Why does solar controller show voltage from panel after moving camper out of the sun?

[tacomabill]

After charging 12 volt AGM battery with solar panel, voltmeter on battery terminals shows 13.13 volts. I pulled the camper into the garage and checked the Sunsaver 20L controller: the wires from the solar panel show 13.03 volts. After an hour, the solar wires show 11.6 volts and after five hours the solar wires show 4.6 volts. Why is the controller showing voltage from the solar panel when it is not in the sun?

 

[Simons]

Is your garage completely dark? Void of any light sources?


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[tacomabill]

Not dark at all. plenty of natural light through windows to work in, but no direct sun on the windows.I will check voltage again after dark.

 

[john61ct]

Voltage means almost nothing.

Like water pressure with a spigot off.

Only amps shows activity.

 

[calicamper]

13.3 is the battery not the panel ?‍♂️.

 

[tacomabill]

To clarify, I measured voltage at the solar controller at the two wires that come in to it from the panel and are labeled "Solar". As stated above, that voltage slowly dropped over several hours after pulling into the garage. Just before dark last night it measured 8 tenths of one volt. This morning with camper still in garage and shortly after sunrise with a little natural light, the panel shows 5.6 volts. So it looks like those numbers are the output from the panel due to indirect light and as the light faded last evening, the numbers dropped. It has nothing to do with the battery which remained at about 13 volts and is still at 13 this morning.

 

[tacomabill]

Agreed. I just did not understand why I got anything coming to the controller from the panel when it was not in sunlight. I now learned that indirect light can energize solar cells, just not very much.

 

[Joe917]

You may be surprised by how much panels put out even on overcast days.
It is a common misunderstanding that panels need direct sunlight.
Partial shading of a panel can dramatically reduce output.

 

[craig333]

More than you think. My patio cover (white) reflects enough light during the day to get over an amp out my controller.

 

[Alloy]

More than you think. My patio cover (white) reflects enough light during the day to get over an amp out my controller.

Reflection and/or high altitute is why solar panel can produce more than the rated output.

 

[Simons]

Just think of your old trusty solar powered calculator that likely never saw real sunlight and was only ever charged by your classroom/office fluorescent lights.


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