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I am considering a small 1kW solar system (4x 250-watt panels). The seller offers them in both 120v and 240v configurations with "micro-inverters". Given a 25-year panel warranty, could the amperage reduction and following lesser (but is it measurable?) heat output of having the inverters output 240v on the AC side have any measurable impact in longevity over running at 120v?

I can as easily do 120v as 240v. Running a line from the breaker box is not a problem. I'm just curious if there's any actual measurable benefit over time with running 240v instead of 120v. I use a 240v outlet for my computer just for the 1%-2% efficiency gain, so I don't need much of an excuse, but I have no idea if DC-AC conversion gains the same benefit.

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    How far away are the panels from the point of energy use? You didn't say "solar panel" and it's the least of what you left off. Will these be grid-tied? Are they ONLY grid-tied or do you want them to work during power outages? Why are you talking about DC? – Harper - Reinstate Monica Jul 24 '17 at 22:16
  • Is there a particular reason you're looking at microinverters? Have you looked at the current NEC Art. 690 requirements for that matter? – ThreePhaseEel Jul 24 '17 at 22:57
  • @Harper - All irrelevant, except for the bit where I forgot to use the word "solar" :) I am purely questioning if 240v will provide any benefit over 120v. – Gordon Jul 24 '17 at 23:04
  • @ThreePhaseEel - Again, irrelevant to the question. – Gordon Jul 24 '17 at 23:11
  • Bigger question -- are you running 120/240V CT with sync'ed 120V microinverters, or running the actual microinverters at 240V? If the latter, are they providing a split-phase output, or are they providing a single phase of 240V standalone? – ThreePhaseEel Jul 24 '17 at 23:24
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Because of Ohm's Law, double the voltage and your transmission losses drop to 1/4 with the same diameter of wire. Go here and punch in your voltage, actual service amperage, distance and tolerable voltage drop in percent (try different numbers here to see the effects of different size of cable).

If the distance is rather far, the calc may start talking about fat wire like 6AWG or larger. Don't buy that, come back and ask us.

14AWG wire at 120V will be 8.333A (repeating of course), and load a 14AWG wire enough for voltage drop to be an important factor. Going 240V cuts that by 75%.

Going 240V also gives expansion "room".

I can't possibly guess whether the build quality of the solar panels in question has cut corners on current pathways (endangering 120V panels) or insulation and component voltage rating (endangering 240V panels). Insulation is generally cheaper than current pathways, so all things being equal I'd favor the higher voltage.

I'm no fan of marrying the PV and the inverter hardware. If either fails, both are scrap, so you are beholden to the build quality on both of them. They are also only good for grid tie. If it's on a roof, love your firefighters.

  • 1) You can do a hybrid (multimode/backup-capable) setup with microinverters, but that forces an AC-coupled topology on you. 2) Generally speaking, positive pressure ventilation beats vertical ventilation anyhow & firefighter vs panel problems are best handled by allocating dedicated roofspace for the firefighters to work (as even with NEC 2017-style module-level rapid shutdown, you still have the potential for broken PV parts to generate hazardous voltages) – ThreePhaseEel Jul 25 '17 at 11:41
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Running a set of implied solar panels (as you didn't use that word in your question) at 240v means the current passing through the wiring is lower for the same amount of power. Lower current also means lower power losses in transmission, although for very short distances, it's not likely to be particularly noteworthy.

For most electronics, the reduction in current will reduce loads on conversion, generally creating a benefit overall.

If the wiring between the two units is the same, one could wonder if one of the two is going to overheat, or is one over-engineered compared to the other.

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Yes for two reasons:

As others pointed out, voltage drop and lost power is reduced with a higher voltage. This becomes more important the longer the circuit gets, that's why most panels are daisy-chained to raise the operating voltage even if they are operating on D.C. until they reach the line inverter.

Additionally though, micro-inverters offer the advantage of eliminating the single point of failure with a single inverter. If an inverter fails you only lose the output of one (or two with some inverters) panels until it is replaced. They also allow you to create a circuit at the higher voltage with only a few panels and to add to the circuit later. On the con side they are more expensive.

Good luck!

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