Common Mistakes in Photovoltaic Installations

A photovoltaic system can reduce electricity costs by up to 90%, but only when it is designed around the way you actually use electricity. Common mistakes in photovoltaic installations are not always visible on the first day. They usually appear later as lower production, limited autonomy, unnecessary equipment purchases or difficulty obtaining technical support.

A correct installation is not simply a matter of placing panels on a roof. It is a technical investment that connects consumption, available space, shading, the electrical distribution board, inverter, battery and future needs. The following are the mistakes worth avoiding before committing to a quotation or equipment.

Incorrect sizing based only on the latest electricity bill

The latest electricity bill is an indication, not a complete energy study. It may cover a mild month, a period when the home was unoccupied or a business operating at temporarily reduced capacity. If the system is calculated solely from this information, it may be smaller or larger than required.

The correct approach examines at least the annual consumption profile and, above all, when the energy is used. A home that runs air conditioning in the afternoon has different needs from a business that consumes mainly at midday. Likewise, a holiday home with intensive use in August or an agricultural installation with pumps and seasonal peaks requires dedicated planning.

The study should also include upcoming changes: an electric vehicle, heat pump, new refrigeration loads, business expansion or an additional residence. This avoids a system that becomes outdated as an investment before it has even paid for itself.

Selecting panels based only on watts

The nominal power of a photovoltaic module does not tell the whole story. Two panels with the same wattage can behave differently at high temperatures, have different responses to shading, different warranties and different mechanical strength.

In Greece, where roof temperatures rise considerably in summer, the temperature coefficient and correct ventilation of the installation materially affect actual production. Compatibility between the panels' electrical characteristics and the inverter and its MPPT trackers is equally important.

The least expensive module is not necessarily a poor choice. However, the lowest initial cost should not be assessed without considering expected production, the product warranty, availability of support and the overall quality of the system.

Underestimating shading and orientation

A chimney, tree, parapet or neighbouring building can significantly limit performance. The issue is not only the shadow itself. Depending on the wiring and inverter technology, shading on part of one module string can affect additional panels.

The site survey should consider shading at different times and seasons. Winter shading, when the sun is lower, is often ignored in a superficial estimate. Complex roofs or installations with several different planes may require separate strings, more MPPT inputs, or a solution using optimisers or microinverters.

Not every system must face strictly south. East–west orientation can be particularly effective when consumption peaks in the morning and afternoon. The right answer depends on the usage profile, not on a general rule.

An unsuitable inverter for the project

The inverter is the heart of the photovoltaic system. Nevertheless, many decisions are made solely on the basis of its power rating in kW. This leads to incorrect choices, especially when energy storage is present or planned.

A reliable string inverter may be sufficient for a straightforward energy-offset system. A residence or holiday home that needs backup during a grid outage requires a hybrid architecture with correctly planned backup loads. Full autonomy requires a stricter study: instantaneous peaks, motor starts, inverter power, battery charging and periods of low solar irradiation must all be assessed.

A system that was not designed for backup does not gain full backup capability simply by adding a battery. It requires the correct electrical architecture, separation of critical loads where necessary and equipment with the appropriate capabilities.

Incorrect battery type or capacity

A LiFePO4 battery is an excellent tool for increasing self-consumption, protection during outages and energy autonomy. However, it is not a solution that should be selected by intuition or by asking only “how many hours will it last?”

Daily and overnight consumption, the loads that must remain active, available discharge power and the desired autonomy must all be calculated. A battery with sufficient kWh but limited power capability may not support a large instantaneous demand. Conversely, an excessively large battery in a system with low winter production can increase cost without delivering a proportional operational benefit.

Scalability should also be considered. If you need basic backup today but plan to add an electric vehicle or make the holiday home more autonomous in two years, a scalable solution is often the safer investment.

Poor mounting and neglecting waterproofing

The mounting structure is not a secondary accessory. It transfers wind, snow and thermal-expansion loads to the roof or ground. Incorrect anchoring points, unsuitable materials or inadequate waterproofing can turn an energy project into a moisture and maintenance problem.

Every surface type requires a different approach: tiled roof, metal roof, flat roof, ground-mounted field or parking canopy. The study must address structural adequacy, water drainage, cable penetrations and corrosion-protection requirements, particularly in coastal areas.

Incomplete electrical protection and poor wiring

Fuses, surge protection devices, isolators, earthing and correctly sized cables are not details that should be removed to lower the quotation. They are fundamental elements of safety and reliability.

Poor wiring increases losses, makes fault diagnosis harder and exposes the installation to mechanical damage. DC cables must be suitable for outdoor use and UV exposure, supported correctly, and not left rubbing against metal edges or where water can collect.

The existing electrical distribution board also requires particular attention. Older homes or commercial premises may need upgrades before a photovoltaic system can be integrated safely.

Ignoring permits, settings and monitoring

A technically correct project can be delayed or fail to operate as expected if the required connection procedures and the rules of the applicable energy-offset scheme are not followed. Conditions, documentation and technical data must be checked before equipment is ordered, not at the end of the project.

The absence of a reliable monitoring platform is another common mistake. Monitoring production, consumption, battery charging and potential faults allows deviations to be identified quickly. Without data, reduced performance can remain unnoticed for months.

How to avoid common mistakes in photovoltaic installations

The safest route starts with a free technical study based on real consumption data and a site survey. Equipment is then selected to operate as one integrated system, with a clear definition of whether the objective is simply a lower electricity bill, backup power or complete autonomy.

Hellenic Energy approaches every project as an energy strategy, not merely a sale of panels. With correct sizing, reliable subsystems and technical support after installation, your investment can deliver predictable performance for years. The correct first step is to request a study before deciding how many panels or batteries you “need”.