Energy from a PV panel or stored in batteries is usually supplied at low DC voltages which are converted through the inverter to AC at 120V or 240V to operate home electrical appliances. For example, a 1,500W maximum load produces that amount plus some inefficiency allowances from the battery bank. The relationships amongst voltage, wattage and current for the household inverter are:

1500W load ÷ 120V house supply = 12.5 amps (A) current flow

And the same by the voltage input inverter are:

1,500W load ÷ 12V battery supply = 125A current flow

The low-voltage inverter current is usually ten times higher than 120V AC on 12V DC configurations, 5 times higher on 24V DC and 2.5 times higher on 48V DC.

Wattage is the product of current and voltage: the lower the voltage, the higher the current. The inverse is also true. A large-sized wire is needed to transport a 125A current through a 12V circuit for 1,500W. Alternatively, a lightweight extension cord can be used with a higher voltage of 120V.

Thick copper wires are costly and make wiring tough, so higher DC voltages and typical 240V home appliances are preferred as they need thinner copper wiring.

Low-voltage electricity cannot travel far efficiently: the current flow needs to be increased to compensate for the low voltage as more power loss is experienced from wire resistance. One solution here is to increase the voltage while decreasing the transmission distance. Alternatively, you can increase the wire size. You may need to apply both options and keep the distance between system components as short as possible while increasing the voltage and wire size.

For example, if a PV array delivers 40A current with a 24ft (7.3m) cable run, a size #0 wire (sometimes known as "#1/0", and "#00" is known as "#2/0") is needed to maintain an electrical loss of 1%. This wire size is quite large (about the same diameter as a pencil), which is difficult to manipulate and quite expensive.

Options include:

1. No changes. Just use the #0 wire.
2. Up the system voltage to 48V and decrease cable size to #6 (Note: doubling the voltage will halve the current to 20A).
3. Let voltage loss increase. With 24V, let the system voltage drop reach 4%, using a reduced size #6 wire. (Wire size #6 carries 40A with loss of 1% for every 6 feet. Corresponding losses occur with corresponding wire size increases.)
4. The selected wire size must carry the current required. A #6 wire is meant for 75 amps max. Losses cannot be exceeded to lengthen wire runs because losses reduce valuable power supply to the inverter.
5. Have two smaller wire sets. Split the PV array wiring to reduce the current to 20A per set. An array set with #4 wire connections will maintain the 1% voltage drop and the smaller wire will be easier to handle. Connect the two arrays to the battery bank or inverter in parallel before combining for a 40A supply.

The low-voltage inverter needs a large current, so thicker connecting cables are preferred. Smaller cables add stress