Every storage device has it's niche application. Capacitors are well suited for high discharge rates and where weight is an issue, at a very high cost. There are better suited technologies available for renewables, depending on the storage required.

Have a look at this site. They have nice graphs on where the different technologies fits into: http://www.electricitystorage.org/technology/storage_technologies/technology_comparison

It's not for free and it'll have high self-discharge.

It's true, it's expensive, the energy density still is not that of a battery (a battery is somehow a kinda capacitor), and it will self-discharge.

But it's not new: super capacitors are used to store regerative braking energy in some trams and metro vehicles.

A capacitor is able to release the energy quite quickly, if needed.

Other means are mechanical rotational systems (wheels and similar things), superconductive coils (the more or less cold temperature comes at a price!), batteries, gas in pressure (such as CO2 deep down into soil).

What's your application?

I anticipate that designing it depends on several factors: how quick you want to let the energy go in and out of it, because this is related to the dielectric material and the technology you adopt; temperature conditions; current and voltage ratings.

Hi Khalid, its an interesting question. I too though about the same idea. Consider the equation C=e0.er.A/d, of course the capacitance of a parallel plate capacitor. It depends upon the "er" value and higher and higher the dielectric values higher would be the C.

A super capacitor of small size, e.g. 2.7v 10F would provide 135J of energy. Check out the following link,

http://www.alibaba.com/product-gs/516316547/ultra_capacitor_2_7v_10f_farad.html

A 3V 1000mAh battery would provide ~ 10kJ

So, 0.135kJ is one-hundredth of the battery power, but if you look at the same size then it would I suppose be 3 times the value ~ 0.4 kJ and kind of okay. But if you look at the same weight then this figure would becomes even greater.

Which means that we may be we are very close in creating a storage device using Capacitor (in future). But again there is leakage issues, with time the energy would get lost. So, everything depends upon the design.

It would be worth to check out design principles of super capacitors. I hope this will provide more insights into the designs.

Every storage device has it's niche application. Capacitors are well suited for high discharge rates and where weight is an issue, at a very high cost. There are better suited technologies available for renewables, depending on the storage required.

Have a look at this site. They have nice graphs on where the different technologies fits into: http://www.electricitystorage.org/technology/storage_technologies/technology_comparison

Thanks for all the answers

There is a environmental issues in making those type of huge battery and even though it is very expensive, the chemical used in it will create environment issues around area. So for power backup they use medium size batteries.

Making a big battery is good idea but there is a limitation due to the environment safety.

Capacitor voltage will decay continuesly and we can,t have a constant potential difference between terminals..

A conventional capacitor does not have the efience to work as a battery, even though, you can see this interesting videos about super capacitors:

https://www.youtube.com/watch?feature=player_embedded&v=OtM6XJlynkk

Batteries have: high energy storage densities and low discharge rates.

Capacitors have: low energy storage densities and high discharge rates (100-1000 times that of batteries).

Super capacitors combine the best of both: high energy densities and high discharge rates.

Recently graphene was accidentally discovered to be a very good material for super capacitors:

http://cleantechnica.com/2013/03/12/a-breakthrough-in-energy-storage-graphene-micro-supercapacitors/

Watch the video: a small piece of graphene was charged for only 3 seconds but it could keep an LED glowing for 5 minutes.

But many more technical aspects and details are still to be worked on, most of which have been stated in the answers above: terminal voltage, operational life (number of charges and discharges before disposal), cost, mass manufacture-ability, environmental suitability of consumer product, consumer feasibility etc.