A 1 kW rooftop system generally requires 10-12 sq. metres (130 square feet) of flat, shadow-free area (preferably south-facing). Actual sizing, however, depends also on local factors of solar radiation and weather conditions and shape of the roof.
The extent of roof area required by a solar PV plant is mainly dependent on two factors:
- Shade-free roof area: Shade-free roof area Unused rooftop area will have to be assessed for incidence of shadows through the year to determine the extent of shade-free area available for installing a rooftop solar PV plant. We emphasise shade-free roof area because shadows affect the PV plants’ performance in two ways Output – When a shadow falls on a PV panel it reduces the output from the plant Panel damage –When a shadow falls on part of a panel, that portion of the panel turns from a conductor into a resistance and starts heating up. That portion of the panel will eventually burn out and the entire panel will have to be replaced. This will not be covered by warranty It is therefore critical to ensure that no shadow falls on the PV plant throughout the year. Shadows that fall on the plant can be from Neighbouring structures – Buildings, hoardings, mobile phone towers, and even trees can cast a shadow on a rooftop PV plant. In many cities worldwide where both residential and commercial buildings have a number of adjoining buildings and other structures, shading analysis will be an important aspect to consider before estimating the actual area available for rooftop solar. The PV plant itself – One row of panels can cast a shadow on the row behind them; the further we move away from the equator, the longer the shadow that is cast and the greater the amount of room required between rows of panels.
- Panel efficiency: Panel efficiency influences rooftop space requirement because efficiency is calculated with respect to the area occupied by the panel. A simple way to understand the relationship between panel efficiency and rooftop space required is to remember that a rooftop plant that uses panels with a lower efficiency rating will require greater rooftop space than a plant that uses panels with higher efficiency rating.