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A Solar PV Rooftop system will give its optimum performance only when the string sizing has been done correctly. In this blog, we will be talking on correct methods of string sizing.

Now let us first understand what a String is. When we connect Solar PV panels, used in solar power plant for generating solar energy for home/industrial/commercial roof top or ground mounted, in series, then it is called a String. String sizing means, what should be the minimum and maximum number of Solar PV panels to be connected in a string, so that system operates at its highest efficiency.

Output parameters of Solar PV panel , used in solar power plant for generating solar energy for home/industrial/commercial roof top or ground mounted ,should match the input parameters of the Inverter, so that the system works at its highest efficiency. If the parameters do not match, or falls out of the range, the system will shut down or will work with very less efficiency. Hence, String sizing must be done correctly.

Parameters of Solar PV vary with change in temperature. With increase in temperature the voltage of Solar PV panel decreases and this need to be consider while sizing the string. One needs to check the Technical Data Sheet of Solar PV panel (as given by manufacturer) for calculating the effect of temperature on a particular Solar PV Panel and then match that with the Inverter input parameters. Until and unless this is done, we can't say that the system is designed perfectly and will perform best.

For example, if the strings are not sized considering the temperature factor and inverter input parameters, then there may be situations when the Solar PV Panel parameters will not match the inverter input parameters and the system will shut down or will under perform.

Our string sizing goals should be ::That we make sure never to supply the inverter excess voltage which may kill itóMax string length. Voc adjusted for temp will decide Max string length.

And also to ensure that we always supply enough voltage to inverter to turn it onóminimum string length. Vmp adjusted for temp will decide Min string length.

So you need to ask your installer, did he consider these parameters while string sizing ? Has he actually done string sizing or made a string by just counting the even numbers of PV panels in series?

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Pradeep Prakash Singhal

Pradeep Prakash is a solar enthusiast/ solar professional by heart. He has been involved in setting up distributed solar at more than 100 sites across India