Posted by nicksanspam on January 19, 2006, 8:56 am
Someone just asked what kind of wire I'd use to connect 6 110 W panels
(660 W at 24 V) to a house 150' away. Losing 1% of the power in each wire
makes (660/24)^2r = 6.6 W, ie r = 0.00827 ohms per 150', ie 1000r/150
= 0.058 ohms per 1000', ie 4/0 wire, almost 1/2" in diameter. Wow.
The Windsun site says $298/100', ie $894 for wire.
But if this is a grid-tied backup system, why not put 2 12 volt batteries
and a low-power inverter in a box near the panels, with more batteries and
a larger inverter in the house? If we make 0.8x660x4.6 = 2.4 kWh on an
average day at a latitude tilt near Phila, that's only 100 watts over 24h,
small enough for a Microsine or OK4U inverter with 3 of Home Depot's $5.84
50' 16 ga outdoor extension cords and (100/120)^2x0.3x4.016 = 0.84 watts.
Nick
Posted by Windsun on January 19, 2006, 9:03 am
If it is 150 feet away, why not just wire the panels up in series and use an
MX60 charge controller - probably cheaper than the wire you would need at 12
volts.
Posted by wmbjk on January 19, 2006, 10:32 am
wrote:
>If it is 150 feet away, why not just wire the panels up in series and use an
>MX60 charge controller - probably cheaper than the wire you would need at 12
>volts.
I got to play with one of those last weekend. Very nice. I'd like to
add one to my setup. When they be on-sale next? :-)
Wayne
Posted by Windsun on January 19, 2006, 11:15 am
Yesterday :)
http://store.solar-electric.com/outpowmxmp.html
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> I got to play with one of those last weekend. Very nice. I'd like to
> add one to my setup. When they be on-sale next? :-)
> Wayne
Posted by nicksanspam on January 19, 2006, 12:59 pm
>If it is 150 feet away, why not just wire the panels up in series and use an
>MX60 charge controller - probably cheaper than the wire you would need at 12
>volts.
Comparing apples to apples, we might have...
1. $894 for 300' of 4/0 24 V wire
$100 for 2 12 V in-house batteries
----
$994, with about 24 Wh/day of wiring loss, or
2. $17.54 for 3 50' 16 ga 120 V outdoor extension cords
$100 for an out-house 120 V or 240 V OK4U
$100 for 2 12 V out-house batteries
----
$217.54, with about 20 Wh/day of wiring loss, or
3. $17.54 for 3 50' 16 ga outdoor extension cords
$100 for an in-house OK4U
$495 for an MX-60
$100 for 2 12 V in-house batteries
----
$712.54, with about 4X the peak current and 320 Wh/day of wiring loss, or
4. ?
I'm thinking the 2 out-house batteries (do they need a charge controller
in this case?) would contribute as much to backup storage as 2 in-house
batteries. With luck and more DOD, they might wear out under warranty and
prolong the life of the in-house batteries :-)
Nick
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>MX60 charge controller - probably cheaper than the wire you would need at 12
>volts.