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Solar Panel Wiring
Wiring of panels in two ways "Series" or "Parallel"
If your panels are 24 volt and your controller and batteries are 24 volt, then you would need to wire your panels in parallel- you would be connection all the positive connections together and separately connect all the negatives together.
You can connect pairs of panels in series (sometimes referred to as a string), connecting the positive terminal of one panel to the negative of the next, to increase the voltage. The effects of Partial Shading on overall efficiency should be taken into account when considering series wiring.

Panels in Parallel

Panels in Series
As you don't know how your system may develop in the future, it would be a good idea to buy your panels in even numbers, making it convenient to wire pairs in series if you want to change, say, from a 24 volt to a 48 volt system.

The next thing to consider is the type of wire to use. We generally think of electricity flowing freely through an electric cable, however cables will have a resistance that will tend to restrict that flow to a small but possibly significant degree. This resistance will be proportional to the length of the cable (the longer the cable the greater the resistance), and inversely proportional to the cross sectional area (a fatter cable has less resistance)
Below is a table showing approximate resistances per meter length for different sizes of copper wire. (Resistance is measured in ohms)
Cable Cross Sectional Area mm2 Approximate Equivalent American Gauge Approx. Resistance per M Length ohms
1.5 16 0.012
2.5 14 0.007
6 10 0.003
So, how do we use this information?
Let's suppose the cables we connect to our solar panels are going to have a 1.5mm2 cross sectional area and are going to be 20m in total length (10m each for positive and negative cables). The total resistance of our cable will be 20 x 0.012 = 0.24 ohms.
Let's suppose that our solar panels are going to be pushing out 20 amps of current, then we can use ohms law to calculate the "voltage drop" along these cables.

ohms law can be stated as: V=IxR
Or, Voltage Drop = Current in amps x resistance in ohms
Earthing PV Panels
Depending on your location, it may be required that your panel frames are earthed, and it is certainly advisable. Non earthed frames can acquire an induced electrical voltage (which may or may not be harmful) or could accidentally come into contact with a live conductor.
Making a good connection between a copper earthing wire and the aluminum frame of a pv panel is not straight forward due to natural oxidation of aluminum, and any manufacturer instructions should be followed. In some cases, the DC circuit should also be earthed, as should the AC circuit.
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