Series vs. parallel: wiring batteries and solar panels
The short version: series wiring adds up the voltages and leaves the amp-hours (or amps) unchanged. Parallel wiring adds up the amp-hours (or amps) and leaves the voltage unchanged. The total energy in watt-hours, or the total panel watts, is the same either way. What changes is the voltage and current your wiring and equipment have to handle.
That one rule covers batteries and solar panels alike. The practical choices are different for each, though, so this guide takes them one at a time. Each section has a calculator so you can check your own setup.
The rule, in two lines
Parallel: current (Ah or A) adds, voltage stays the same
In a series connection, the positive terminal of one battery or panel connects to the negative terminal of the next. In a parallel connection, all the positives connect together and all the negatives connect together. Many systems combine the two. For example, two pairs wired in series, with the two pairs then connected in parallel, is called "2S2P".
Batteries in series vs. parallel
Take two identical 12.8 V, 100 Ah LiFePO4 batteries. Each one stores 12.8 × 100 = 1,280 Wh.
| Wiring | Voltage | Capacity | Energy |
|---|---|---|---|
| Series (2S) | 25.6 V | 100 Ah | 2,560 Wh |
| Parallel (2P) | 12.8 V | 200 Ah | 2,560 Wh |
Same energy, different voltage. So the choice comes down to what voltage your system needs.
Battery bank calculator
Why higher voltage helps: current and wire size
Power equals voltage times current, so the same load draws less current from a higher-voltage bank:
| Bank voltage | Current for a 2,000 W load |
|---|---|
| 12.8 V | about 156 A |
| 25.6 V | about 78 A |
| 51.2 V | about 39 A |
These figures leave out inverter losses, which push the real current a little higher. Lower current means thinner, cheaper cable, smaller fuses, and less energy lost as heat. Wire losses rise with the square of the current, so halving the current through the same cable cuts those losses to a quarter. That's why larger RV, cabin and home systems usually run at 24 V or 48 V. A small 12 V setup that powers 12 V appliances directly is often simpler at 12 V.
When to choose each for batteries
- Series when your inverter or charge controller needs a higher voltage (24 V or 48 V), or to keep currents and cable sizes manageable for big loads.
- Parallel when your equipment is 12 V and you want more runtime, or to add capacity to an existing 12 V system.
Rules for connecting batteries safely
- Use matching batteries: same chemistry, voltage, capacity, brand and model, and ideally the same age. Mismatched batteries share the load unevenly.
- Charge each battery fully before connecting them, so they start at the same state of charge.
- Check the manufacturer's limits. Many lithium batteries limit how many can go in series or parallel, and some can't be wired in series at all. The manual will say.
- Fuse it properly. Parallel banks in particular can deliver very large fault currents. Follow the battery maker's fusing and cable-size guidance.
- Balance the wiring in parallel banks. Take the main positive from one end of the bank and the main negative from the other end, or use bus bars, so every battery sees a similar cable length.
- Never mix chemistries, such as lead-acid with lithium, in one bank.
Portable power stations are a closed system: the batteries inside are already configured, and you can't wire them in series or parallel yourself. Some models accept a manufacturer-made expansion battery. Use only the accessories the manufacturer approves for that model.
Solar panels in series vs. parallel
Panels follow the same rule. Wire them in series and the voltages add. Wire them in parallel and the currents add. Total panel watts are the same either way. Using an example 100 W panel with an open-circuit voltage (Voc) of 22.5 V and a short-circuit current (Isc) of 5.8 A:
| Two panels wired in… | Array Voc | Array Isc | Rated power |
|---|---|---|---|
| Series | 45 V | 5.8 A | 200 W |
| Parallel | 22.5 V | 11.6 A | 200 W |
Use the numbers on your own panel's label or datasheet. They vary between models.
The limit that matters most: maximum input voltage
Every charge controller and power station lists a maximum solar input voltage, and often a voltage range, such as "12–60 V". Exceeding the maximum can damage the equipment. Because series wiring adds voltage, it's the main way people go over that limit by accident.
There's a catch: a panel's Voc rises when it's cold. Spec sheets give Voc at 25 °C (77 °F), and on a freezing, sunny morning the real figure can be noticeably higher. The datasheet's "temperature coefficient of Voc", usually written as a negative percentage per °C, tells you by how much:
Example, using a coefficient of 0.30% per °C (check your own datasheet) and a coldest morning of 14 °F (−10 °C), which is 35 °C below 25 °C:
- 3 panels in series: 22.5 × 3 × (1 + 0.003 × 35) = 67.5 × 1.105 ≈ 74.6 V. Too high for a 60 V input.
- 2 panels in series: 22.5 × 2 × 1.105 ≈ 49.7 V. Within a 60 V limit, with some margin.
Use the coldest temperature you realistically expect where the panels will be used, not the average. For permanent installations in the US, the National Electrical Code (section 690.7) requires this kind of cold-temperature correction.
Solar array calculator
The default values are an example only. Replace them with your panel's label and your controller's or power station's manual.
Series or parallel for panels: the trade-offs
| Series | Parallel | |
|---|---|---|
| Voltage | Adds up, so watch the input limit | Stays at one panel's voltage |
| Current | Stays at one panel's current | Adds up, so watch the current rating and wire size |
| Partial shade | One shaded panel drags down the whole string, though bypass diodes limit the damage | A shaded panel mostly affects only itself |
| Long cable runs | Lower current, so thinner cable and lower losses | Higher current, so thicker cable |
| Low light / morning | Reaches the controller's start-up voltage sooner | May sit below the minimum input voltage in weak light |
| Extra parts | Usually none for one string | Branch connectors, and often fuses once you have three or more strings |
A common approach is to put as many panels in series as the input voltage allows, with a safety margin for cold, and add parallel strings for more power. With a portable power station, the input voltage limit usually decides it for you.
Two more rules: only combine panels with closely matched electrical specs, especially within a series string, where the lowest-current panel limits the rest. And don't exceed the maximum input wattage your power station or controller can actually use. Extra panel watts beyond that are wasted, and some devices don't allow it at all.
Frequently asked questions
Does series or parallel give more runtime?
Neither. For batteries, total energy in watt-hours is the same either way. Higher voltage just means less current for the same power. Runtime depends on the watt-hours and your load. Our battery runtime calculator works it out.
Is series or parallel better for solar panels?
Series usually performs better with long cable runs and in weak morning light. Parallel copes better with partial shade. Which one you can use often depends on your controller's or power station's maximum input voltage, so run the cold-weather check above first.
Can I mix different batteries or panels?
It's best not to. Mismatched batteries charge and discharge unevenly. Mismatched panels in series are limited by the weakest one. If you must combine different panels, parallel strings of identical panels are the more forgiving option, provided each string has a similar voltage.
How do I find my panel's Voc and temperature coefficient?
Both are on the label on the back of the panel and on the datasheet. Look for "Open-circuit voltage (Voc)" and "Temperature coefficient of Voc". If you can't find the coefficient, ask the manufacturer rather than guessing.