size wire from PV to CC

[Ray Strickland]

The PV will be 125 feet from controller.
I hope to make this system 48 volts

I have 3 SolarWorld SW 335 panels
OCV=47.4V
Vmpp=37.8
Isc=9.62A
Impp=8.93A
Midnite classic 200 MPPT

I plan to add
Midnite E-Panel 175A for Magnum MS-PAE
8 Trojan T-105 6V 225 AH with float charge 52.8 for 48 Volts

I have 2 ?'s
1.  what size wire do  need from PV to CC and should I wire them in series or parallel.
I am unable to understand the wire charts.

2. will the solar panels bring my batteries to float charge with 6 to 7 hrs of sun just north of the Florida state line.

Thank You

[Westbranch]

to properly answer Q#2 we need to know the DoD and when the loads are running, like during the day or at night, as day loads will come off what the panels produce, first, whatever is left over goes to the batteries...

hth

[Ray Strickland]

Question 2- I plan to have my freezer, Refrigerator and well until I have more panels. This will be all the time as they should not all be running all at once all the time. The well will take the most power I understand. I think the well uses 1.5 to 2 kw when running, but it should not run much during the night.

How do i config the panel to run a 48 volt system. with a 125 ft run?

thanks

[Westbranch]

well,  those panels need to be at least 2 in series (2S) in order to get a high enough voltage to charge a 48V bank, since you have 3 panels you will have to have 3 in series (3S) or buy a 4th panel for 2 x 2S. 

Have you used the String Calculator http://www.midnitesolar.com/sizingTool/displaySizing.php   

to confirm the suitability of the panels configuration at 3S?

you also need to check out the voltage drop for the distance from PV to CC and CC to Battery...

Here is one calculator.  http://forum.solar-electric.com/forum/solar-news-reviews-product-announcements/solar-information-links-sources-event-announcements/60-voltage-drop-calculator

ADD:   that fridge will suck back at least 1.5 to 2Kwh per day and so will the freezer so that puts you into the 4.5 to 6 Kwh per day with the pump....

hth

[Ray Strickland]

I understand that I need more panels. If I add 5 more panels do they have to be the same voltages and wattage or can they be different?

[Resthome]

I understand that I need more panels. If I add 5 more panels do they have to be the same voltages and wattage or can they be different?

Best to make them the same.

[Westbranch]

If you want to get the most production from all the panels, you  will want them all the same, otherwise  variances in output occur if you mix and match.

[Kent0]

Ray,

The best choice of wire size, number of modules in series, and charge controller choice depends on the high and low temperatures where you are located. And on any plans for future expansion.

Looking at the data sheet values for "performance at 800 W/m², NOCT, AM 1.5" shows Vmp at 34.5 volts. It'll be even lower when it is hot outside, probably closer to 31 volts when it is above 95°F outside. By the time you consider any wire loss, there won't be enough to equalize batteries and barely enough to keep the PV array at max power when the batteries reach the absorption voltage. So in warm climates two of these modules in series isn't a good choice with a 48-volt battery. This shouldn't be news to anyone - it is the same situation as four 36-cell modules in series.

For a 48-volt battery, the modules should be wired three in series. That rules out the Classic 150 because, with three modules in series, it goes to hyper Voc at 7°C. Unfortunately, three modules in series will require that you use the larger breakers and larger combiner box.

The sizing tool for the Classic 200 shows that you can connect twelve modules wired in four series groups of three. If you plan on wire size that would allow you to expand the PV array to that size in the future, you should have a minimum wire size of #6 copper.  That will handle the maximum current safely. With #6 the wire loss, with 12 modules, will be about 3.3%. Increasing the wire size to #4 copper will reduce the wire loss to 2.1%. Increasing the wire size to #3 copper will get the wire loss down to 1.6%. Anything larger than 3 probably isn't worth the expense. Considering that you know that this system will expand to at least six or nine modules, I think #4 copper is probably the best choice for the wire going to the PV array.

[mike90045]

sizing arrays - Never use a prime number.  (well, you could have a $2K, 600V controller, and use a bunch of panels in series, but why)?

If you are looking at #4 copper, price out using #2 aluminum, and if you need any special fittings. Most UL gear has tinned connectors, and is rated for aluminum or copper wires. But you have to check.   Aluminum is less expensive than copper, but has more resistance so you have to go 2 gauges larger (#10 to #8, #4 to #2)

[vtmaps]

For a 48-volt battery, the modules should be wired three in series. That rules out the Classic 150 because, with three modules in series, it goes to hyper Voc at 7°C.

Kent,
is it such a bad thing to be in hyperVoc at 7° C? 

He won't damage a classic 150 until the voltage gets above 198 volts, unlikely in his location. 

By the time the sun is high enough to make any useful power, the panels will warm up and the classic will come out of hyperVoc.

The classic 150 has greater power handling capacity than the classic 200, and it is always better to run controllers at a lower percentage of their capacity.

To be honest, if it were my system in that location, I'm not sure whether I would choose a classic 150 or classic 200...  but it's not obvious to me that the classic 150 is a wrong choice.  On the other hand, you have a lot of credibility with me and I would be a bit uncomfortable ignoring your advice.

--vtMaps

[Kent0]

I wouldn't design for hyper Voc to happen for average conditions. Hyper Voc should be a rare event.

Even in Tallahassee the average low temperature is less than 45°F (7°C) in the winter. So with three of these modules in series a Classic 150 will start most mornings from November through February in hyper Voc. Even though that first hour of the day is low output time, that will be a lot of lost energy over the winter.

[Kent0]

The hyper Voc mode is a non-operating mode that the Classic goes into to prevent catastrophic failure from over voltage. It's better not to be so close to the maximum voltage rating of the transistors and capacitors at all. The Classic 150 isn't a suitable choice to use with three 72-cell modules in series in cold climates. Even in relative warm climates, like where you are at, a Classic 200 is a better choice for a 48-volt system with three 72-cell modules in series.

[Ray Strickland]

I have chosen the Magnum MS4448PAE and MidNite E-Panel (magnum) MNE175STM-L-240.
What I need to know now is do I need the Magnum ME-ARC50 to monitor or will the MidNite classic do all that? Will the ME-ARC50 monitor more that the classic or the same things?

[Kent0]

You'll need the ME-ARC50 to control the inverter and make changes to its settings.

[CDN-VT]

The hyper Voc mode is a non-operating mode that the Classic goes into to prevent catastrophic failure from over voltage. It's better not to be so close to the maximum voltage rating of the transistors and capacitors at all. The Classic 150 isn't a suitable choice to use with three 72-cell modules in series in cold climates. Even in relative warm climates, like where you are at, a Classic 200 is a better choice for a 48-volt system with three 72-cell modules in series.

Yes , Thanks , Im 4Vdc off of max VOC. 146Vdc at -15c ,, then again if I see sun in full winter , that's another anomaly .

Thanks Kent, the wire Gent is working great & has a new account !!

VT