There are a number of different things you need to know before working out the roof space required for solar panel installations.
First you’ll need to know the dimensions of the solar panels and the size of the system. Then work out whether the panels will fit better upright or sideways. Here’s what you’ll need:
Once you have this information you can work out how much roof space is needed for your system.
Now you're ready. Here’s how you calculate the area required:
Size of the system (in Watts – e.g. 5kW = 5,000 Watts) ÷ Size of the solar panel (in Watts) = number of panels required. Round up to a whole panel if you want to meet or exceed the target capacity. Work out how many square meters or square feet each panel takes up.
For example, a 470W REC Alpha Pure-RX panel measures 1728mm by 1205mm (68.0 by 47.4 inches), taking up 1.728 x 1.205 = 2.08 sqm, or about 22.4 square feet. For a 5kW target, 5,000 ÷ 470 = 10.64, so 11 panels provide 5.17kW and take up about 22.9 sqm, or 246 square feet. These are panel dimensions and rated DC capacity, not a prediction of electricity production. [1] A little bit of space will also be needed in between each panel for fixing the panels to the racks—this will depend on what type of racking system is used. The usable roof area must also allow for obstructions, shade and locally required fire-access pathways and setbacks; have the installer check the layout and roof structure. [2] [3]
Which direction do your panels need to face? If you don’t have enough roof space on a single roof face, you can consider splitting your system into 2 different orientations. The original advice here was written for Australia, in the Southern hemisphere, where North is generally the preferred direction. In the continental United States, an unshaded South-facing roof generally provides the best annual production. East and West can also work; the output difference depends on location, roof slope and shading, so compare the actual roof faces with a tool such as PVWatts. Changing orientation changes electricity production (in kWh), not the panels’ rated system capacity (in kW). [2] [4] Is there a minimum number of panels facing in one direction? This depends on the inverter you choose. A string inverter has a minimum voltage in order to work. The more panels in one “string”, the higher the voltage will go. There is no universal six-panel minimum: the installer must follow the selected inverter and module specifications. Microinverters operate at individual panels, so that string-length rule does not apply to them. [5]
About the Writer: Chris wrote this article for an Australian solar-energy audience in 2015.
Updated content · November 15, 2026