Parallel panels with different VOC

[JKFlipFlop]

If you parallel 2 different types of 12 volt panels with different VOC's..... ie 22.5 and 19.7 will the universe explode?

[sensij]

Nope, universe continues to exist. Assuming you are using a pwm controller, it won't matter much at all.

[Mike90250]

What will happen, is the PV array voltage will be reduced to the lowest voltage panel in the system. Your 22.5v panel will only produce 19.7v So your 100W 22.5V panel just turned into a 87w panel. (just using 100w as a round # to calculate with)

[JKFlipFlop]

In order for 1 panel to drag down the voltage of another, would'nt the weaker panel have to accept/absorb some current from the stronger one? If so wouldnt the blocking diodes prevent this.
Ohms law doesnt make sense in this scenario

[sensij]

In order for 1 panel to drag down the voltage of another, would'nt the weaker panel have to accept/absorb some current from the stronger one? If so wouldnt the blocking diodes prevent this.
Ohms law doesnt make sense in this scenario

No... the IV curve of solar panels allows the panel voltages to adjust at the expense of current. At any point along that curve, Ohms law is fine. For a PWM controller, that voltage is set by the battery, so it doesn't really matter what panels you put in parallel, they won't affect each other.

MIke's comment applies to an MPPT controller, which will seek the maximum power in total from the array. Different algorithms may settle on different voltages, but you would probably get a compromise between the Vmp of each. When operating voltage is pulled less than the Vmp, you'll see a small bump in current, so the power losses aren't quite as bad as suggested.

[karrak]

JK flip flops, that brings back memories of designing state machines in the 1970s and early 80s. Not used much now because of microprocessors.

Solar cells are basically a forward biased diode. When you shine light on them charge is transfered from the negative side to the positive side of the diode. This build up of charge generates a voltage across the diode. When this voltage reaches the forward conduction voltage of the diode (around 0.5V) the charge will flow back through the diode to the negative side again. Thus if you have a disconnected solar cell in the sun current will be going round and round in the cell. If you connect an external circuit to the cell the current goes through your circuit rather than staying in the cell. If you put two panels in parallel, the panel with the higher voltage will push current back through the other panel which will raise the voltage of that panel and reduce the voltage of the higher voltage panel. The voltage of the two panels in parallel will be between the low and the high voltage.

The diodes in the panels are not blocking diodes, they are bipass diodes and are in parallel with strings of solar cells. They are there to let current flow trough sections of the panel if they are in shadow.

Simon

Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger github.com/simat/BatteryMonitor
Latronics 4kW Inverter, homemade MPPT controller

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