arranging 24 panels

larrybc1 · November 2011

hi..just wanted to see if I am figuring this right..have 24-, 210 watt evergreen panels and intend to arrange them as follows:
2 strings of 6 panels to 1 FM-80 controller and
2 strings of 6 panels to the other FM 80.
VOC is 23.1 VMP is 18.3, IMP 11.48 and ISC 12.11 amps..
It will feed a 48 volt battery bank..so my calcultaions are as follows:

VOC is : 6X 23.1= 138.6 (max 150)..climate is tropical never below 70 degrees
VMP for charging 48 volt battery bank is: 109.8 (18.3 X6)

AMPS is 2560 watts/48 =52.5 for each array/ controller...

Is this the correct way to figure it? thks for the help again Larry

BB. · November 2011

Re: arranging 24 panels

Looks OK to me... By the way, I think your total array wattage is 2,520 watts, not 2,560 (is not going to change anything).

I am no expert, but does not the Outback controller have a shutdown at 140 VDC (and cancel warranty above 150 VDC)? Have you read the Outback requirements in detail around that point?

You are close--but if you never go below 70F--looks OK.

-Bill

stephendv · November 2011

Re: arranging 24 panels

Why not do 3 x 4 instead so as not to surf so close to the edge?

niel · November 2011

Re: arranging 24 panels

stephendv wrote: »

Why not do 3 x 4 instead so as not to surf so close to the edge?

i totally agree that 3 strings of 4 is much better and safer for the controllers. why chance it? this may change the v drop for your wiring, but it may be necessary to upgrade the wiring rather than risk the controllers in the higher voltage arrangement.

ggunn · November 2011

Re: arranging 24 panels

BB. wrote: »

Looks OK to me... By the way, I think your total array wattage is 2,520 watts, not 2,560 (is not going to change anything).

I am no expert, but does not the Outback controller have a shutdown at 140 VDC (and cancel warranty above 150 VDC)? Have you read the Outback requirements in detail around that point?

You are close--but if you never go below 70F--looks OK.

-Bill

Just to add - a lot of gear these days has "black boxes" that record the maximum DC voltage that has been applied to it. Even if your gear survives an overvoltage event, the fact that it happened is recorded, so if you ever have a warranty claim over any issue at all, the first thing the manufacturer does is check that register. If you have ever stressed the unit with an overvoltage condition they will use it as a reason to deny the claim and void the warranty (i.e., deny all future claims) on that piece of gear.

Vic · November 2011

Re: arranging 24 panels

I'm with stephen, three strings of four panels.

Assuming that this IS off-grid, as this is that section, then at this power level, there is a 48 volt battery bank(?), then four modules per string would yield a string Vmp of about 73.2 volts -- just enough if there IS a 48 volt battery.

Running these MPPT CCs at a Vin of 110-ish volts reduces the efficency. This loss shows up as heat in the CC. From my experience with MX-60s with a Vin of 106ish volts, is that the CC's fan runs more than I like when in Float, and in warm weather, as the efficency loss is not linear vs rising Vin, but some exponential factor. If the OP's climate is such that it never gets below 70 F, then, summer heat for the Power electronics could easily be a factor.

For a new porject here, have decided on a string Vmp of about 93 volts for the Midnite Classic 150s, having learned from the current 106 V to the MX CC.

And, ggunn, is correct about the current gen CCs. They seem to record the Voc Max. Think the Fm CCs have a max Vin of 145 volts for operation, and the warranty voiding V is 150.0. My MX CC has a high Voc of 141 V now. Was 139 V , until last Winter.

Perhaps too many assumptions on my part. Vic

larrybc1 · November 2011

Re: arranging 24 panels

stephendv wrote: »

Why not do 3 x 4 instead so as not to surf so close to the edge?

If I did the 3 strings of 4 wouldnt the problem be that i would be close to min charging level for a 48 volt battery banK? 18.3 VMP X 4 = 73.2 It is going to be in a hot climate on a metal roof so was concerned about charging the 48 volt battery bank thks Larry

Vic · November 2011

Re: arranging 24 panels

Hi Larry,

(One of the issues in attempting to help someone configure a system, is information regarding that system and its environment. I am not able, just now, to perceive just where this system will be located).

OK, so, I believed that most probably the configuration of four panels per string with three strings per array. I, normally, would like to run a sting Vmp of around 90 volts. BUT, this seems a bit difficult, as strings of five panels is not a handy divisor for the quantity of 24 panels.

