages.

I believe the recharge phenomenon is due to the fact that when the CRT is charged, the dielectric (glass) becomes electrically polarized, i.e., the positive and negative charges in the molecule become separated. When the CRT is discharged, some charge remains to cancel out the dielectric polarization. After some time the dielectric returns to normal, but this extra charge remains and so the CRT is apparently recharged.

Regards.

But total energy is very small as the self-Capacitance of CRTs is very small.

I have seen only a Russian TV having external capacitor in parallel [quite less than a μF]. Sorry it is some 30 years back and I can't recall the exact value].

Even then the idea behind is Capacitance-storage. Inspite of Super-Capacitor it has a meagre storage which only can be used as Back-up to BIOS cell replacement or like it.

"But total energy is very small as the self-Capacitance of CRTs is very small."

That is precisely what the calculations of post 26 illustrated!

"I have seen only a Russian TV having external capacitor in parallel".

In contrast, I've never seen a TV CRT that did have an external capacitor. Oscilloscope CRTs, yes, but TVs, never.

It is approaching 60 years ago that that first CRT caught me by surprise. I was aware of the danger, but wrongly assumed that letting it sit for a month or more would dissipate the charge. That CRT, and every other TV and computer CRT I've seen since (I've repaired literally hundreds), all had a conductive coating on the inside of the glass envelope, and another coating, usually a form of carbon, on the outside. Those two coatings, separated by the glass, constitute the capacitor. I've never wanted to risk destroying a meter trying to measure that capacitance.

Gadepalli

The Electricity company will have, over time, the ability to change the price that it offers for the subscribers electricty. Nobody can expect a free ride.

Cost of electricity bought from the Electricity Comany will be one price and the cost of electricity bought by the Electricity Company will be different, I do not know whether any company has a significant track record of buying electricty in small amounts but if too much is proferred then the price will move.

Somebody can build an economic model and suggest how it might develop. The other alternative for the Company is to accept , say 100KW of electricity from it's current customers and then shut the doors when they have too much!

Sleepy

Pumped storage is only economical where the geography permits. If the elevation change is adequate and close enough to the power source, then it may be economically viable. Using the tides to store water to run turbines utilizes pumped storage, sometimes. Of course, you gotta have a mountain close by to build a storage pond.

If you design an elevated storage tank to use as energy storage, you will find that the cost of building the tank would make the project uneconomical. Most people live on the plains, so, an elevated storage tank would be required or a piping system to run many miles to a spot that's high enough to do any good. The costs per KWH would be astronomical.

My idea that I have mentioned before on CR4 will eventually come to pass. That is, a global grid of solar power. When the sun isn't shinning here, we get the energy from where it is shining. What makes this feasible is the new found ability to transfer DC current long distances economically. As this system takes hold, motors will gradually be built for DC instead of AC and, therefore, no inverters will be required. The elimination of using heat to make electricity will be one hellava accomplishment. The worldwide solar grid is better than fission or fusion.

The worldwide solar grid will come to reality in about 50 years. That is, if we can stop the radicals from destroying the world. Well, we can't plan on that happening. If it happens, then, so be it. Prevent it if we can, but don't use it in planning for the future, just keep on truckin.

Have some fun today,

PAPADOC

RMFR

PAPADOC

Your comment about using DC instead of AC is very welcome.

In fact, I have been using a 12 V DC pedestal fan directly connected to a 40W Solar PV Panel. In our country, at this part of the year, Sun comes out in intensity by about 8 AM. As long as the sun shines, without any cloud coming in between, my fan works most satisfactorily. It ceases to work from about 1630 hrs. It does not ask for any replacement battery. Except for periodical lubrication of the ball bearings of the pedestal fan, there is practcally no expence whatsoever.

I wish that more and more DC appliances will be used in future.

The only plausible alternative is pumped storage of water, which I have already suggested.

There are many plausible alternatives. Flywheels are not only plausible, but have been proven to work. Obviously, supercapitor banks are plausible, albeit expensive. There are any number of less efficient, but still plausible, mechanical methods (lifting huge solid weights, etc).

