Confused on panel voltages??

[John Calf]

G'morn.

I keep reading about solar panels being 12 and 24 volts. I just bought 2 Hanwha 295 watts Q4, starting to piece my system together and the specs range is in the 35 volts average, open and closed circuit. What am I missing here besides not being very solar knowledgeable.
I'm thinking the MPPT will determine my battery bank which will be 24 volts and adjust to the incoming voltage from the panels?

TYIA

[Rob Beckers]

Hi John,

You are right that the MPPT charge controller will take care of converting the panel Voltage to that of the batteries. I've written an article about MPPT controllers vs. the older PWM type controllers, and how they work: https://www.solacity.com/mppt-vs-pwm-charge-controllers-whats-difference/

The solar panel Voltage is determined by the number of solar cells in it. Traditionally, panels that charge 12 Volt batteries have 36 cells in them. That makes it so they run at around 18 Volts, just enough to charge a 12 Volt battery (which charges closer to 15 Volt).

The panels you have have 60 cells. When they do not produce any current (open circuit) their Voltage is around 37 Volt. When you connect the two wires coming out together they produce lots of current (in the sun), but now the Voltage is zero (after all, you short-circuited the output). Turns out they produce the most power at around 30 Volt, that is when their product of Voltage and current is the most (power equals Voltage times current). So, Voc (open circuit Voltage) is about 37 Volt, Vmp (maximum power Voltage) equals about 30 Volt.

For a battery bank of 24 Volt (which charges close to 30 Volt) you need at least 72 solar cells in series to charge it reliably. That means you need two 60-cell panels like yours connected together, doubling their Voltage, and an MPPT charge controller, to charge those batteries.

Hope this helps!

-RoB-

[John Calf]

Helps? You just made my day and provided some info I wanted without even asking, thanks a bunch Rob