Gday,newbie here,appreciate any help

Mungrelguts

New Member
Joined
Jun 25, 2022
Messages
6
I’ve been given 12x 250w panels and need some educating on size of controller and bank capacity for an off grid 12 volt system.
 

curiouscarbon

Science Penguin
Joined
Jun 29, 2020
Messages
2,293
good day,

connecting solar panels in series is generally a good design choice.

each battery charger has a maximum safe voltage input limit. some are 75 volts, some lower, some much higher. it's very important to set it up so that voltage limit is never reached in practice.

temperature will change the voltage of a solar panel. usually colder means higher voltage. often listed as a percent change per degree C. usually 25C is the base temperature.

connect two identical panels in series, that will multiply voltage by two.

the safest way is to find weather record of lowest temperature ever seen in the location(s) it will be installed at, then calculate what each individual panel's voltage would be at that temperature, then use that to calculate how many can be connected in series before magical smoke might start escaping from the charger.

this way, if you have three "40V" panels connected in series and expect 120V max and connect it to a charger than can only handle 130V max, the low temperature at your location can cue you into limiting to two in series if it results in more than 43.33 V sort of deal.

hope this helps, good luck with your project ☀️
 

Bobert

Solar Addict
Joined
Jan 15, 2022
Messages
763
I’ve been given 12x 250w panels and need some educating on size of controller and bank capacity for an off grid 12 volt system.
Unless you already have other equipment it will probably be cheaper and better to go with 24 or 48v. This high amp 12v controllers are expensive.
 

Mungrelguts

New Member
Joined
Jun 25, 2022
Messages
6
Thanks mate,it does help,educating myself on this subject is my priority for now so all info is great..Im in northern Australia so 25C is extremely rare and for only one or days a year if any.My daily usage is low and my wife and and I have adjusted our lives to 12v appliances mainly,we still need and use now an inverter and generator.im trying to figure out the size of controller and banks we need to balance the system.We acquired 12x 250w panels so am building it from the top down..we can always use more power if need be.
 

Mungrelguts

New Member
Joined
Jun 25, 2022
Messages
6
Thanks mateWhat’s a ball park figure for something I’d need? With a 24/48v system would I need to adjust everything else?,happy to pay as we already live off a12 v system just obviously not as big as the panels we now have
 

Mungrelguts

New Member
Joined
Jun 25, 2022
Messages
6
Yes,I’d like to be able to run the air con without the generator,plus run a larger freezer outside,also to grow into it as we build more,lights ,fan etc,plus we could easily use more power now just to balance the excess
 

Mungrelguts

New Member
Joined
Jun 25, 2022
Messages
6
We live in the bus now and are at the limit of our solar power usage ,we are about to build on the other side and I’d like to set the new solar system up under the roof D0DC63AF-01B2-4F17-99AE-FA164090D10C.jpegDED77FA1-7CCF-4F76-A74B-0E4A50DB8B38.jpeg
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
11,561
12 panels x 250W = 3000W (under ideal conditions, normally 75% to 85% of this)
3000W / 12V = 250A, / 24V = 125A, / 48V = 62.5A
If you orient half the panels towards morning sun and half toward evening, about 0.7x as much current.

Planning for lots of growth, definitely go 48V. You can add a DC-DC converter or battery charger to give some power to 12V system.
You need to get all specs from PV panels, ideally their data sheet (gives temperature coefficient too.) Then you can design a series/parallel array within voltage and current limits of a charge controller or all in one inverter.

You need to determine the wattage of all simultaneous loads and the starting current of large motors (typically 5x running current.)
Also consider ambient temperature. Wattage capability of inverter derates when hot.

My system is grid-backup. When grid is down, PV is enough to power A/C, and small battery provides starting surge. Large PV array, extra power just doesn't get used. With your array making 1500W to 2500W, need small enough AC to power that and charge batteries.
 

Mungrelguts

New Member
Joined
Jun 25, 2022
Messages
6
Thanks mate,the air con is small,even if we start it with the generator,happy to do it.orientation is limited to northerly.im in northern Australia,I understand the starting loads of all we need,just trying to get my head around building it from the top down in lamens terms..I’ll be researching the 48 v set up and how I can adjustA084CA75-8E1F-4847-9085-FCB4DDE6B6CE.jpeg
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
11,561
Make everything work/start automatically without the generator. Maybe disable some devices when running others to stay within inverter capacity.

Data sheet https://gold-coast-solar-power-solu...ds/2015/09/JA-Solar-250W-panel-data-sheet.pdf

Temperature coefficient of Voc -0.33%/degree C. You can use that and your location's record coldest temperature (how many degrees below 25 degrees C) to determine how high Voc will go. Probably something less than 16% voltage increase.

Biggest question is how much you want to spend. There are 48V inverter/chargers around US $1500, and others run several $thousand. Depends on power, quality, brand. 3kW, or 30kW? And choose battery. Probably a lithium battery 5kWh or larger would accept the full output of your PV array. If you do have any large motors (pump, etc.) battery needs to supply the surge.
 
Top