Over paneling

this is an example for a generic set of Chinese panels where all the specs are known. notice the change in voltage depending upon temp the temp based change is from 31.62 at average high temp and 50.45 at the record low temp in the early morning. thats a single panel sox2 for two, x 3 for three etc. I would search the forum a bit for people who have used the santan panels and they might be able to give you and idea of the temp based changes

goitalone said:

What would be safe area not knowing the temps part of the equation?

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I don't use the calculators, mostly because I don't know for sure what they are doing. The equation is not that complicated, and with simple algebra you can get what you want. Here's the equation:

Vmax = Voc + (Tmin - Tstc) * (TCVoc * Voc)

Tstc (temperature at standard test conditions) is universally (I think) 25°C
Voc is the open circuit voltage of the panel at STC
Tmin is the lowest temperature that might be expected (in °C)
TCVoc is the Voc temperature coefficient for the panel you are looking at. It has units of % per °C, and is usually negative.
The equation gives you Vmax, which will be the maximum open circuit voltage coming out of the panel when the temperature is Tmin.

So you figure out what the coldest temperature will be where you are installing the panels (be conservative, and bet it will be colder than you may think), and plug in the Voc and TCVoc from the specs of the panel.

Horsefly said:

I don't use the calculators, mostly because I don't know for sure what they are doing. The equation is not that complicated, and with simple algebra you can get what you want. Here's the equation:

Vmax = Voc + (Tmin - Tstc) * (TCVoc * Voc)

Tstc (temperature at standard test conditions) is universally (I think) 25°C
Voc is the open circuit voltage of the panel at STC
Tmin is the lowest temperature that might be expected (in °C)
TCVoc is the Voc temperature coefficient for the panel you are looking at. It has units of Volts per °C, and is usually negative.
The equation gives you Vmax, which will be the maximum open circuit voltage coming out of the panel when the temperature is Tmin.

So you figure out what the coldest temperature will be where you are installing the panels (be conservative, and bet it will be colder than you may think), and plug in the Voc and TCVoc from the specs of the panel.

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problem is the specs are not listed on the site he posted with the santan panels. if somebody has the specs for that panel as pictured its easy to calculate.

ken morgan said:

problem is the specs are not listed on the site he posted with the santan panels. if somebody has the specs for that panel as pictured its easy to calculate.

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Ooops. My bad. I just assumed he had that.

With some sleuthing on the Google, he could probably figure out the manufacturer and model of the panels, and find a spec sheet. Short of that, he could just use the coefficient from another panel, keeping it a little high just in case. My panels have a TCVoc of -0.31%/°C (I'll fix my other post, as the units are not V/°C).

Horsefly said:

Ooops. My bad. I just assumed he had that.

With some sleuthing on the Google, he could probably figure out the manufacturer and model of the panels, and find a spec sheet. Short of that, he could just use the coefficient from another panel, keeping it a little high just in case. My panels have a TCVoc of -0.31%/°C (I'll fix my other post, as the units are not V/°C).

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no worries, you have always seemed to be very helpful to others. i was trying to help him but without the TCVoc all i could do was say aim for xx and pray.

Well, think I'll just go with four 410W panels and do what I read a guy on the EcoFlow FB community did with one of his Delta Pros:

Voltage (Vmp)* 31.35
Current (Imp)* 13.08
Quantity* 4

All panels wired in series =

Volts: 125
Amps: 13.08
Total Power: 1635
Loss % 0

Should be ok I think.

Thanks for the help...wish me luck I guess!

goitalone said:

Well, think I'll just go with four 410W panels and do what I read a guy on the EcoFlow FB community did with one of his Delta Pros:

Voltage (Vmp)* 31.35
Current (Imp)* 13.08
Quantity* 4

All panels wired in series =

Volts: 125
Amps: 13.08
Total Power: 1635
Loss % 0

Should be ok I think.

Thanks for the help...wish me luck I guess!

Click to expand...

Careful! You should be using the Voc (instead of Vmp) to determine the maximum voltage you will see. You said your Voc was 37.2V, so four in series will be just under the max 150V your system can take. If the temperature at sunrise is only a small bit under the 25°C at which the Voc is spec'd, you will exceed the 150V max input of the Delta MPPT, and it *WILL* fry it.

Horsefly said:

Careful! You should be using the Voc (instead of Vmp) to determine the maximum voltage you will see. You said your Voc was 37.2V, so four in series will be just under the max 150V your system can take. If the temperature at sunrise is only a small bit under the 25°C at which the Voc is spec'd, you will exceed the 150V max input of the Delta MPPT, and it *WILL* fry it.

Click to expand...

Wait, so it should be VOC * Imp?

Voltage (VOC)* 37.12
Current (Imp)* 13.08
Quantity* 4 = 148 VOC?


BTW, I found the data sheet for the 410W panels I was considering:



That help any?

And could someone point me to a calculator I could use to figure the temp part out?

And which temp/temps are used again for the calculations? ?

Wait, think I found one:



Still don't understand it.

goitalone said:

Wait, so it should be VOC * Imp?

Voltage (VOC)* 37.12
Current (Imp)* 13.08
Quantity* 4 = 148 VOC?


BTW, I found the data sheet for the 410W panels I was considering:

View attachment 110766

That help any?

And could someone point me to a calculator I could use to figure the temp part out?

And which temp/temps are used again for the calculations? ?

Click to expand...

Good. The specs include the "Temperature Coefficient of Voc" as -0.29%/°C That is the number that plugs into the equation I posted earlier.

