24 or 48 volt inverter

summitdweller · March 2013

I am about to upgrade tp a true sine inverter and was wondering if there is a downside of going all the way to a 48 volt instead of 24 volt inverter? I do have a small system now and it will probably never get bigger than 2500 watts of panels. I know you would need to buy more batteries at a time to be able to wire 48 volt. Inverter about the same cost. So which way to go 48 0r 24?

Also which pure sine wave inverters have the least sleep/ no load draw?
Thanks

niel · March 2013

Re: 24 or 48 volt inverter

the only disadvantage i can think of for 48v battery banks is that any expansions to the battery bank will involve 4 12v or 8 6v batteries in another string instead of 2 12v or 4 6v batteries for a 24v string.

looking at the up side here for 48v is you won't need to buy another mppt cc as the one you've got should cover the 2500w in pv and the wiring may have lower losses due to the higher voltage.

most of the better ones will have about 10% or less for the draw. even better ones have a search feature to sense for a load to turn on the inverter above a certain set wattage and it will shut it down too when the load goes below that wattage set point. you will pay more for better features, but look over the magnum line of inverters.

BB. · March 2013

Re: 24 or 48 volt inverter

48 volt inverters tend to be higher rated capacity... Which means that you may be looking at a 4,000 watt or larger inverter and, possibly, 2x the idle or tare current (wasted energy) instead of the smaller 2,500 watt inverter you where originally looking at.

Also, depending on your bank AH capacity and configuration, you can have twice as many cells to monitor/add distilled water too vs a 24 volt bank.

It can be a bit more difficult to find 48 volt rated circuit breakers/fuses (you may be stuck ordering over the Internet--so you will need some emergency backup stock of parts--probably a good idea anyway--especially for remote installations). And if you get a larger 48 volt inverter, keeping a spare on the self is probably not an option--and finding a "cheap" 48 volt emergency backup inverter may be more difficult (not that high end 24 volt inverters are cheap either).

Lastly, if you want to go with any DC devices, you can find more 24 volt native devices (truck and marine equipment) vs 48 volt. But if you are going with 120 VAC inverter anyway--that may not be an issue.

Regarding which inverter--What features are you looking for (remote On/Off, search mode, inverter vs inverter/charger, etc.)?

-Bill

northerner · March 2013

Re: 24 or 48 volt inverter

I made the decision to go with a 24 volt system but am regretting this now as I've decided to expand the system more than I originally had anticipated. I was debating the issue with the # of batteries that a 48 volt system requires as well, and was the reason for going to 24 volts. If you decide to expand on the battery bank size (within the 1st year) with a 24 volt system that is undersized, you may wind up with more than 2 parallel banks of batteries, which can be done, but there may be issues keeping the batteries balanced if cable impedances are not identical. Really best to get the battery bank capacity right first. And as Niel mentions, expanding a 48 volt system would require a whole new 48 volt string.

Thinking back, I would have gone with a 48 volt system, as efficiencies are better due to lower current draws, and the mppt controller can handle more as Niel mentions.

As for inverters, I decided on the Outback and have not regretted that decision. A 48 volt inverter will also be more efficient with inverting, as the conversion voltage (120 vac) is closer, than with 24 volts.

summitdweller · March 2013

Re: 24 or 48 volt inverter

Definately need an inverter/charger do want a search mode. Would I need a bigger generator to charge the 48v vs 24 volt system I have just a honda 2000i? Do not use the generator much as get great sun but want everything to jive. Am looking at the outback but will check out the magnums as well. have no intention of using dc devices.

Photowhit · March 2013

Re: 24 or 48 volt inverter

I too, went 24 volt, but then bought a larger place and would have gone 48 volt, but I had already purchased a large forklift/traction battery in 24 volt. I think for the same size inverters, 48 typically are slightly more effiecent. I think Outback's have the lowest inverter draw at about 20 watts Magnums are very close and shouldn't effect a purchase choice. If your looking for smaller inverters ExelTech makes smaller inverters in 48 volt models.

