MPPT behaviour when battery voltage is higher than MPP voltage

Q&A and troubleshooting
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1

Hello

I’m trying to pick an MPPT charger for a setup with 4 solar panels and a 48V battery. I would prefer to arrange them in 2 strings and use two MPPT 100/20 units. However, I see that at the high end of the temperature range, the MPP voltage will be 52.7V according to the MPPT calculator, which is lower than the maximum battery voltage.

So my question is: what will the MPPT algorithm do in this case? Will it shut down when it sees that it cannot operate at the MPP, or will it reduce the current draw and move to a suboptimal working point in order to reach 100% SOC?

2

This situation happens every night when the sun slowly goes down.

So, don’t think about it…

3

I’m not so worried about what will happen at night, more that the charger will not be able to fully charge the battery mid-day when the panels are hot.

4

You’ll have to set it up in one string of four panels and select the appropriate charger.

Or cool down the panels by watering them :smiling_face_with_sunglasses:

5

From Section 6.1 of the manual

The solar charger will commence battery charging as soon as the PV voltage is 5V higher than the battery voltage. For charging to continue, the PV voltage must remain at least 1V higher than the battery voltage.

If Vmp falls below battery voltage + 1V it may continue to charge at less than Pmp, but if Voc falls below battery + 1V it will stop. Remember, power falls of very quickly between Vmp and Voc. You should look for panels with a higher voltage.

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6

Excellent, thank you.