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Need HELP! 9.1kW solar system charging batteries with my generator.

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as simply as i can put it is there are some math errors:

i only see crown offering 390ah rated batteries in a 6v meaning your battery bank is wired in series meaning your going up in voltage NOT in ah.  this means you have a 48v bank with only 390ah, 16 of these batteries wired series parallel would get you 48v at 780ah and so on.

the solar array should be wired series parallel as well and provide a consistent 4,560watts  and about 147-150 working amps for i.e. charging batteries or covering system usage from the inverter etc. 


a weak link is your solar controller.  your current controller is only capable of an 80ah charge rate.  only a bit over half of what your solar array can provide.  this means slower charge and less available power.  adding another midnite solar controller wired parallel would give you up to a working 160A charge rate.  and allow you to utilize the full power available from your panels.  capable of handling slightly more than what you have available from your solar array and would be recommended.

as far as generator charging, the generator charges the batteries using your charger inverter.  the 3 stage charge setup should take almost 2 hours to charge these batteries from 50% and maintain maximum efficiency.  where as your solar also utilizes a 3 stage charging process but currently will take twice as long (at full capacity in bright sun) to charge unless you add another controller.

as far as your question pertaining to ac wiring YES the gen output would wire to the ac input of the inverter as long as you dont already have grid power or any other form of ac power going to the input.  if you do you would need a transfer switch.

recommendations: add a solar controller. and your current battery bank at 48v does NOT have sufficient reserve to run without charging for a long period of time.  there definitely needs some adjustments.  either 8 more of what i believe are currently 6v batteries to make a 2nd bank wired series parallel or even going with the crown 290 12v, 8 of these series parallel would yield 1160ah. adding the 8 you already have gives a total of 1550ah.  but this all requires revisiting the solar controller and redoing the charge time math. 

great setup none the less.  on the right track.  i have done solar installations professionally for about 16 years now.  if you would like more info feel free to PM me im glad to help.  :)

addendum, you do NOT need to worry about overcharging or frying your batteries charging from gen power or solar as your inverter charger and solar controller are 3 stage and have over charge protection.  i would be more concerned with the overall ah of the system and with depleting to a 50% charge frequently.  definitely try not to let the batteries get that low before charging unless absolutely necessary.

tdry253 said:

"01 - Four star classic 150 double PV center includes MidNite Solar Classic 150 MPPT Charge Controller"


"and two MMPT charge controllers".

He has multiple AC inputs on the Radian GS8048, for grid and generator, no need for a transfer switch to flip between them.

10% of C/20 is what the battery manufacturer recommends (39A), or a max of 25% of C/20 (97.5A).  The batteries will get more cycles out of them following the recommended amperage (but at the cost of more propane and generator wear if his oversized array can't keep up with the current draw).  But for griddown, if the generator does run at the lower amperage to charge the batteries at the recommend rate anyway, then it's also a good time to run the well pump, turn the frig/freezer up to "high", vacuum the house, make something in the microwave, let the women folk blowdry and curl their hair, watch a movie, etc   

If he configures the Radian setpoints correctly for the batteries it'll start the generator and charge the batteries automatically at whatever charging amps specified and shut it down when the charging it complete - there's no concern the batteries will drain too deeply (unless the genny fails to start and he didn't set the cutout voltage on the Radian correctly).  And contrary to one statement above, the inverter works if the grid is down.

Don't understand the grief everyone is giving tdry253 about the sizing of his system or suggesting he doesn't understand "the math".  If his plan is to sell back to the grid now and have a small battery backup (and generator) to run a few critical items if the grid goes down I think he made fine choices on his gear.  Seems to me that either some don't understand what he has or don't understand how what he has actually works.

BOTH the math and the description of the batteries etc have changed since the first post.

My maths is based on the items listed and 16 years of certified experience in the industry. I quote by what's listed not what the website says may have been available in a package that he may or may not have. I offered my expertise and assistance and I stand by it. 8 6v 399ah batteries wired in series to get a 48v system is only 390ah no ifs ands or buts. You up in voltage you don't up in ah. That's how it works. And crown does not list a 12v 390ah battery so unless it's an unlisted 12v 390 ah battery then the bank is only 390ah.

C value means nothing. The batteries do NOT control how fast they are charged. The inverter charger and the solar controller controls the charging rate. Both are 3 stage chargers to maintain maximum efficiency.

At the end of the day the battery bank under a nominal load obviously relative  with what he has turned on will yield approx 4 hours before fully depleting the usable voltage and he only wants to deplete to 50% so that's about 2 hours. 

Not really up to debate. If my experience and advice is not wanted I assure you no hard feelings. I do this every day. Free advice was just a Courtesy.


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