Cariboocoot · March 2013

Re: 24 or 48 volt inverter

Downside to 48 Volt system: getting circuit protection and disconnects rated for the Voltage. It exists, but of course it costs more. Pretty easy to handle 24 Volts, but 48 Volt systems actually experience Voltages over 60 so need to be able to switch it off at those levels.

Some basic relevant info: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power

NorthGuy · March 2013

Re: 24 or 48 volt inverter

Cariboocoot wrote: »

Downside to 48 Volt system: getting circuit protection and disconnects rated for the Voltage. It exists, but of course it costs more. Pretty easy to handle 24 Volts, but 48 Volt systems actually experience Voltages over 60 so need to be able to switch it off at those levels

I used Midnite Solar MNDC for my 48V system. It is rated for 125V DC and worked really well. The 63A DC breakers were rated for 150V DC.

Cariboocoot · March 2013

Re: 24 or 48 volt inverter

NorthGuy wrote: »

I used Midnite Solar MNDC for my 48V system. It is rated for 125V DC and worked really well. The 63A DC breakers were rated for 150V DC.

Yes, all very good stuff. That box is over $200.
Compare to a simple 150 Amp Bussmann breaker for $45: http://www.solar-electric.com/mr60ampdccib.html
The latter will work on a 24 Volt system, but not on a 48 - even though it's rated at 48 Volts - for just the reason I mentioned.

If you need the bigger power capacity available with 48 you need it. And you will pay for it.

Photowhit · March 2013

Re: 24 or 48 volt inverter

Cariboocoot wrote: »

Compare to a simple 150 Amp Bussmann breaker for $45: http://www.solar-electric.com/mr60ampdccib.html
The latter will work on a 24 Volt system, but not on a 48 - even though it's rated at 48 Volts

When I go to the linked breaker they make it clear that they use UL rated thermaoplastic for the the case and leaver, but don't say the breaker is UL listed...
...but in the other things you might, like they include the midnite solar Din rail Baby box (for $28 ) and midnite din rail breakers for $11 UL rated for up to 150 volts. 80 and 100 Amp breakers are also available at $39 for this box (takes 2 slots)

northerner · March 2013

Re: 24 or 48 volt inverter

Cariboocoot wrote: »

Yes, all very good stuff. That box is over $200.

I got the Midnite Solar MNDC with 250 amp breaker for my system as well, and thought that price was actually a good deal. Those big breakers usually go for around $100 and up, and the box includes the breaker. The only issue I had with the box was it was a bit cramped, and it's not totally universal if you need to change it over from right side to left side. In most cases, you won't need to, but I did due to the limited space and layout of my system. I was able to change the orientation, but it took a bit of doing.

NorthGuy · March 2013

Re: 24 or 48 volt inverter

northerner wrote: »

I got the Midnite Solar MNDC with 250 amp breaker for my system as well, and thought that price was actually a good deal. Those big breakers usually go for around $100 and up, and the box includes the breaker. The only issue I had with the box was it was a bit cramped, and it's not totally universal if you need to change it over from right side to left side. In most cases, you won't need to, but I did due to the limited space and layout of my system. I was able to change the orientation, but it took a bit of doing.

They have a mirrored model MNDC-250-L. I used it. Although, I had to wait couple weeks to get it.

northerner · March 2013

Re: 24 or 48 volt inverter

NorthGuy wrote: »

They have a mirrored model MNDC-250-L. I used it. Although, I had to wait couple weeks to get it.

That's good to know, thanks NG!

mike95490 · March 2013

Re: 24 or 48 volt inverter

Charging from a Honda 2000i, limits your choice of chargers, as that generator has little overhead to waste on
chargers with poor Power Factor. This applies to 24 & 48v systems.

I'd lean toward a 48V system, and if 4, 12v "marine deep cycle" ~100Ah batteries give you enough capacity, that's what I'd use. If you grow beyond them, your next bank could easily be 8, 6V, 200Ah golf cart batteries. When those give out, you will have an inkling of what your needs at that point are, if you need even larger banks of L16's - or whatever.

24 or 48 volt inverter

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