Im sorry again, but this is simply not true when expanded to WIRE LOSS. > No; AC voltages and currents... (Root-Mean-Square). > RMS voltages and currents have the *same* effective > values, voltage drops, and losses as DC. 120vac and > 120vdc are completely equivalent.
Yes, as far as VOLTS and as AMPS as averages are concerned. Such as average power. A 1500W resistor will be 1500W whether on DC or RMS AC. But the power loss in wires feeding that resistor will have greater loss on AC because of two factors important in distribution systems: 1) SKIN EFFECT where the AC current is pushed to the outside of the wire so that not all the wire is carrying the same current. Thus the wire is not as effective since not all of its copper is being used in an AC system 2) Peak power losses. As you note, the RMS current is the same, but the PEAK current is 1.4 times higher during the peak of the waveform and since that is where the most power is delivered that is also where the most loss occurs in the wire. So the average power lost in the wire for AC is almost twice (1.4 squared) the loss in the same wire at DC. Google it... That is why the entire industry is looking at DC transmission lines now that we are finally getting to the point where the up and down conversion is becomming cost competitive with transformers... Bob -----Original Message----- From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Lee Hart via EV Sent: Wednesday, June 08, 2016 2:03 PM To: Electric Vehicle Discussion List Subject: Re: [EVDL] Off-grid solar house and electric car charging Robert Bruninga via EV wrote: > Still not true. The output of microinverters is at 240 VAC and the > average current in the wires will be double as the same number of panels at 480 VDC. But each microinverter has its own wire. The total current may be twice as much in a 240v system as in a 480v system; but there are twice the number of wires, each half the size. You wind up back where you started. > Further, AC peak currents are 1.4 times higher than DC so the peak > currents (where the losses are) are 2.8 times greater No; AC voltages and currents are normally expressed in RMS (Root-Mean-Square). RMS voltages and currents have the *same* effective values, voltage drops, and losses as DC. 120vac and 120vdc are completely equivalent. > The difference in buying #6 wire instead of #12 is only $180 versus > $30. Or you can ignore the extra 10% or so losses and use #10 wire. > But over the life of the system (20 years) the losses in your solar > system can add up to many thousands of dollars. Sure; it's basically an economic decision. How much can you afford up-front, to reduce long-term losses? It's further complicated because when you eventually scrap the system, much of the cost of the copper is recoverable. Note that this is the EV discussion list. Besides these tradeoffs, weight is also an issue. You may be ahead by deliberately undersizing the wire to save weight. The benefit from weight reduction can exceed the efficiency loss. Racers know this well! > Maybe I am just being nitpicky, but my solar arrays are all over my > yard and house. Some runs are over 300 feet! (shortest is maybe 60'). Ah; no wonder you are so concerned with wire lengths. I definitely consider 60-300 feet *long* runs! The PV panels on my house are only 20' from my circuit breaker panel. -- "IC chip performance doubles every 18 months." -- Moore's law "The speed of software halves every 18 months." -- Gates' law -- Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Read EVAngel's EV News at http://evdl.org/evln/ Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA) _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Read EVAngel's EV News at http://evdl.org/evln/ Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
