Series raises voltage and parallel raises current; controller limits and the actual shade pattern determine the useful arrangement.
Wiring solar panels in series or parallel changes the voltage and current your MPPT controller sees — and that matters for wire sizing, controller selection, and performance in partial shading.
The basics
Series wiring — connect positive of panel 1 to negative of panel 2:
- Voltages add: 2× 20V panels → 40V input
- Current stays the same: 5A in → 5A out
- Needs thinner wire for the same wattage
Parallel wiring — connect all positives together, all negatives together:
- Current adds: 2× 5A panels → 10A input
- Voltage stays the same: 20V in → 20V out
- Needs thicker wire for the same wattage
Total wattage is identical either way: 2× 100W = 200W regardless of configuration.
Why series is usually better for vans
1. Smaller wire for the PV run
Power = Voltage × Current. Higher voltage means lower current for the same power. Lower current = smaller AWG wire for the roof-to-controller run. A 400W series string at 40V draws 10A — manageable in 10 AWG. A 400W parallel array at 20V draws 20A — requires 8 AWG or heavier.
2. MPPT controllers perform better at higher input voltage
Most MPPT controllers have a minimum input voltage for efficient operation — typically 5V above battery voltage (so ~17–18V minimum for a 12V battery system). At higher PV voltages, the controller has more headroom to operate efficiently across varying light conditions.
3. Early morning and late afternoon performance
At low sun angles, panel output voltage drops. A series string at 40V peak can still power the MPPT effectively when voltage sags to 25V at dusk. A parallel array at 20V peak can drop below the controller's minimum threshold at the same times.
When parallel makes sense
Shading is your primary concern: In series wiring, a shadow on one panel limits current for the entire string. In parallel, a shaded panel only affects that panel's output — the others continue at full current. For builds where trees or obstacles will frequently shade one panel while another gets full sun, parallel (or series-parallel) may produce more net output.
Your MPPT can't handle the series voltage: A 3-panel string of 20V-Voc panels in series = 60V. Some budget MPPT controllers max out at 50V. Parallel keeps voltage at 20V. Always check your controller's max PV input voltage.
Series-parallel: the hybrid approach
Four panels → wire as two series pairs, then connect the pairs in parallel:
- Two pairs at 40V each, wired in parallel → still 40V, but 2× the current
- Keeps voltage manageable, handles higher total wattage
- Good for 400W+ systems on a 12V MPPT controller
Practical example: 400W system on a 12V van
| Config | PV voltage to MPPT | PV current | Wire needed |
|---|---|---|---|
| 4 panels parallel | 20V | 20A | 8 AWG or thicker |
| 2S2P (2 series × 2 parallel) | 40V | 10A | 10 AWG |
| 4 panels series | 80V | 5A | 12 AWG |
Four panels in series at 80V is usually fine for a quality MPPT rated 100V input, but verify your controller's limit. The 2S2P configuration is the common practical choice for 4-panel systems.
Worked planning check
For two example 200W panels rated 20V and 10A at maximum power, series gives 40V at 10A and parallel gives 20V at 20A. Both are nominally 400W. Recalculate cold Voc and protection before changing connections; neither arrangement guarantees better shaded yield.
The figures or dimensions in this example are explicit planning assumptions, not a product test or an installation specification. Replace them with your equipment data and actual measurements.
Planning questions
Should campervan solar panels be in series or parallel?
Compare the resulting voltage and current with the controller limits and evaluate the actual shading pattern. Series adds voltage; parallel adds current. Neither is universally best.
Why does a solar panel produce less than its rated watts?
Nameplate power uses specified test conditions. Sun angle, temperature, shade, dirt and charging-system limits change actual output. Size from seasonal daily energy, not maximum watts alone.
Can I add another panel later?
Recalculate cold open-circuit voltage, short-circuit current, controller output, mounting, cable and protection first. Matching wattage does not prove panels are electrically compatible.
Related
- Solar setup guide
- How to install solar panels on an RV
- Best MPPT charge controllers for RV
- MPPT vs PWM charge controllers
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Jack Kennedy is a self-builder who has built two vans. He created Roam Wired to simplify conversion planning and share free tools, supported by affiliate links.
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