Factors of Selection Solar Panels for Roof-Top Solar Applications

Factors of Selection Solar Panels for Roof-Top Solar Applications

Although roof-mounted solar systems operate similarly to ground-mounted ones, the considerations for selecting solar panels for these two applications are vastly different. 

In this article, we are going to review ten main factors the solar installer should consider while selecting solar panels for rooftop PV systems.

1. Project and Panels Capacities

It is necessary to know the amount of energy the End User wants to generate from the solar panels besides answering the following questions at the design phase.

  • Does the End-User want to cover the entire load at all times without withdrawing electricity from the municipal grid?
  • Does the End-User seek to get enough energy to charge a battery backup to consume electricity only in times of the electricity shortage of the grid?
  • Does the End-User look to obtain enough electricity to run the entire project. For instance, in the residential solar applications, the householder runs all the electrical devices regularly via a solar power system?
  • Does the End-User want a certain amount of energy enough to cover a portion of that load?

In other words, by identifying the End-User needs of loads, the solar designer can note the nominal sizes of the various solar panels available in the market and choose the appropriate economically and technically solar panels required to obtain this capacity, and determine the type of inverter needed and size the rest of the other components of the solar systems.

2. Efficiency of Solar Panels

After listing the appropriate solar panels in the market. The solar designer compares the efficiency of the solar panels and tries to choose the one with the sufficient efficiency for the solar application because the installation of a solar power system on the roof depends on the available installation area up there since most of the buildings’ roofs include tanks and other external equipment for air conditioning, heating, and others).

Choosing the panels with higher efficiency enables the End-User to obtain more electricity by using fewer panels that make the system able to generate the optimal amount of electricity possible from the limited space on the roofs.

The question is: what is solar panel efficiency?

Solar panel efficiency is the ratio of the electrical energy produced from the panel and converted from the solar radiation befalling it.

For example, we have two panels of similar dimensions, and with different efficiencies, the use of a higher-efficiency module will ensure more electrical energy when exposed to the same amount of solar irradiation. Therefore, the system will require fewer panels and less installation surface area.

3. Solar Panels Dimensions

The design of a rooftop solar power system is mainly conditional on the available space to install the solar system, therefore choosing a panel with an appropriate capacity, high efficiency, and relatively small dimensions allows the solar designer to make optimal utilization of the available space to generate the highest possible amount of energy.

In the installation phase, large panels require more efforts in moving them from the ground to the surface (workplace), which may entail additional costs on the installer that can be avoided by choosing the relatively small dimensions of panels.

4. Weight of the Solar Panels

Identifying the mechanical weight installs on the rooftop, it is essential to know the condition of the roof surface where the installer will fix the solar system, and the solar designer has to think about it. Can the roof surface stand the weight of the panels and the mounting structure he has chosen? Or should the solar designer consider another option?

The weight of the solar panels is a critical factor that the solar designer should consider, especially in rooftop solar applications, to avoid damage or collapse of the roof because of the overweight since it could not stand to carry the solar system. 

Moreover, the weight of the solar panels affects the selection of the mounting structure specifications that will hold them. The use of relatively heavyweight panels will incur additional costs to reach the solar panels to the surface (Additional workers, crane, etc.).

5. Solar Panels Annual Aging Factor

The Solar designer must consider the annual aging factor while choosing the solar panels and try to select the solar panels that are suitable for the End-User project in terms of capacity and have the lowest rate of annual aging to ensure that the solar system will generate the highest possible amount of energy over the long period.

The aging factor is a degradation percentage that indicates the amount of decrease in the power production of the solar panels during the operation’s period means that the solar panels produce less electricity from the same amount of sunlight.

6. Solar Panels Mechanical Properties.

Also, it is crucial to consider the mechanical properties of solar panels to find out their resistance to various weather circumstances that may arise during their period of operation. Some questions shall be assumed while doing the design:

  • Do the selected solar panels stand the winds occurring in the project location? 
  • Do solar panels have a high value for what is known as negative mechanical load? 
  • Do solar panels bear a positive mechanical load? 
  • Can the solar panels stand the weight of falling snow?

By comparing the different values ​​of the negative and positive mechanical loads, we can form a more accurate idea of ​​the appropriate option for our project by knowing the surrounding climatic conditions.

For example, dividing the solar cell into two halves or three equal parts contributes to increasing the strength of the solar panels and improves their performance in cloudy weather conditions and shade. These solar panels are called half-cut cells and third-cut cells.


  • The positive mechanical load is the load that results from the external force of gravity from the material (for example, snow) when it falls and accumulates on the solar panels.
  • The negative mechanical load defines as the load resulting from the force of the wind, which may cause damage to the solar panels when exceeding the maximum wind values ​​the solar panels can stand, besides the limited value of the frame it is made for, and the one of the mounting structures.

7. Solar Panels Compatibility with The Inverters

Inhomogeneity of the electrical components in a single solar power system occurs because of using diverse solar panels having mismatching technical parameters which are different or don’t have identical electrical features like ( voltage, wattage, amps) or selecting an inverter that is not compatible with the solar array. The inhomogeneity causes a severe loss of the overall output power of the solar power system. Therefore, It’s necessary to use the same solar panels in the arrays for solar power systems.

Some solar panel manufacturers produce solar inverters compatible with their different models of solar panels. On the other hand, many of the manufacturers specialized in making solar panels only, so the solar designer must check the suitable inverters’ availability on the market and compare their nominal data with one of the solar panels to ensure the inverter fits for them. Or should the solar designer choose another inverter or select panels compatible with the specifications of the available inverter?

The solar designer must consider the following factors while selecting the solar inverter:

  • Open Circuit Voltage of the solar array.
  • Short Circuit Current of the solar array.
  • The capacity of the solar array.

These values ​​must correspond to the technical parameters ​​of the inverter. Otherwise, the solar system will not operate and may cause high risk and heavy damage to the facility.

8. Reliability of the Solar Panels Brand

The solar installers are always looking for highly reliable Tier1 panels from well-known distributors having safety certificates, IEC, LE, flash certificates, and certified guarantees. To ensure the solar systems work with required efficiency over the life without failures doubts that the panels may occur dangerous fires.

Bankability should also take into account as a criterion for choosing Tier1 solar panel brands, the advantage of bankability goes to solar panel brands that have high financial confidence from various financing agencies and thus can fulfill their obligations towards their customers, including product warranties and performance guarantees.

9. Aesthetic Design

Many solar manufacturers offer several options for the panels concerning the elegant appearance. It is possible to buy solar panels with a white, black frame or even frameless to suit the solar application. Although the purpose is to generate electricity, there is no obstacle to obtaining an attractive modern appearance. (choosing panels, For example, black solar panels with a black frame, where their efficiency is lower than the panels with a white frame).

10. Project Location and Installation Area

A project location with a high amount of solar irradiation in the Sun Peak Hours is a factor when deciding to rely on solar energy to generate electricity. Moreover, enough installation area of the solar system shall be in space suitable for the number of panels needed to produce the required electricity. This area must be sufficiently exposed to solar irradiation and without shading.

Residential, commercial, or industrial solar applications also require sufficient installation areas to accommodate the number of solar panels needed to generate electricity to cover the consumption, but if this space is insufficient, how the solar designer overcomes this obstacle.

Select high-efficiency solar panels with small dimensions and high power output to overcome the limited installation area obstacle.

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