Is 91.24 Voc of panels combined okay for a 100/50 smartsolar?

[JanC]

Hi,

I'm just looking for some advice about exceeding voltage of MPPT controllers. I live in Portugal. Winters are very mild. It rarely ever gets below 0°. I found this coefficient factor spreadsheet that says for -1 to -5 you should calculate 1.12 times your rated Voc. So for me it would be something over 102 Voc. Is that okay, or should I rather connect the panels in parallel and buy more expensive wires.

Thanks

Jan

 

[Rocketman]

Do not exceed 100v going into the mppt. Or you may wake up one cold winter morning and your mppt is dead. (Just when you don’t want it to be dead).

Now if you want exact Voc - post all the info from your panels. Be sure and include the exact temperature coefficients. But your numbers sound about correct - so I doubt it will change.

Solution 1 - Just divide your panels in half and put half in parallel- like 2s2p or 3s2p. What size of wire are you using? - you may not need to change it.

Solution 2 - change up the mppt - 150/45 or 150/60 (I believe those are the 150v sizes around the 100/50.

Good Luck

 

[400bird]

Your panels should have a temperature compensation specification on the data sheet. Using that, you can calculate the actual open circuit voltage at the low temperature in your area.

You really do need to treat the max voltage as a hard limit. If PV voltage goes above that there is no guarantee the charge controller will survive.

 

[JanC]

Do not exceed 100v going into the mppt. Or you may wake up one cold winter morning and your mppt is dead. (Just when you don’t want it to be dead).

Now if you want exact Voc - post all the info from your panels. Be sure and include the exact temperature coefficients. But your numbers sound about correct - so I doubt it will change.

Solution 1 - Just divide your panels in half and put half in parallel- like 2s2p or 3s2p. What size of wire are you using? - you may not need to change it.

Solution 2 - change up the mppt - 150/45 or 150/60 (I believe those are the 150v sizes around the 100/50.

Good Luck

This is the datasheet of the panel I'm planning to buy. I want to buy that 485w panel x2. It's not in english, but it's probably possible to figure it out. I didn't buy anything yet, no wires, nothing. I didn't want to go higher with the controller, because the 150/45 would cost me almost 200 € extra. I was thinking of going with 150/35 instead. It would cost exactly the same as 100/50, but I would have to sacrifice some power because the amperage would be exceeded in this case. I will have a 24v battery bank.

 

[MisterSandals]

So for me it would be something over 102 Voc.

Temp coefficient of your panels looks like .34% / deg C

If it gets to freezing, 0C, thats 25 deg C change.

(45.62Voc x 2) x 25 x .0034 = 7.75V increase

91.24V + 7.75V = 99Voc

So if your panels get below freezing while fully illuminated, its possible/likely that you will exceed the Victron's 100V limit. While there "may" be some leeway built in, its likely the unit will be worthless once exceeded.

 

[400bird]

Two questions on the calculations:
Do you calculate using the temp coefficient of VOC? That would be -0.27%, a little better (for the OP using a 100 volt max charge controller) than 0.34% you used.

Second, do you calculate from 25c or from the listed nominal temperature of 43 +/-3?
That would significantly increase the cold VOC on these panels.

 

[MisterSandals]

Do you calculate using the temp coefficient of VOC? That would be -0.27%, a little better (for the OP using a 100 volt max charge controller) than 0.34% you used.

I do calculate temp compensation with Voc. The .34% i got from the attached spec.

Second, do you calculate from 25c or from the listed nominal temperature of 43 +/-3?

The spec sheet stated STC was 25C which is the standard testing conditions. Should nominal temperature be used in this calculation? I am not familiar with what nominal temp is used for...

I am willing to learn.

 

[chrisski]

This is the datasheet of the panel I'm planning to buy. I want to buy that 485w panel x2. It's not in english, but it's probably possible to figure it out. I didn't buy anything yet, no wires, nothing. I didn't want to go higher with the controller, because the 150/45 would cost me almost 200 € extra. I was thinking of going with 150/35 instead. It would cost exactly the same as 100/50, but I would have to sacrifice some power because the amperage would be exceeded in this case. I will have a 24v battery bank.

