# Solar Battery Comparrison

#### Knowlittle

Joined Mar 16, 2016
45
why does a solar cell (18-21v) have less "power / amp" than a 12v battery ?

Please guys / gals, MAKE IT SIMPLE !

Thanks

#### nsaspook

Joined Aug 27, 2009
11,749
Tell us what you think about it.

#### Knowlittle

Joined Mar 16, 2016
45
It doesnt make sense !

#### Knowlittle

Joined Mar 16, 2016
45
Why now would an 18-21v (.56amp)solar panel have less amp than a 12vac (2.16amp) battery ? See this is what makes no sense !

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#### Alec_t

Joined Sep 17, 2013
13,776
The major factor determining the current they can provide is the effective internal resistance of the two things. The lead-acid battery has a lower resistance than the panel, so is able to provide a higher current. However, note that the 2.16A spec for the battery is the maximum allowed initial charging current; not the current it can provide. You are comparing apples with oranges.

#### Knowlittle

Joined Mar 16, 2016
45
Then what is the batteries amps ?

#### Alec_t

Joined Sep 17, 2013
13,776
Could be 100A or more (for a short time!). That's just a guess. It is the connected load which determines the current. Ask the manufacturer what the maximum current draw is.

#### ErnieM

Joined Apr 24, 2011
8,362
By "power / amp" I assume you mean either power or amps (or current), as "power / amp" is equal to volts.

Power can be calculated by P = I*E (power = voltage * current)

The solar cell is rated for 18V when drawing .56A under full sun or such. 18V * .56A = 10.08 Watts

The battery will supply 13.5V at 2.16A initially. 13.5V * 2.16A = 29.16 Watts

#### hp1729

Joined Nov 23, 2015
2,304
why does a solar cell (18-21v) have less "power / amp" than a 12v battery ?

Please guys / gals, MAKE IT SIMPLE !

Thanks
Light doesn't provide as many current carriers per volume than a battery and solar cells only convert a fraction of those.

#### wayneh

Joined Sep 9, 2010
17,405
why does a solar cell (18-21v) have less "power / amp" than a 12v battery ?
First, it depends on the specific cell and battery. I'm sure I could find a panel and a battery that would show the opposite relationship.

But the basic answer is that you may be confusing voltage and amperage capacity. They are two very different things. Voltage is called an intrinsic property, it does not depend on scale. Cells in a lead-acid battery each develop the same voltage regardless of size. Solar cells are similar - the voltage they can reach depends on their makeup and construction.

Amperage capacity is an extrinsic property. It depends completely on scale. A typical car battery has hugely more capacity than a little AA, or even 8 of them in series (to give 12V). You don't want to start your car with just any 12V battery, you need a big one! Same with solar panels, if you need a lot of power you'll need a large panel.

A battery is very energy dense - a lot of power in a small package. Solar energy comes to us in a very diffuse way. We need a large panel to collect and concentrate the power.

#### Knowlittle

Joined Mar 16, 2016
45
Ok thanks. So here is another question....the motor ALMOST wants to run with this solar panel, is there any type of circuit a person can build that would "streamline" the output of the solar panel in order to make the motor turn ?

#### hp1729

Joined Nov 23, 2015
2,304
Ok thanks. So here is another question....the motor ALMOST wants to run with this solar panel, is there any type of circuit a person can build that would "streamline" the output of the solar panel in order to make the motor turn ?
More solar cells in parallel to supply more current.

#### ErnieM

Joined Apr 24, 2011
8,362
Motors are particularly difficult for solar panels to run because they have a high initial starting current, and when you try to pull too large a current from a solar panel the voltage drops, and can dr to near zero.

So when you attach a motor it draws this large current, the voltage goes low, which means the power is near zero also, and all you do is pump a large current thru your stalled motor.

A battery in the middle works great as they can supply high currents for brief times no problem. Some schemes use a capacitor for a kick start of current too, but you typically need a large cap for this task.

What size cap depends on how much and for how long you need that current. Do you know that?