Adding to system question

hillside

That's what we do, right? Add to our system?

So after no response to my last questions--(I don't blame anyone; I'm hopeless, I know )

I have 3 panels ready to add to my basic system. With these 4 L16 batteries, I've been told here that I need in the range of 1300-1400Watts, (Currently at 1000W)

The 4th panel I was going to buy is not available, so with 3 good panels (235W) should I wire them in series or parallel?

I will use a Steca 30Amp PWM controller. Unless advised otherwise, of course. (But it's on the shelf of slightly used parts.)

littleharbor2

235 watt panels are 60 cell 20 volt nominal panels. You need an MPPT controller to properly use them. You haven't mentioned your system's voltage. What is it?

BB.

Yea... As LH2 says, we really need details. Many (most/all?) 235 Watt panels are Vmp~30 volts, although, you may have some ~36 volt panels too (not 20 volt--typo I think). 

For a PWM controller on a 24 volt battery bank, you need a Vmp~36 Volt panels (72 cell) to have high enough voltage to reliably/quickly recharge your battery bank.

In very hot/sunny weather, you can get a Vmp drop to 80% of STC ratings (rough numbers)-- 80% of Vmp-std 30 volts is 24 volts... And you really need >30 volts to charge a 24 volt lead acid battery bank.

Note that Vmp curves are relatively rounded... So, if your battery bank is at 25 volts, you will still get some charging current... But we want to do this right. Details matter.

-Bill

hillside

The 4 panels now show (at peak sun) 65.7 volts at the controller (from the panels) and they are in series/parallel.

I've seen a high of 29V on the controller but that was only once, while most peak readings show 28V.

Someone here suggested adding another string with it's own separate controller to boost the wattage for these batteries. So this would not be connected to the first array except to feed more to the batteries. (Correct?)

I'd rather do that than scrap the new SRNE 40A controller I have now as it wouldn't take the wattage/amps.

If needed I'll buy another mppt controller.

The panels I 'd like to add are 3 Hanwha 235, Vmp 30.1, Voc 36.8, Imp 7.81 and 1

Thanks

littleharbor2

BB. said:

Yea... As LH2 says, we really need details. Many (most/all?) 235 Watt panels are Vmp~30 volts, although, you may have some ~36 volt panels too (not 20 volt--typo I think). 



-Bill

My reference to 20 volt panels, as noted is referring to their "Nominal" voltage in an off grid, battery charging sense. Just as 12 volt batteries are nearly dead at 12 volts and need to be charged at up to 15+ volts when doing corrective charging.. 72 cell panels are considered 24 volt NOMINAL as 36 cell panels are considered 12 volt nominal. If there were 20 volt batteries these 60 cell panels would be perfect for charging, using a basic PWM controller.  Granted, some of the 300+ watt 60 cell panels have high enough voltage to properly charge and equalize a 24 volt battery. As cell efficiency increases the voltage of panels also increases and some day this NOMINAL reference may not apply as it does today.

Photowhit

Please give people enough information to answer you question, I'm pretty sure this is my 3rd time suggestion this to you! Perhaps the reason for;

hillside said:

So after no response to my last questions

The panels you are thinking about with a "235watts, Vmp 30.1, Voc 36.8, Imp 7.81" Will be hard to add, they are too low a vmp to be effectively used on a24 volt system  with a PWM charge controller, and can't work with many/most inexpensive MPPT type charge controllers because the VOC for a string of 3 will be above 100 volts (above the limit, as I recall, on your current MPPT charge controller) and in parrallel, the charge controller doesn't have the facility to raise the voltage, so you have the same problem with too low a voltage.

Look around and see if you can find a good deal on some 72 cell panels, they would havea vmo high enough to be effectivly used on a 24 volt bank in parrallel,  so long as thee isn't a long distance to the charge controller/battery bank.

hillside

It's a 24 volt system Sorry I left that out/-corrected.

Here is the current set-up: 4 250V panels.

In some way, can I add 3 more 235W 24 V. panels to produce the needed wattage or amps to satisfy these large batteries?

hillside

250 WATT panels

hillside

If I recall, the suggestion was adding another string separate from the first with it's own controller...as it was stressed that I don't have enough wattage with the one array for these batts.

Photowhit

hillside said:

In some way, can I add 3 more 235W 24 V. panels to produce the needed wattage or amps to satisfy these large batteries?

If the panels  are the " Vmp 30.1, Voc 36.8, Imp 7.81" panels  then you would have to use a  MPPT  type  charge  controller that could  handle   a string of 3 panels, with the higher  VOC of  the  string.  Might look into the different MPPT type controllers  to see if there is one that  can handle  120  volts or  so  maximum voltage. 

I'm  sure the  midnite Classic 250 would and there is sort of a deal on them unless sold out   that   were made  for  a special order/system and somehow Midnite  has   been left   holding them. They  are  a  stripped   down  version, but Midnite makes good   stuff.  The ones  sold    by private  vendors  don't  have a warranty,   but  Midnite was  sellinng  some   with  the  remainnder of the 5  years from manufacture  warranty.

Discussion about them here;

http://midniteftp.com/forum/index.php?topic=4606.0

I think many/most of the less expensive MPPT type, like yours and the Renogy Rover, don't wat to  see anny  more thann   100   volts  (VOC).

If you can find some 72 cell panels at reasonable cost, they could be used with a PWM charge controller and likely a lower overall cost.

