Help me decide 24v or 48v

malibuskier

I am upgrading the solar system on my houseboat and need some advice.  Here are my current components:
8 - Lifeline L16T 6v batteries (400 AH)
4 - 250W panels (soon to be 6) - 4 Astro Energy & 2 Kyocera
Outback Flexmax 80 charge controller
Magnum mini power center
* Currently I have a Magnum MS2812 inverter.  I am going to purchase a new one either MS4024 or the 48v version if I go with 48v system.

I have an old Kohler 7.5kw generator as well.

All my lights run off 12v and there are enough of them that a DC to DC converter will be part of the system.  I just don't really want to mess with converting everything to 24v or 110v.  

I'm looking for any guidance/advice/pros & cons about 24v vs 48v before I purchase my inverter/charger.  Any help would be appreciated.

Dave
 

Estragon

The only reason I can think of off-hand to go with 24v is you would have two strings of batteries, so when a battery fails you could unhook one string and still have power (though 1/2 capacity). I assume you have no equipment that runs 24v.

You can sometimes get by with a bad battery in a 48v system by taking the bad one out and basically run a 46v system by adjusting inverter and controller settings though.

With a 48v system, the controller is putting out 1/2 the current to the batteries, which is easier on it. Same with the inverter, though I assume an equally rated inverter would have beefier components to handle the higher currents. The 80a controller should be fine with 6 panels, but 48v gives more ability to add if you want.

One potential issue is pv wiring. At 48v, 2 strings of 3 may work best. At 24v, 3 strings of 2 may be better. If the specs are close on the panels, it likely won't matter.

With 2 strings of pv, you could get away without a breaker on the + of each string, but I would install them anyway as they can be handy for switching if need be.

Photowhit

So is there a reason for the upgrade? is the 2800 watt inverter not cutting it? I would assume your primary charging is from the genny. The array is undersized for your battery bank, heck you have @900lbs of batteries!

If the batteries are fine and not too old, you should be fine and likely better off switching and increasing the array would mean an additional charge controller if you stayed at 12 volts....

...but if it's working for you, I would keep it until the batteries fail then look at upgrading. I know 4 strings of batteries is not a great idea, but to keep things at their lowest cost, I like to wait until something fails or is about to fail.

In general <2000 watts of panels and you should be fine on a 24 volt system, if you intend to move to a larger array then I would seriously think about moving to a 48 volt system.

malibuskier

Photowhit said:

So is there a reason for the upgrade? is the 2800 watt inverter not cutting it? I would assume your primary charging is from the genny. The array is undersized for your battery bank, heck you have @900lbs of batteries!

If the batteries are fine and not too old, you should be fine and likely better off switching and increasing the array would mean an additional charge controller if you stayed at 12 volts....

...but if it's working for you, I would keep it until the batteries fail then look at upgrading. I know 4 strings of batteries is not a great idea, but to keep things at their lowest cost, I like to wait until something fails or is about to fail.

In general <2000 watts of panels and you should be fine on a 24 volt system, if you intend to move to a larger array then I would seriously think about moving to a 48 volt system.

Inverter upgrade is due to 2800w limit.  Short term useage loads make the 4000w a worthwhile upgrade.  Batteries are also new - upgraded from 6CT (300 AH).  6 panels fit comfortably on the penthouse roof but I could fit 8 with a little creativity.  I'm just trying to be as smart as I can with what I have.  The panels are the primary charging system and the generator is an on demand/as needed type thing.  We really only run a refrigerator, gas stove (who knew a gas stove would pull so much 110v - 30 amps to broil!) and a 32" tv.  

Dave
  

Estragon

>  We really only run a refrigerator, gas stove (who knew a gas stove would pull so much 110v - 30 amps to broil!) and a 32" tv.  
>
> Dave
>   

I assume it's a gas stove with an electric broiler element- the sort of thing you only use at the dock, not on the hook. Might be worth considering an upside down broiler (aka grill)!

That said, I put a 2kw inverter on the boat because the admiral likes foamed milk with coffee, and only the microwave could do it. Turns out the milk works better on a gas range in a metal pan and a mixer gizmo, so the inverter rarely gets used.

softdown

You are currently in a grey area with 1500 watts. If you think you will likely wind up at 2000 watts, I would go 48 volt myself. 

Photowhit

malibuskier said:

Inverter upgrade is due to 2800w limit.  Short term useage loads make the 4000w a worthwhile upgrade.  Batteries are also new - upgraded from 6CT (300 AH).  6 panels fit comfortably on the penthouse roof but I could fit 8 with a little creativity.  I'm just trying to be as smart as I can with what I have.  The panels are the primary charging system and the generator is an on demand/as needed type thing.  We really only run a refrigerator, gas stove (who knew a gas stove would pull so much 110v - 30 amps to broil!) and a 32" tv.  

Dave
  

If the broil is what's keeping you at such a large system, I'd get a gas broiler (I'm pretty sure my brothers gas stove has a drawer at the bottom or some type of gas broiler.

You have 800 amp hour battery bank at 24 volts, that is a larger system than my house, and I use a 4000Kwh array.

I run an air conditioner and all types of kitchen appliances, not a broiler, but a pizzaz pizza oven and a toaster oven. I only have an 1800 watt inverter...

I would guess this is a weekend use boat, but even then I would want a 5% charge rate, 800 amp hours would require 40 amps. That would require about a 2500 watt array...

BB.

Are you going to use a house generator of some sort to charge the battery bank with DC current? 12 and 24 volts are common marine alternator sizes--48 volt may be difficult to find off the shelf (plus regulator)?

-Bill

Marc Kurth

Keep in mind that your specific batteries like to be charged hard, not gently. You should have a minimum charge rate of 160 amps if you go with a 24v, 800 amp battery bank - if you are deeply cycling them. 

You can use a smaller charger if you are only going shallow, but it may impact battery life.

Going to 48v works in your favor on that item.

Marc

malibuskier

OK, after a few discussions and a lot of reading, it has been determined that a 24v system is the way I'm going to go.  Since jumping up to 48v system would require a rewire of my mini mag power center (among other things), the juice is not worth the squeeze to me.  I'm going to add 5 260 panels to my current 1,000W of panels (3 strings of 3 panels each) and go from there.  This will allow for roughly 13.5% inefficiency (caused by a variety of factors) and still feed the maximum into the controller.  Hopefully it allows me to not need my generator very often.  Thanks for all the advice and the interaction...

Dave

softdown

2300 watts of panels presents a significant argument in the 48 volt camp. Though with two separate panel ratings, it is likely that two charge controllers will be called for...even at 48 volt.