Article 690 of the NEC mandates that #8 AWG or #6 AWG are the smallest wires that can be used with grid tied solar panels and inverter systems, and for solar panel output circuits, #10 or #12 AWG are allowed. A ground rod is also recommended if the installation area is prone to.
A practical rule of thumb is: most home AC units need about 3–12 modern 400W panels to run in strong daytime sun, while 5–19 panels plus a battery bank is more typical if you want several hours of cooling that continues into evening.
This comprehensive guide provides everything you need to correctly size solar wires: calculation formulas, wire size charts for common configurations, voltage drop tables, and NEC code requirements specific to photovoltaic systems. Proper solar cable sizing .
Generally, the inverter should be sized to match about 80–100% of your system's DC rating. For example, if you have a 5 kW solar array, you might choose a 5 kW inverter.
The exact number depends on AC size: a small window unit (500W) needs 1 to 2 panels, a 1-ton central AC or mini-split (3,500W) needs 8 to 9 panels, and a 2-ton central AC (5,000W) needs 12 to 13 panels.
What size solar panel do I need for my 120Ah battery? For a 12V 120Ah battery, you would need around 300W of solar panels, assuming your location receives about 5 hours of peak sun. You can achieve this with three 100W panels, two 150W panels, or one 300W panel.