PV Arrangement?

[D. Abineri]

I have 16 250W USED panels (V(oc) about 35V, I(sc) about 6A) that I am hoping to connect to an MPP lv5048 along with 48v of battery.

Which arrangement of panels might work best for me. No shade to worry about.

Thanks

 

[JeepDaddy]

Max PV input voltage for the LV5048 is 145Vdc. 4 of your panels in series would be 140Vdc. The manual says typical amperage of 80A, so you should be OK there, not knowing your Imp.

So 4S4P would be a good place to be, IMHO.

 

[D. Abineri]

Thanks JeepDaddy, that confirms what I was thinking. I appreciate your response.

 

[MichaelK]

Max PV input voltage for the LV5048 is 145Vdc. 4 of your panels in series would be 140Vdc. The manual says typical amperage of 80A, so you should be OK there, not knowing your Imp.

So 4S4P would be a good place to be, IMHO.

I don't think so. What are the winter lows in your location? Around freezing, your typical 250W panel might bump up to around 40Voc, which would be 160V on a frosty morning.

You can use Midnight solar's string calculator to determine exactly what the Voc will be. I myself wire four panels in series, and typically am seeing around 135V at certain times of the day, but I'm using a 200V controller. That is just too close to 145 to be comfortable.

MidNite Solar - Classic Sizing Tool.

MidNite Solar is the industry leader and manufacture of quality Renewable Energy System electrical components and E-Panels.

www.midnitesolar.com

 

[D. Abineri]

Thanks Michaelk. If the panels are at least 10 degrees of the latitude, might this allow for 4s4p? Are inverters in general that sensitive to the max DC voltage input?

 

[wattmatters]

So 4S4P would be a good place to be, IMHO.

I wouldn't go above 3S with that Voc limit. Add 20% margin as cold temperatures increases their Voc quite a bit.

3 doesn't divide into 16, so it maybe a 15 panel array of 3S5P is better choice.

I have 16 250W USED panels (V(oc) about 35V, I(sc) about 6A)

Are those numbers correct? I'm struggling to believe the Isc is that low for a 250W panel.

Imp will be lower, so if that's no more than 6A, 250W/6A = Vmp of at least 41.7V

Something's not right.

 

[D. Abineri]

The panel is not necessarily still 250 Watt as it is used and has likely degraded somewhat.

 

[MichaelK]

The panel is not necessarily still 250 Watt as it is used and has likely degraded somewhat.

It's not necessarily degradation. Some of my very best performing panels were repo's, pulled off someone's roof. More likely, it was just routine lower output because the panel was not exactly perpendicular. Assuming a 250W/30V panel produces 8.3A, then 85% of that is 7A. A small misalignment, and you could easily loose another amp.

Thanks Michaelk. If the panels are at least 10 degrees of the latitude, might this allow for 4s4p? Are inverters in general that sensitive to the max DC voltage input?

When you say 10 degrees, you are meaning 10 degrees above/below the equator? Does that mean you never see freezing temperatures? If that's the case, you might squeak by with four? But, it's your call. You buy the new electronics if they get fried.

 

[D. Abineri]

Actually I meant 10 degrees off what it should be at my latitude. Are inverters really that sensitive input DC?

Thanks.

 

[MichaelK]

Actually I meant 10 degrees off what it should be at my latitude. Are inverters really that sensitive input DC?

Thanks.

I've never bought an AiO unit. I've always gone with component systems. I wouldn't risk a charge controller that way. The voltage limits though in my opinion are a backdoor indicator of quality. The higher the voltage limits, the higher the quality. Maybe not for everything, but higher voltage limits makes system design more flexible.

About panel angle, if you set it to your latitude, your panels will be perpendicular exactly twice per year, on the equinoxes. Setting the panels 10 degrees lower lets the sun "rock" over perpendicular, and increases the overall average insolation. In the real-world though I just use the pipe and eyeball it.

 

[D. Abineri]

Do you mean 10 degrees lower to the horizontal or 10 degrees more from the horizontal? If you leave it at your latitude doesn't the sun also "rock" over that latitude direction also, but more uniformly I would have thought?

 

[Just John]

I have 16 250W USED panels (V(oc) about 35V, I(sc) about 6A) that I am hoping to connect to an MPP lv5048 along with 48v of battery.

Which arrangement of panels might work best for me. No shade to worry about.

Thanks

I would recommend 3 in series, once it gets cold you can exceed the limits of the charge controller. Then parallel the three series strings.

Assuming these are the Santan used panels.

