# Thread: Question on Solar Panel and Solar Battery

1. ## Question on Solar Panel and Solar Battery

Hi. I have been reading around and looking at Youtube demo on Solar Panel charging deep solar batteries. While all seemed well and straightforward, I have a doubt that I cannot figure out. Hope anyone which experience can shed some light. Thanks

A typical battery comes with one + and - connector. So the solar panel wired to charge controller, which wires down to the battery + and -. Now a device (assumed same voltage DC) is also connected clamp to that solar battery +/- connectors. Assuming the device is drawing 5Amp, battery is 50AH and solar panel is producing 2A (just a random figure) at that time, won't the device consuming 5A blows the solar panel, since all cables are connected to the same battery connector.

I got the impression that if a device draws more amps from the source, the fuse burns. So what actually happens when there is no fuse limiter?

2. ## Re: Question on Solar Panel and Solar Battery

The load draws 5A. If the panel can only supply 2A, then the battery will be supplying 3A.

If the battery is flat and the panel is the only source, then the output voltage will drop.

Assuming that the load has a fixed resistance, when the voltage drops, the current drops.

The voltage will drop until V/R=2A, which is the max deliverable by the panel.

However, in most operating condition, the battery is charged to some extend by the panel when there is no load, and it will aid the panel and deliver the 3A current when there is a load that demands that current.

And the current flowing thru the panel never exceeds 2A.

3. ## Re: Question on Solar Panel and Solar Battery

Thank you Limsgp for the explanation. Now I can plan my installation further.

I was thinking of using digital timer to switch on the AC-DC battery charger at night only to top up whatever balance left to the battery.

4. ## Re: Question on Solar Panel and Solar Battery

Actually, for a solar panel powered applications, it is important to first calculate the total power(energy) requirement (Day + Night) and the total power deliverable by the panel (Day). (Energy is the more accurate term)

If they are equal, then the system is feasible or meaningful as a "free/green" power source.

E.g. The load draws on average 1A current continuously. In the Day, the panel supplies 1A to drive the load, and the other 1A will charge the battery, total 2A. At night, the battery will discharge 1A to drive the load and the panel will be off-duty.

The battery should have a capacity of at least enough to power the device thru the night. In the example above, that will be 12AH (1A for 12 hours).

*Voltage considerations have been conveniently left out of the picture to simplify things.

the above is assuming predictable fine weather conditions. to factor in overcast weather etc.., the max output capacity of the panel will have to be higher and the battery should have some excess capacity.

If supplementary power supply is required (e.g. to charge the battery), then the system is not very efficient or meaningful as a main power source. But if the panel is not the main source but just to provide additional power to reduce the bill a little.. then that is fine..

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