Solar panels in series vs parallel: how to wire them right

When you DIY a solar install, panel wiring is the most confusing call. Here it is in 5 minutes: series adds voltage, parallel adds current, mixed adds both.

Series connection

Connect + of one panel to − of the next. Voltage adds, current stays the same. 3 panels at 40 V and 10 A in series → 120 V and 10 A.

• Pros: less cable loss, thinner cheaper wire
• Pros: ideal for MPPT controllers that accept high voltage (50-150 V)
• Cons: if one panel fails or shades, the whole string drops
• Cons: high DC voltage (>120 V) is more dangerous

Parallel connection

Tie all positives together and all negatives together. Current adds, voltage stays. 3 panels at 40 V and 10 A in parallel → 40 V and 30 A.

• Pros: if one panel fails or shades, the rest stay at 100%
• Pros: lower voltage, safer
• Cons: requires much thicker cables for high current
• Cons: more cable losses

Mixed (series-parallel)

For larger installs: group panels into strings (series) and parallel several strings. Balances voltage, current and fault tolerance. Standard for most mid-sized residential.

Rules to not fry anything

• Only parallel panels of the same model and orientation
• Max string voltage must NEVER exceed your controller's or inverter's Vmax
• Use blocking diodes in parallel to prevent reverse currents
• Fuse each string (parallel strings can dump current into a failed one)

Before wiring see how to pick an inverter and review common install mistakes.