How to Model Energy Yield Over Terrain Using PVSyst + PVCAD Mega

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For nearly three decades, PVSyst has retained its place as the industry-standard software for modeling the yield of PV arrays. However, as one of the oldest photovoltaic software programs, even its greatest champions will admit that the user interface is cumbersome and some of the functionality can be clunky and difficult to use.

PVSyst’s challenges become particularly apparent when creating energy yield models for utility-scale project sites on the rolling terrain that is far more common to fixed tilt and tracker projects today. At PVComplete we have added features to make it easier to overcome these challenges.

PVSyst has the ability to model terrain losses by creating a 3D layout in their Shade Scene Construction tool, however, the user interface makes it difficult to draw large project layouts quickly and there are several limitations:

  1. There is no way to change individual tracker heights or slopes within a PV field in a PVSyst simulation. A work-around is to assign each tracker or table to its own field, however, unless you have at least two trackers/tables in a field, PVSyst will not be able to accurately read the row spacing or pitch from the shade scene and will produce false results. 
  2. PVSyst cannot model backtracking unless all the trackers in a layout are at the same level and slope, which means you cannot model both terrain losses and backtracking at the same time in PVSyst, only one or the other. 
  3. PVSyst cannot run a simulation with trackers at different slopes in the same shade scene at all, regardless of backtracking, though they can be at different elevations. Fixed tilt racking is slightly better since backtracking is obviously not an issue. For fixed tilt, PVSyst will allow up to 8 different slopes (in the east-west direction) but in reality, most utility projects have racking at hundreds of different slope angles.
Typical tracker array in PVSyst on flat terrain

Fig. 1 Typically tracker array in PVSyst on flat terrain. Unable to consider tracker slopes or tracker heights.


Trackers with varying heights but the same slope

Figure 2: Trackers with varying heights but the same slope, PVSyst will model this but not with backtracking.

Our utility scale layout and PVSyst export features make it easy to produce 3D shade scenes for even very large utility scale projects in minutes — much faster and more efficiently than the native construction tool. PVCAD Mega addresses these challenges in the following ways:

  1. Each 1-axis tracker is automatically placed in it’s own field (one field in the shade scene will contain two rows, to allow PVSyst to read the row spacing or pitch). 
  2. For fixed tilt racking, PVCAD Mega creates a shade scene with each table elevated to its average height and the same slope.
PVCAD As Built - Realistic Site Rendering

Fig. 3 – PVCAD As Built – Realistic site rendering. Arrow signifies exports variable height and slope to create precision PVSyst output.


Figure 4: Trackers with varying heights and slopes, PVSyst alone cannot model this type of array layout. PVCAD Mega PVSyst integration makes it possible.

For single axis trackers, PVSyst cannot model backtracking and terrain height at the same time. Our solution is to export two shade scenes, one to model the backtracking and one to model the terrain. The first shade scene has all trackers at the same height and slope to model backtracking. The second shade scene has all the trackers elevated to their average height to model terrain losses. To get the most accurate yield prediction, you can apply the terrain losses from the second scene as a % loss to the results model. 

PVCAD Mega can also export all shade scenes per the Figure 3 scenario, with all the trackers set to their proper height AND slope to most closely match reality. Our hope is that PVSyst will someday update their software to model this nuanced actual site scenario.