Solar panels Series Vs Parallel

[charlie22824]

I think I know the correct answer. I just wanted to post on here before I started ordering things. I have 2 12v 200watt Renogy solar panels. That will be powering two 12 v 400ah LiFePo4 batteries that will be connected in Parallel. (I bought the RTX 2000 Ac it will pull the most power on my system). what i'm trying to figure out is can I hook my Solar panels up in series to a charge controller while having my batteries in parallel? my solar panels are around 20-25ft away from the batteries. I was trying to see if I could do this safely so I could save some money on wiring and the charge controller, etc. I will be mostly in unshaded areas too.


Solar Panel Specs:

 

[mikefitz]

Assuming a MPPT solar controller. you can connect the panels in series. My guess is that you will need more solar to keep up with the RTX2000 AC unit.
400 watts of solar in a 12v system needs a 30 amp controller.

Mike

 

[rmaddy]

I was trying to see if I could do this safely so I could save some money on wiring and the charge controller

These are somewhat conflicting goals. If you put the panels in series you need an MPPT SCC which is more expensive (and better) than a PWM SCC. But you have less current so the wiring is cheaper. If you put the panels in parallel you can use a PWM (or an MPPT) SCC but you have more current and need thicker wire.

If you might add more solar in the future you should plan for that now to save money in the long term. If you get an MPPT SCC that supports 100V max PV input voltage then you can add a 3rd panel in series. If you use wiring now that can handle 20A instead of 10A then you can double your solar from 2S or 3S to 2S2P or 3S2P. Though at that point you need a much higher amperage SCC to handle the extra power. Point is, if you plan for the future you can save money by buying something now that can handle the growth versus buying something small now and then buying the larger one later.

 

[littleharbor2]

If you use a PWM controller you will be losing a lot of power. The voltage output of those panels is very high and will get lost. PWM amps in, = amps out. MPPT watts in = watts out.

 

[charlie22824]

thank y'all for the help!

 

[Risky Rob]

Wouldn't the panels in series be 24V, while your batteries in parallel are 12V?

 

[rmaddy]

Wouldn't the panels in series be 24V, while your batteries in parallel are 12V?

Two of those panels in series would be 54Voc. You would definitely want an MPPT SCC and not a PWM SCC for that arrangement on a 12V battery bank. A PWM SCC would mean you must put the two panels in parallel. Either way, the MPPT SCC is the better option.

 

[Risky Rob]

Two of those panels in series would be 54Voc. You would definitely want an MPPT SCC and not a PWM SCC for that arrangement on a 12V battery bank. A PWM SCC would mean you must put the two panels in parallel. Either way, the MPPT SCC is the better option.

The Optimum operating voltage is 22.6 so with the 2 in series you would have more like 45V. My 100W panels in series are about 31V and go to a 24V MPPT charge controller then a 24V battery. Could a charge controller take 45V and charge a 12V battery?

 

[rmaddy]

Could a charge controller take 45V and charge a 12V battery?

An MPPT SCC can. It takes whatever input power it can get from the panels (regardless of voltage and amperage) and it converts that power into battery charge voltage and corresponding charge current. The main requirement for most MPPT SCCs is that the panel voltage needs to be about 5V higher (or more) than the battery charge voltage and the panel array Voc must be less than the SCC's max PV input voltage. So those 200W panels would work in either parallel or series on a 12V battery bank with an MPPT SCC.

My panels put out around 120V and it charges my 24V battery just fine. It would work on a 12V battery too.

 

[STW]

Also be aware that you will probably on get about 70% of your solar panel rating. So about 280 watts for the 400 watts of panels. Tilting can help a little.

 

[Risky Rob]

An MPPT SCC can. It takes whatever input power it can get from the panels (regardless of voltage and amperage) and it converts that power into battery charge voltage and corresponding charge current. The main requirement for most MPPT SCCs is that the panel voltage needs to be about 5V higher (or more) than the battery charge voltage and the panel array Voc must be less than the SCC's max PV input voltage. So those 200W panels would work in either parallel or series on a 12V battery bank with an MPPT SCC.

My panels put out around 120V and it charges my 24V battery just fine. It would work on a 12V battery too.

Wow, I didn't realize that. I just discovered that my controller will take 100V maximum.

 

[rmaddy]

I just discovered that my controller will take 100V maximum.

That's a common limit. Mine happens to support 150V. Just remember that Voc increases as the temperature decreases. So make sure the Voc can't get higher than 100V in the coldest temperatures your panels will ever see.

 

[Hedges]

This A/C?

Dometic CoolAir 2000 RTX 12 Volt Air Conditioner

Energy efficient, 12 volt powered rooftop air conditioner for RVs and camper vans. Free Shipping!

www.vanlifeoutfitters.com

"19 amps in eco mode" x 12V = 228W.

400W of panels delivering about 70% is 280W when aimed directly at the sun, less in hot weather.
If 6 hours effective sun (check an insolation calculator), 1680 Wh/day, should run the A/C for 7 hours or so.
Hey, this might even work! I was expecting to see only a couple hours operation (which it would be at full power.)

 

[charlie22824]

This A/C?

Dometic CoolAir 2000 RTX 12 Volt Air Conditioner

Energy efficient, 12 volt powered rooftop air conditioner for RVs and camper vans. Free Shipping!

www.vanlifeoutfitters.com

"19 amps in eco mode" x 12V = 228W.

400W of panels delivering about 70% is 280W when aimed directly at the sun, less in hot weather.
If 6 hours effective sun (check an insolation calculator), 1680 Wh/day, should run the A/C for 7 hours or so.
Hey, this might even work! I was expecting to see only a couple hours operation (which it would be at full power.)

yes

 

[charlie22824]

thank you for the help guys

 

[charlie22824]

This A/C?

Dometic CoolAir 2000 RTX 12 Volt Air Conditioner

Energy efficient, 12 volt powered rooftop air conditioner for RVs and camper vans. Free Shipping!

www.vanlifeoutfitters.com

"19 amps in eco mode" x 12V = 228W.

400W of panels delivering about 70% is 280W when aimed directly at the sun, less in hot weather.
If 6 hours effective sun (check an insolation calculator), 1680 Wh/day, should run the A/C for 7 hours or so.
Hey, this might even work! I was expecting to see only a couple hours operation (which it would be at full power.)

yes its actually pretty dope. I ran it non-stop on a wattage meter with other things Hooked up and 17hours of non stop running on auto mode it used only 5.12kwh of electricity. (Eco mode would of dropped it probably another 10-15% on power consumption compared to auto.

 

[littleharbor2]

now all they need to do is make it affordable

 

[charlie22824]

now all they need to do is make it affordable

yeah no doubt. I got mine at Racked up and go. for 3k with a kit where most other companies just want 3-3800 for the ac alone. it is very over priced because it has 12/24v stamped on it.