Rooftop Solar System

Top Criteria To Select The Capacity of Your Rooftop

There is rising competition in the commercial sector globally. To meet the energy requirements, there is a huge demand for rooftop solar power systems among commercial establishments in Australia. With so many users for solar panel installation in Sydney, they would like to know the right capacity for the rooftop solar power system.

Criteria To Determine The Capacity For Rooftop Solar PV Installation

1. Project Scope

For designing a solar PV plant that best fits your requirements, it is essential to define the project scope, i.e. the purpose of rooftop solar PV installation. The reason for rooftop solar power system installation may be one or more of the following:

  • To support electricity requirements during the daytime.
  • To reduce the use of traditional fuels like diesel.
  • To keep the appliances and machines running during power outages.
  • To support lighting loads.
  • To generate power for use at nighttime.

2. Site Surveillance

The site surveillance involves inspecting and determining whether the roof is suitable for rooftop solar PV installation or not. Site surveillance involves looking for the following:


For countries such as Australia located in the southern hemisphere, a north-facing roof will be an ideal choice for a rooftop solar power system.

zero dollar upfront cost

Shade-Free Roof Area

For rooftop solar PV installation, it is essential to determine the shade-free roof area.

The rooftop is assessed for shadow areas because when a shadow falls on solar panels, it reduces the energy output. Also when a shadow falls on a certain portion of the solar panel, it causes the temperature of the solar panels to rise, causing damage. For installation of a rooftop solar power system of capacity 1 kW, a shade-free rooftop area of approximately 100 sq. ft. is needed.

3. Calculating The Solar Energy Availability

The amount of solar energy available for you to use is determined by the amount of solar energy falling on the solar panel per day. The amount of solar energy availability is expressed in kWh/m2/day. (kilowatt-hours-per-square-meter-per day). The rooftop solar power system varies greatly from one location to another in Australia. A solar panel of 1 kWp (kilowatt peak) can generate solar power of 4 kWh.

4. Calculating The Amount of Energy Required

The amount of energy required can be calculated based on the load of the equipment that needs to be supported. Total energy requirement per day (Wh) = Wattage of appliance x Number of appliances x Working hours.

Based on the amount of energy required, the capacity of the rooftop solar power system is chosen.

5. Size of The Solar System 

Let us consider the load supported by the solar PV system to be 1.8 kWh/day.

Safety margin added = 30%

Insolation assumed to be 4 kWh/m2/day

System size = (Energy requirement x 1.3)/insolation level

= 1.8 x 1.3/4

= 0.585 or 585 Wp.

Number of panels = System size / Panel rating

In this case, we assume the panels are 130 kWp at 12V.

Number of panels = 585/130

= 4.5

This means that the solar PV system requires 5 panels of 130 kWp at 12V.

Size Of The Inverter

When considering inverter size, a safety margin of 45% is applied.

Inverter size = Total wattage of all appliances x (1+ 45%)

Following the above-mentioned criteria can ensure seamless supply of solar power with minimal expenses. Keep this criteria in mind.

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