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Charles Gomes asked

Solar Vmpp_min vs Reality vs mppt efficiency

I'm trying to calculate if 5 panels in parallel would supply energy efficiently to charge a lifepo4 24v bank. Here is my topic in the subject:

https://community.victronenergy.com/questions/70097/best-mppt-controller-for-an-overland-5-panels-setu.html


Based on the Solar panels manufacturer info: Sunpower SPR-A450-COM I calculated the Vmpp_min in a hot 45 degrees day to be 36.98Volts.

The battery Max voltage is 28.8V plus 5V voltage drop on Charge Controller + 1V drop on wiring the output needs to be at least 34.8 Volts that means on a very hot day I still should be able to charge.

Is there an efficiency curve graph for MPPT controllers so I can check the efficiency of supplying voltage close to the minimum required vs double the required voltage ?


Looking at other users @MichelG solar output, I found that voltage is not as linear as I expected after reading https://www.alternative-energy-tutorials.com/solar-power/pv-array.html



MPPT ControllersMPPT SmartSolar
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Charles Gomes avatar image Charles Gomes commented ·

As a note, I've used this formula to calculate Vmpp_min

Module Vmp_min = Vmp x [1+ ((Tmax + Tadd - TSTC) x (Tk_Vmp/100))]



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michelg answered ·

Hi Charles, don't worry about the linearity of the output. That's the job of the SmartSolar MPPT to make it "stable", belive me it works perfectly.

I had to change 80% of my first installation, because the MPPTs I was using did not work as exepected, and they killed a set of batteries. Since I use Victron products, no issues at all.

In my current setup, 2x 3 arrays, 4 arrays have 5 PV panels in serie south orientated, 2 arrays have 6 panels in serie west orientated. Twice 2 arrays + 1 array, connected to one of the MC4, voltage can go up to 120Voc, but usually 105Voc.

Then when charging the batteries, VDC decreases (absolutely normal) and Amps grow in the input size of the MPPT). It manages the rest for the batteries.

2x 2 PV in serie + 1x PV, each group connecting to each own MC4 connector of the MPPT will work fine.

Have fun

Michel.

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Charles Gomes avatar image Charles Gomes commented ·

Thank you, I'm still wondering how did you get your fridge temperature in the dashboard. I'm working on Wemos ESP32 + blynk but wondering if it would be easier to just use Victron API's

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