You asked if it is Voc * Imp. Not sure what you are asking, but it is the Voc that will burn up your MPPT.

Here's how it works. On a cold morning just as the sun is starting to touch your panels, there is no current being produced, so what is there is the Voc (open circuit voltage). The Voc is higher as the temperature goes down. So on an especially cold morning the Voc of each panel will be higher than the spec Voc, which is at STC (Standard Test Conditions) of 25°C. Midnite Solar coined the term "Hyper Voc" for this extreme Voc at cold temperatures.

So let's say that the coldest you would ever expect the temperatures where you mount your panels will be at 32°F, which is 0°C. The equation I posted earlier was:

Vmax = Voc + (Tmin - Tstc) * (TCVoc * Voc)

So now we have all the variables for your case:
Voc = 37.12V
Tmin = 0°
Tstc =25°
TCVoc = -0.29%/°C

So the Vmax, which is the open circuit voltage for that panel at 0°C, is

37.12 + (0 - 25) * (0.0029 * 37.12) = 37.12 + (-25 * 0.107) = 37.12 + 2.6912 = 39.811V

That is for one panel. Now if you put four panels in series, the total max Voc is 4 * 39.811 = 159.2V

Since your MPPT says it can handle a maximum of 150V, there is a very high likelihood that on one cold morning your MPPT would be fried by those four panels.

Hopefully that all makes sense. Hyper Voc is one of the things that really needs consideration in most parts of the country.

goitalone said:

Wait, think I found one:

Temperature Coefficient for Photovoltaic Modules online Calculator – Photovoltaic for Europe

www.pv4.eu

Still don't understand it.

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That doesn't deal with how Voc changes with temperature. It's only showing you how the power goes up or down with temperature.

I'm not certain, but I think if you do a search on "Hyper Voc" you may find a calculator. Of course, you can just use the equation.

Wet1 said:

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

Click to expand...

There ya go! (Although, I still prefer to just use the equation, rather than hope some random website gets it right)

Edit to add: I plugged in the numbers from above, and it does give the right answer. So in this case, that calculator is good!

Horsefly said:

There ya go! (Although, I still prefer to just use the equation, rather than hope some random website gets it right)

Edit to add: I plugged in the numbers from above, and it does give the right answer. So in this case, that calculator is good!

Click to expand...

I had calculated mine a while ago. IIRC, I came up with the same numbers they did.

Wet1 said:

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

Click to expand...

Thanks, I had already saw and booked marked that site yesterday, but now from last several replies from you two, I now understand the whole picture.

So, would wiring in series/parallel change the Hyper VOC or no?

I keep reading that the MPPT will/should limit to 15A if you go over like in series parallel.

Should this not be attempted?

I really had hoped to be able to charge closer to the solar max of 1600W and if I had known all this, I probably would have built my own system with a controller with higher voltage limits.

goitalone said:

So, would wiring in series/parallel change the Hyper VOC or no?

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Panels in series makes the voltages add together. In parallel the currents add together. So if you have two panels in series, the hyper Voc for the series set is 2 * 39.81 = 79.62V. If you take another two panels in series and put those two, 2-series panels in parallel, the hyper Voc stays at 79.62, and the current is double what it would be for one series set.

goitalone said:

I keep reading that the MPPT will/should limit to 15A if I gone over like in series parallel.

Should this not be attempted?

I really had hoped to be able to charge closer to the solar max of 1600W and if I had known all this, I probably would have built my own system with a controller with higher voltage limits.

Click to expand...

Generally (I don't know your MPPT), the voltage limit on an MPPT is a hard rule. If you go over it, it will probably cause damage to the MPPT. The current limit on an MPPT is generally the max the MPPT will output. Even if you have more power coming into the MPPT, the MPPT will limit the output current to 15A.

The idea of over-paneling is that you can put extra PV panels on, so that even when the panels are not putting out their max power you can still get 15A out of the MPPT.

Ok, so this is what I ended up with:

150V/15A/1600W
===============

New Risen 335W Solar Panel
$150.00 x 6

3s2p:

Open circuit voltage (VOC): 45.9 V
Max power voltage (VMP): 37.65 V
Short circuit current (ISC): 9.40 A
Max power current (Imp): 8.90 A

Mixed configuration - Each spec wired in Series, then all wired together in Parallel

Volts 112.949


Amps 18
(18 - 3 = 15A)

Total Power 2034W
(15 x 112.949 = 1,694.235)

Maximum Voltage Calculator​

Solar panel open circuit voltage (Voc)

45.9

Number of solar panels wired in series

3

Lowest expected temperature

32°F

Temperature coefficient of Voc

-0.32%/°C
-
Calculate

Maximum open circuit voltage of your solar array:

= 148.7V

Sound about right?

Yep, I put those numbers into the equation I posted earlier, and it works out to be 148.7V. That's really close to the 150V max for the MPPT (if the MPPT hasn't changed). Are you very, very, very sure that the temperature will never get below 32°F? If so, you are probably OK to use those panels, 3 to a string.

yes, I live in Central Florida and if it were ever forecasted anywhere near that I'd just not use it.

goitalone said:

yes, I live in Central Florida and if it were ever forecasted anywhere near that I'd just not use it.

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Ok, but just to be clear: "not using it" means you will disconnect the panels from the charge controller.

Correct

Or I could disconnect 1 panel off each string.

I’ve been reading this thread.
I thought measuring the panels at the point where they plug into the EcoFlow Delta Pro with a voltmeter would give you the correct cumulative total volts?
Mine always read about 65 volts with
180w panels x 6
In series.