# Small solar power constant charge to charge a big capacitor.

#### ratstar

Aug 20, 2018
485
Is there any way to do this, say to charge the capacitor even on cloudy days, As far as I can think, the small charge will reach voltage equalization with the capacitor and itll just block too early.

But I bet there is an easy way to do this, because its such a common thing going on. Anyone know?

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
As far as I can think, the small charge will reach voltage equalization with the capacitor and itll just block too early.

That is the state in which the capacitor is typically called "charged".

#### Externet

Aug 24, 2009
886
Just apply/know the formulas beyond
voltage (V) in volts = current (I) in amperes x resistance (R) in Ohms :

Charge (Q) in Coulombs = current (I) in Amperes x time (t) in seconds
and
Energy (E) in Joules = voltage (V) in Volts, x charge (Q) in Coulombs
and
Charge (Q) in Coulombs = capacity (C) in Farads x voltage (V) in Volts

Note that the second and the fourth above merged can become

Capacity (C) in farads x voltage (V) in Volts = current (I) in Amperes x time (t) in seconds

I made this a long ago. Print it !

Last edited:

#### ratstar

Aug 20, 2018
485
Thanks for replies.

wouldnt charging with a capacitor be better than a battery, because there is no reverse to the charging current in the system?

#### Externet

Aug 24, 2009
886
Your 'small' solar panel charging current (I) is like the dripping into a bucket with capacity (C) during time (t) filling to a level (Q).
"No reverse to the charging current" ???
What will be the use of the charged capacitor ?

#### ratstar

Aug 20, 2018
485
You discharge it on a second loop with your "on switch relay", in the loop its in with the solar panel its in its non discharging state - it should just fill up- and wont give any electrons off until the second loop is actually closed, then it will neutralize.

I think its another feature of passive (cap) versus active (battery) components, i could be wrong tho.

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
Once you've been able to afford the cost of capacitors to replace the storage capacity of a rechargeable battery, what will you need to do to your load to handle the input voltage changes which will be much greater than if you had used batteries.

Sure, you could have a DC to DC converter on the output (in addition to the MPPT controller on the input for maximum efficiency).

You will also probably need active charge leveling on the capacitors, since the type of capacitor needed to get such high storage capacity is generally limited to a very low voltage.

Capacitors may have a role to play in the future, especially if you need to fast charge an electric vehicle (and I'm talking in 2 to 3 minutes), but then we will be using capacitors for what they're good at (very fast charge and discharge) not what they're (currently) bad at (efficient storage of energy).

#### Ratch

Mar 10, 2013
1,098
Just apply/know the formulas beyond
voltage (V) in volts = current (I) in amperes x resistance (R) in Ohms :

Charge (Q) in Coulombs = current (I) in Amperes x time (t) in seconds
and
Energy (E) in Joules = voltage (V) in Volts, x charge (Q) in Coulombs
and
Charge (Q) in Coulombs = capacity (C) in Farads x voltage (V) in Volts

Note that the second and the fourth above merged can become

Capacity (C) in farads x voltage (V) in Volts = current (I) in Amperes x time (t) in seconds

I made this a long ago. Print it !
View attachment 42971

The west triangle is correct for energy dissipation of a resistor, but wrong for energy storage of a capacitor. The correct formula for capacitor energy storage is

.

The reason a capacitor is different is because, unlike a resistor, a capacitor cannot change voltage instantaneously. Therefore the energy has to be integrated over time. You can learn all about it here. https://www.google.com/search?q=ene...ECAUQCA&biw=1536&bih=759#imgrc=WBLSj_tXAcZxDM:

Ratch

#### Ratch

Mar 10, 2013
1,098
Is there any way to do this, say to charge the capacitor even on cloudy days, As far as I can think, the small charge will reach voltage equalization with the capacitor and itll just block too early.

But I bet there is an easy way to do this, because its such a common thing going on. Anyone know?

Although just about the whole world uses technical slang by saying a capacitor "charges" and "discharges", that is not correct. A capacitor contains the same charge at any working voltage. For any charge a voltage inserts onto one capacitor plate, the same charge leaves the opposite plate for a net change of zero. However, one plate contains more charge that the opposite plate. It takes energy to imbalance the plate charges that way, and the energy divided by the charge imbalance will be the voltage. Therefore, to be syntactically correct, you should say a capacitor is "energized" or "de-energized". Remember, a capacitor stores energy, not charge or voltage.

Ratch

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