The article takes a look at the basic factors to be considered to self-test the feasibility of a rooftop solar PV system, before calling the experts for the detailed site survey.

Dont waste your roofs

With falling prices of solar photovoltaic modules and increasing prices of diesel, the electricity from a solar plant is almost at par with diesel generated power. Almost every manufacturing unit in Pakistan has setup diesel generator power plant as a backup for their power requirements during power outages. Typically, such companies have huge rooftop area which receives unobstructed sunlight throughout the day, thus providing a good opportunity to set-up a rooftop PV system.

Solid and secure installations on your roof

Before going for a detailed site survey, if a client wants to perform a quick feasibility check, he or she should consider the following parameters:

1. Shadow test: To collect maximum sunlight during the day, the solar PV panel should face as much south as possible. The rooftop must be checked for the shadows of trees or adjoining builds etc., particularly from south direction. A clear rooftop without any shadow from all around is an ideal case for solar PV installations. In case there is shadow on rooftop, a detailed analysis of time and direction of sunlight needs to be performed by an expert to estimate the energy received by rooftop.

Not an inch will get wasted of your roof top for solar cells

2. Rooftop type:  The load carrying capacity of the roof should be checked. The solar panels with structure typically weigh 15Kg per Sq. meter. This weight varies with technology and type of structure.

The solar cell installations kept very near to the roof surface

3. Sizing of solar system: Size of solar system depends on the rooftop area available for panels. This can be calculated by dividing the available area by each panel area and multiplying it by panel’s rated output. For estimate purpose, 70% of rooftop area can be used for panel’s installation. Certain solar panels in market can use as high as 90% of rooftop area, but have much higher cost. As a thumb rule, 10 Sq meter area is required for 1 Kw capacity solar system.

Size of solar system = Panel’s rated output*(Rooftop area / Each panel area)*70%

The roof tops of apartment buildings being utilized

4. System output (annual units generated): The output per panel and hence system output depends on panel efficiency and the solar radiation at the site. These two factors define CUF (Capacity Utility Factor) for solar system for a particular location. For Pakistan typically 19% CUF is taken for estimation. The annual number of units generated by solar system can be calculated as: Units Generated Annually (in Kwh) = System Size in Kw * CUF * 365 * 24 As a thumb rule, 1 Kw capacity solar system generates 1600 – 1700 Kwh of electricity per year. The CUF varies with the geographical location of the installation site

Solar powered village house roof top