150.8 VOC on 150v SCC?

[Smeeg]

There are used 245 watt panels with a VOC of 37.7 each for $50 each on FB marketplace close to me. My plan was to use a MPPT SCC with 150voc max could I use 4x panels in series?
37.7 VOC x 4 = 150.8 VOC I was hoping this might be possible since the panels are used?
(Northeast USA NY it defiantly gets cold here)

 

[pollenface]

You realise that's 37.7voc @ 25°c

I suggest 3s for 113.1voc and put any spares on another SCC or use for other projects.

 

[hwy17]

Panels go over VOC when it's cold so that's way too high unless it's a midnite with hyperVOC.

Maybe 4 in a 2 parallel 2 series config?

 

[Smeeg]

You realise that's 37.7voc @ 25°c

I suggest 3s for 113.1voc and put any spares on another SCC or use for other projects.

Do people normally run two smaller SCC then run two different series strings to them or do they wire the panels in parallel with one SCC?

 

[pollenface]

Do people normally run two smaller SCC then run two different series strings to them or do they wire the panels in parallel with one SCC?

You can do either, but you have to stay well below the voltage limit of your controller. Voltage rises as temps fall.

What's your coldest temp that you've ever felt where you live?

 

[zanydroid]

What's your coldest temp that you've ever felt where you live?

Isn't it better to use ASHRAE climate data or PVWATTs data (if it shows it's work on min temp in its CSV output) than semi-guessing?

Or, starting from the official data and then adjusting temps down for safety based on memory feels. I don't trust adjusting to more lenient side for VOC frying risk based on human memory

 

[Smeeg]

You can do either, but you have to stay well below the voltage limit of your controller. Voltage rises as temps fall.

What's your coldest temp that you've ever felt where you live?

It can get into the teens like 13-19 fahrenheit

 

[Hedges]

Do people normally run two smaller SCC then run two different series strings to them or do they wire the panels in parallel with one SCC?

two strings in parallel is fine, unless 2x Isc exceeds ratings of inverter for input.
How does wattage of four panels compare to battery voltage x amperage of SCC?

Two strings in parallel, if shade falls on one you're more likely to lose entire output of string, compared to two MPPT or two SCC.

You can orient the two strings differently, catch morning and afternoon sun for more hours, lower peak current.

It can get into the teens like 13-19 fahrenheit

Use historical record cold for your location.

But in your case, 2s is fine. Extreme cold and temperature coefficient causes up to about 16% increase in voltage, not 50%

 

[Smeeg]

two strings in parallel is fine, unless 2x Isc exceeds ratings of inverter for input.
How does wattage of four panels compare to battery voltage x amperage of SCC?

Two strings in parallel, if shade falls on one you're more likely to lose entire output of string, compared to two MPPT or two SCC.

You can orient the two strings differently, catch morning and afternoon sun for more hours, lower peak current.



Use historical record cold for your location.

But in your case, 2s is fine. Extreme cold and temperature coefficient causes up to about 16% increase in voltage, not 50%

So a 150 VOC max is really 124 VOC max?

 

[Hedges]

150 VOC max is 150 VOC max, for SCC.

124 Voc for a PV string at 25 degrees C could be 150 Voc at -27 degrees C, assuming -0.4%/degree C.

Some panels have -0.4% temperature coefficient, some -0.3% or other value.
I used -15 degrees C as a very conservative figure for my location.
(-15 - 25) x -0.004 = 0.16, positive 16%

The engineers at Midnight got clever with their classic, and if voltage exceeds 150 they don't start the switch-mode buck converter.
They can tolerate Voc up to 150V + battery voltage without damage.
Not aware of any other brands with that feature, so you have to design to record coldest temperature. Just select panels by specs.

 

[Smeeg]

150 VOC max is 150 VOC max, for SCC.

124 Voc for a PV string at 25 degrees C could be 150 Voc at -27 degrees C, assuming -0.4%/degree C.

Some panels have -0.4% temperature coefficient, some -0.3% or other value.
I used -15 degrees C as a very conservative figure for my location.
(-15 - 25) x -0.004 = 0.16, positive 16%

The engineers at Midnight got clever with their classic, and if voltage exceeds 150 they don't start the switch-mode buck converter.
They can tolerate Voc up to 150V + battery voltage without damage.
Not aware of any other brands with that feature, so you have to design to record coldest temperature. Just select panels by specs.

Thank you I found this calculator to play around with its helpful. The more I think about I think two SCC with a series string to each makes more sense since the wiring is easier & if one SCC fails the whole system isn’t down

Solar Panel Maximum Voltage Calculator - Footprint Hero

Calculate the maximum open circuit voltage of your solar array. Find your max solar panel voltage to correctly size your solar charge controller.

footprinthero.com

 

[Hedges]

Just remember to make temperature coefficient a negative number like it says!
I tried it, got wrong answer because I entered as positive.

PV panels have come down in price to where a quality MPPT SCC may be significant fraction of cost, or even as much.
I would guess if you're using a 12V battery and 40A SCC, 2 of your panels would about fully load it on a cool clear day. Had they been a lower wattage panel, 2s2p might have been a better fit.

Higher voltage battery like 24V or 48V lets SCC process considerably more power, in which case more panels on one saves you money.

For an inexpensive system, look into AIO that have both MPPT SCC and inverter. Among those, there is a range of Voc allowed, some supporting longer strings.

 

[efficientPV]

It can get into the teens like 13-19 fahrenheit

I thought you said you lived in NY.

 

[pollenface]

It can get into the teens like 13-19 fahrenheit

oops, posted, then saw you already found a calculator