How to choose a reliable contractor for a photovoltaic installation?

Nov 24, 2021Expert advice, Solar

Photovoltaic installations on our market are a relatively new product, although they have been built around the world for nearly four decades. From the moment the small three-pack appeared, i.e. the amendment to the Energy Law of July 26, 2013 in which the issues of purchase of renewable energy produced by the so-called Photovoltaic installations are becoming more and more popular among prosumers. The greatest interest in installations was in 2015, when the call for applications in the Prosument program was announced along with a 40% subsidy and the entry into force of the RES Act of February 20, 2015, and with it the possibility of selling surplus energy at guaranteed rates of PLN 65 and 75 per 1 kWh , and in 2019 and 2020 in connection with the introduction of the possibility of energy balancing and supporting programs such as “My Electricity”.

At that time, a lot of installation companies were established. The vast majority of these are companies after retraining from hydropower solar installations or other construction industries, and not only having no experience in the energy industry. The market is so receptive that it accepts everything and everyone. Investors, often without experience or knowledge on the proper implementation of a photovoltaic installation, are not able to properly verify the contractor. The effects of this today are such that these installations are often emergency, do not produce the assumed amount of energy or do not meet Polish standards. 2016 has slightly verified the market. Contractors who appeared for a while because there was an opportunity to earn, today they are gone. Some of them, however, still remained.

Many entrepreneurs try to attract investors with very attractive installation prices. But is this a good approach? Are cheaper installations really just as good as the more expensive ones? Do all installations contain the necessary components for proper and failure-free operation for many years? Are they made in accordance with the construction practice and regulations? Are they safe for the user?

Unfortunately, the low prices of the offered solutions very often result from very poor quality components. There are also companies that very often offer the installation of panels by people with very little experience. This may result in a number of irregularities, which include, among others:

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Nieprzestrzeganie zasad bhp w trakcie montażu,


Stosowanie niskiej jakości paneli pozbawionych atestów i znaków jakościowych,


Wykorzystanie słabej jakości przewodów i innych pomniejszych elementów instalacji elektrycznej mogących być w przyszłości źródłem awarii,


Zastosowanie nieodpowiednich systemów montażowych uniemożliwiających dobre przytwierdzenie paneli do powierzchni dachu,


Niewłaściwy sposób przytwierdzenia konstrukcji do dachu,


Zły dobór typu i mocy inwertera oraz niejednokrotnie jego niska sprawność

This is mainly due to the lack of knowledge among investors about photovoltaics, which is why the industry is full of entrepreneurs who promise “golden mountains”. They often offer very low-quality products, bend information about their efficiency, or give incorrect calculations regarding the payback period of the installation, and propose oversized solutions that go beyond the needs of customers. Savings on labor are also time savings, so makeshift solutions are used. Unreliable installers assume that if you can’t see something, you can do it for “art”. Unfortunately, such an action can have far-reaching consequences later.

With this type of investment, it is not worth saving on trifles. Savings of a few or even a dozen or so percent at the investment implementation stage, they will take revenge on you during operation, and they will have a lot of time for it, after all, the installation is to work continuously for 25-30 years. Most of the mistakes made at the assembly stage may only be revealed after a few or several years, when the warranty period for the modules and the inverter has already expired, and it may be impossible to pursue the investor’s claims. How to avoid mistakes during the implementation of the investment? How to choose a reliable contractor? First of all, it is worth looking at photos or projects of a potential artist. Some companies compromise themselves by posting photos of poorly made installations. I used it for this article. The worst thing is that they don’t even know that they are making mistakes, so they keep repeating them among other clients. Below I will present a few elements that will help to assess the contractor’s knowledge and points that are worth paying special attention to.

pay special attention

Sprawdź czy panele nie są zacienione

One of the main problems with home installations is shading. From the point of view of the operation of the entire installation, shading a single panel is an extremely unfavorable phenomenon, resulting not only in a significant decrease in the efficiency of the installation, but also its overheating and failures. This phenomenon is called Hot-Spot and causes permanent damage to the panels. The most dangerous are shading of small areas, when the bypass diode does not work and a reverse current flows through the cell. The cell heats up to temperatures reaching 250 degrees Celsius, causing the protective foil to burn out and causing irreversible changes in the silicon structure, and in extreme cases it may lead to self-ignition of the foil. Therefore, photovoltaic panels should be installed in unshaded places, which, unfortunately, is often ignored by some installers. Retailers and designers have to deal with many shadow-generating elements such as bay windows, swallows, chimneys and trees. Often, the desire for profit and ignorance of the investor’s interest.


