Solar PV System Sizing

solar energy solutions

Are You Buying a Solar Panel for Your Rooftop?

Let’s understand what is meant by “Rooftop Photovoltaic Power Station, or Rooftop PV System” it’s a photovoltaic system that has its electricity-generating Solar Panels mounted on the rooftop of a residential or commercial building or structure.
One of the crucial first steps to consider is Solar Sizing.

Doing a proper solar PV system sizing would help you answer questions like:

  • How much should be the Solar PV capacity?
  • What Solar Panel size to buy?
  • How much should be the Inverter/ Battery size?

Not doing a proper Solar PV sizing can result in not installing the right kind of Solar PV system.

In this article we look at all the critical elements when sizing a Solar PV system.

Interested to know more?

Let’s dive in.

Solar PV System Components

To size the Solar PV system, we need to understand the different components of a Solar PV system.

The different components of the Solar PV system are:

  • Solar PV module
  • Solar Inverters
  • Load
  • Charge controllers
  • Batteries

Solar PV Module (Solar Panels) :

Solar Panels contain Solar cells that convert incident sunlight into Direct Current (DC).

To achieve the required voltage and current, group the panels into a larger array (PV array). Connect the PV modules in series or parallel to provide the desired voltage or current.

Solar Charge controller :

It controls the output voltage and current from the solar panels to the battery. It helps to prevents overcharging and discharging of current.

Solar Inverter :

It converts DC output of the Solar panels to usable AC (Alternating current).

Batteries :

These store the power generated from the Solar which is in the form of Direct Current (DC).

Load :

These are the appliances that use the power generated from the Solar PV or Grid.

Energy Efficiency

Before doing Solar Sizing, consider ways to build in efficiency into the system. Bring in efficiency by implementing energy efficiency measures. This reduces the Solar Power output from the Solar PV system.

Some of the measures to implement more efficiency into the systems are:

  • Use efficient appliances / devices
  • Look for ways to use natural resources like sunlight, wind etc. This reduces the dependency on fossil
    fuels. It also reduces energy costs.

Solar PV System Sizing

1) Solar Panel Load Sizing

Determine the power consumption demands

Calculate the Total Watt hours per day :

This is calculated by measuring the average watt hours consumed by different appliances per day.

Then Calculate the Total Watt hours per day to be output by the Solar modules :

Multiply the Total Watt hours per day by 1.3(the energy lost in the system). This gives the Total power that needs to be supplied by the Solar Panels.

2) Solar PV Array sizing

Different size of PV modules will produce different amount of power.

Sizing a Solar PV module 

In the previous step we calculated the Total Watt hours to be output per day by the Solar modules. Now calculate the average daily peak sun hours in your location. Divide the total output to be delivered by the Solar PV system by the daily peak sun hours. This gives approximate array size in KWh. Divide this value by the efficiency factor of the solar panels to get the power output of the Solar panels.

To calculate the number of panels needed – Divide the Total Watt hours to be produced by the rated power output of the PV modules. This provides the number of PV modules needed.

3) Solar Inverter Sizing

Solar Inverter converts The DC output from the Solar Panels to usable Ac power. Hence sizing the Solar Inverter is important so that the conversion happens properly.

The inverter is rated in Watts. The inverter watt rating should be same or more than the Solar PV systems watt rating.

In case of appliances like motors the Inverter size should be a minimum 3 times the capacity of those appliances. This is to handle the surge current during starting those type of appliances.

For grid tied system, the input rating should be same as PV array rating to allow for safe and efficient operation.

4) Solar Charge Controller Sizing

The Solar Charge controller is rated with Amps and Volt capacities.

Choose a Solar Charge controller to match the voltage of the PV Array and Batteries. Ensure that the solar charge controller has the capacity to handle the current supplied from the Solar PV system.

5) Battery Sizing

A battery is not needed in case of Solar On-grid system. It is needed in case of Solar Off-grid system or Hybrid Solar system( a mix of Solar On-grid or Solar Off-grid).

Choose a battery with a capacity equal to or more than that of the Solar panels.

Battery capacity is measured in Ampere hours. Find out the Watt hours by multiplying Ampere hours and voltage of the battery.

Ex: For a 40AH, 10V battery the Watt Hours figure is 40(X) x 10(Y) = 400 WH (Z)

This means the battery should supply 400 Watts for 1hr or 200 Watts for 2 hrs i.e the more energy
you take more faster the battery is discharged.

However one cannot take all the power from the battery. This is because once the voltage drops below to that of the equipment it’s supplying, it will not be able to power it.

Solar PV system sizing
Solar Sizing



In this article, we looked at the different components of the Solar PV system and how sizing needs to be done for the different components of the system. Doing proper sizing of the Solar PV system ensures that the system delivers optimum output as per the user requirements.

If you are looking for installing a Solar PV system for you residence or commercial property , Apollo can help you in getting the proper Solar sizing done. Contact us if you have any requirements. Do let us know any feedback/ comments related to the content of this blog.

Apollo Power Systems Pvt Ltd

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