[Homestead] [Fwd: Re: Alternative inventory:Solar]
Don Bowen KI6DIU
don.bowen at earthlink.net
Tue Dec 25 12:13:33 EST 2007
At 12/24/2007, you wrote:
> The line losses for DC are greater than for AC.
Not the case, the current flowing in a wire does not care is it is AC or
DC, it cares only for the amount of current and the amount of
resistance. This is known as I squared R losses. To continue from the
power formula, P=IE (power in Watts equals current in Amps times
Voltage). A much more important formula is Ohms law I=ER (current in Amps
= Voltage times resistance in Ohms). Substituting around yields the
formula used for line losses P=I^2R (Power in Watts equals current in Amps
squared times resistance in Ohms)
Wire has resistance so you can see in the above the losses rise by the
square of the current. Using the 12V to 120V example. Current flow in the
12V circuit will be 10 times the current in the 120V circuit. The line
loss in the above example at 12V is 1000 times line loss at 120V. Notice
polarity has no input.
Many RE systems are going to 24 and even 48 volts to reduce line
losses. From 12 to 24, the line losses are cut to one quarter and 48 is
another 75% cut.
The advantage of AC is the ease of changing voltages. The line to your
house is often 7200 Volts while to the house is 240. The transformer on
the pole does this reduction easily. Your 200 Amp house hold system only
needs 6 Amps to the pole so not only are line losses reduced but
significantly smaller wire is needed.
Don Bowen Awl Knotted Up KI6DIU
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