Description of PD IEC TR 63149:2018 2018

This document is aimed at building mathematical models for calculation of the distance between arrays, to farthest avoid shading and reasonably reduce the land usage of PV farms.

In general, there will be longest south-north shading on the day of the winter solstice. The boundary condition to calculate the south-north (S-N) distance between PV arrays used in this document is based on winter solstice. The longest east-west (E-W) shading is on the time when the sun is in the east. The users can change the boundary conditions (date and time) depending on local conditions (latitude, land limitation, facing direction, etc.), the formulas are all the same.

The shading distance calculation is based on date and time boundaries, not based on shading energy losses that may be very complicated. The no-shading distance calculation in this document is only for the distance between PV arrays, not for other surrounding objects, but the formula can also be used to calculate the no-shading distance between the objects and PV arrays. Where shading occurs on the PV array site other calculations are required that are not within the scope of this document. The no-shading distance calculation is based on the northern hemisphere in this document, but all fomulas can also be used for the southern hemisphere.

The no-shading calculation model is different for fixed PV arrays and PV systems with solar trackers. This document derives mathematical models for both fixed PV arrays and solar trackers.

For solar trackers, there are 2 different coordination systems: the Ground Horizontal Coordinates (GHC) and Equatorial Coordinates (EC).

This document provides land usage calculations of PV farms for the following array types:

• Fixed PV array on flat-land and face to the south

• Fixed PV array on flat-land and face to non-south direction

• Fixed PV array on tilted land and face to the south

• Horizontal E-W tracking in Equatorial Coordinates

• Tilted E-W tracking in Equatorial Coordinates

• Pole-Axis tracking in Equatorial Coordinates

• Double tracking in Equatorial Coordinates

• Solar Azimuth tracking in ground horizontal coordinates

• Manual solar altitude tracking in ground horizontal coordinates

• Double tracking in ground horizontal coordinates

In the following clauses, the different coordinates systems are introduced and the land usage calculations for different operational models are provided.

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