For the tiny demand you mentioned, batteries (particularly the lithium chemistries) would work well. Some think that batteries will be the likely grid wide storage solution for renewable energy, because the round trip efficiencies are quite high (about the same as flywheel storage with modern battery chemistries). Following this logic, some see vehicle-to-grid as a means to implement grid storage. If batteries were frozen at current tech (as used in a Nissan Leaf, for example) but dropped in price substantially, then batteries would be the obvious way forward. With current battery prices, the power company would need to give me a large incentive for shortening the life of the batteries in my electric car. I'd rather see storage in fixed batteries, rather than in those optimized for transportation needs. (There are tradeoffs in power vs energy density that affect who a battery can best be used.)

However, for practicality (for people connected to the grid), it is far cheaper to sell power into the grid during peak times and buy it back at a low rate at night. Everyone benefits, and you are doing your part to clean up the grid. In many locations in the US (and this could be much different where you are) this is one of the best methods for making solar panels pay off economically.

If ships the size of crude oil tankers end up as transportable energy storage units it is quite possible that super conductors could be used. The infrastructure necessary to maintain appropriate termperature may work and be more affordable at that size.

Cheers

I know how superconductors are useful in transporting electric energy; how are they used in storing electric energy?

There was a pumped water storage system made, using high efficiency pumps and generators, etc. The final result was approximately 50% efficient and they were proud of that result. The water supply and dam were already built, so there was no additional cost for that part of the system or it would not have been built, as not economically efficient. Reducing the cost of high efficiency, low pollution power generation from wood combustion at the level of the individual home user is the approach I am working on. It is certainly true that it is difficult to share research results with the public if he research costs are expected to be reimbursed by being charged to development of a marketable product. There is a factor of approximately 5X to 10X needed in reduction of costs of current systems, and additional factors in the reduction of pollution and increase of range of power output. Wood as an auxiliary heat source is now being used by a significant number of people in the "99%" here in the USA, but not as auxiliary power. Advances in reducing costs of high temperature low corrosion metals and insulation performance will be needed. Can these technical details be discussed in an open forum?

Using wood as an auxillary source of power is tantamount to use of Sun. The time scale of convesrion of Solar energy to wood, perhaps is the shortest. While the efficiency of Photosynthesis that ultimately results in formation of wood is said to be about 7 percent, and in this reaction there is also release of Oxygen, which is a bonus. In case of PV power generation, there is no bonus except, clean generation of power, that too at about 14% (Even more now) .

Hence wood as a fuel is good.

As electricity is an energy carrier, it makes more sense to store energy in a primary form and convert it when needed for carrying to where it is needed.

Pumped water storage isn't all that efficient, and it doesn't work in flat or dry locations. Compressed air is good for storing energy ( US patent number 5,832,728), but there is a trick to it. Most systems compress the air but cool the compressor with air and expand the air but often have to reheat the expanding air. Efficiency is about 15%. Do not waste the heat. Cool the compressor by making steam and use the steam to reheat the air. Ambient temperature air and water goes in and ambient temperature air and distilled (drinkable) water comes out, so it is thermodynamically efficient. At 300C, one can store about 1 kwhr in volume of about 1 cubic foot. Insulated air tanks last a long time and do not use scarce or toxic materials, as batteries do.

One option not yet discussed is using electricity to split hydrogen from water and later recombine the hydrogen and oxygen, either in a fuel cell or in an internal combustion engine. This would work in the plains, and will be necessary before the transportation economy can shift from fossile to hydrogen based fuels.

A research update is available:

http://www.nrel.gov/hydrogen/proj_wind_hydrogen.html

It's definitely an option as a stone between the fossil fuels and a cleaner alternative. It'll be interesting to see this stage of transition unfold.

Another option of course is pursuing things like carbon capture technology - it doesn't solve the problem of limitations on fossil fuel reserves, but at least it'll minimise their impact while reserves last!

I think the developments in electrical engineering and alternative fuel development at the moment are fascinating, and it's such a great time to be involved in the industry. I found an article about where engineering's headed in the future which sums it up quite nicely here: http://www.topengineeringjobs.com/article/5591/future-developments-in-electrical-engineering/. It's not overly technical but it makes some very interesting points so it's worth a read.

Ultracapacitors have been the holy grail of the electric vehicle world for decades. The link in Solar Eagle's post is a good example. A device with the high energy density of a battery and the high power flow and lifespan of a capacitor is ideal for mobile applications.

A good resource in this subject is www.ultracapacitors.org. They have descriptions and links for installed systems now in use, news on current research and a forum for discussion.

