charging a 48v battery bank from 24v 300w solar panels

[genicide]

Will I be able to charge a 48v 170ah agm battery bank from 24v polycrastalline solar panels

 

[mmacleod]

With the right charger and quantity of panels yes, you will ideally want an MPPT controller and to put your panels at least 2/3 in a string so that combined voltage is higher than 48v.

 

[genicide]

My batt bank is 4 strings of 170ah monbat 12 gel batteries. And I want to use 18 x 300w 24v panels to charge them

 

[ProAsm]

You have several choices on what to do here.
1. Run your panels in 2 sets of 9 with each set of 9 going to it's own 24 volt controller charging half the battery set, ie 24 volts.
2. Run your panels in 2 sets of 9 then series the 2 together giving you 48 volts.
3. Buy a 24 volt Inverter
Only problem you going to have here is your total charge will always only be 2700 watts instead of 5400 which I think is what you intended in the first place.
The only possible problem I see doing it as in (2) above is the actual voltage, because a 48 volt panel actually puts out 58 volts, whereas a 24 volt panel actually puts out 37 volts, so when seriesing 2 of these you gonna end up with 37 x 2 = 74 volts instead of 58, so hope your controller can handle that.
Maybe go for (1) above, but like I say, it depends on your controller.

 

[mmacleod]

A decent MPTT charge controller should be able to take 150V, you'll have to look at the maximum voltage output specs for your panels to see how many you can have per string and to figure out how many amps per string (so you can get a charge controller with right amp rating).

Assuming the right charge controller I don't see why you would have any problems.

 

[oober]

At 5400W/48V you have 112 Amps, good luck finding a charge controller that can do that. You probably going to need 2 charge controllers.

Edit. Or not. http://www.bhgpower.co.za/product/120a-mppt-solar-charge-controller-12243648v/

 

[mmacleod]

At 5400W/48V you have 112 Amps, good luck finding a charge controller that can do that. You probably going to need 2 charge controllers.

Assuming he can put 3 in series in a string for 150v max (what most MPPT controllers take as max these days) - which is of course a big assumption the Voc for 24v panels may be too high for that.
And assuming 15A per string (bit of a thumbsuck), that is a 90A controller roughly, which is towards the higher end of whats on the market but is available, two 50A controllers that work together is perhaps a better option though.

Of course the above is all just thumb sucking, without the actual panel specs with the Voc and max amps etc.

The main question is, are the batteries actually big enough to warrant that much juice, or should he rather either have more batteries or make some of panels rather just go straight to the inverter.

 

[oober]

Assuming he can put 3 in a string for 150v max (what most MPPT controllers take as max these days) - which is of course a big assumption the Voc for 24v panels may be too high for that.
And assuming 15A per string (bit of a thumbsuck), that is a 90A controller roughly, which is towards the higher end of whats on the market but is available, two 50A controllers that work together is perhaps a better option though.

Of course the above is all just thumb sucking, without the actual panel specs with the Voc and max amps etc.

The main question is, are the batteries actually big enough to warrant that much juice, or should he rather either have more batteries or make some of panels rather just go straight to the inverter.

Sorry how do you get to a total of 90A? 300W * 18 = 5400W. You need a controller that can output at ~48V. Ie 5400/48 = 112.5A. Assuming no losses.

 

[mmacleod]

Sorry how do you get to a total of 90A? 300W * 18 = 5400W. You need a controller that can output at ~48V. Ie 5400/48 = 112.5A. Assuming no losses.

Ergh, yeah you are right, sorry temporary brain slip I was so focused on the input amps that I forgot to also check the output amps.
So realistically he probably needs 2x 60A controllers or 3x 40A controllers, 120A controller is large. Though I still wonder if its maybe not oversized for the batteries.

 

[genicide]

Ok what would you suggest I do here is my load profile I have 30 led 3w ligts total, 1.1kw borehole pump that wil run 20min per day, 2 garage motors, 1 gate motor 2 selfone chargers, microwave 800w, double door fridge freeze A+++ rating box deepreeze, 2 dstv decoders 1x 50inch led 1 x 32 inch led, 300w woodsaw for about 1 hour a day, ligts I was told to run off 12v, the inverter I am using is a devel sps 6000w with 45A mppt charger and I will have another mppt 100A charger, the batteries is 180ah monbat gel vrla batteries, if need be I will change some of this system

 

[zeely]

Ok what would you suggest I do here is my load profile I have 30 led 3w ligts total, 1.1kw borehole pump that wil run 20min per day, 2 garage motors, 1 gate motor 2 selfone chargers, microwave 800w, double door fridge freeze A+++ rating box deepreeze, 2 dstv decoders 1x 50inch led 1 x 32 inch led, 300w woodsaw for about 1 hour a day, ligts I was told to run off 12v, the inverter I am using is a devel sps 6000w with 45A mppt charger and I will have another mppt 100A charger, the batteries is 180ah monbat gel vrla batteries, if need be I will change some of this system

what about geysers?

 

[thehuman]

what about geysers?

Solar geyser .
Directly heating water with sun is alot more efficient than photovoltaic → battery → inverter → element

 

[richjdavies]

Pumps are hard:
1.1kw borehole pump -- the cranking amps on that might be a problem
Woodsaw - same problem, when it starts it will likely use > 300W... how much more will depend on how much load it's under.

Wouldn't want to break you inverter and kill your batteries just because some grit got in the borehole!

 

[thehuman]

Will be beter to get a borehole pump made for solar panels