Line loss/resistance over distance

5 Posts
Dec 12, 2006 09:28 pm
Line loss/resistance over distance

I have a need to install my PV panels about 200 feet from my inverter/main panel.  My concern is about voltage loss due to resistance from the larger distance.  Thoughts?  Would running my panels to output  48V instead of 24V or 12V make any difference?  Should I just not worry about it?
 
163 Posts
Dec 13, 2006 10:32 am
Re: Line loss/resistance over distance

Jeff,

The higher the voltage that you can operate at the lower your losses will be. That's why the power utilities operate their distribution lines in the kilovolt range.

Some MPPT Charge Controllers can (or so I've read) accept voltages over 100V and still bring the output back down to 48V, so its possible that you could wire your panels for even higher than 48V.

One option that I would recommend is to increase the size of wire running from the panels back to the Charge Controller. An increase from say #12 to #10 will reduce your loss. However, you will need to check that you are still code compliant with the number of cables in the conduit once the size is increased.

Another option is to place a PV Combiner Box near to the panels and run single pair of #4 or #6 or #8, depending on the total output of your panels, from the Combiner Box back to the Charge Controller.

All of this will depend on the system that you have, but the folks at AE seem to know what they are talking about, and once they know what system you have they should be able to help you.
 
578 Posts
Dec 13, 2006 12:10 pm
Re: Line loss/resistance over distance

more details, what modules do you have?  what is your battery bank voltage and inverter?  where are you located geographically (for temperature deration)?

odds are the answer will be an MX60 to run at higher voltage.    A combiner box at the array, and that way you only have to run two large wires rather than multiple medium wires.

I'll be glad to help design your system, I just need some more info Smiley

- james - Alt-E staff

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Dec 14, 2006 03:54 am
Re: Line loss/resistance over distance

Solar converters MPPT PT 90-30 and PT 48-40 etc.
can also charge any battery (12-24-48V) from
a higher voltage source (panels put in series).
Then the cable can be modest (AWG 6-8) still
with minimal losses. MX60 though definitely the
best controller if max voltage do not exceed 150V.
 
351 Posts
Dec 14, 2006 01:26 pm
Re: Line loss/resistance over distance

"Then the cable can be modest (AWG 6-8) still with minimal losses."

If you define minimal losses to be 2% voltage drop, you can only push about 173 watts on 8 AWG for the 200 feet (48V).

With any substantial amount of power, he is going to be on a larger wire size, probably in the 1/0 to 4/0 range.

Still waiting to hear more details from the OP. First solution I would look at is moving the inverter.  Many people think it has to be close to the main panel. Does the OP just believe that, or does he have a real reason for it ?

 
Dec 15, 2006 06:40 am
Re: Line loss/resistance over distance

Dear friend Ken:

One can go higher than 48 volt with
serial coupling of 3-5 panels...
They will have Open Circuit voltages of 80-90V
Shorted functioning circuit voltage somewhat lower.
(Usually number of panels x ~16V)
Therefore is the Kaneka thin-film (Voc=90V!)
so attractive. At these higher voltages the
current and line loss drops drastically!

Outback MX60 charge controller takes Voc max 150V
Solar Converters PT 90-30 charge controller takes Voc max 180V
Please redo the calculation at these higher voltages & lower currents and you will see for yourself!
Still battery voltage can be kept at 12 or 24V
Then maximum power tracking (MPPT) boost will be good!
That is: On cold days one will gain ~30% increase in charge
current.
Only in the power cable Panel-2-controller will be
high voltage. Controller-2-battery will still be nominal ~12V or 24V or 48V!
« Last Edit: Dec 15, 2006 06:43 am by Bhikkhu Samahita »
 
5 Posts
Dec 15, 2006 11:25 pm
Re: Line loss/resistance over distance

more details, what modules do you have?  what is your battery bank voltage and inverter?  where are you located geographically (for temperature deration)?

- james - Alt-E staff

James - this is a proposed system in Western MA. I really want to install PV spring 2007 but have a couple of concerns to address.  First, we may not stay in our house due to jobs, so I'm seriously looking to install a system I could reasonably move with me to another house.  While my roof pitch/orientation are near perfect for this (MA) location, my roof is extremely high (almost 45').  Since I will be installing much of this myself and I want the possibility of easily relocating, a ground mount system is far more appealing at this time.  I have open, unobstructed space on my lot so I can optimize orientation and adjust angle through season easily with ground mount.

I'm looking to install somewhere between 2 and 3 Kw, ground mounted on my lot about 150' from house, so I'm allowing 200' including running wiring through basement to interverter to be located near main panel.

I'm on grid and because of both startup costs and proximity of inverter to gas water heater and furnance in basement, I'm not installing a battery bank at this time (yes, I know there are safe H2 venting solutions).  Thus I'm looking for some panels, inteverter, meter/cutoff mains and associated wiring . 

I'm open to thoughts/insights.
 
462 Posts
Dec 27, 2006 02:51 pm
Re: Line loss/resistance over distance

 .
« Last Edit: Dec 27, 2006 02:55 pm by Tom Mayrand »
 
462 Posts
Dec 27, 2006 02:54 pm
Re: Line loss/resistance over distance

Jeff, why not move your inverter outside, at your array. Then run cheaper 120V romex to your AC panel.
 
5 Posts
Jan 24, 2007 06:56 pm
Re: Line loss/resistance over distance

I agree with tom.  Keeping your DC system components close is smart design.  It will save you cost on heavy DC wiring and potential voltage loss.  AC voltage loss is much less of a concern. Many exterior rated grid-tie inverters are available.
 

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