Sevaral questions for you, Larry:
!. What is the exact model number of the panels? or better yet, a link to the data sheet.

2. What is the nature of the battery bank, and its environment. I assume that the batteries will probably be FLAs, but what do I know. And, when the panels are Hottest, what do you think the battery temp will be?

3. Roughly, what might be the Lat/long of the site?

Strings of five would be better, but this this does not seem to work out with the 24 panels you mentioned.

The largest functional issue running strings of four would be trying to EQ a cool or cold battery bank with HOT panels. The CC needs about 3ish volts of headroom for its operation, that is, Vin would need to be about three volts above the target battery voltage for the charge stage the CC needs to perform. This string voltage would probably be OK, but, cannot really know without some more info from you.
Thanks, Vic

larrybc1 · November 2011

Re: arranging 24 panels

Vic wrote: »

Hi Larry,

(One of the issues in attempting to help someone configure a system, is information regarding that system and its environment. I am not able, just now, to perceive just where this system will be located).

OK, so, I believed that most probably the configuration of four panels per string with three strings per array. I, normally, would like to run a sting Vmp of around 90 volts. BUT, this seems a bit difficult, as strings of five panels is not a handy divisor for the quantity of 24 panels.

Sevaral questions for you, Larry:
!. What is the exact model number of the panels? or better yet, a link to the data sheet.

2. What is the nature of the battery bank, and its environment. I assume that the batteries will probably be FLAs, but what do I know. And, when the panels are Hottest, what do you think the battery temp will be?

3. Roughly, what might be the Lat/long of the site?

Strings of five would be better, but this this does not seem to work out with the 24 panels you mentioned.

The largest functional issue running strings of four would be trying to EQ a cool or cold battery bank with HOT panels. The CC needs about 3ish volts of headroom for its operation, that is, Vin would need to be about three volts above the target battery voltage for the charge stage the CC needs to perform. This string voltage would probably be OK, but, cannot really know without some more info from you.
Thanks, Vic

exact model number is es 210 fa3 evergreen 210 panels..[URL="http://www.solarsystemsusa.net/evergreen-es-a-210-watt-poly-solar-panel/

will probably be FLA batteries in an enclosure..not sure what batt temp would be but average outside air temps there at my location in Philippines would be a low temp of 75 degrees and high temp of 87 degrees

location roughly N 1430.0 and E 119.30
thks for the help Larry

stephendv · November 2011

Re: arranging 24 panels

Eeesh, tricky to get some panels to fit nicely into a 48V system while still being under the 140V limit. With the 2 x 6 you're quite close to the 140V limit, and with the 3 x 4 and given your highish temps you're potentially looking at a Vmp of 66V (while requiring about 65V for EQ). Not ideal.

If you haven't bought the controller yet, consider getting one of the midnite solar models with the hypervoc functionality that can handle 198V Voc. If that's not an option, perhaps go for the 3 x 4 configuration and see whether you can comfortably EQ in summer (all the while taking real measurements of Voc in winter if you can) - and if you can't EQ then change to 2 x 6, at least you wouldn't have destroyed a controller at that point. Not sure really

Vic · November 2011

Re: arranging 24 panels

Hi Larry,

Thanks for the added info, will look @ it later today, BUT, I think that four modules per string would be OK, and you could still EQ any reasonable FLA battery via PV.

However, still, the ideal string config would be five modules per string.

If you could consider this, and could snag one additional module, then one array of three strings of five, and one array of two strings of five, this would allow you to have great margins and use all of the PV that you have ... but just need that pesky additional module.

When battery temps rise, all of the battery voltage parameters drop. When the PV modules warm, their voltages also drop. One problem in EQing can present itself when the batteries are cold, and the PV HOT. The Power curves of PV modules are fairly flat, such that if there is insufficient PV Voltage available at the ideal Vmp, the MPPT CC can often find a point where there is enough V to EQ, but with less current available. THe situation you derscribe, where the battery bank is in an enclsure (assuming this is outside), can allow the batts to warm a bit during the hottest season, thus lowering the required EQ voltage a bit. AND, if you had another charge source other than the PV, EQ could easily be done from a grid or generator connection in case the PV power was insufficient. Generally, the highest EQ voltage is about 64 volts @ 25 degrees C, will look at the temp comped Vmp of the Evergreen PV you will be using, later today.

And, if this were my system, I'd probably use the Midnite Classic sereis CCs, but still, I think that six modules per string in a hot climate is asking a lot from any 150 Vin max rated CC.

