How to Wire Solar Panels: Series vs Parallel (Diagrams)

Wiring solar panels in series adds their voltage, and wiring them in parallel adds their current. Four 100 W panels rated 18.5 V and 5.4 A make 74 V at 5.4 A in series, or 18.5 V at 21.6 A in parallel. Either way you get the same 400 W. The right choice depends on your charge controller or inverter, your wire run, and shade.

This guide uses one example panel for every layout so you can compare the numbers. It is a typical 100 W, 12 V-class panel. Check your own panel’s label, because real specs vary.

What is the difference between series and parallel solar wiring?

Think of voltage as pressure and current as flow. Series wiring stacks the pressure. Parallel wiring widens the pipe. The power is the same in both cases, because watts = volts × amps.

• Series: 74 V × 5.4 A = 400 W
• Parallel: 18.5 V × 21.6 A = 400 W

What changes is the wire size you need, how much power you lose in the wire, how shade affects you, and which equipment can accept the result.

How do you wire solar panels in series?

Here is the series “diagram” for four panels, written as a connection list. Each panel has one positive (+) and one negative (-) MC4 lead.

The math for four of the example panels in series:

1. Working voltage: 4 × 18.5 V = 74 V
2. Working current: stays at 5.4 A
3. Open-circuit voltage: 4 × 22.5 V = 90 V
4. Power: 74 V × 5.4 A ≈ 400 W

Pros: low current, so thinner wire and less loss over long runs. Cons: shade on one panel pulls down the whole string, though bypass diodes in each panel limit the damage. High voltage also needs a controller or inverter rated for it.

How do you wire solar panels in parallel?

In parallel, every positive lead joins one positive bus and every negative lead joins one negative bus. With two panels you can use an MC4 Y-branch connector. With more, use a combiner box with a fuse for each panel or string.

1. Working voltage: stays at 18.5 V
2. Working current: 4 × 5.4 A = 21.6 A
3. Short-circuit current: 4 × 5.8 A = 23.2 A
4. Power: 18.5 V × 21.6 A ≈ 400 W

Pros: one shaded panel barely affects the others, and the voltage stays low. Cons: high current means thick, costly wire and more loss on long runs.

How does series-parallel wiring work?

Series-parallel gives you a middle ground. Build two strings of two panels each, then join the two strings in parallel. Each string must have the same number of the same panels.

1. String A: Panel 1 (+) to Panel 2 (-). String A outputs are Panel 1 (-) and Panel 2 (+).
2. String B: Panel 3 (+) to Panel 4 (-). String B outputs are Panel 3 (-) and Panel 4 (+).
3. Join both string positives (Panel 2 + and Panel 4 +) with a Y-branch or combiner.
4. Join both string negatives (Panel 1 – and Panel 3 -) the same way.
5. Result: 2 × 18.5 V = 37 V, and 2 × 5.4 A = 10.8 A. Power: 37 V × 10.8 A ≈ 400 W.

Should I wire my solar panels in series or parallel?

Start with your equipment. It sets the rules.

• PWM charge controller: wire in parallel. PWM controllers need panel voltage close to battery voltage. A 12 V-class panel on a 12 V battery works; extra voltage is simply wasted.
• MPPT charge controller: use series or series-parallel. MPPT converts higher panel voltage into charging current, so you get thinner wire and less loss. Stay under the controller’s max PV voltage.
• Grid-tie string inverter: wire in series strings sized to the inverter’s MPPT voltage window. See what size solar inverter you need.
• Microinverters: no series or parallel DC wiring. Each panel plugs into its own microinverter, and the AC outputs share a trunk cable.
• Partial shade: parallel (or more, shorter strings) handles uneven shade better.

Why does series wiring lose less power in long wire runs?

Wire loss rises with the square of the current. Here is a worked example with a 30 ft run from the array to the controller, using 10 AWG copper wire (about 1 ohm per 1,000 ft).

