How Much Space Do Solar Panels Need?

11 Sep 2020

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With the abundant sunshine and expensive electricity in Australia, solar power is an excellent investment for homes and businesses. However, the space requirements of solar panels must also be considered before an installation. For example, this is not a problem in large industrial roofs, but high-rise buildings have less space with respect to their indoor area.

Most solar panels commercially available have a capacity in the range of 250 to 400 watts. This means that one kilowatt of capacity requires three or four, while one megawatt uses between 2500 and 4000. The wattage and size of a solar panel are determined by its design:

  • Solar cell material: monocrystalline silicon, polycrystalline silicon, or thin-film substrates like cadmium telluride or CIGS (copper indium gallium diselenide).
  • Number of solar cells: 60 or 72 in most cases.

Monocrystalline solar panels have the highest efficiency, which means they offer more watts per square metre. Polycrystalline panels are slightly less efficient, requiring extra space for a given capacity. Finally, thin-film panels are the least efficient and the most demanding in terms of space. Most solar power systems currently use mono- or polycrystalline silicon panels.

Comparing 60-Cell and 72-Cell Solar Panels

60-cell solar panels are often referred to as residential, while 72-cell panels are described as commercial. However, this is a naming convention and not a factor that limits their applications; a house can use 72-cell panels and a corporate building can use 60-cell panels without problem. The exact dimensions of solar panels can change slightly depending on the model and brand, but their approximate sizes are the following:

  • 60-cell solar panel: 1.7 m tall and 1 m wide, with an area of 1.7 square metres
  • 72-cell solar panel: 2 m tall and 1 m wide, with an area of 2 square metres

Since both solar panel types have the same width, the racking material needed per panel is the same in both cases. This is a key reason why 72-cell modules are preferred in large commercial and industrial solar projects – the owner can install a given capacity with less panels, racking material, and hours of labor. On the other hand, 60-cell modules are popular in residential settings, where their smaller size makes them easier to handle.

Assuming the same solar cell material, a 72-cell panel will have 20% more wattage than a 60-cell panel. Since both units have the same width, their solar cells are arranged in rows of six. However, the 72-cell panel is 12 rows tall, while the 60-cell panel is 10 rows tall.

Typical Wattage of Mono- and Polycrystalline Solar Panels

As mentioned above, monocrystalline solar panels have higher wattage. This is an advantage when space is a limitation, since the installation can fit more watts per square metre. However, the capacity of a solar panel is also determined by the number of cells:

  • A 60-cell solar panel will have a typical capacity of 250 to 300 watts if polycrystalline, and 310 to 350 watts if monocrystalline.
  • A 72-cell solar panel will have a typical capacity of 300 to 350 watts if polycrystalline, and up to 400 watts if monocrystalline.

Keep in mind these are typical capacities, and not technical specifications of a specific brand. Most solar panels commercially available will fall within these ranges, but you may find exceptions. With the large number of brands in the market, a good recommendation is purchasing solar panels from a Tier 1 manufacturer.

As an example, assume you need a 2-MW solar power system for an industrial facility, and you have two solar panel options: a 72-cell 340W polycrystalline module, and a 72-cell 390W monocrystalline module. Assuming a panel size of 2 square metres, the number of panels and total space covered would be the following in each case:

  • 340W polycrystalline – 5,883 panels covering 11,766 m2.
  • 390W monocrystalline – 5,129 panels covering 10,258 m2.

The installation with polycrystalline panels is around 15% larger. Since these panels have a lower efficiency than the monocrystalline option, they must cover a larger area to reach 2 MW. However, this is only an issue when space is a limitation. Corporations that go solar also consider factors like the cost per watt, solar financing options, and services included in the offer.

Using 60-cell modules for this project would be impractical, since the total number of modules to install increases sharply. However, the amounts can be estimated to illustrate the concept, assuming the following module specifications: a 60-cell 270W polycrystalline panel, and a 60-cell 310W monocrystalline panel. Consider that each panel covers 1.7 m2 in this case.

  • 270W polycrystalline – 7,408 panels covering 12,594 m2
  • 310W monocrystalline – 6,452 panels covering 10,968 m2

Even if space is not a limitation, the total number of individual panels increases significantly with 60-cell units. This requires more man-hours of labor, increasing installation costs.

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