Over-sizing PV panel capacity to MPPT charger

chewface

New Member
Joined
Sep 17, 2021
Messages
4
Hi all;
I'm planning on buying/building an off-grid 5KW PV system with LifePo battery bank for my retirement home in the rural Philippines. Trying to figure out how many panels to buy assuming that I go with a Growatt SPF5000TL-HVM (5Kw) hybrid charger-inverter. The Growatt specs indicate a max input of 450VDC. However I read on different solar installer website that you should design an off-grid system with enough panels to provide up to 133% of the inverter capacity (which is 5,000 watts for this Growatt model), presumably to compensate for the lower real-life voltages from the panels due to less than max sunshine conditions? If I understand this correctly, then assuming the PV panels are 440watts (JA Solar) and are connected in series then I can connect 12 or even 13 panels in a single string? Would appreciate the advice of more experienced solar gurus out there.

A related question, what would happen to the built-in MPPT controller in a max full sun scenario? Would the MPPT charger shutdown or fry?
 

Wellbuilt

Solar Addict
Joined
Sep 14, 2020
Messages
893
I’ve never heard any one complaining about to many solar panels .
I just bought 30 panels 295 watt .
I use 15 now . And will ground mount 15 more soon .
I have plenty of power for most of the year but live in a cold area with lots of snow🥶
In June I charge up in a few hours in January I run the Honda every day 🤷‍♂️
You could allways add a extra charge controler and panels and use them in bad weather .
I only charge with 9 panels in the summer months , but next week I’ll add a extra string and by November I’ll use all 15 I’m thinking 30 panels should keep me charged year round without snow .
On a dark gloomy day in December give me 200watts or a bit more , if I could get 400 watts in it would be helpful
Plus the sun pops out for a hour of 2 every day and I can get some good power
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
10,669
Most important parameter of any PV input is maximum voltage. You have to consider record coldest temperature of your location, temperature coefficient of panels, and adjust their Voc accordingly. Using that Voc(max on cold day) you can determine if 12 or 13 panels in series is acceptable.

Is there a maximum short-circuit current spec? That would determine how many strings of panels could be put in parallel.

You can parallel two strings of panels, with each having a different orientation. If 90 degrees apart (e.g. aimed at 10:00 AM and 4:00 PM sun), peak power would be 0.7x as much (under direct sun, not counting extra reflecting off clouds), so 1.4x the PV panel wattage could be used without production clipping.

PV panel wattage output under normal conditions (PTC) is about 85% of rated (STC). Standard Test Conditions are one full sun (1000W/m^2) flashed on panel which is at 25 degrees C. Usually panels are warmer, so we over-panel a bit. Sometimes on a cool bright day we see 100% output or more.
 

Bripromo solar

New Member
Joined
Oct 28, 2021
Messages
3
Yeah Hedges is right cool temperature can spike or increase your voltage on these panels cause your inverter to shutdown!! First calculate your VOC, you still want to stay under 450V inverter maximum.
 
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