For some installers, mounting panels behind shadow obstructions is sort of a standard. In the photos below you can see a very clear shadow cast on the panels. Even though only a small part of the panels is shaded, the power drops throughout the installation.


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Sprawdź czy konstrukcja jest zamontowana według instrukcji producentów, czy jest prawidłowo dobrana oraz czy instalację wykonano zgodnie z przepisami

It is unacceptable to save on structural elements. Unfortunately, this often happens when there is a strong pressure on a low price. Each element is worth a few or a dozen zlotys. Multiplied by dozens of pieces, it already gives several hundred zlotys in savings. This is often the amount for which better offers, made by professionals, lose. Every specialist knows what is included in a properly made installation and it is impossible to do well below the cost.


All elemThe structure must be matched to the type of roof and the type of panels. But it is not enough. They also have to be installed in the right way to withstand, above all, gusts of wind and snow loads. ClMounting brackets must be mounted on the longer sides of the modules – it is unacceptable to mount them on the shorter sides or at distances from the ends of the module other than the manufacturer’s recommendations. The assembly rules in accordance with the module manufacturer’s instructions must be strictly followed. Both construction manufacturers as well as producers of photovoltaic panels publish assembly instructions, but some installers “know better” how to do Now they assemble and do it “in their own way” because he has done so many installations and no one has fallen yet. By the time. It should be noted here that, in addition to the problems with the strength of the elements, the installation not in accordance with the manufacturer’s instructions carries the consequences of losing the warranty.


Zwróć uwagę na estetykę wykonania

Of course, the main purpose of the installation is to generate electricity and the most important thing is the economic aspect, but the appearance and aesthetics are also important. Something like this is unthinkable in well-made installations.

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Sprawdź czy zamontowane są właściwe elementy konstrukcji i zabezpieczeń

An example of the team’s unpreparedness for work may be the installation of improper structural elements or electrical protections, affecting the safety and lifetime of the installation. Failure to take into account the appropriate class of protection of overvoltage protections or improperly selected overcurrent protections may lead to permanent damage of the inverter. This damage is not covered by the manufacturer’s warranty. It would seem that the installer’s domain is his skills in the field of electrical work. Nothing could be more wrong. Installers should be knowledgeable not only in this area. They should also have skills related to building elements of the load-bearing structure, making mounting and through holes and securing them against leakage.

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Sprawdź czy montaż zapewnia odporność na warunki pogodowe

Particular attention should be paid to installations mounted on roofs covered with sheet or steel tiles. In the case of such a covering, the installation of the installation involves puncturing the sheet metal. The place of installation must be very carefully and precisely protected against both corrosion of the sheet metal and leakage. Otherwise, the entire roof will have to be replaced in a few years. The same is true for panels that are exposed to high wind loads. It is absolutely forbidden to extend the panels beyond the outline of the roof.

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Sprawdź czy zastosowano odpowiednie kable i poprowadzono je we właściwy sposób

Cables used in photovoltaics work in harsh weather conditions, and in addition, they are expected to work reliably for 30 years. Cable management should be aesthetic and loops should be avoided. Also the tubes and, as a last resort, the conduits should be made of materials resistant to UV, attached in a way that prevents their abrasion, tearing off or being moved by the wind. What can be seen in the photo below only proves that the installation was done carelessly, and the contractor has no idea what materials to use. The cables will be replaced after a few months. There is a danger of death if the insulation is abraded. A photovoltaic installation is not a toy. Panels connected in series reach voltage up to 1000V (thousand Volt).


Sprawdź czy uziemiono konstrukcję oraz ramy paneli

Unfortunately, many installers do not know how to properly make a grounding system for photovoltaic structures and modules. The correct connection of the grounding wires between the modules is often underestimated with the use of factory-made, specially prepared holes in the frames. Most installers do not use the galvanic connection (grounding) of the panel frame to the structure at all. Some people sometimes only ground the structure, which is also a big mistake. The frames of the panels are made of anodized aluminum so they do not conduct electricity! Many errors also appear in the implementation of the earthing itself, especially in objects that do not have an earthing system. They should be completed from scratch and sometimes these works are not included in the price of the installation. Check what materials were used for the earthing, whether they are resistant to corrosion. Well-chosen materials are stainless steel and aluminum.

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Sprawdź czy zastosowano odpowiednie zabezpieczenia przeciwprzepięciowe

The power plant must not only have appropriate overvoltage protections but also be properly installed. In addition, it is necessary to conduct regular inspections and measurements of the PV installation and to use a monitoring system appropriate to the scale of the investment, which will guarantee that it will work with the appropriate parameters. Taking this type of action will allow to detect and remove failures on an ongoing basis, minimizing their negative impact on the efficiency of the entire installation. Conducting regular inspections is also a matter of ensuring the safety of people in the vicinity of the plant and compliance with health and safety regulations.

