Inverter Sizing and Selection for roof top PV system


Inverter selection for installation of roof top PV system will depend upon

  • Energy output of the array
  • Matching of allowable inverter string configuration with size of the solar array in KW and size of individual modules with array.
  • Whether we decide to have one central inverter or small multiple inverters.

Why multiple inverters make sense?

  • If array is spread over number of roofs that have different orientations and tilt angles then the maximum power points and output currents will vary. If it is economical, installing a separate inverter for each section of the array which has the same orientation and angle will maximize the output total of array. Inverters with multi power point trackers will assist us in achieving this
  • They allow system to operate even if one inverter fails
  • They improve the balance phase in accordance with local requirements
  • They allow system to be modular, so that increasing the system will involve adding predetermined number of modules with one inverter

There is one downside to it, that low power rating inverters will be more expensive.

Inverter Sizing:  Currently available are rated for-

  • Maximum DC input power
  • Maximum DC input current
  • Maximum specified output power i.e. the AC power they can provide to the grid

The maximum power of the array is calculated using the following formula:

Array Peak Power = Number of modules in the array x the rated maximum power (Pmp) of the selected module at STC.

The designer shall follow the manufacturer’s recommendation when matching the peak power rating of the array to that of the inverter.

Many manufacturers will provide the maximum rating of a solar array in peak power for a specific size inverter.

In De-rating module performance, the typical PV array output in watts is De-rated due to:

  • Manufacturer’s tolerance of the modules
  •  Dirt and Temperature.

Posted by: Prateek Sikka

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