The 5 most common solar panel installation mistakes (and how to avoid them)
A properly functioning solar panel system starts with a flawless installation. Yet in practice, we often see the same installation issues come up. These mistakes can lead to power loss, malfunctions or even dangerous situations. In this blog, we list the five most common mistakes and show you how to avoid them:
1. Incorrect string configuration
What causes the issue?
Panels are connected in the wrong series (string), causing the inverter's maximum voltage (Vdc) to be exceeded or to fall short.
Consequences:
If a string configuration is incorrect, the inverter may shut down due to too low or too high voltage, or it may operate less efficiently. As a result, the solar installation won’t reach its full potential. This is especially problematic in cold weather conditions, when panel voltage increases.
Prevention:
Always use a string configuration tool provided by the inverter manufacturer. This tool helps you determine exactly how many panels you can connect per string without exceeding voltage limits. Pay close attention to the inverter’s minimum and maximum input voltage and temperature dependence, as panels generate higher voltage at lower temperatures. Finally, check the datasheets of both the panels and the inverter to ensure the setup is technically sound.
2. Incorrect or mixed MC4 connectors
What causes the issue?
MC4 connectors from different brands or types are mixed or not properly clicked together.
Consequences:
A poorly executed electrical connection can seriously compromise safety and performance. High contact resistance, often caused by loose or incorrect connections, generates heat at the contact points. This can lead to melted connectors or, in the worst case, fire. Poor connections also reduce current conductivity, causing power loss or intermittent failures that are hard to trace.
Prevention:
Always use original MC4 connectors from a single brand to avoid mismatched dimensions. Ensure each connection is fully clicked into place. Crimping the cables? Use the correct crimping tool.
3. Ignoring shade effects
What causes the issue?
Panels are installed in shaded areas without using optimizers or microinverters.
Consequences:
When shade falls on even a small part of a panel, it can significantly impact the entire system. Due to the "Christmas light" effect, a few shaded cells reduce the performance of the whole string. Since solar panels are connected in series, the weakest panel dictates the output of the entire string. This can lead to major (and ongoing) power losses, sometimes up to 20–30%.
Prevention:
Perform a thorough shade analysis before installation to understand how sunlight moves across the roof throughout the day and across seasons. Choose roof areas free of structural shade from trees, chimneys or dormers. Can’t avoid shade? Then use power optimizers or microinverters to ensure each panel operates independently.
4. Incorrect cable sizing and routing
What causes the issue?
Installers often use cables that are too thin, or route them over unnecessarily long or inefficient paths.
Consequences:
Cables that are too thin lead to voltage drop, energy is lost between the panels and the inverter, reducing system output. Thin cables can also overheat, potentially melting insulation or causing fire. Poor cable planning also affects reliability and increases the risk of malfunctions.
Prevention:
Calculate the correct cable cross-section based on length and current, and aim for a maximum voltage drop of 1.5% for efficient operation. For standard PV systems, use at least 4 mm² cable. For longer distances, go for 6 mm² or more to reduce power loss. Route cables neatly, secure them properly and avoid sharp bends or pressure points that can lead to damage or wear.
5. Inadequate grounding or missing surge protection
What causes the issue?
Grounding is either overlooked or not correctly installed. Surge protection is skipped or placed incorrectly.
Consequences:
Without proper grounding, metal parts may carry voltage in case of faults or damage, posing a risk of electric shock. The system is also more vulnerable to lightning strikes or grid voltage spikes, which can cause severe damage. Such damage often isn’t covered by warranty, especially if the installation doesn't meet safety standards.
Prevention:
Always follow the NEN1010 guidelines and applicable grid codes during installation to meet legal requirements. For systems with more than one string or voltage over 600 volts, a Type II surge protection device (SPD) is mandatory on both the AC and DC side. Install SPDs as close as possible to the inverter or distribution board and ensure proper grounding.
Bonus Tip:
Always take photos of the mounting system after installation. These are useful for inspections, insurance and future service.
Avoid Installation Issues with ESTG
Most installation problems can be prevented with the right preparation, tools and attention to detail. At ESTG, we support installers with expert advice, training and high-quality components, so you can avoid problems before they happen.
Not sure about a design or installation? Get in touch with our technical specialists.