5 factors to consider when choosing a solar panel size


Historically speaking, there have always been two different sizes of solar panels. One with 60 cells for residential roofs and one with 72 cells for larger commercial projects. This worked because the size of a solar cell was measured in a uniform unit. However, this will change in 2021 (see our article on developments in 2021). The solar panels that are now being introduced have different sizes with the common denominator being that they are a lot larger than their predecessors.

Extra choice is nice! But what exactly should you look for when choosing the right size solar panel? We will explain it to you in this article.

5 factors

There are a number of factors to consider when choosing the right size of solar panel for the job:

  • The load-bearing capacity of the mounting system (mechanical load)
  • The compatibility of the inverter
  • Labour legislation (larger panels are heavier!)
  • Design flexibility
  • Storage and logistics

Each of these bullet will be explained separately below.

Mechanical load


Solar panels are not only becoming larger, but also heavier. The mounting system used to mount the panels on the roof must be designed to handle this weight. Also, the standard mounting lengths of these systems are often incompatible with panels that are wider than 1100 millimetres.

Longer/wider modules also have a greater chance of micro-cracks if they are not installed with the correct mounting system. Check with the manufacturer of the solar modules whether clamping on the short side is permitted and up to what mechanical load (2400 or 1800Pa). If damage to the modules has occurred due to the use of an incorrect roof mounting system, the product warranty may be invalidated.

The Autarco Apex and Matrix roof mounting systems are already fully compatible with the 182 millimetre modules (450 Wp).

The compatibility of the inverter


Many of the new modules, and specifically those generating more than 500Wp, have higher current voltages than the average inverter can handle. Autarco inverters will be upgraded to 14A DC input and 16A DC input to create more possibilities for larger solar panels.

Also, thanks to the Autarco ‘digital twin’ and current weather data, we can make an accurate calculation of the maximum output of a solar power system. This enables us to ensure that the inverter can cope with any situation.

Labour legislation


Once again: solar panels are not only getting bigger but also heavier! Current legislation states that if a solar panel weighs more than 23 kg, it must be lifted onto the roof by more than one person. Heavier panels will therefore most likely mean that more installers are involved in a project and therefore less efficiency.

The MHI and our new 405 Wp solar panels both weigh less than 23 kg. Panels with a maximum output above 420Wp are either:

  • Heavier than 23 kilograms
  • Use glass that is thinner than 3.2 millimetres (strongly discouraged!)

Design flexibility


A length of between 1700 and 1800 millimetres is ideal for solar panels on a residential pitched roof. This is exactly how three solar panels fit next to each other.

On roofs with several obstacles, it is advisable to use smaller panels. These often generate a higher yield than larger panels due to a higher degree of design flexibility (you can often fit more!).

Storage and logistics


Crucial but often forgotten: a standard forklift has ‘forks’ of 1200 millimetres wide. These can only lift solar panels larger than 1800 millimetres on the ‘long’ side. This can have consequences for the delivery if it is not possible to load the forklift from the side.

Furthermore, it is already advisable to unpack pallets full of panels with two staff members. This is certainly a requirement for larger panels. The right number of personnel must therefore be available for this.

Autarco’s advice

Do not be blinded by the number of Watt peak that a solar panel can generate. Make sure the solar panels you buy have an efficiency of at least 205W/m2 but also take into account other factors including: logistics, system assembly and of course the total expected installation costs.