Distances and wiring

drsockmonkee · May 19

Hi,

I have a garden shed that I am playing with solar on.

I have a

Renogy Solar Charge Controller 12V/24V Auto MPPT

with two Renogy 100w solar panels wired up (positive wires into an adapter that will allow for you to wire two panels together into the same pair of wires) to my charge controller.

It is on top of my shed and the battery bank is two cheesy batteries from COSTCO in a toolbox in the back of the shed.

of course my neighbor planted a tree right against the fence and it is now shading my panels.

I am thinking of relocation of the panels, but I do not want to put them on my house.

How far do you think I could run the wires from the panels to the charge controller?

thanks.

Wheelman55 · May 19

OP. I use this app to calculate wire size needed over a specific distance.

https://www.southwire.com/calculator-vdrop

You need to choose max voltage drop (3% is the norm), then plug in the distance in feet, voltage (VOC) and amperage (ISC) that you’ll be sending. The app will tell you what gauge wire you need.

Simple.

drsockmonkee · May 19

sorry... I am such a goof. I do not know what to put.

Image: https://us.v-cdn.net/6024911/uploads/editor/qx/vchz4o4me7k8.png

Wheelman55 · May 19

OP. For voltage put in the VOC and for amps put in ISC. These numbers are in the back of your Renogy panels.

BTW. 12 volts is quite likely not the correct ISC.

Question. Are you running your two panels in series? If in series you double the VOC (voltage) number. Amps stay as listed on back of panel.

If you have the two panels wired in parallel you double the ISC (amps). Volts stay as listed on back of panel.

Clear as mud;)

drsockmonkee · May 19

Image: https://us.v-cdn.net/6024911/uploads/editor/47/ufj8j2w1jf3m.png

the wire I have is like this.

Wheelman55 · May 19

OP. Take a picture of the label on the back of your panels and post to this thread.

Or attach a link to the panels like you did for the wires.

drsockmonkee · May 19

@Wheelman55
I have two 100 watt panels that I have in series. (positive from both into an adapter then out of one wire onward) then on to the solar charge controller

drsockmonkee · May 19

Image: https://us.v-cdn.net/6024911/uploads/editor/ot/xmmqgfqus1sj.png

my panels are these...

drsockmonkee · May 19

found this... but....

Image: https://us.v-cdn.net/6024911/uploads/editor/3n/kxfm0zk7cnnw.png

BB. · May 19

I have another wire calculator... At least I know how to use this one.

And Costco batteries are generally pretty good for the price. Need to know which batteries you got. Normal "car batteries" should not be deeply cycled as they will not last very many years.

6 volt @ 200 AH "golf cart" batteries are a good deal and will last 3-5+ years.

Assumptions:

2 x 100 Watt panels
100 Watts / 17.5 Vmp (voltage max power) = 5.71 Amps Imp current max power (close enough for most panels)
2 * 17.5 Vmp = 35 volts Vmp
Imp = 5.71 amps

Normally, we aim for 1-3% voltage drop. In your case, you can have more drop (long runs with small diameter wire) if copper is "too expensive" for your project.

For the calculator, lets say you are running 40 feet (one way run) on 10 AWG wire:

https://www.calculator.net/voltage-drop-calculator.html?necmaterial=copper&necwiresize=2&necconduit=steel&necpf=1&material=copper&wiresize=0.4066&resistance=1.2&resistanceunit=okm&voltage=35&phase=dc&noofconductor=1&distance=40&distanceunit=feet&amperes=5.71&x=40&y=20&ctype=nec

Result

Voltage drop: 0.54
Voltage drop percentage: 1.55%
Voltage at the end: 34.46

So, 2x panels in series, 40 feet one way run, on 10 AWG copper cable... Looks good (1.55% voltage drop).

Generally, tilt the panels to your latitude for best year round harvest. You can use a solar calculator to estimate your average hours of usn per day by month (nearest major city)

http://www.solarelectricityhandbook.com/solar-irradiance.html

For example, to calculate your daily harvest... Say 5 hours of sun (good summer number for most places):

200 Watt panels * 0.61 off grid DC solar system efficiency * 5.0 hours of sun = 610 WH per day
610 WH per day / 14.5 volts charging = 42 AH @ 12 volt battery bus

Some quick estimates (assuming NO SHADE on panels).

-Bill

drsockmonkee · May 19

6 volt golf cart

Image: https://us.v-cdn.net/6024911/uploads/editor/09/unn5g5144fv2.jpg

drsockmonkee · May 19

drsockmonkee · May 19

drsockmonkee · May 19

the old charge controller is dead... it got replaced a couple of days back... and I am thinking of 'growing' the system..

question is what part, and do i need to actually do some 'real' planning/learning.. the initial effort was kind of Meh...

Grow the battery pack?

Grow the 'Array'?

Move the system? (damn neighbor)

Wheelman55 · May 19

OP. You are in good hands now with Mr. BB:)

drsockmonkee · May 19

@Wheelman55

Texas... East of Rockwall

drsockmonkee · May 19

@BB.

Do you have an insight as to what is the most important component to pay attention to?

Wheelman55 · May 19

drsockmonkee said:

@Wheelman55
Texas... East of Rockwall

Texas…Terlingua..way offgrid.

Wheelman55 · May 19

drsockmonkee said:

@BB.
Do you have an insight as to what is the most important component to pay attention to?

Your loads…meaning what do you want to power?

BB. · May 20

The battery (bank) is the "heart" of your system... So understanding how to size the battery for your needs is critical.

You can estimate your loads (Watts * Time; Amps * Time * Working Voltage) etc... Or you can measure the loads too using different types of meters...

DrSock. How familiar are you with Volts, Amperes (Amps), Amp*Hours, Watts, Watt*hours, and such? And are you OK with basic Math (simple algebra)?

I have no issue with helping you learn... But I do want to understand your level of electrical experience so I don't frustrate you with too simple or too advanced for you at this point.

-Bill

Distances and wiring

Renogy Solar Charge Controller 12V/24V Auto MPPT

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