Why the Outback FX2012T Inverter?

[Alex9]

I'm trying to help my mother with her solar setup. Just moved into a new house and needs electricity soon. Grid isn't an option. I bought an Outback FX2012T Inverter used and want to sell it to her (no profit) because she's goin to go the high end equipment route and her electric needs are going to be much higher then mine. The fx2012t is for a 12v system only but I've been reading that 12v systems are inefficient compared to 24v, 48v.... I still don't understand why but I think it has to do with the higher volts vs higher amps on a 12v? Anyway, the outback line of inverters come in 24v, 48v... etc versions at about the same price. Is it a bad idea to start with a 12v system and the fx2012t? Should she be going straight for the 24v or 48v system with the end goal in mind?

I'm trying to help her out because she's far from understanding any of this stuff. I think this inverter is the way to go for her. I'm just not sure about the 12v/24v/48v thing. The guy I bought it from was upgrading to a 48v system himself.

[inetdog]

The fx2012t is for a 12v system only but I've been reading that 12v systems are inefficient compared to 24v, 48v.... I still don't understand why but I think it has to do with the higher volts vs higher amps on a 12v? Anyway, the outback line of inverters come in 24v, 48v... etc versions at about the same price. Is it a bad idea to start with a 12v system and the fx2012t? Should she be going straight for the 24v or 48v system with the end goal in mind?

In a word, yes. It is a bad idea. It will be inefficient right now, especially if you need long runs of wire between batteries and inverter. It will be harder to maintain your batteries if you need enough Amp-Hours that you have to parallel batteries instead of using a series string of 2, 4 or 6 volt batteries. It will be harder to add more battery capacity later on. And all that is assuming that you would be using an MPPT Charge Controller to keep the panel string voltage high and current low, even though you use 12 volts at the batteries.

A 12 volt system might make some sense for a very small system that can make do with only one battery or if you have significant 12 volt DC loads. Otherwise, no way. Even is you already own all of the 12 volt components, you may end up scrapping them when you try to expand the system.

[Sunking]

12 volt systems are for toys and RV's with small power needs. A home system demands 48 volts minimum up to 400 volts.

It is all about the relationship of Volts, Power (watts), Current (amps), and Resistance and a physical law of Ohm's Law which is 12 very simple formulas. One of the important Laws are the 3 Laws of Power.

Power or watts = Voltage x Current in amps

1000 watts = 12 volts x 84 amps
1000 watts = 48 volts x 21 amps
1000 watts = 13,200 volts x .075 amps

It takes some rather large copper wire to carry 12 volts at 83 amps. The minimum size copper wire you can safely use is #4 AWG. However at 12 volts with 83 amps on #4 AWG wire can only be used up to about 5 feet. Beyond that and you loose very large amounts of voltage and power.

That should tell you why electric utilities use extremely high voltage. Your house is likely being fed by a medium voltage of 13,200 volts to your transformer.

[Alex9]

In a word, yes. It is a bad idea. It will be inefficient right now, especially if you need long runs of wire between batteries and inverter. It will be harder to maintain your batteries if you need enough Amp-Hours that you have to parallel batteries instead of using a series string of 2, 4 or 6 volt batteries. It will be harder to add more battery capacity later on.

Could you explain that part a little more? Why do people bother with the 12v inverter at that price? Also, is it practical for her to start off with a small system on 24v/48v and build on it? Off the bat she would have to start with atleast 4x6v for 24v or 8x6v for 48v. Which voltage would be ideal price/efficiency wise?
I appreciate your help.

[RussN9ZP]

I'm guessing the 12v inverter is more targeted toward the RV and boat market.

[Alex9]

12 volt systems are for toys and RV's with small power needs. A home system demands 48 volts minimum up to 400 volts.

It is all about the relationship of Volts, Power (watts), Current (amps), and Resistance and a physical law of Ohm's Law which is 12 very simple formulas. One of the important Laws are the 3 Laws of Power.

Power or watts = Voltage x Current in amps

1000 watts = 12 volts x 84 amps
1000 watts = 48 volts x 21 amps
1000 watts = 13,200 volts x .075 amps

It takes some rather large copper wire to carry 12 volts at 83 amps. The minimum size copper wire you can safely use is #4 AWG. However at 12 volts with 83 amps on #4 AWG wire can only be used up to about 5 feet. Beyond that and you loose very large amounts of voltage and power.

