Single Classic 150 Max Array Size Help

[Matrix]

I have 9 REC TwinPeak 2 Poly 285w panels.  I have used the MN Solar sizing tool several times to try and configure more panels at 285 watts STC  for a larger Array ... but it looks like I have maxed out at 9, no matter how I configure the Series and Parallel connections.    Best I can do is 3S 3P

Is there a way to safely configure more panels into the Classic 150?  What am I missing? 

Then I thought.   The panels are rated at 285w STC ... but will they really ever do that much on my roof?  I have never seen more than 2000 watts AND the NMOT rating is 214w per panel.  So I ran the numbers using all the NMOT specs from the REC spec sheet.  And if I plug those numbers into the Sizing Tool ... it looks like I can run a 3s 4p array and a total of 12 panels. 

Is it safe to use the NMOT specs (some spec sheets call it NOCT) for sizing an Array?   Is there any other way to get a larger array on a single Classic 150?

Attached are the 2 different results using the sizing tool.  One for the 285w and One for the 214w. 

[ClassicCrazy]

The only time I ever see the maximum power output of a  PV is when it is well below zero degrees F and sunny in the winter - not much humidity to interfere with sunlight potential . They put out more power when they are colder - at least the silicone type PV do . Sometimes they are even over their sticker rating. But the rest of the year - nope .

I am guessing the design doesn't want too many watts on there so the controller isn't getting so hot . The other consideration is the VOC  on those very cold days I mentioned above.

I didn't look at the alternative specs you are using so won't comment on that .

Larry

[Westbranch]

the problem is a SPIKE in the voltage made by the PV, as noted by others, that occurs at sunrise, in winter, when the sun first hits the panel,, logically at the time the PV is at its coldest....  and exceeding Hyper VOC is not a warrantied item...

It is not good to design  a system that will have the equipment , ie CC, run at > 75 to 80% of max values.... beyond those % the excess is usually  dissipated as HEAT and excess heat is detrimental to electronics...

If you want more input the safest  way is another CC, either a KID or a Classic, array size determines the cost effective choice...

hth

[Vic]

Hi Matrix,

First,   have you seen this Document (?):
http://www.midnitesolar.com/pdfs/Classic-String-Sizing-Tool.pdf

You really should use the STC rating when inputting data into the MN  String Sizer.

NOCT  (Normal Operating Cell Temperature)   is probably estimated by the Classic String Sizer.   A quick rule-of-thumb to approximate operating conditions for PV Power production,   is to multiply STC rated power by 0.75   ...

In your data for STC values,   you note that your coldest temperature is 50F.   Believe  that you are in FL,   but  is 50 F,   essentially the coldest temperature ever recorded  for the location of the system?

As it is,   the Sizer results note that the Classic 150 will enter HyperVoc  at about -99.4 F,  in the first set of Sizer results.

On a 24 V system,   seems that you really should NOT add one more string of 285 W PVs.   Would not suggest adding any more PVs at all.   This is one of the main drawbacks of 24 V (and especially 12 V) systems.   CCs are rated for maximum current output.   A 24 V system  can only produce (nominally) half the power of a 48 V system,   for the same CC output current,   and it seems that you are right about at maximum.   There can be small additional differences in the exact difference,  based upon the relative differences in the PV String voltages into the CC,  and this added effect on efficiency  of the CC.

IMO,   FWIW,   Vic

[Matrix]

OK,  Thanks.  I was pretty sure I was near Max.  I have seen a few systems in the "Owner Installed System Pics" forum that were 24v and a few I found were larger Arrays than  my 2.5 KW array,  So I thought Maybe I had missed something.  I would like to add 3 more 285w  panels, making my system a 3.4Kw system  ... but I guess that is out of the question.

Does the Kid work in with a Classic in Follow me Mode?  Does it have any Aux ports?

And no,  that we DO get colder than 50*,  I was  in a hurry and thinking more about average lows and not lowest single lows.  The coldest I have even seen it here at night was 15* and that was one night in 14 years.  Annually we have a few times where it hits mid-low 20's before sun up.  On those days it probably warms to around 45 mid day.   So over site in my part.     Thanks for pointing it out.

[ClassicCrazy]

No the Kid will not work in follow me with the Classic far as I know.

You can look up the control features in the Kid manual .

Larry

[estragon]

I think you could safely add pv to a classic by setting a sane output current limit to prevent it from running flat out for too long.  Maybe something like 75a?

The advantage to doing this would be to use the extra pv to still get a decent amount of current from the array in light overcast conditions.

[Matrix]

I think you could safely add pv to a classic by setting a sane output current limit to prevent it from running flat out for too long.  Maybe something like 75a?

The advantage to doing this would be to use the extra pv to still get a decent amount of current from the array in light overcast conditions.

Would the limiting be done by settings inside the Classic 150/local app?  Or is there some other way to limit current "to prevent it from running flat out for too long"?    I think there is also a setting to limit input voltage.  Would that help ... to set it say, slightly higher than it is now with a 3s3p array,  but limit the input voltage from the array so that a 4s3p array would not exceed the CC's voltage and amp maximums ? 

This would obviously not be the best use of the New Arrays potential power,   but it would at least allow for a slightly more powerful array that would not exceed the CC's max ratings.    And I can get 3 panels cheaper than the cost of 3 more panels plus another Classic 150. 