If you never plan on going to a 48 volt system, the 100/50 would be fine if you stay below 100. Record cold 99 VDC is too close for me. If it was above 90 VDC possibility, I’d be collecting data on cold days to see the temp. The real weather station is 20 miles from where I’m at and in the middle of a valley, and I’m at the edge of that valley by the mountains. My record cold is slightly different than the record cold of the weather station. I’m finding on weather underground I can’t get the historical data for my local weather station, but the Phoenix data forum 20 miles away pops up.

As a guy who bought a 100/50 for 12 volts with the intention of upgrading to 24 volts, one Reason I did not go to 48 volts when the upgrade came around was the 100/50 only does 12 or 24 volts not 48. For some of my power requirements of 2 kw for hours on end, a 48 volt system would have been nice, but not an option because that meant another SCC purchase.

 

[400bird]

I do calculate temp compensation with Voc. The .34% i got from the attached spec.

I only questioned this because I would have used this 0.27% listed here on the data sheet.

The spec sheet stated STC was 25C which is the standard testing conditions. Should nominal temperature be used in this calculation? I am not familiar with what nominal temp is used for...

I also don't know, I was hoping you did. I see both temps referenced in the spec sheet.

I am willing to learn.

Same! That's why I'm asking questions.

 

[fromport]

I only questioned this because I would have used this 0.27% listed here on the data sheet.
View attachment 126909

I also don't know, I was hoping you did. I see both temps referenced in the spec sheet.

Same! That's why I'm asking questions.

For calculating adjusted Voc:
Vadj = Voc × {100% + [(Tmod - 25°C) × TC Voc]}
Vadj is the temperature adjusted voltage
Voc is the module’s rated open circuit voltage
Tmod is the temperature of the PV module
25°C is the STC condition we must adjust from
TC Voc = Temperature correction factor in %/°C
When it gets colder Voc goes higher

Same goes for MPPT voltage:
For adjusting the Vmppt voltage:
Vadj = Vmp × {100% + [(Tmod - 25°C) × TC Vmp]}
Vadj is the temperature adjusted voltage
Vmp is the module’s rated maximum power voltage
Tmod is the temperature of the PV module
25°C is the STC condition we must adjust from
TC Vmp = Temperature correction factor in %/°C
When the temperature gets warmer, the Vmppt gets lower and

Panels in general have different Voltage correction factors for no load (Voc) and under maximum load (Vmp)

 

[HighTechLab]

Put the panels in parallel and you will be fine.

If you exceed 100v on the input, then the controller will short the PV input clamping the voltage down to 0v to protect itself.

They are difficult to get out of this protection state.

There would be no benefit (and added cost) going with the 150v controller in this situation. The only reason to go with the higher voltage is if you later plan to upgrade to a 48v system - at that point you could use the same 150v controller and add more panels to it (up to 6 panels even)! Obviously you are paying for this now instead of later though...

 

[Owen Parker]

Not to hijack this thread, but I am in a very similar situation wanting to use two panels on the roof of my van and the VOC of the xl 450w-ish panels all dancing on the edge of 50 which is cutting it too close for my Victron 100|50.

I was going to go parallel but most people say to go series as your panels will work better earlier and later in the day in the winter, etc., plus it dodges the need for more breakers and combiner box, etc. Even though I plan to never be anywhere cold in the van, it is still possible for freak cold snaps in the southern US, although if I ever am somewhere where it is below 40F, I will have made a horrific navigational error. But still...

Could I not just hit the solar disconnect if there was any chance of the temperature dropping below freezing? Or maybe even get real fancy and set up a temperature relay to do something similar? Just trying to think outside the box. I would be elevating my standing to say I was a newb when it came to all this solar 'stuff'... I'd be interested to know if it would be so simple as disconnecting the panels in an iffy scenario, weather-wise, from the gurus...

 

[400bird]

Owen,
If you have a 12 volt system, I'd just run the two in parallel with a couple Y connectors. The voltage and current is so low (on the PV side) it will be within specs on a single breaker.