Here are the Power Charts for the Midnite CCs:
http://www.midnitesolar.com/images/classicFrontPage/graphs.php

More later, Vic

Cariboocoot · November 2011

Re: arranging 24 panels

Just to mention that when you're looking at V-max in of charge controllers that is based on Voc. Voc will be achieved the moment light is on the panels, i.e. first thing in the morning. Even in a "hot climate" it is not necessarily hot at that time of the day. Deserts, for instance, are notorious for being extremely hot by day and extremely cold by night. Even deserts located at latitude 52 degrees.

BB. · November 2011

Re: arranging 24 panels

If cool weather is rare--You could wire up a couple switches to swap in the the panels (panels in when warm, panels out of circuit when cold/first thing in the morning).

I wonder is it would be worth wiring in a thermal switch (there are industrial thermal switches with SPDT configurations). Automate the low temperature detection to avoid a (possibly expensive) mistake.

Once the sun is up and shining, typically the panels are going to warm up quite a bit.

-Bill

Vic · November 2011

Re: arranging 24 panels

Good comments, Coot and BB,

From personal experience, running highish Vin to the CC in warm climates causes the "tounge to hang out" on the CC, even when delivering surprisingly low currents during float. Here with the 106 Vmp string V, in Float during the summer, it is common to see the string V to run about 123 V. Even when delivering 1.5 to 2 amps to the battery bank, the MX-60 fan would run at about 30% duty cycle. This was with an ambient temp in the eithties F in the power room.

Naturally, having some largish opportunity loads will bring down the Vin to a more reasonable value. And we now do run A/C in the power room and elsewhere, which brings down Vin and also cools the environs, which helps the CC rid itself of heat.

IMHO 90-95 volts into these legacy CC (MX and FM) is just better for their innards, reduces string I, compared to the four module approach, and delivers robust margins, as well as creating smiles on the CC's screen.

MHO, Vic

mike95490 · November 2011

Re: arranging 24 panels

My array of 15 evergreens is in 5x3, I have 20F in winters, and 105F in summer. 6 was too much, 4, not enough. Most charge controller home pages have a string calculator on them, to input your Panel and temp ranges, and it comes back with how good of a match it is.

Cariboocoot · November 2011

Re: arranging 24 panels

Also if a charge controller shuts down from high Voc early in the morning, it may not come back on-line when the panels warm up and the Voltage drops. Midnite Solar's will (the hyperVoc is a wonderful addition) but I can tell you from experience that some of the MX60's won't, others will, depending on which version is running and what the Voltage gets up to.

Best to err on the side of caution and set the system up so that this possibility is remote. At least you don't have to worry about the 1.3X Voc factor we deal with up here!

BB. · November 2011

Re: arranging 24 panels

Vic, you probably are correct... But assuming that is true, it does limit the positive benefits of MPPT (high array voltage and low array current).

I wonder how that works out with the other major controllers out there (Midnite, MorningStar, etc.).

-Bill

larrybc1 · November 2011

Re: arranging 24 panels

Vic wrote: »

Good comments, Coot and BB,

From personal experience, running highish Vin to the CC in warm climates causes the "tounge to hang out" on the CC, even when delivering surprisingly low currents during float. Here with the 106 Vmp string V, in Float during the summer, it is common to see the string V to run about 123 V. Even when delivering 1.5 to 2 amps to the battery bank, the MX-60 fan would run at about 30% duty cycle. This was with an ambient temp in the eithties F in the power room.

Naturally, having some largish opportunity loads will bring down the Vin to a more reasonable value. And we now do run A/C in the power room and elsewhere, which brings down Vin and also cools the environs, which helps the CC rid itself of heat.

IMHO 90-95 volts into these legacy CC (MX and FM) is just better for their innards, reduces string I, compared to the four module approach, and delivers robust margins, as well as creating smiles on the CC's screen.

MHO, Vic

Hi All.thks for all the great info..I need to make sure the system is right because once I get the stuff down to my location will be very hard to order anything else..looks like the best thing to do is snag one more panel and run 3X5 strings to one controller and then 2X5 to the other...so then VMP would be 91.5 (18.3X5) for five panels and the VOC drops down to 114 (22.8X5)...any other considerations before I order the other panel? thks Larry

Vic · November 2011

Re: arranging 24 panels

Larry,

If you can manage to get the additional panel, this seems to be the best of the available approaches.

Good luck with the new system. Vic

arranging 24 panels

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