[ClassicCrazy]

Remind me again what are you trying  to do ?
A friends system has a second controller of a different type and we just set that voltage absorb about a volt less than the main controller so it will cut out before the main and not interfere with anything but still add power when the batteries are low.

Larry

[Matrix]

Remind me again what are you trying  to do ?
A friends system has a second controller of a different type and we just set that voltage absorb about a volt less than the main controller so it will cut out before the main and not interfere with anything but still add power when the batteries are low.

Larry

I am trying to increase my array size so that I can get - even just a few 100 - extra watts power off the array.   This way I can run a larger hot water heater element off of AUX 1 diversion, without doing a direct connection to the heater with a separate array.  The wire runs are just to complicated for that. 

I am just looking for ways to increase the arrays output for the least amount of money, or system set up changes.  Adding 3 more panels to my existing 3s3p in a 4s3p arrangement would be the easiest and most cost effective.  But as of now based on feed back in this thread, I do not think a single Classic 150 can work with a larger array .... unless ... as noted above ... there is a way to limit current and / or voltage from the larger array to keep it with in the operating specs of the Classic 150.

[Vic]

Matrix,

Not much time now ...

I did not run 3S X 4 through the Sizer,   you  can see what this yields.

One added string of PVs with close (+/- 5% or so),  but with fewer watts/PV may let you approach the Max recommended of 1.2 Classics.

Going to 48 V is probably expensive ...   Later,  Good Luck,   Vic

[estragon]

I think you could safely add pv to a classic by setting a sane output current limit to prevent it from running flat out for too long.  Maybe something like 75a?

The advantage to doing this would be to use the extra pv to still get a decent amount of current from the array in light overcast conditions.

Would the limiting be done by settings inside the Classic 150/local app?  Or is there some other way to limit current "to prevent it from running flat out for too long"?    I think there is also a setting to limit input voltage.  Would that help ... to set it say, slightly higher than it is now with a 3s3p array,  but limit the input voltage from the array so that a 4s3p array would not exceed the CC's voltage and amp maximums ? 

This would obviously not be the best use of the New Arrays potential power,   but it would at least allow for a slightly more powerful array that would not exceed the CC's max ratings.    And I can get 3 panels cheaper than the cost of 3 more panels plus another Classic 150.

You can limit both/either input and/or output current, from the menu it's under charge->limits.  I think it's also settable in LA. 

If your bank will take more current, or you have another way to use more current that would be produced by adding a second classic and more pv, you might want to consider doing so.  2 classics running at well under max load would likely last longer than a single classic running flat out, and also gives you some redundancy for when one fails.

Adding another string and limiting current makes most sense if your climate is such that you often get lightly overcast days.  I find having extra pv helps get to absorb on days when I otherwise likely wouldn't.

[Matrix]

Matrix,

Not much time now ...

I did not run 3S X 4 through the Sizer,   you  can see what this yields.

One added string of PVs with close (+/- 5% or so),  but with fewer watts/PV may let you approach the Max recommended of 1.2 Classics.

Going to 48 V is probably expensive ...   Later,  Good Luck,   Vic

Thanks vic.  I have run Run the numbers thru the sizer at STC for a 285 watt 4s3p array.  Unless there is a safe way to limit things ... 4 285 watt panels in series and using 3 parallel groups is just too large for one classic.  Unless there is a way to do limiting that is safe and effective ... all-be-it limiting the arrays potential.

I may just start planning now for another set up 9 panels and a second classic.  But boy that is a bunch of wiring.  :/   Going to 48v is not really in the budget.

[dgd]

Thanks vic.  I have run Run the numbers thru the sizer at STC for a 285 watt 4s3p array.  Unless there is a safe way to limit things ... 4 285 watt panels in series and using 3 parallel groups is just too large for one classic.  Unless there is a way to do limiting that is safe and effective ... all-be-it limiting the arrays potential.

Matrix,
There is absolutely no need to limit 'things' if you were to connect your 4s3p array to a Classic 150. It does not matter what the array is capable of in power production, the Classic will not be damaged or blow up or let the magic smoke escape,,
All that will happen is that the Classic may current limit at its rated 90+ amps for a 24v battery bank. As long as the classic is mounted in a common sense location where there is sufficient air flow around it then temperature should also not be a problem. You can take some simple steps to mitigate temperature increase, don't cram other stuff next to it, consider mounting it on a plate of aluminium or old large heat sink, etc..
In any case the internal fans will keeps it operating and even if the electronics or pcb get too how then the Classic will shut downuntil it cools down (I have never seen this ever happen with the 40+ Classics i have installed)
As for the nameplate wattage of your PV array, you will often actually get significantly less than this, even on a bright sunny day, maybe 70 to 80% and obviously much less on average days.
Having an over sized array will mean greater daily power into your bank because with low power generating conditions the larger array will raise the minimum power level through the Classic.
My own PV array is twenty 140W PVs in a 5s4p array which nameplates to 2.8Kw with pV voltage 90v into a Classic 150 charging a 24v battery bank. Despite others opinions that the Classic will heat due to the 90v to 28v conversion I rarely hear the turbo fan working even when the output current is 85+ amps.
I have the Classic in a basement garage where temperate varies not to much fron 23c
its on a wood wall with a 400mm by 200mm plate of 10mm aluminum plate behind it and a real thick layer of heat sink compound between them (mostly squeezed out!)

dgd

[Matrix]

dgd, when u say 'turbo fan' is that the only fan in the classic? My fan runs off and on regularly thru the charge cycle. Is that the same fan as the turbo fan?