Watts are Watts, but how to make them

[DixieMtCR]

I'm Adding a couple of 320w Renogy panels to my system. The panel specs are as follows.

• Maximum Power: 320W
• Maximum System Voltage: 1000V DC (UL)
• Open-Circuit Voltage (Voc): 40.1V
• Optimum Operating Voltage (Vmp): 32.7 V
• Optimum Operating Current (Imp): 9.79 A
• Short-Circuit Current (Isc): 10.36 A
• Maximum Series Fuse Rating: 15A
• Operating Temperature: -40°F to 185°F

Would it be better to series the panels for 65.4v @9.79A or to parallel them for 32.7v @ 19.58a. I realize that there will never be more than 640w out of the panels. But, what in your experience does a MPPT charge controller like. Power served up as amps, or served up as volts? Or does the algorithm in the CC just takes what it gets and it makes no difference?

I have noticed with the other (2) 3s2p 100w panel sets I have, that the series 3s configuration gets the voltage up so the CC will start working. Oregon needs a little help to get the solar working.

Ken

 

[robby]

Normally 65.4V at 9.79A would be better but you have not stated what Inverter or charge controller you have.

 

[MisterSandals]

But, what in your experience does a MPPT charge controller like.

Which MPPT? What is max input volts? Is there a specified MPPT range?

Or does the algorithm in the CC just takes what it gets and it makes no difference?

Pretty much, that's what MPPTs do. Just stay below max input volts (based on Voc with 15% leeway).

 

[DixieMtCR]

Normally 65.4V at 9.79A would be better but you have not stated what Inverter or charge controller you have.

the inverter is a Renogy 3000w 12v PSW inverter.
The MTTP CC is a 40A 100v max input voltage Epever look alike for 12/24v systems

 

[DixieMtCR]

Which MPPT? What is max input volts? Is there a specified MPPT range?

Pretty much, that's what MPPTs do. Just stay below max input volts (based on Voc with 15% leeway).

the inverter is a Renogy 3000w 12v PSW inverter.
The MTTP CC is a 40A 100v max input voltage Epever look alike for 12/24v systems
View attachment 87256

 

[DixieMtCR]

I also might add that the MTTP CC feeds 8 100Ah Deep Cycle Lead Acid RV batteries.

They are wired in parallel for a 12v system. Until the rain and snow stop for the season, I will run it as a 12v system.

I have everything ready to switch over to a 24v system.

CCs will remain the same
Panels will remain the same
New 24vdc Giandel 4000w psw Inverter will replace the Renogy 3000w.
Batteries will be configured from 8p to 2s4p for a 24vdc system

The 120vac feeds the house through a 30A commercial 10-circuit Manual Transfer Switch and is intended for OFF-GRID ONLY (no feed back) emergency power for the house. We lose grid power a lot where we live. And for weeks in extreme storm conditions which have occured several times in the 20+ years we have lived here. Our 10Kw generator works but when we can't get out for gas, we need the solar.

 

[rmaddy]

I would put them in series. The higher voltage allows power to be produced in lower light conditions (earlier and later in the day typically). This will be more important when going from 12V to 24V.

But note that when in series the higher voltage does require the disconnect switch/breaker (assuming you have one) that can handle the higher volts. The lower amps also allows for smaller wire to the charge controller.

The MTTP CC is a 40A 100v max input voltage

Your panels have a Voc of 40.1V. In series that would be 80.2V. It would require temperatures close to -57ºC/-71ºF to reach 100V so you are good. Note that you are a bit over paneled with 640W if you have a 12V battery due to the 40A charge current limit of the SCC. But not by that much so it will be fine. At 24V you could add 2 more panels for 2S2P.