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Harbor Freight Thunderbolt Magnum 100 watt system

The data plate on the back of he panel should tell you open circuit voltage, and maximum power output voltage...

could be 36v open, and 23ish loaded...
 
Severence said:
Why are my panels putting out 24 volts? Is that normal?
Click to expand...
PV panels are not like batteries i.e. a single, relatively stable output voltage, they are very sensitive to shaded cells and how much load is on them. The two principle voltages are Voc and Vmp (Voltage Open Circuit and Voltage Maximum Power).

Voc is when there is no load on the panel, this is usually about 21.6V (0.6V per cell x 36 cells = 21.6V) for a 100W panel.

Vmp is the voltage at which the maximum power is generated (see below), this is usually around 18.5V for a 100W panel.

It is your SCC's job to convert that 18.5V (or 37V for a 24V nominal panel) down to whatever your battery needs. Charging a typical 12V nominal battery requires up to around 14.4V, the voltage going into a SCC must be higher than this in order to 'push' current through the battery (i.e. overcome the battery's own potential).

IV_curve_solar_cell.png
Edit: Clarified why PV panels have a higher voltage than a battery.
 
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