Specifications:​

• Rated Power: 250W
• Open circuit voltage (VOC): 37.6 V
• Max power voltage (VMP): 30.3 V
• Short circuit current (ISC): 8.85 A
• Max power current: 8.27 A
• Power Tolerance 0/+3%
• Maximum system voltage: 600V (UL)
• Fuse Rating: 15 A
• Weight: 41 lbs.
• Dimensions:64.95 × 39.05 × 1.37 in

3 in series gives 112 VOC, 90.9 working voltage (the charge controller has a limit of 110 working voltage).

 

[wattmatters]

3 in series gives 112 VOC

Yep and that's at standard temps. This voltage goes up a fair bit as the temperature drops. How much depends on how cold it gets. If below freezing is expected then might want to add 20% for safety margin. That brings it up to ~134V, which is still inside the Voc limit of the inverter.

Personally I wouldn't risk 4S on such an inverter.

 

[Just John]

Yep and that's at standard temps. This voltage goes up a fair bit as the temperature drops. How much depends on how cold it gets. If below freezing is expected then might want to add 20% for safety margin. That brings it up to ~134V, which is still inside the Voc limit of the inverter.

Personally I wouldn't risk 4S on such an inverter.

Yes, that's what I said.

 

[D. Abineri]

Hey guys, where do you see the 110v limit on the input of the charger? Why would the input limit for the inverter (145V) be so much higher that the max input for the charger (110V)? What's going on here?

 

[Just John]

Hey guys, where do you see the 110v limit on the input of the charger? Why would the input limit for the inverter (145V) be so much higher that the max input for the charger (110V)? What's going on here?

The manual for the LV 5048 says:

PV INPUT / SOLAR CHARGING
Max PV Input Power 8000W (4000W each input)
Max PV Input Volt 145VDC (open circuit Voc)
MPPT Range 60 - 110VDC
Number of PV Input 2
Max Charging Current 160A (80A X 2)

The MPPT range says the "working voltage" AKA VMP on your solar panel needs to be between 60-110v.
Your VOC (open circuit voltage) of the solar input needs to be below 145v. Be warned, in cold temperatures it can exceed that rated value on the panel label.

That's why your panels have both numbers, and your manual kindly provides the range.

If you have the used Santan panels I quoted the specs for above, then only two in series gives 60.6v, and if you have a long wire run, you might have a problem getting the 60v minimum needed. That's why I said 3 in series is ideal, 112.8 (VOC) is under the 145v limit, and 90.9v (VMP) is well within the 60-110 MPPT range.

 

[D. Abineri]

Thanks, Just John. I am finding the PV Array MPPT Voltage Range 60 -115V. But then doesn't this limit the total panel input to the inverter, which seems to be specified at 145V? It sounds like you are saying that if the PV input is ,say, 140V then it will burn up the charger because the charger limit is 110V? Why is the 145V max even specified if this would destroy the charger. Please help me to understand this if you would, I know I am missing something. Thanks.

 

[MichaelK]

Thanks, Just John. I am finding the PV Array MPPT Voltage Range 60 -115V. But then doesn't this limit the total panel input to the inverter, which seems to be specified at 145V? It sounds like you are saying that if the PV input is ,say, 140V then it will burn up the charger because the charger limit is 110V? Why is the 145V max even specified if this would destroy the charger. Please help me to understand this if you would, I know I am missing something. Thanks.

You have to understand that the voltage the panels are producing can vary by large amounts over the course of a day. I've seen the Vmp vary from 89V to 124V from my arrays with clear sunny weather over the course of the day, and depending on the load applied.

The 110V value is the "working" limit, with a built-in safety factor to account for load and temperature changes. The 145V limit is the drop-dead limit when exceeded the electronics go poof and make pretty fireworks!

The Voc is the highest voltage that the panels can produce under open circuit conditions. That typically happens every single time the controller senses the battery is fully charged and stops current flowing to the batteries. When the controller switches back on, the electronics are exposed that Voc until the load drops it down to Vmp.

BTW, the voltage limit does limit the maximal power coming in, but that is compensated for by adding parallel strings of more panels. With each string bringing in only 8amps, at say 112V, you get more power by adding more parallel strings, up to 80amps.

 

[Just John]

Thanks, Just John. I am finding the PV Array MPPT Voltage Range 60 -115V. But then doesn't this limit the total panel input to the inverter, which seems to be specified at 145V? It sounds like you are saying that if the PV input is ,say, 140V then it will burn up the charger because the charger limit is 110V? Why is the 145V max even specified if this would destroy the charger. Please help me to understand this if you would, I know I am missing something. Thanks.

I was just going by what the spec sheet Google found told me:

http://www.mppsolar.com/v3/catalogs/split%20phase%20LV5048.pdf

But @MichaelK answered your question.

 

[wattmatters]

Yes, that's what I said.

Yep, I was agreeing with you. Just emphasising for the OP the panel Voc rating alone isn't enough.