For off-grid system, there are three commonly used system voltage: 12, 24, or 48. Although it is possible to select differing voltage and power levels, the industry uses the following guidelines.
System Size PV/Battery Voltage
Up to 2 kWh per day 12 Volts
From 2 to 7 kWh per day 24 Volts
Over 7 kWh per day 48 Volts
The PV industry has standardized on modules with 12 or 24 Volt nominal output.
In this arrangement there are two rows of four solar module panels. Both rows are interconnected in series, increasing the system voltage. If you look carefully and pretend that each PV module is a battery, you can follow the series connection. The positive of one module connects to the negative of the next and so on. When each 12 volt panel is connected in a series grouping of four, the voltages are additive, resulting in a 48 Volt array.
Once both rows of panels are at the same system voltage, which in this example is 48 V, the array may be connected in parallel. The negative lead from each row is connected, as is the positive lead. Together, the two rows 48 V array will deliver additional current flow (power) to the load.
References: The Renewable Energy Handbook, by William H. Kemp.
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