DSSR50 Maximum Solar Panel Power - 400W, 405W, 435Watts ?

[Charles Gomes]

I've a SBMS0 and a DSSR50 that I want to install to my cargo trailer. (Short cable run)

It will be used to charge a 300ah24V lifepo4 bank that in turn will be used to run a 24V Truck AC. (Yes the trailer is insulated). All I want is to have the AC maintain the interior temperature.

I'm shopping for panels and I mostly find 108cells or 120 cells. Harder to find new 72 or 60 cells panels.

I'm wondering if I wire 4 x 435Watt solar panels to my DSSR50 it would cause problems.

I'm down in South Florida close to Miami and rarely temperatures would go down to 15C about 60F.

Here are some panels that I found on Clearance from Local distributors.

JA Solar 405W Solar Panel 108 Cells JAM54S31-405/MR Clearance 

Hyundai 435W Solar Panel 108 Half-Cell HiN-T435NF(BK) Clearance 

Gstar – 365W GSP6G60M (H)

Given that I will install on the roof of the trailer, I am trying to maximize power with the minimum amount of panels.

For example the Hyundai panels have :

Impp = 13.56 - Isc = 14.32

14.32 x 4 = 57.28 . Seems under the 60A max for the DSSR50. 

Given that winter is never freezing here would the DSSR50 be able to handle ?

Thank you all in advance. In Special Dacian for his great solution.

[Dacian Todea (electrodacus)]

The 108 and 120 cell panels are actually just two 54 or 60 cell panels in parallel in a single panel.

Since you will be in a hot environment so panels will likely be quite hot you may want to look mostly at 120 cell (60x2) panels since the max power point voltage will drop with temperature and you want to be above 29V at the DSSR50 input.  Your cables will be short so no significant voltage drop there thus mostly need to consider the voltage drop due to panel temperature.

 

Looking at the Hyundai 435W panel  Vmpp = 32.1V and that seems fairly good but this is for +25C panel temperature and that will require ambient temperature to be somewhere around -5C or -10C depending on airflow.

If ambient outside is +30 to +35C you can expect panel temperature around +65C to +70C

70C means 45C delta above the STC of 25C  and at 0.25% /K for this panel you have around 11 to 12% lower Vmpp when panel is at +70C  so possible to get around 28.5V Vmpp but since there are no other losses (cable voltage drop super small and same for DSSR50) it should be fine as battery will typically be below 27V.

When panel is cold and in full sun charge current will actually be Isc = 14.32A and if there is edge of cloud effect it can be up to 20% more than that so up to 17A possible usually for shorter periods of time.

4 of this panels will be pushing above the limits of the DSSR50 with full passive cooling and when to that you add the possibility that ambient will be quite high it will be to much.

I will say 3 panels are absolutely no problem in any conditions but 4 may possibly damage the DSSR50 in some particular circumstances.

That STC rating for panel is not the max you can see from them and max can be up to 20 even 25% above that.  So simple rule will be to keep the Isc below 50A could get a bit over that 51 or 52A but no more than that so 13A Isc per panel in order to be able to use 4 panels. 

 

There will be no issues in having 4 of those 365W panels I expect about 11A from each in normal conditions so just 44A from 4 of them.

[Dacian Todea (electrodacus)]

Yes the 440W 120cell panel will be a good choice assuming is also at a good price and also the dimensions are good for your application since is a bit longer than the others you considered.

Hopefully panel will not get that hot as it is also the top of your van so you will have a hard time cooling the van.