Series vs. Parallel Wiring - Which is best?
Series vs Parallel Solar Panel Wiring: Complete Guide for New Zealand
Should you wire your solar panels in series or parallel? Many of our customers have heard that parallel wiring can reduce shading issues, and tell us that this is what they will do - but it's not always the best option considering the electrical properties of their solar array and the equipment they will be connecting to.
The choice is a trade-off between minimising shading (if this is an issue), and reducing power losses. Furthermore, it is important to understand how the wiring configuration will affect the total voltage and current in your solar panel setup and ensure it is compatible with your solar charge controller (MPPT).
The Trade-Off: Series vs Parallel Solar Panel Wiring
Parallel Wiring Configuration
When you connect solar panels in parallel, you double the current while the voltage remains the same. For example, with two 10A panels in parallel, you get 20A of current at the same voltage.
The main drawback is cable losses. Power loss in cables is proportional to I²R (current squared times resistance). Since parallel configurations produce higher current, you experience significantly greater resistive losses in the cabling. This means more energy is wasted as heat in the wires between your panels and charge controller.
Advantage: Parallel configurations handle partial shading better. If one panel is shaded, the other panels can continue operating at full capacity without being dragged down.
Series Wiring Configuration
When you connect solar panels in series, you increase the voltage while current stays relatively low. This dramatically reduces cable losses because the I²R losses are minimal when current is low, even if cable resistance is the same.
Potential drawback: When panels are wired in series, shading on one panel can reduce output of the entire string. However, many modern solar panels include bypass diodes that mitigate this problem, minimising the impact on overall array performance.
💡 Expert Recommendation
For most modern solar installations in New Zealand, series configuration is typically preferred, unless you have severe shading issues (like one panel being completely blocked for extended periods). The reduced cable losses usually outweigh the shading concerns, especially given the bypass diode protection in contemporary panels.
1. How to Wire Solar Panels in Series
To wire solar panels in series, connect the positive terminal of one panel to the negative terminal of the next panel.
Voltage: Adds up from each panel
Current: Stays the same as for one panel
Series Wiring Example
Three solar panels, each with:
- Open Circuit Voltage (Voc): 40V
- Short Circuit Current (Isc): 10A
If wired in series:
- Total Voltage (Voc): 40V + 40V + 40V = 120V
- Current (Isc): Same as one panel = 10A
✅ Series wiring increases voltage, but current stays the same!
2. How to Wire Solar Panels in Parallel
To wire solar panels in parallel, connect all the positive terminals of the panels together, and connect all the negative terminals together.
Voltage: Stays the same as for one panel
Current: Adds up from each panel
Parallel Wiring Example
Three solar panels, each with:
- Open Circuit Voltage (Voc): 40V
- Short Circuit Current (Isc): 10A
If wired in parallel:
- Total Voltage (Voc): Same as one panel = 40V
- Current (Isc): 10A + 10A + 10A = 30A
✅ Parallel wiring keeps voltage constant, but current increases!
Solar Charge Controller (MPPT) Considerations
When you wire your string of solar panels, you need to consider your charge controller's specifications:
Input Voltage Limit (Voc)
The series configuration must not exceed the maximum PV input voltage (Voc) of the MPPT charge controller. If your series configuration exceeds the controller's voltage range, you risk damaging the controller.
Input Current Limit (Isc)
The parallel configuration must not exceed the maximum PV short-circuit current (Isc) that the controller can handle. If the total current from the panels exceeds the input current limit, the controller may fail.
⚠️ Safety Warning
Always check your MPPT solar charge controller specifications before wiring your panels. Exceeding voltage or current limits can permanently damage your equipment and void warranties.
How to Decide: Series, Parallel, or Series-Parallel Configuration?
Often, an optimal solar panel design combines series-parallel wiring to balance the voltage and current while ensuring they stay within safe controller limits. We will cover advanced wiring configurations in a future knowledge article.
In the meantime, our solar design tool, ANYKIT, automatically calculates the best configuration for wiring any string of solar panels, taking into account your specific panels and MPPT controller specifications.
Quick Reference Table for Solar Panel Wiring
| Wiring Type | Voltage Behavior | Current Behavior | Benefits | Use When… |
|---|---|---|---|---|
| Series Wiring | Adds up across panels (Voc sums) | Stays the same as one panel (Isc fixed) |
• Lower cable losses (I²R reduced) • Thinner/cheaper cables possible • Better efficiency over long runs • Works with higher voltage MPPT controllers |
You need to raise voltage to meet the MPPT voltage window of your charge controller. |
| Parallel Wiring | Stays the same as one panel (Voc fixed) | Adds up across panels (Isc sums) |
• Better partial shading performance • Each panel operates independently • Safer lower voltages • System stays operational if one panel fails |
You need to increase current without exceeding controller current limits. |
Final Tips for Solar Panel Wiring in New Zealand
- Always refer to your MPPT charge controller's specifications (maximum input voltage and current ratings) and ensure your solar panel wiring configuration stays within the controller's constraints.
- Use a solar design tool like LUX Solar's ANYKIT to calculate the optimal configuration and ensure you get the solar fundamentals right.
- Consider New Zealand's weather patterns - if you experience frequent partial shading from trees or buildings, factor this into your series vs parallel decision.
- Use appropriate gauge cable to minimize resistive losses, especially in parallel configurations with higher currents.
Need Expert Help with Your Solar Installation?
Our technical team can help you design the perfect solar panel configuration for your specific needs.
📧 Email: technical@luxsolar.co.nz
📞 Phone: 027 458 9674
Frequently Asked Questions
Can I mix series and parallel wiring?
Yes! Series-parallel configurations are common and often optimal. This approach allows you to balance voltage and current requirements while staying within your MPPT charge controller's specifications.
What happens if I exceed my MPPT controller's voltage limit?
Exceeding the maximum input voltage can permanently damage your MPPT charge controller. Always check the Voc (open circuit voltage) of your series string, especially on cold sunny days when panel voltage is highest.
Is series or parallel better for New Zealand conditions?
For most New Zealand installations, series wiring is preferred due to lower cable losses and modern bypass diode protection. However, if you have significant shading issues (trees, buildings), parallel or series-parallel configurations may be better.