Outback Charge Controller - Panel Configuration

[Eleanor]

We're looking at installing a couple of Outback Flexmax 80 charge controllers. I've run our 180W panels through the string calculator

www.outbackpower.com/resources/string_sizing_tool/?page_id=resources&subpage_id=string_sizing_tool

and have come up with a configuration of 4 parallel strings of 4 panels in series for one controller. Each string has a maximum current of 30A so I think the total current to the controller is 120A? Am I right in thinking that anything over 80A will just be left to heat up the panels and isn't a problem? I've put -20C as the lowest temperture and this gives an maximum open circuit voltage of 139V.

I know 40A is a lot to lose at the top end but I'm more concerned about getting more output at the lower end. I think the output will be limited to 1.92kW/controller (panel MPP is 24V) so 3.84kW for both which is far more than we'll ever need. We've already bought the panels and could always add another controller later I suppose. Please tell me they won't go up in smoke wired like this! 

[Justme]

I would consider 139 far to close to the 145v cut off & more importantly the 150v release of magic smoke.

If I have this right you have 32 x 180watt panels (so 5.8kW)

But are reducing that to 3.8kW.

Whilst I am doing a similar thing with my 1.2kW 12v array (IE 100amps reduced to 80amps) I think you are taking it a bit to far.

[billi]

Eleanor

I would not stretch the configuration   so close to the limits of the controller  ,he will have to work harder and perhaps gets much warmer   ...........

I would use 5 Strings  with 3 Modules  in Series , or 7 Strings  with 2 Modules in Series

I have seen  over 2400 watt on my FM 80 Display


Oh Justme was faster

[billi]

.....How many Modules do you have ?are they exactly 24 Volt  VMpp?

Your Victron  has a 50A  charger or ?  so that would allow  upto  1200 watt  AC coupled  PV to your Victron Inverter via  an GTI(cheap)   ,if you like the rest of the panels connected as well .......


Edit :  But not sure  how that works  when battery  is full  , it would / does   work in my setup cause i start dumping power when battery is about 90%full

[Eleanor]

Thanks, I've scuttled off for a bit more of a think on this but shall return  

[rogeriko]

Which panels are they? model number?

[rogeriko]

Just connect the panels directly to the batteries you will need every amp you can get. MPPT controllers are not as efficient as they say. Why lose the watts you have just spent your money on.

[Justme]

Just connect the panels directly to the batteries you will need every amp you can get. MPPT controllers are not as efficient as they say. Why lose the watts you have just spent your money on.

I refer the good gentleman to Eleanors signature.


Not only that but all the equipment connected to the battery will be subjected to voltages they are not designed for.

Are you really suggesting that you would connect nearly 6kW with no controls?

[rogeriko]

Nothing wrong with connecting 5.8kw of panels to 1000Ah batteries it will still take 5/6 hours of full sunshine to charge them and thats without using any power in the house. The NOCT rating of the panels will probably give you only 140 watts up north so it will take even longer to charge. A SIMPLE controller to cut out some of the panels can be installed if you do not use all the power otherwise turn on the garden lights. I have some huge systems here powering street lighting etc that charge the batteries at over 200A and have yet to see the controllers reducing the charge rate. If you know how much power you use everyday you have to put about 1.5 times that amount in. If you have already bought the outback controller connect it to the right amount of panels and use the auxilliary output relay to connect/disconnect all the other panels so you are not losing any power at all. This can also be achieved with a simple voltage sensing relay that cuts in and out at say 28v. |If you live in the house 99% of the time the controllers will be running at full poweranyway. The thing with living off grid is that you always need more power so every amp counts. There is nothing more beautiful than watching those 1000Ah batteries bubbling away at 30v.

[billi]

Roger

as far as i understand it  ,the panels  produce only 24 Volt so not enough  to charge a 24Volt Battery

[rogeriko]

Thats why we need to know the model number. as long as they are 27v + mpp panels they are fine. Dont forget as voltage rises amps drop so panels are actually self regulating. I do not have a controller at all in my house and on the rare occasion when the batteries reach 31/32v the amps have already reduced by about 50% simply because of this factor. I wonder exactly which panels Eleanor has because all panels that actually are sold as 24v have a open circuit voltage of 30 something. I they produced 24v mpp panels with open circuit voltage of 30v no-one would need a controller at all the panels would self limit the charging. Look at the graph of a panels output compared to the volts and you will see what i mean.

[billi]

Roger ,  you may be right , but you may be wrong as well    (i guess Panel will peak at 27 Volt  when warm)

I have no intention  to advice someone with an expensive battery  in not getting a popper charging idea !

I assume  that Eleanor stays below 1 GBP   per  watt including the 2 outback   for her 5000 watt PV
and i assume  that Eleanors  consumption  is much much smaller than yours  and that her  loved battery  will be full each evening for more than 6 months of the year

Sure same idea  in my head , just get one outback and a solid state relay and dump all extra  ( Dump in a positive way ,ie Dump  as a hot bath  with gorgeous friend  )  (if one can connect the rest of  panels direct to the battery )

I have no problem  to experiment .....but at least  one  source  in an off grid setup  should be able to provide a proper charge


I agree  today , that i would think twice  to invest into expensive controllers   , but I can highly recommend   Outback , not  only because  of the product ,  more because of their warranty procedure  (i got two replacements  in my 5 years  outback time  without hassle shipped to my home at their costs ,  even the reason for the errors were not  cleared, ........... the errors appeared could have been my fault as well....

Billi

[rogeriko]

Yes indeed I have read all about Eleanor and her love affair with her batteries. I am sure everything will work out fine, I am just questioning the logic of putting up 32 panels and then only effectively getting the power from 20. There are many solutions to this problem. All the off grid houses here have energy hungry people living in them full time so the poor controllers never have a chance to do their fancy equalising charge/absorbtion charge/float charge. I have added extra panels to some houses to make sure the batteries do get fully charged by the end of the day even with their air conditioners on. Off Grid is not an easy science.

[biff]

Morning Billi,
             My new solar array is rated at approx 650watt, x 141vdc approx.i only have the equivelant of 4 x vmp(35.4)panels which are each rated at 24 volt. i require the voltage to go up past the 138volt to make sure that it dumps the excess into the water heater.
    Even 12 volt x 80watt panels will give off 21 volts but normally more like 17.5volts. the specs are different from brand to brand,
                                                                                      Biff

[billi]

Biff,   i know,  a  what is called  12 volt panel  is normally producing  over 17 volt  Vmp and around 22 Voc

Eleanor said hers are 24 Volt Vmp  

and   my guess is  , that the panels will not reach high enough  volts , when they are warm

Off Grid is not an easy science.

Hey Roger, thats true  , i never  considered , that my young son  would be such a big consumer  ,when i  produced  him