VOC question from beginner

[ggoodwin]

Hi

I am trying to put together my fist 12V system, spec details attached below. I was following the tutorial by Will on this page (https://watts247.com/product/pip-1012lv-ms/?wpam_id=3). This page features the same MPPT I purchased.

The MPPT docs say "Max PV Input Voc 102V", and the solar panels say "open circuit Voltage 24.3V" (x4 panel total would be 97.2). These numbers do not seem to add up to how I think they should. I was expecting a panel total around 84 and a MPPT Voc at 145 (maybe my MPPT and the one in the video are not the same, or I am not taking something(s) into consideration).

My question is can I safely run 4 12V 100W panels on this MPPT unit, and if not is there an easy fix (reduce panels, swap out the MPPT)?

any help or advice appreciated.

thanks

PIP-1012LV-MS - 12V 120VAC 1000W AC output, 500W Max 40A Mppt Solar Input

https://www.mppsolar.com/v3/catalogs/PIP-LV.pdf

Solar Panels:
Renology
part of this kit. https://www.amazon.com/gp/product/B07CTKT56Y/ref=ppx_yo_dt_b_search_asin_image?ie=UTF8&th=1

and battery:
LiTime 12V 230Ah Plus Low-Temp Protection LiFePO4 Battery, Built-in 200A BMS, Max 2944Wh Energy

LiTime 12V 230Ah Plus Low-Temp Protection Deep Cycle LiFePO4 Battery,

LiTime 12V 230Ah LTCP LiFePO4 battery with 2944Wh usable energy has low-temperature protection. Weighing only 45.22lbs.

www.litime.com

 

[Rocketman]

That is a really limited charge controller…

The issue is as panels get cold the voltage increases- so a cold clear winter morning the voltage will be higher. Four of those panels in series cannot be put on a 102v max Solar charge controller…

You have some options.
Best option for Four panels - 2s2p - put two panels in series into a string - then get a branch connector and put two strings in parallel.

You also could put four panels in parallel. (If panels are in 3p or more each panel or string must be fused).

Edit: it is usually best to plan out on paper everything,making a drawing, include everything (all specs and wires and fuses) and running it by some others to make sure everything is good BEFORE you buy anything. That way you don’t buy something that doesn’t meet your needs or upgrade path- like a very limited charge controllers, etc.

 

[FilterGuy]

Hi

I am trying to put together my fist 12V system, spec details attached below. I was following the tutorial by Will on this page (https://watts247.com/product/pip-1012lv-ms/?wpam_id=3). This page features the same MPPT I purchased.

The MPPT docs say "Max PV Input Voc 102V", and the solar panels say "open circuit Voltage 24.3V" (x4 panel total would be 97.2). These numbers do not seem to add up to how I think they should. I was expecting a panel total around 84 and a MPPT Voc at 145 (maybe my MPPT and the one in the video are not the same, or I am not taking something(s) into consideration).

My question is can I safely run 4 12V 100W panels on this MPPT unit, and if not is there an easy fix (reduce panels, swap out the MPPT)?

any help or advice appreciated.

thanks

PIP-1012LV-MS - 12V 120VAC 1000W AC output, 500W Max 40A Mppt Solar Input

https://www.mppsolar.com/v3/catalogs/PIP-LV.pdf

Solar Panels:
Renology
part of this kit. https://www.amazon.com/gp/product/B07CTKT56Y/ref=ppx_yo_dt_b_search_asin_image?ie=UTF8&th=1

and battery:
LiTime 12V 230Ah Plus Low-Temp Protection LiFePO4 Battery, Built-in 200A BMS, Max 2944Wh Energy

LiTime 12V 230Ah Plus Low-Temp Protection Deep Cycle LiFePO4 Battery,

LiTime 12V 230Ah LTCP LiFePO4 battery with 2944Wh usable energy has low-temperature protection. Weighing only 45.22lbs.

www.litime.com

Short answer: You probably should not try to use 4 panels in series with the mppt on that inverter

The Voc adds with each panel in series. Panel Voc is 24.3V. Array Voc is 4 x 24.3V = 97.2V.

The max Input voltage of the inverter is 102V. This seems like it would work but..... you have to figure out what the voltage rise of the inverter will be in cold weather. Unfortunately, I don't see the temp coefficient for the panels so you can't calculate it, but 97.2V is close enough to 102V that it would probably be a problem in cool weather.... let alone cold weather.

Adjusting Solar Panel Voc for temperature

When designing you solar panel system, it is important to adjust you solar panel Voc for temperature in order to ensure you do not over-voltage the PV inputs of your solar charge controller. This paper shows how to calculate the Temperature...

diysolarforum.com

I would recommend putting two strings of two panels in parallel for your system

 

[ggoodwin]

ok, thank you guys. Yeah, cold will be a factor - i am in Wyoming and it is 12 degrees F right now, and it has been colder. This definitely gives me somethings to research.

 

[MichaelK]

A simple quicky rule of thumb is that voltage goes up ~1.11X at freezing, and 1.25X at -40F. So, your panels would exceed 102V even before the temp drops to freezing.

97.2V X 1.11X = 107.9V

 

[Rednecktek]

Run your panels in 2s2p and you'll be golden.

 

[littleharbor2]

Last time I checked, 24.3 x 4 = 101.2 volts. OOPS!! Never mind.

 

[MichaelK]

Last time I checked, 24.3 x 4 = 101.2 volts.

At what temperature? Which temperature correction coefficient are you using?

 

[littleharbor2]

At what temperature? Which temperature correction coefficient are you using?

I'm simply adding the Voc from the solar panel data. Anything under 25 Celsius will be higher Voc.