Solar Panel Wiring: Series vs Parallel Explained
In short, Series adds Voltage, keeping Current constant. Parallel adds Current (Amps), keeping Voltage constant. If you use an MPPT controller, wiring 2 to 3 panels in series is almost always superior because high voltage wakes up the MPPT earlier in the morning and allows thinner wiring down from your roof.
Example: Two 200W Solar Panels (20V, 10A each)
Wiring in Series
Connect (+) of Panel 1 to (-) of Panel 2.
- Total Output Voltage: 40 Volts (20V + 20V)
- Total Output Current: 10 Amps
- Total Power: 400 Watts
- Wire Needed: Thinner 10 AWG wire
Wiring in Parallel
Connect (+) to (+) and (-) to (-) using branch MC4 connectors.
- Total Output Voltage: 20 Volts
- Total Output Current: 20 Amps (10A + 10A)
- Total Power: 400 Watts
- Wire Needed: Thicker 8 or 6 AWG wire
The Shade Problem: Why Shading Hurts Series Strings
Think of a series solar circuit like a garden hose with someone standing on it. The current through all panels in series must be identical. If a single tree branch or roof AC unit casts a shadow across 20% of one panel, that panel's internal resistance shoots up, throttling current through the entire series string down to a trickle.
In a parallel arrangement, if Panel 1 is shaded, it drops its output, but Panel 2 continues pumping its full 10 Amps straight into the controller completely unaffected.
The Sweet Spot: Series-Parallel (2S2P)
If you have 4 panels on your RV roof, the ultimate configuration is Series-Parallel (2S2P): wire two panels in series to create String A (40V, 10A), wire the other two panels in series for String B (40V, 10A), and connect both strings in parallel. You get high 40V voltage for MPPT efficiency, but if String A is shaded by an awning, String B continues generating at 100% capacity.
Empirical Technical Specification Reference
| Design Factor | Standard Recommendation | Safety Margin |
|---|---|---|
| Continuous Load Limit | 80% Sustained Circuit Capacity | 1.25x Overcurrent Fuse |
| Voltage Drop Threshold | NEC 310.15 / ABYC E-11 | ≤ 3% for Critical DC Circuits |