Understanding series vs parallell for batteries and panels

If you have a PWM charge controller you run '12v' panels in parallel for 12v system or 2 '12v panels in series for a 24v system.
I'd keep my batteries at 12v since most things operate via 12v.
Larger systems might go to 24v batt bank or even 48v but would requires a transformer to get it back to 12v for say lights and other 12v appliances
PWM operates at battery voltage, the panel voltage is drawn down to that of the batt.

MPPT has the ability to find the max power point of the panel and instead of operating at batt voltage can operate at MPP, this type of controller can transform the input power to batt voltage for charging. MPPT can handle series panels and transform the MPP to batt voltage.

Voltage drop is based on current so that there would less voltage drop with series. So you have 5 x 100 watt '12v' panels, all in series, the current is 5A but the MPP is 5 x 18 or ~100v versus 25A x batt voltage (parallel). Of course the input limits of the controller should not be exceeded, they are not all the same. Voltage drop calc includes current squared so you see that 5 squared is much smaller than 25 squared. Voltage drop is loss of power and keeping the current low means you can use smaller wire. This is how 120v is deliered to you home, the high 'tension' (voltage) is delivered to a transformer near your home, this allows for less loss of power over the transmission lines.

So for PWM, 12v system = parallel.

MPPT, 12v system, either is the same. 2x100w = 200 watts, either 10Ax18v in parallel or 5Ax 36v in series.

Upping the batt to 24v would require a 24v inverter and a 24v to 12v transformer for the lights.

In short, PWM, parallel. MPPT, either cuz the MPPT can buck the higher input voltage to batt voltage.

Panels operate over a wide range of voltage and the power changes over this range.
PWM operates @ batt voltage while MPPT scans the IV curve and tries to operate @ max power and then transform to batt voltage.

ignore the red/blue boxes!


There are many things that change the shape of these curves, like the amount of sun and the heat of the panel. Small system do fine with PWM, larger systems can benifit for the added cost of an MPPT controller. Panel heating in one thing that reduces power for MPPT. Heat reduces the max power point, this is the reason a '12v' panel has 'overhead' up to 17-18v. As the panel heat the Vmp reduces, PWM controller don't loose power until extreme heat.

They do make higher voltage panels 24v, 72v, ...

The sticker on the back is based on what I call one SUN or 1000 wh/meter squared. This is clear blue day with the sun perpendicular to the panel. Haze polution clouds poor panel angle and now say you are at 1/2 SUN, the panel makes ~1/2 power. This sticker info does not account for heat and panels get hot. The sticker info is based on 20C and that might happen when it is 0C or below.