Photowhit

FWIW - If the panels are the " Vmp 30.1, Voc 36.8, Imp 7.81" panels, they would not bbe considered  24 volt nominal panels. to be considered 24 volt nominal panels,  the panel should produce 35 - 42 volts VMP.

hillside

If I go with the MidNite 250 should I wire the 3 in series or parallel?

Photowhit

hillside said:

If I go with the MidNite 250 should I wire the 3 in series or parallel?

In series! Almost  all  the MPPT type charge controllers can't increase voltage only reduce it. So in  parallel, you would still have only 30.1 VMP and realistically something more  like  28 volts  max once  warm ( NOCT), before running through the charge controller. 

In series The Midnite Classic can handle 250 volts VOC (adjusted to your low temperature)

They have an online calculator to see what it can handle;

http://www.midnitesolar.com/sizingTool/

hillside

Thanks...got time for a stupid question?

I can afford the MidNite Classic, or some other high end controller. But I recall reading (here, I think) that the controller does not step up charging but steps it down to keep the battery bank from overcharging.

So, what does a $700-1,000 controller do that a $200. MPPT can't?

BB.

The step up vs step down... We are talking about input voltage to the controller vs output voltage to the battery bank.

Solar charge controllers are, for the most part, buck mode switching power supplies. A "buck converter" can only take higher voltages and down convert them to lower voltages. And they tend to be the most efficient type of switching converter, and if you are, for example, setting up your array 10's to 100's of feet from the charge controller/battery shed, the higher voltage solar array cost much less in copper wire from the array to the battery shed (something like 1/8th the cost of copper wire if you double the array voltage).

https://en.wikipedia.org/wiki/Buck_converter
https://en.wikipedia.org/wiki/Boost_converter
https://en.wikipedia.org/wiki/Buck%E2%80%93boost_converter

There are boost converters (that raise voltage from input to output, and buck-boost converters that can take high/same/lower input voltages to output voltages). Just not usually done because there is not really much need (it is generally "free" to make a higher voltage solar array by wiring panels in series or series/parallel connections--Plus the savings using thinner copper wire).

There are a few boost solar charge controllers out there... Genasun is one that I am aware of:

https://sunforgellc.com/genasun/ (click on browse product)
https://genasun.eu/

Perfectly good solar charge controllers (as far as I know). Just tend to be smaller size (4-10 amps?) for portable applications.

In general, what makes MPPT charge controllers is the relatively large inductor (typically a toroid) inside the charge controller (cost of copper and cost to "wind" the inductor). Some MPPT charge controllers have relatively low input voltages (less than 100 VDC max input), and others are higher (140-150 VDC to 600 VDC). Higher input voltage controllers tend to cost more. And the typical higher end off grid MPPT controllers are around 60-90 amp output (typically 12-48 volt or a bit higher battery bank nominal voltage).

You can find very inexpensive MPPT charge controllers--Some are OK, others are not. And many of the "cheap" variety over the years have shown to be PWM type controllers with "MPPT" simply stamped on the outside of the case.

Generally, the higher cost MPPT charge controllers have more internal programming options, sometimes external outputs (for controller vent fans, optional loads, etc.)... And some have Internet Servers inside to allow partial or full control over the Internet.

The higher cost controllers have a generally good reputation (some folks do have issues). And the under $200 MPPT controllers--There are some out there that seem to be OK... Others not so good.

While our forum here is hosted and paid for by Northern Arizona Wind & Sun (NAWS or https://www.solar-electric.com/), "we" (NAWS) does not have any problem with us discussing any and all models and brands of solar related equipment. If you or others here have some particular brands/models you want to discuss--Go for it.

-Bill "not an employee or paid by NAWS volunteer moderator" B. 

Photowhit

BB. said:

You can find very inexpensive MPPT charge controllers--Some are OK, others are not. And many of the "cheap" variety over the years have shown to be PWM type controllers with "MPPT" simply stamped on the outside of the case.

People calling PWM controllers 'MPPT' had gotten so prevalent that some of the cheap ones sold on Amazon would even 'fess up' to them actually being PWM controllers even when marked MPPT. Now you will often see inexpensive ones showing the 'guts' so you can see the coil which makes converting the voltage possible.




As to the cost difference, better features, wider specs, and more dependability (some of which comes from having wider specs/parameters). For example your 30 amp MPPT only accepts up to 100 volts VMP, Midnite makes one for around $300 that accepts up to 150 volts and can pretty much handle any over paneling (current wise)

I some of the features of the Midnite 250 have been removed so they could make it less expensively for the contract. It has the older version of the Graphics panel with out voice/speaker (which is removable and can also be remotely  located like inside, for people like me who's system is installed in another shelter.) I'm not sure if it's disabled in that version, but the Classics can also send a small current out when the charge controller reaches a set point, like reaching 'float' it can send a current out to trigger a relay to start loads. Nice when you want to run a load and not draw down your battery, such as a water heater. In this manner you could run the water heater only off of available 'extra' power from your array and not from the battery bank.

If the  charge controller can handle wider  input and deliver wider output, then there  should be less stress onn the system to deliver well within specs. This  could often be seen in other electronics you  may encounter, like inverters. If they have a narrow range of acceptable input voltage, then they have, in general, a cheaper build. 

hillside

Wow, great answers, thank you guys.