Outback Charge Controller - Panel Configuration

[Eleanor]

The panels have MPP voltage of 24V and open circuit voltage of 30V 

[Eleanor]

Thanks for all the suggestions. My babies are going to have a charge controller and we'll just go for installing half the panels next week with one Outback and look at what to do with the rest later. Probably go for 5x3 or 7x2 to get the open circuit voltage down. We can easily wire the panels as suggested to disconnect some if necessary. The whole system is oversized and geared towards getting the most out of it in the winter months and as Billi has said our usage is very low so losing output in the summer shouldn't be a problem.

[rogeriko]

Seeing as they are 24v mpp panels they are perfect for charging the batts when they are low ie 23/24v. As the batteries charge the voltage rises and the panel amps will drop. Actually at 30voc there will be no current at all produced by the panels. So put half on your controller and the other half directly connected with a manual switch so that when the batteries are down which is how they are going to be all winter you can connect all for a few hours to boost the charge rate and then let the controller finish the job.

[Justme]

 

Put them in a 50/50 east/west set up.

Then the east facing ones can be uncontrolled & the west facing ones controlled.

[billi]

Like said  before , if a part of panels  uncontrolled  are able  to be connected  directly  to the battery , the outbacks Aux relay  is able to switch those on and of in relation to battery voltage , while the others connected to the MPPT of the outback will carry on charging , as well Eleanors Victron can switch an AC  load on at say 28 Volt  and of at say 27   V

So i would agree that possibly  one  Controller is fine

 

Billi

[rogeriko]

Good idea Justme, full power in the morning and controlled charging in the afternoon to finish the cycle. The controller manufacturers must be hating this thread.   I can just see the advertisments now, Self Regulating Solar Panels for Battery Charging.

[billi]

would you  install a setup for your customers with a 10 thousand  Euro Battery  (for example)  , without a proper chargecotroller ,Roger ?

[rogeriko]

I do install controllers on my systems but if I had Eleanors 24v panels that cannot possibly overcharge the batteries I would love to try an experiment with them. Actually yes there are 3 setups here without a controller and nothing bad has happened. the first one is mine I have a voltmeter in the kitchen and we just turn stuff on. The other two are in houses with 1000ah batteries but the ladies living there refuse to cook on gas they cook on electric everyday and then use the dishwashers. So maybe occasionally the batteries get a full charge and equalise but it is definately not a daily occurence. These systems were installed years ago and the owners both said "why" when I told them I could put controllers on their panels. Flooded batteries are fairly lenient but AGM and GEL batteries definately need a controller.

There is one situation that I have encountered that even charge controllers cannot help and that is when 1 battery in the string goes bad/short then the controller thinks the battery voltage is low and goes on full/boost charge and kills all the batteries.

[Outtasight]

As strange as it may seem, given my usual ramblings on MPPT charge controllers and batteries, I concur with Rogeriko (almost).

The defining factor here is that the surplus panels that can't produce power through the Outback are just the right Vmp rating (24.0V) to provide maximum power boost with no controller when the batteries are flat.  But only when the batteries are flat at 24.0V and only when the panels are used singly and in parallel with short, high current capacity wiring.

By the time you get to 27.3V (float level) the panels will be so far off their Vmp point and in the near vertical drop on the power curve, heading towards the Voc point where they produce no power at all.

In fact, they're a little bit on the low side in terms of Vmp to be truly usable singly.  This is because to connect them to the battery without a controller, you need reverse current blocking diodes installed on each panel that is in parallel.  This will reduce the available Voltage by 0.5-1.0V (depending on how good a diode you use).  Otherwise, by the time your Outback has pushed the bank up to 27V and more, the uncontrolled panels will be drawing reverse current and loading the system.

But then I'd have reverse blocking diodes on all the PV strings at the point where they combine to prevent partial shading losses from one string to the next, even on the strings connected to the Outback input.  This applies where you have more than 2 strings in parallel or where part of the array is at any risk of partial shading from trees or the like.

But the diodes will mean that these panels will only deliver full power when the bank is on death's door at 23.0V.  If that's not what you're after then you have to go for at least 2 panels in series and a charge controller, preferably a MPPT one.

Hot weather will also stop the single panels from working at all.  Above 25C their Voltage probably drops away by 0.1V per degree C and so by 30C, you're down another 0.5V...

Unless your panels are connected by massive wires just 50cm long, you'll lose another couple of points of a Volt in the wiring.

So it's looking more and more marginal that single 24.0Vmp panels can significantly charge anything but a 24V battery bank that is heading for the scrap yard 

Now, taking in all the little Voltage losses above, panels that have a Vmp of 26.0V at 25C would work a charm without a charge controller (but again only as a bulk phase booster).

[biff]

I have been lucky enough with our voltage of 120vdc.i believe i can configure almost any kind of panel to fit into the system as long as the amps are near enough.I have a few 2kw chinese controllers,2kw for wind and 600wattt for solar in each controller.I plan to have 3 strings heading into a forklift bank approx 600ah(at least),with 3 seperate controllers sending the excess power150ft into the house to power the water heaters,,ordinary immersion heaters.
    It should be simple enough as long as i dont have any switches and wire the dump straight into the immersion without the thermostat.These controllers have a big sign on the front which paul would love "MADE IN CHINA", but i had a feeling from word go which is a few years ago that these controller would be good because they made sure that nobody could mistake their point of origin and sure enough they are an exellent controller.I have seen one of these controller being mistakenly abused so much they got so hot the digital clocks on the from all read 8888888 and i could not put my hand near it,i used a big house fan to cool it down and loaded everything to the hilt and 10 minutes later all was hunky dory in the storm.
  So my plan is to have these three strings,two to heat water and one to compliment the wind turbine, the controllers dump at 138vdc,which some people might think is a bit low,however it means that the water heaters will get more power.I would like to be able to set each controller to dump a little later but i am not sure how to do that,perhaps a longer cable from the batteries,?
Oh,!! and today is a fantastic sunny day with my first 120volt array dishing out 127 x 5amps continiously since 10.30am,
                                                                     Biff