You might see some clipping on the 50 amp controller. 900 watts is about 75 amps at 12 volts. But considering the panels will be flat on the roof, you probably won't see much clipping.

Do you really want to watch temps and need to remember to disconnect the PV when it's cold? What if you sleep in or need to charge the battery?

 

[chrisski]

I was going to go parallel but most people say to go series as your panels will work better earlier and later in the day in the winter, etc.,

I just ran some test for early morning production in a solstice and I got perhaps an extra 10 Wh out of 900 watts of panels by going 3s instead of 2s. Pretty insignificant.

More Panels in Series for More EarlyProduction

Do you really see earlier production by putting panels in series to exceed the charging threshold? I don't, but I'd like to hear your experiences. I thought I was getting a bit of watts doing this, but I’m not. For example panels set up 3S for a potential 66 volts to squeeze more watts early...

diysolarforum.com

I’m going to look at cloudy weather today, but I expect insignificant differences also.

 

[HighTechLab]

If the ISC is under 10 amps, 2 panels in parallel with 10awg PV wire doesn't need any overcurrent protection - the weakest link is the source - even if you short circuited a 30a fuse (the size needed to protect the wire), then the fuse would never blow because ISC is below fuse rating.

Your solar controller can operate at 5v over battery voltage. that's roughly 30vdc. Your panels have minimal output at this low of a voltage.

 

[Pi Curio]

This is the datasheet of the panel I'm planning to buy. I want to buy that 485w panel x2. It's not in english, but it's probably possible to figure it out. I didn't buy anything yet, no wires, nothing. I didn't want to go higher with the controller, because the 150/45 would cost me almost 200 € extra. I was thinking of going with 150/35 instead. It would cost exactly the same as 100/50, but I would have to sacrifice some power because the amperage would be exceeded in this case. I will have a 24v battery bank.

Personally, I would never go that high and close to the 100V SCCs limit at the STC. Maybe, I'd be comfortable enough if the total Array Voc would be at 91,24V(2x45.62V) at -5C.

Obviously, it might just be my preference.

You can always go with parallel connecting the two 485W, and it will work fine at 24V system voltage but it's not ideal. The only difference might be if you one day decide to use these two panels in series or want to use more of the same panels on the same SCC to get the most out of it.

I'd prefer to have more options down the road if possible by opting for panels that can fit in series and parallel within the SCC limits.

Best,
D.

 

[JanC]

Thank you for all the advice. I will connect them in parallel. It's probably the easiest solution

 

[Skagit]

Victron has an MPPT calculator you can put all the specs from the panel into as well as your location and the lowest temperature and then it'll do all the math for you.

 

[Pi Curio]

Thank you for all the advice. I will connect them in parallel. It's probably the easiest solution

Tell us a bit more about what kind of solar system are you planning to build.

If you are still in the planning stage and didn't yet start purchasing, there's still time to talk the design through.

Let's start with these panels you've mentioned previously, what's the cost per panel? Are these the only panels available or perhaps the maximum size you can fit within the limitations you have for solar? Please, provide a link to the store you are considering buying the panels from.

You've said it will be a 24V system, 100Ah, 200Ah?

Also, 100/50 SCC, what is your reasoning behind this SCC pick?

Talk us through the details a bit.

It's very possible there might be a more economical and better-performing design, depending on what is your ultimate design goal here. Is it a smaller system for powering essentials or something else?


Best,
D.

 

[Owen Parker]

Owen,
If you have a 12 volt system, I'd just run the two in parallel with a couple Y connectors. The voltage and current is so low (on the PV side) it will be within specs on a single breaker.

You might see some clipping on the 50 amp controller. 900 watts is about 75 amps at 12 volts. But considering the panels will be flat on the roof, you probably won't see much clipping.

Do you really want to watch temps and need to remember to disconnect the PV when it's cold? What if you sleep in or need to charge the battery?

I have a 24v battery/system. Is all of this still relevant? I have decided to run them in parallel anyway as it completely removes the issue, plus with a 24v battery, the panels would have to be running very low to not be higher voltage than the battery, plus I'll never be in the cold for very long since I'm mobile and the primary goal is to not 'do cold' .