question

xiansolar avatar image
xiansolar asked

MPPT charger sizing

Hello, I am doing research on a DIY PV off-grid solar for my home. I have decided on using LG NeON R LG375Q1C-V5 panels on a 3-series x 3-parallel configuration (9 total). The panel stats:

Vmpp=37.2V Voc=42.8V
Impp=10.09A Isc=10.83A

The battery system will be 24V. Doing my own calculations I concluded that a SmartSolar MPPT 150/50 would be able to handle the array, but when I plugged in the values to the Victron MPPT calculator it suggested a SmartSolar MPPT 150/100.

My config:

https://mppt.victronenergy.com#djE7Y3VzdG9tLDMsMyw1NCwtMTAsNzAsMjQsMTAuMSwwLjAzNywxMC44MywzNzUsMzcuMiwtMC4yNCw0Mi44LDEsMjEuMg==

Could you help me understand why the calculator suggested that I get a charge controller with a max PV short circuit current of 70A when the short circuit current of my array would be ~33A? Is nominal PV power the reason? Thank you.

MPPT Controllers
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

2 Answers
seb71 avatar image
seb71 answered ·

You have 375W x 9 = 3375W PV array.

When used with a 24V (nominal voltage) battery, a 100A MPPT can output 24x100 = 2400W (in fact slightly more - about 2880W - because the actual battery voltage is higher than the 24V nominal voltage).

If you did not purchase anything yet, you should consider going with a 48V battery.


Also make sure you used the correct voltage temperature coefficient and the actual lowest temperature possible at your place. You are getting dangerously close to the 150V limit.


If you stick with a 24V battery, you could also consider getting only 8 of those PV modules, in 4-series / 2-parallel configuration, with a 250/100 MPPT.

2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Warwick Bruce Chapman avatar image
Warwick Bruce Chapman answered ·

At 24V with the same MPPT you get 50% of the PV power that you would at 48V. At 12V, you’d get 25%.

Ohms law.

48V battery voltage vs 24V makes your MPPTs, cabling, connectors half the price.


Here’s a good explanation from clean energy reviews:

img-5099.jpg


img-5099.jpg (616.0 KiB)
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.