# Storing power in a capacitor

Can a capacitor be used to collect up small bit of electric, from a small solar panel for example, then release that charge when it reaches a certain level?

I dont pretend to know much, or anything about capacitors but of this is possible then it could come in very useful to me.

Any pointers or advice on this subject would be amazing

Can a capacitor be used to collect up small bit of electric, from a small solar panel for example, then release that charge when it reaches a certain level?

It can but it is not as easy as that. A lot depends on the voltage you are charging it up with and what you want to discharge it into.

Depending on what you want to do you could need a lot more circuitry. For example a photographic flash works on that principle but there is a lot more electronics surrounding it.

I see. Well, lets say i want to send the power into 4 rechargable AA's. Although i understand it wouldnt be too effective, what would the best process / circuit be?

Well, lets say i want to send the power into 4 rechargable AA's.

So what sort of voltage is the solar panel producing?
Is it greater or less than the 6V you need to charge the battery?

It is not a good example though because you simply do not charge batteries like this in bursts, you charge them with a continuous current.

the panel i have will produce about 1.2v in a medium light. thats why i was thinking about collecting the power up and either injecting it into the battery, or using it as some kind of secondry power source to momentarily save battery power

the panel i have will produce about 1.2v in a medium light.

That means the capacitor can only charge up to 1.2V, this is insufficient to charge your battery.

You have to use that 1.2V to drive a voltage inverter to boost the voltage to say 8V and then use a conventional battery charging circuit to condition this to charge your battery.

There are also chips designed for harvesting small amounts of energy, example being the LTC3588:

This happens to use a capacitor as intermediate storage, so I reckon the datasheet might be an

Energy stored in a capacitor is proportional to voltage squared (e=1/2 CV^2). So it might be best to boost voltage as high as possible before storing depending on what it powers when you use it.

yendis:
Energy stored in a capacitor is proportional to voltage squared (e=1/2 CV^2). So it might be best to boost voltage as high as possible before storing depending on what it powers when you use it.

No, the volume and cost of a capacitor is also proportional to CV^2, so there is no need to go for high
voltages. The energy storage in a capacitor is limited by the breakdown field strength across the dielectric
and the volume of dielectric.

Energy = (1/2) C V^2 = (eta/2) Vol E^2
where eta = permittivity of the dielectric, Vol = volume of dielectric, E = electric field strength

Note that eta is very small, and Vol is very small (in cubic metres), so that E has to be extremely
large in practical capacitors (10^8 V/m is not unusual)

I dont see that the extra component cost necessarily cancels out the aim of getting more energy. It depends on the application.