Solar panel
A small solar panel, the 6 V 1 W epoxy kind in STEM kits and solar builds. Aliases: solar cell, photovoltaic panel, PV panel, 6V 1W solar panel.
A solar cell is a current source set by the light, with a diode across it. Light
knocks electrons loose and they flow out of +, around the circuit and back into
-. The same junction is also a diode, and as the load lets the voltage rise it
takes more and more of that current back inside. With nothing connected all of it
goes back; with a short across it none does. A panel is a string of cells in series,
twelve here, which is where its 6 V comes from.
Pins
| Pin | What it does |
|---|---|
+ |
The red lead. |
- |
The black lead. |
While it runs
The slider is the sunlight, in watts per square meter: 1000 is full sun, the condition the panel is rated at, and a cloudy day is a few hundred. The readout is the voltage across the panel.
What the model gets right
Current, not voltage. In full sun the panel gives about 0.2 A from a short up to about 5.5 V, then the voltage rises to about 7.2 V with nothing on it. So it charges a battery at the rate the light sets, and a charger on it pulls its voltage down to the battery's.
The maximum power point. Into about 36 ohm it gives 1 W at 6 V and 167 mA, its rating.
Dim light. The current follows the light; the open voltage barely does: about 6.7 V at half sun.
The diode standing for the string is fitted to what these panels are sold with: 7.2 V open, 0.2 A short and 1 W at 6 V. That fit is an assumption from a product listing, not a datasheet.
What it does not model
Temperature (a hot panel loses about half a percent of its voltage a degree), the angle of the sun, partial shading, and a blocking diode, which is a separate part.
Common mistakes
Expecting 6 V from it under any load. It is a current source: into a big load it gives what the light makes, at whatever voltage that comes to.
Charging a lithium-ion cell straight from it. Use a charger such as the TP4056, which stops at 4.2 V.
See it in action
Solar sensor node charges an 18650 from the panel through a TP4056. Open it at /templates.