- #1
Artlav
- 161
- 1
Given: a ~3W monocrystalline solar panel, originally from a panel+battery+light pack from early 90s, spent a decade in a box, then a decade on the roof under the sun and elements, unconnected to anything.
I wanted to finally put it to some use.
The circuit is straightforward - the panel charges a bank of ultracapacitors through a diode, the ultracapacitors then power some LEDs through a buck driver.
However, there are several problems:
1. Current keeps dropping and changing in arcane ways.
For example, i disconnect one lead of the panel and put an ammeter along it. It would be supplying 5-6mA of current. Then, i short circuit the panel for a second, and connect the lead back across the ammeter - it now gives 80mA.
How the heck is that possible?
The current drops again after a while, and just poking pincers across the contacts for a moment gets it going again. It's not the bank - same thing happens with a resistor as the load.
2. The panel is a set of cells in series. If one cell is obscured while others are in full sunlight, the current drops over ten times. It's 10mA with blue sky only, 100mA with the sun on whole panel, but 5-6mA with one of the cells in shadow.
3. The panel gets pretty hot in the direct sunlight - almost 60*C. Not quite strange, but is it supposed to happen? I read that solar cells don't like getting hot - how is it solved then?
3 is straightforward, 2 i suspect is solvable by something called bypass diodes, but I'm completely mystified by 1.
Why does that happen, and how can it be fixed?
In general, what kind of aging effects a panel that spent a decade unconnected in daylight would show?
I wanted to finally put it to some use.
The circuit is straightforward - the panel charges a bank of ultracapacitors through a diode, the ultracapacitors then power some LEDs through a buck driver.
However, there are several problems:
1. Current keeps dropping and changing in arcane ways.
For example, i disconnect one lead of the panel and put an ammeter along it. It would be supplying 5-6mA of current. Then, i short circuit the panel for a second, and connect the lead back across the ammeter - it now gives 80mA.
How the heck is that possible?
The current drops again after a while, and just poking pincers across the contacts for a moment gets it going again. It's not the bank - same thing happens with a resistor as the load.
2. The panel is a set of cells in series. If one cell is obscured while others are in full sunlight, the current drops over ten times. It's 10mA with blue sky only, 100mA with the sun on whole panel, but 5-6mA with one of the cells in shadow.
3. The panel gets pretty hot in the direct sunlight - almost 60*C. Not quite strange, but is it supposed to happen? I read that solar cells don't like getting hot - how is it solved then?
3 is straightforward, 2 i suspect is solvable by something called bypass diodes, but I'm completely mystified by 1.
Why does that happen, and how can it be fixed?
In general, what kind of aging effects a panel that spent a decade unconnected in daylight would show?