1. Round-trip wire length: 30 ft × 2 = 60 ft
2. Wire resistance: 60 ft × 0.001 ohm/ft = 0.06 ohm
3. Parallel (21.6 A): 21.6 A × 0.06 ohm = 1.3 V drop. 1.3 V ÷ 18.5 V = about 7% lost.
4. Series (5.4 A): 5.4 A × 0.06 ohm = 0.32 V drop. 0.32 V ÷ 74 V = about 0.4% lost.

A common target is 3% drop or less. The parallel layout would need much thicker wire to hit that. The series layout passes easily.

How cold weather raises solar panel voltage

Panels make more voltage when they are cold. A sunny winter morning can push a series string over your controller’s limit and damage it. The label’s Voc is measured at 77°F (25°C), so you have to correct for your coldest expected temperature. NEC 690.7 sets the rule.

1. Coldest local temperature: -4°F, which is -20°C.
2. Degrees below 25°C: 25 – (-20) = 45°C.
3. Voltage increase: 45 × 0.28% = 12.6%.
4. Cold Voc per panel: 22.5 V × 1.126 = 25.3 V.
5. Four in series: 4 × 25.3 V = 101 V.

That is over a 100 V controller’s limit, even though the label math said 90 V. In that climate, use 2S2P on a 100 V controller, or buy a 150 V controller for 4S.

What wire, fuses and connectors do you need?

• Wire: outdoor-rated PV wire or USE-2, often 10 AWG for small arrays. Size it for current and voltage drop.
• Current rule: NEC 690.8 sizes PV circuits from short-circuit current with safety factors, often Isc × 1.56 for wire. Example: 23.2 A × 1.56 = 36.2 A for the 4P layout.
• Fuses: when three or more strings run in parallel, fuse each string. A fault in one string can draw current from all the others.
• Disconnects: add a DC breaker between the array and the controller, and another between the controller and the battery.
• Connectors: use matching, genuine MC4-style connectors and the right crimp tool. Mixed brands can overheat.

Avoid mixing panel models. In series, current is limited by the weakest panel. In parallel, voltage is limited by the lowest-voltage panel. If you must mix, put identical panels in the same string. A matched solar panel kit avoids most of these problems.

How do you wire a small 12 V system step by step?

1. Cover the panels or work at night, so they make no power.
2. Connect the battery to the charge controller first, through a fuse or breaker. Most controllers need this to detect battery voltage.
3. Wire the panels in your chosen layout and check the open-circuit voltage with a multimeter.
4. With the PV breaker off, connect the array to the controller. Then switch the breaker on.
5. Connect DC loads or an inverter to the battery, each through its own fuse.

For a full parts list, see our solar setup for a shed. To size the array first, try the solar power calculator. More beginner projects are in our DIY solar hub.

Safety note: Solar panels make power whenever light hits them, and you cannot switch them off. DC arcs can start fires. Low-voltage 12 V projects are reasonable for careful DIYers. Anything grid-tied, any 120/240 V AC wiring, and any roof array should be designed and installed by a licensed electrician. Follow the National Electrical Code (NEC Article 690) and pull local permits. Roof systems also need rapid shutdown under NEC 690.12.

Frequently asked questions

Is series or parallel better for solar panels?

Neither is better in all cases. Series is better with MPPT controllers and long wire runs. Parallel is better with PWM controllers and partial shade.

Can I wire two different solar panels together?

You can, but you lose power. Match current for series and voltage for parallel. A separate charge controller for each panel type is often the cleanest fix.

How many solar panels can I put in series?

As many as keep the cold-weather open-circuit voltage under your controller or inverter limit. Multiply Voc by the cold correction, then divide the limit by that number and round down.

Do I need fuses for two panels in parallel?

Usually not for two, because one string cannot back-feed more than its panel can handle. Check the panel’s max series fuse rating. With three or more strings, fuse each one.

Sources

• NFPA 70: National Electrical Code (Article 690)
• U.S. Department of Energy: Solar Photovoltaic System Design Basics
• U.S. Department of Energy: Off-Grid or Stand-Alone Renewable Energy Systems

Last updated: October 2026. Panel specs are examples; use your own equipment’s datasheets. This article is for information only and is not electrical advice.