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Sprawdź w jaki sposób są transportowane i montowane panele

The first mistakes of the installation crews can very often be made before they reach the site of the future installation. Poor protection of the modules during transport can lead to mechanical damage, which can then cause, for example, the formation of hot spots, which are a frequent cause of panel failure. Therefore, photovoltaic panels should be properly secured, marked and, if possible, gently handled during handling. It is absolutely forbidden to walk on the modules. It causes microcracks in the links and, consequently, the formation of the so-called hot spots. With a larger installation, work should be well planned so that there is no need to make corrections to the previously installed modules.


Already at the stage of building the load-bearing structure, many mistakes can be made. Currently, most of the photovoltaic micro-installations in Poland are installed on the roofs of residential buildings, covered, among others, by tile. Installers like to work on such roofs because the mounting structures are simple and easy to implement. But aren’t mistakes made about this? Incorrectly selected height of the mounting hook, haste or carelessness are later problems with cracked or incorrectly re-laid tiles. It is not uncommon to see hooks not tightened to the rafters or even hooks lying on the tiles. Covering tiles should be sawn so that they fit well after re-laying. Errors at this stage, in consequence, include cracked tiles, leaking roof and significant material damage to the investor. Often, the defects become apparent only after a few rains, when rainwater leaks reach the interior of the building. Inadequate height of the mounting hook translates into incorrect height of the modules installation above the roofing. Mounting the modules at a distance of less than 10 cm from the roof sheathing hinders their ventilation, causes a higher operating temperature of the modules and, as a result, a decrease in the power of the photovoltaic generator. If the installer incorrectly plans the places of connection of the bearing profiles, e.g. between modules or too close to the end of the bearing profiles, deformation of the entire structure may occur under the influence of additional snow or wind loads. At this stage of the assembly, the post-completion inspection carried out by the person supervising the works or the investor is very important.

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A typical mistake when installing modules is their incorrect orientation. They should be installed vertically, with the connecting cables facing downwards, or horizontally. Sometimes, however, the installer, in order to save the number of wires, installs the modules in a vertical arrangement – one row above the other junction boxes facing each other. As a consequence, water may leak into the box on the wires of poorly built modules and corrosion of connecting elements. Another error is improper routing of the return wires in DC circuits, which can create the so-called induction loops. An induction loop during a nearby lightning discharge may generate a high voltage that damages the inverter despite the installation of safety elements. This type of damage is not covered by the inverters warranties. The inverter is a significant cost of installation, so it is worth protecting it properly.

Sprawdź miejsce instalacji inwertera

The installation location of the inverter can also be the cause of installer errors. It must not be built in unventilated places, in thermally insulated attics, where high temperatures may occur in summer. Inverters require ventilation and cooling as they themselves are a source of heat generation and overheating will lead to automatic shutdown. A similar situation may occur in the case of buildings on the southern wall of the building, which is illuminated by the sun’s rays. Not all installers of photovoltaic systems have sufficient knowledge and experience in the field of electricity, which translates into problems and errors when connecting the inverter to the power grid. On-grid inverters are very complex electronic systems that convert direct current generated in photovoltaic modules into alternating current synchronized with the power grid. Errors in this regard are a problem with starting the inverter or its incorrect operation.

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Żądaj protokołów pomiarów

At the end of the assembly work of the photovoltaic installation, measurements of the DC / AC electrical parameters and additional, requiring permits, must be performed, confirming the correctness of the installation. The investor should receive a report of these measurements, including the positive result of measurements of insulation resistance, effectiveness of protection against electric shock, and effectiveness of lightning protection. Only after completing the entire investment process and carrying out the tests, the installation may be submitted to the local DSO for commissioning. Measurements of the PV installation allow you to verify the correct operation of the entire system or chain of modules. Small drops in performance, caused by, for example, damage to a single module or incorrect installation are often impossible to detect just by reading the operating parameters of the inverter. Therefore, such measurements must be made directly on the modules, while measuring their working conditions. It should be checked if the modules generate the amount of electric energy appropriate for a given level of insolation, if they have adequate insulation or ground resistance. Solar modules can also be damaged during transport or installation due to improper handling. Taking measurements allows you to detect this type of irregularities on an ongoing basis. Every self-respecting installer should have an appropriate measurement kit and, after the work is done, prepare a measurement report. Moreover, measurements of PV installations have a preventive effect.

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