August 31, 2015

How to Calculate Solar Energy Required

Hello Readers,

This is Ankit, founder of I am going to discuss my views on calculating solar power requirements for running electrical loads of any capacity.

What Should We Know ?

  • We must be aware of the power rating (in watts) of the devices that is needed to be powered with Solar Power Plant.
  • Quantity of devices.
  • Number of Hours of Operation
  • Solar Panels generate DC Electricity and to convert this DC electrical energy into AC Electricity, Inverters are used.

Power rating of the devices are mostly provided in the user manuals and specification plates on the devices itself.

How to Calculate Load ?

For Example  : A normal Ceiling Fan ( for residential purpose ) consumes approximately 60 Watts;

If it runs 18 hours a day the amount of electrical energy it will consume is 18 * 60 Watts = 1080 Watts.

Now if we have a 100 Watt-Peak solar panel, it will generate 100 Watts of Electrical Energy ( theoretically ) under standard required conditions , i.e The intensity of sunlight should be maximum.

If this Solar Panel is Exposed to sunlight for a duration of 8-10 Hours it should ideally generate 800 Watts to 1000 Watts of Electricity.

Under normal conditions a solar panel generates 6-7 Units (0f its capacity) of Electricity per day. A 100 Wp Solar Panel will generate 600 – 700 Watts of Electricity Per Day.

It means that our solar panel of 100 Watt will not be able to run a ceiling fan of 60 Watts for 18 Hours a Day. For this purpose 2 Solar Panels of 100 Watts or 1 Solar Panel of 200 Watts or any combination of panels that sum up to 200 Watts will be needed. 2 Solar Panels of 100 Watts will generate 1200 to 1400 Watts of Electricity Per Day.

A Battery ( of rated capacity ) can be used to store the energy and by connecting Inverters to this battery the electrical power can be supplied to the run the fan.

We can’t connect solar panel to batteries directly as there is a possibility of overcharging and burning. To prevent overcharging of batteries a Charge Controller is used between Solar Panels and Batteries that work as a regulatory device.

The Formula ?

The formula is simple ,

” Rated Capacity of Device(s) ”  x “Quantity ” x “Number of Hours of Operation” = Electrical Energy Required

” Electrical Energy Required ” x 1.5 = Solar Panel’s Wattage Required  ( I am using a factor 1.5 to consider losses , climatic conditions and load variations in mind )

Note : These are approximate calculations to give you a rough idea. Actual Calculations may vary.

We have developed A Solar Energy Calculator for approximate calculations of Residential Loads. Here is a link to this calculator –

Please Review and leave your comments so that we can make it better.

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