Your installation should have a mechanical layout plan to determine the materials needed as well as to help visualize your power station layout. The plan will also help you to determine required overall design functions. Configurations may include:

• PV array only
• PV with wind hybrid system
• Micro hydro only
• Any of the above and a generator backup

There are too many configurations to consider all possible installation arrangements here. Kindly refer to the respective inverter and other equipment manuals for custom-design reconfiguration requirements. For example, the image shows the schematic for an off-grid design that uses PV and wind power. There is no ground wiring shown for simplicity.

PV Arrays

PV arrays can be roof-mounted or ground-mounted, with or without a tracking unit. Both mountings are connected similarly, except that the NEC requirements for roof-mounted PV arrays demand a Ground Fault Interrupter (GFI) device. This automatically disconnects from the PV array when over-current, water leakage or insulation faults occur, all of which can cause fire from overheating. GFIs are not required for pole, ground or tracker mounts.

Step one in PV array wiring is determining the battery voltage in use. Typical PV modules use 12V or 24V. The steps for increasing PV array voltage are series or parallel connection of the wiring modules which will increase current flow. Four 12V modules connected in series will generate 48V output. Every module has a weatherproof junction box with knockout holes to fit liquid-free strain-relief bushings which are pressed into the junction box holes and positioned with a retaining nut. Flexible cable runs between the junction boxes to complete a series or parallel connection.

Check that the right wire gauge and type are used for an outdoor (wet) installation. Use the NEC/CEC code book to confirm the wire choice with your local electrical inspection authority.

For example, you could connect sixteen 12V, 75W module arrays in 8 sets of 2 pairs. Two modules wired together in series form a 24V set and all the wiring goes into a combiner box with all negative wires together. Positive leads go to individual circuit breakers or fuses (giving each set a 5A rating).

The circuit breaker output goes to the positive (+) terminal at the voltage controller that is wired in series. Parallel connection is completed with terminal strips connecting all wires to the primary DC supply cable.

So, with everything wired up:

• 16 modules x 75 W per module = 1,200W peak for the array
• 2 x 12V modules wired in series = 24V
• Current from array = 1,200W peak / 24V = 50A maximum

For a 12V array with 16 modules connected in parallel, the current would be twice as high (100A). Conversely, a 48V array would give a current of 25A. The amount of power in watts is constant, no matter how the modules are connected. A higher voltage permits a smaller conductor cable to be used while lowering energy losses and cost.