Essential Information

Once a solar panel is exposed to light it will generate electricity.

Working with electricity is dangerous and care needs to be taken. If you have any doubt about working with electricity then consult a qualified electrician.

• Working with solar PV arrays can be extremely hazardous.
• Solar panels produce a voltage when exposed to light.
• Solar panels connected together in an array are often configured to produce high voltages. Panels can be connected in series or parallel.
• Solar panels connected together in an array will always produce a voltage even if there is a fault with the panel.
• Opening and closing any contacts while the solar array is under load will lead to arching at the contacts and these can be dangerous.
• Fuses and circuit breakers do not operate like their AC counterparts.

Take all the precautions necessary before installation, during installation and when testing the solar array.
DC Cable Installation- General Guidelines

• Cable should always be double insulated and polarized.
• DC Connectors should always be used.
• Cable or fuses should never be disconnected when under load.
• Cable from the solar pv modules should follow the shortest route to the array combiner boxes.
• All DC cable should be clearly identifiable
• Cables should be laid in parallel and loops should be avoided - except where they enter a building
• Cables should never be lain in a hazardous space.
• Cables should never be paled near to lightning conductors.
• Cables should always be tested for polarity in accordance with specified regulations.

DC Wiring - Modules and Strings

Care must be taken when connecting modules into strings. This applies when connecting modules together in series - the positive of one module is connected to the negative of another and so on. All cables must be given string numbers - for ease of identification later on and when testing for faults etc.

When testing solar modules the following applies:

• Testing for polarity - ensure that DC polarity is correct and that the positive wire core is used only for positive connections and negative wire core is used for negative connections.
• Check that the open circuit voltage of the string equals the sum of the open circuit voltages of all modules in the string.
• Check the short circuit current of the string against the datasheet for the appropriate module used.

Power Losses and Voltage Drop in Cables

Power losses in DC systems are due to voltage drop. Stand-alone DC systems typically operate at a lower voltage, 12V, 24V or even 48V DC.
Care must be taken when selecting the size of the cable to be used. If too small a cable is used then the voltage drop increases and in an off grid or stand alone system this can have a major impact on stand alone systems where the battery voltage is lower than expected.

Volt drop can be calculated from the formula: V = I x R, where V is the volt drop in the cable (V), I is the current in the cable (A) and R is the resistance of the cable is (ohms. Note resistance depends upon the length of the cable and cross sectional area (CSA) of the cable.
Resistances for Metric Cable