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There is no one connection method that is always best on board. I look at the panel data, shade from the boat, cable length, and the regulator's limits before I recommend series or parallel.
Same panels, different electrical figures
In a series connection, the panel voltages are added together. In a parallel connection, the current is added together when the panels operate at the same voltage. The combination thus changes the requirements for the regulator, cables, and protection.
A hypothetical example with two identical panels
Assume that each panel at its maximum power point delivers 20 V and 5 A, i.e., 100 W. Without losses and under identical light conditions, the calculation becomes:
| Connection | Voltage at power point | Current at power point | Power |
|---|---|---|---|
| Series | 40 V | 5 A | 200 W |
| Parallel | 20 V | 10 A | 200 W |
This is a calculation example. The regulator's maximum voltage must be checked using Voc in the cold, not the 20 V at the power point.
Why consider series?
Higher voltage and lower current on the panel cable can be useful for longer cable runs. Series can also provide the voltage the regulator needs to charge a battery bank with a higher voltage. In return, the sum of the panels' open-circuit voltage must be kept within the regulator's limit at all relevant temperatures.
Why consider parallel?
Parallel can be relevant when you want to keep the panel voltage down. In return, the total current becomes higher, and that affects cable selection and the PV input's current limit. The need for fusing of parallel strings must be assessed based on the data for the panels and the installation.
Shade requires more than a rule of thumb
On a boat, the boom, mast, and equipment can cast shadows at different times. I would therefore map out where the panels can actually be placed before choosing a connection. The effect of shade also depends on the panel's internal design and the regulator; "parallel solves all shading" is too simple.
If the panels face different ways or have very different operating conditions, separate regulators may be worth investigating. The gain must be weighed against price, space, and more connections.
Can you mix an old and a new panel?
This requires a check of the electrical data. The same wattage does not necessarily mean the same voltage and current at the power point. I would usually start with identical panels in a common group because it makes the assessment simpler.
Send photos of the panel labels, the regulator model, and a sketch of the placement. Then I can help evaluate both the current connection and a possible expansion.
Sources and manufacturer documentation
This guide was written by SejlStrøm. Technical information was checked on September 22, 2026. Always use the documentation for the specific model and version.