All these comments seem very good, however, if one had to rig up something today for electricity enough to power an office, (lights, computer,phone, etc.) what would be available for electrical storage at a reasonable price that is also not overly complicated? Are the Edison batteries a viable option? Before WW2 Edison batteries powered trucks that ran on electricity alone.(Dykes Automobile and Gasoline Encyclopedia, 1938)

my understanding is that:

Edison batteries for that size application are now only being manufactured in China and they ain't cheap. they seem last forever though. so i am sure there is a breakeven point somewhere.

better yet here are some links on how to build your own Edison batteries.

Edison cells fell out of favor primarily because they lacked one critical ability: the ability to wear out. A 100-year service life at 100% efficiency meant you didn't have to buy a whole new set of batteries every four years.

One major advantage they have is that you can make them yourself. They are really pretty simple internally, while modern lead-acid batteries are not.

the level of understanding and experimentation seems to be rising on home builts

http://www.youtube.com/watch?v=K84PywMwjZg

http://www.noonco.com/edison/

or you can buy the Chinese variety here:

http://www.beutilityfree.com/Electric/Ni-Fe

Electrical energy can be stored in an inductance as (1/2)*L*I² similarly as we do in capacitance provided we will be able to connect the two ends of the inductance by a mechanism(a Bridge Thyristors or SCRs) before current or inductive energy dissipated as spark. Then current in the close looped inductance will gradually decreases as time lapse due to the resistance of the coil which makes the losses as I²*R . After some time whole stored energy will be decreased to zero.

But we can also keep the energy as long as we want provided we are able to make coil resistance as zero. This can be done by cooling the copper conductor to 4.2 K (minus 269.0 C, minus 452.1 F) temperature at that stage the copper conductor becomes as superconductor whose resistance will be zero (please refer in internet on " Superconductor") and electrical energy remains forever and we can tap this energy for some other purposes as improving the power system transient stability and other purposes.

I did my M.S. Thesis on "The application of super conducting Coil with Thyristor interface for transient stability enhancement" in 1984.

If a fault occurs near any load bus or weak generator bus, a weak generator in power system tries to go out of synchronism as input power(fuel) cannot be brought to zero immediately so generator will accelerate and store input energy as kinetic energy and try to go out of synchronism unless some corrective action is taken once fault is cleared. In that instance generator is heavily loaded (extracted power by supper conductor coil located at weak generator bus) with super conducting coil to make it to decelerate again when it decelerate superconducting coil that time pump it energy in the system. This kind of corrective action repeated with the help of Thysitors control till that generator comes into synchronous speed and works as normal.

Now lot of research is going on different alloys to make superconductor at high temperature or normal temperature. Once researchers succeed super conductor at normal temperature then there will be a revolutionary change will take place in power transmission, electrical machines and even power generation and utilization as similarly happened after invention of fiber optic in 1940(Taking the idea of light dose not travel in strait line but needs media that may not be necessary a straight line as proposed at the end of 1800 century in England) similarly invention of transistor (semiconductor) around 1950 that time un imaginary things we are seeing and doing today.

Regards.

I think that CAPACITOR really STOREs for long time [If leakage is minimized] but INDUCTORs store INSTANTNEOUSLY; as soon as the the source removed it will die out like:

Dear Hajee

The wave form you have shown does not match to energy dissipated in air if the close path of inductance is opened. It does not oscillate the wave form you have shown. Can you put it in mathematical form for the wave? Wave form does not have any information on the y-axis.

Now I have attached the diagram that shows how the super conductor inductance is charge to store energy via Thyristor(SCR) bridge interface. The following is the brief description of the Thyristor bridge what I explained in my post dated 05/15/2012:

1. Charging of inductance OR storing of the energy: Thyristors Th-1 & Th-4 will conduct for positive half cycle of AC voltage upon gating & Th-2 & Th-3 for negative half cycle.

2. No charging OR further no storing of energy: Further storage energy is not required then either Th-2 & Th-4 OR Th-1 & Th-3 will conduct to make the close path required by current in Inductance.

3. Discharging the stored energy in Inductance: The function of the Thyristors will be same as indicated in #1 but the gating to conduct the Thyristors will be delayed by 180 degrees.

I hope this will clear to understand what i said in my earlier post.

Thank you to all