Newbies here, going to put 3560W solars on my 28FT RV. Voltage questions?

[Riley]

Hi, I have a 28-foot 1990 RV, and I am going to put 8x 445W 72Split-Cell Silver Mono Solar Panel by Solarever on it, which is 3560w total.

Each of them comes with an open VOC of 50.1 and a max VMP of 41.39.

My battery is 4x Ampere Time 24V 100Ah LiFePO4 Deep Cycle Lithium Battery, Built-in 100A BMS.

I was going to go with Growatts with a 48v system, but I realized they have a minimum MPPT range of 60V and max PV open-circuit voltage of 145 VDC(https://www.amazon.com/gp/product/B08HD5XQ9T/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1), which means I can't do four panels in a series.

I am concerned that this means my system won't charge on cloudy days, as the only thing I could do is two panels in serial, which is about 80V; it's barely above the required minimum voltage.

I have found "Victron Energy SmartSolar MPPT Tr 250V 100 amp". Since this system can handle 250 volts, I can do four panels in series, so I should have much better charging at sunrise or cloudy days.

Can someone confirm that I am going down the right path? Thank you!

 

[MisterSandals]

Can someone confirm that I am going down the right path?

Sounds like you have the max input issue figured out correctly.

Messing with numbers:
3560W / 51.2V = 70A available charging amps.

100Ah x 48V x 2 = 9600Wh battery
9600Wh / 3560W solar = 3.56h to recharge

Sounds like a well proportioned system.

 

[Riley]

Sounds like you have the max input issue figured out correctly.

Messing with numbers:
3560W / 51.2V = 70A available charging amps.

100Ah x 48V x 2 = 9600Wh battery
9600Wh / 3560W solar = 3.56h to recharge

Sounds like a well proportioned system.

Got it, thank you! I found 250V MPPT is too expensive. do you think just a 150V MPPT with three panels in series would be too close to the maximum? (each panel has a 50.1V open circuit, it's going to go a little bit over)

If I only do two panels in each series, do I really lose charging because of volt? I noticed these panels got 30 Volts and 0.03 amp while they sit in my enclosed garage, so it seems they can reach higher voltage than my battery anyways.

 

[sunshine_eggo]

Got it, thank you! I found 250V MPPT is too expensive. do you think just a 150V MPPT with three panels in series would be too close to the maximum? (each panel has a 50.1V open circuit, it's going to go a little bit over)

Yes. NEVER go over PV input voltage. Cold weather also causes voltage increase. At freezing, your 3S panels will likely be about 161V.

If I only do two panels in each series, do I really lose charging because of volt?

No. Higher voltage can actually be about 1-2% less efficient than voltages closer to the battery. There is a greater loss associated with the greater voltage conversion.

If you have long PV wire runs (way longer than an RV will require), the higher voltage may offset that 1-2% and possibly even improve output due to reduced power losses in the wiring.

I noticed these panels got 30 Volts and 0.03 amp while they sit in my enclosed garage, so it seems they can reach higher voltage than my battery anyways.

That's how they work. First light = voltage. As the light gets more intense, you produce more amps.

They'll be pushing ~82Vmp - more than enough for 48V and for the 60V MPPT floor.

Having an array with 2S4P vs. 3S?P (8 is not divisible by 3, but let's say you get another panel for 3S3P) is the 2S4P array will be a little more shade tolerant with the additional strings.

If you have an absorption fridge in your RV, running it on AC will completely drain your battery in 36 hours.

Growatts tend to have a high idle consumption. Not sure what you're getting, but a 3kW unit will burn 50W continuously or 1.2kWh/day - a notable portion of your total battery capacity. Higher wattage consumes more.

 

[Riley]

Yes. NEVER go over PV input voltage. Cold weather also causes voltage increase. At freezing, your 3S panels will likely be about 161V.



No. Higher voltage can actually be about 1-2% less efficient than voltages closer to the battery. There is a greater loss associated with the greater voltage conversion.

If you have long PV wire runs (way longer than an RV will require), the higher voltage may offset that 1-2% and possibly even improve output due to reduced power losses in the wiring.



That's how they work. First light = voltage. As the light gets more intense, you produce more amps.

They'll be pushing ~82Vmp - more than enough for 48V and for the 60V MPPT floor.

Having an array with 2S4P vs. 3S?P (8 is not divisible by 3, but let's say you get another panel for 3S3P) is the 2S4P array will be a little more shade tolerant with the additional strings.

If you have an absorption fridge in your RV, running it on AC will completely drain your battery in 36 hours.

Growatts tend to have a high idle consumption. Not sure what you're getting, but a 3kW unit will burn 50W continuously or 1.2kWh/day - a notable portion of your total battery capacity. Higher wattage consumes more.

Wow. didn't know Growatts consume that much, thank you so much! I think I am going with MPPT charge controllers anyways, my roof won't fit 8 panels and I am going to need 2 MPPT controllers.

 

[sunshine_eggo]

Wow. didn't know Growatts consume that much, thank you so much! I think I am going with MPPT charge controllers anyways, my roof won't fit 8 panels and I am going to need 2 MPPT controllers.

Read the other thread.