72 volt wire sizing

[ozarkflyer]

Good morning - I recently purchased a Classic 150 charge controller to upgrade my system and I haven't found any wire sizing calculators that go up to 72 volts.  I need to know the proper size wire to run from a new pole.  The panels are Sharp ND-205U1 - 6 @ 205 watt @24 volts running a distance of 65 feet total - coming into the controller @ 72 volts and then charging a 24 volt battery bank.  I did the math and came up with #4 - but I would appreciate someone double checking for me.

This upgrade has me a little nervous because I have not a single problem since I installed my system 6 years ago - and I hate to mess with a good thing.   I know my panels are not true 24 volt panels - but they have worked perfectly thru my Ananda Power center controller. 

Thanks
Oz

[Halfcrazy]

How many panels?

Ryan

[ozarkflyer]

Oops - fixed - there are 6.

[Halfcrazy]

Are they 3 in series and 2 strings? and is the 65ft one way or round trip?

Ryan

[ozarkflyer]

Yes and one way.

[Halfcrazy]

Well I get a 1.45% drop on #8 wire using the Wizard. It will have a total of 14 amps max running through it.

Ryan

[ozarkflyer]

Thank you = you saved me some $.

[Robin]

I am confused? There are three panels in series. 36VOC and 28.9 max power voltage. You mentioned that you are using the Ananda charge controller. Ananda never had an MPPT controller. It would then have to be a PWM controller. If you have a 24V battery, this is not a good match to put three in series. You couls almost get away with one in series, but with warm tempoeratures, it would not work. You need an MPPT controller. Do you have one?

[Halfcrazy]

He has a Classic 150 he is upgrading the system.

[mike90045]

This link goes to a great spreadsheet, for calculating wire losses at different voltages and currents

http://www.solar-guppy.com/download/voltage_drop_calculator.zip

It's at a closed solar site, but the spreadsheet is still maintained and accessible there.

[ozarkflyer]

Wow - this thread is still alive.

I have another question
Preinfo:
I am off grid and right now I have 6 Sharp 205 watt 24 volt panels going thru an Ananda power center to a Xantrex Sw4024 and 8 L-16 Trojan batteries.  I also have a Power Spout hydro electric generator that I use during wet and cloudy times off my spring - I use a Xantrex C-40 as a diversion load going to a standard 110 volt water heater element in a water heater tank before my Aquastar on-demand propane water heater.  Water heating seems to be almost nonexistent.  My system works great (except for water heating) and most days I am charged up by noon. I have a propane generator that the inverter automatically starts to always keep the batteries in good shape on extended cloudy days.

I am soon switching the Sharp panels to run thru the classic 150 at 72 volts and then adding 6 true 24 volt 180 watt Conergy panels I recently purchased to go thru the Ananda.

My 8 Trojan batteries are in great shape after 6 years - but I plan on replacing them with 12 new ones when their 10 years is up.

I am really going to be swimming in power.

My question is ---  how can I use all this extra power I am going to have to heat water in my preheat tank?

[Allen15]

Hi.  If you are still pondering things in this thread, you might check out http://www.presolarnet.com/products/liberty_box.htm at least for an idea on how to heat water.

I don't know if this is a functional product that one can actually buy now or now, but the concept is based upon using a specially configured MPPT charge controller with about 4 panels or so, to produce a *higher* voltage (160 Vdc) to plug into an electric heating element in a standard electric water heater.  In this case, the charge controller load is not a battery bank running at 12, 24, 48, 60, or 72 volts, but rather a heating element running at 160 volts DC.

The concept makes for much easier routing of power from solar panels to water heater, with no plumbing required, and no heat losses from piping from solar thermal panels.  Even if you can't yet buy their system, there might be enough information for a handy person to make their own, as long as they can find a water heater element to run on the voltage that they can supply with their charge controller...  (I believe a standard AC water heater element will run off of 160 Vdc)

That might be much more efficient and easier than trying to figure out how to get your existing system to better heat water, if it is not doing that well already.