That should tell you why electric utilities use extremely high voltage. Your house is likely being fed by a medium voltage of 13,200 volts to your transformer.

Wow, that makes sense now.
With a good mppt charge controller is it ok to wire a bunch of 145w 12v panels adding the voltage together vs amps into a 48v battery bank? Is there a particular reason to use 24v pv if 12v pv can be had for half the price?

[inetdog]

Wow, that makes sense now.
With a good mppt charge controller is it ok to wire a bunch of 145w 12v panels adding the voltage together vs amps into a 48v battery bank? Is there a particular reason to use 24v pv if 12v pv can be had for half the price?

Look at the price per watt when comparing the panels. And look at the manufacturer's reputation. Other than that, look at whether the 24 volt panels will make your installation any easier or harder. Both 24 volt panels and 12 volt panels are available because you need to match them to a 12 volt battery system or a 24 volt battery system when using a PWM Charge Controller. Since current in = current out during the on cycle with PWM, a higher voltage / lower current panel would be throwing away power. And a 12 volt panel just would not be able to charge a 24 volt battery.

[Alex9]

And a 12 volt panel just would not be able to charge a 24 volt battery.

I'm definitively going to use a good mppt charge controller for the system. I understand that a single 12v panel couldn't charge a 24v system but if several were wired together adding up the volts could that charge a 24/48v system. Maybe they have to be wired in series and parallel to make strings of 24/48v depending on the system volts being 24/48? Is that all there is to it?
I'm looking to buy those dmsolar 145w panels. They've been getting good reviews for output and quality. Since I found out that 12v systems are for toys and small RV applications, I'm thinking I should plan for either a 24v or 48v system. Outback and Midnite mppt inverters seem to be universal for those voltages.

[Sunking]

Wow, that makes sense now.
With a good mppt charge controller is it ok to wire a bunch of 145w 12v panels adding the voltage together vs amps into a 48v battery bank? Is there a particular reason to use 24v pv if 12v pv can be had for half the price?

No I would not use standard battery panels with a MPPT controller. I would use Grid Tied panels because they are less expensive $/watt and run much higher voltages. I would look to run the panel voltages up around 100 to 120 volts on a 48 volt battery system.

[Alex9]

No I would not use standard battery panels with a MPPT controller. I would use Grid Tied panels because they are less expensive $/watt and run much higher voltages.

I guess I'm getting back to that rule of thumb, upto 1000w for 12v, 2000w 24v, 2000w 48v.... If I understand roughly, higher voltage systems are more efficient but when you can't afford buying a 48v system right out you have to start with 12v and then when you have the money get rid of all of it and start fresh with 48v?

I would look to run the panel voltages up around 100 to 120 volts on a 48 volt battery system.

It seems that the bigger panels that you're talking about have more and more volts in comparison to the smaller 12v panels. If I can't afford buying those can I take 8x145w 12v panels and connect them all in series in one string into the FlexMax80?

I feel like I'm speaking a different language then all of you :/

[Sunking]

If I can't afford buying those can I take 8x145w 12v panels and connect them all in series in one string into the FlexMax80?/

Well yes but to operate at 48 volts will require a minimum of 4 12 volt panels wired in series.

However if you cannot afford GTI panels, then there is no way you can afford battery panels because battery panel $/watt cost is higher then Grid Tied panels.

[Alex9]

Well yes but to operate at 48 volts will require a minimum of 4 12 volt panels wired in series.

However if you cannot afford GTI panels, then there is no way you can afford battery panels because battery panel $/watt cost is higher then Grid Tied panels.

So if I understand you, GTI panels are cheaper $/watt because you're just buying the panels, whereas on an off grid system you need panels and batteries.

[Mike90250]

I think GTI panels are less expensive, because more are manufactured than battery system panels. Same parts, cables, connectors, just a subtle difference the way the tabbing wire is strung. It's the old principle "Cheaper by the Dozen". Mass production drives the cost down. Same reason golf cart batteries, are half the price as "solar" batteries.

[Sunking]

So if I understand you, GTI panels are cheaper $/watt because you're just buying the panels, whereas on an off grid system you need panels and batteries.

No just simple supply and demand. Battery panels are 36 cells low voltage and there is not much of a market for them.

[noglider]

Alex9, what did you end up doing?