Shadings for trackers with complex topography

[spelland74]

Hello,

I want to model trackers in complex topography. I saw in the PVsyst help that for trackers "The program chooses one significant tracker in the middle of the system, and evaluates the shading factor table for this element only, using the neighbor trackers, but neglecting other eventual shading sources."

I am wondering, if I define different tracking planes (shading objects) at different elevations, whether PVsyst will take the elevations into account to calculate the shading. If so, how? Does the program pick one tracker in the middle of each tracking plane/each shading object?

I was also wondering whether backtracking is always uniform across all tracking planes. I am interested in modelling a case where backtracking is different for different planes.

Best regards,

Sophie

[André Mermoud]

For the first question: this strategy of choosing one tracker in the middle of the array is indeed an approximation suited for "big" tracking arrays; it is used only for the evaluation of the shading factor applied to the diffuse component.

The impact of other environmental objects is supposed to be not very significant for the diffuse (which is probably an acceptable assumption). But the calculation of the shading on the beam component takes indeed these objects into account.

The backtracking calculation is dependent on the neighbour trackers. This algorithms of this calculation are difficult to establish, and only suited for well delimited conditions like regular tracker arrays. We didn't develop backtracking algorithms for neighbour trackers which are, for example, at different altitudes.

This is the reason why PVsyst requires that all tracking arrays are identical and "regular".

By the way, if we had different backtracking conditions for different parts of the system, the plane orientation would be different for each of these groups of trackers at a given time. We have not developed such a complexity in the simulation of tracking systems up to now.

[spelland74]

Thanks Andre for the quick and helpful reply.

[spelland74]

Hello,

I have a follow up question concerning creating a shading scene for tracking planes in complex terrain. Is this possible? I tried creating a "ground" object with different elevations, but this ground object seems to have zero impact on the shadings calculated (I get the same answer with or without the ground object).

Is there a way of positioning tracking planes on top of a "ground" object? If not, is there a way of creating tracking planes on a sloped surface? Or is the only possible approach to this problem to just create tracking planes that are at different elevations?

Best regards,

Sophie

[André Mermoud]

The ground object is a new tool, and we did not yet have time for developing all related features, like positioning trackers on it. This will be done for a next version.

You can always define trackers at different altitudes.

However with such a system the backtracking strategy is not well defined. PVsyst cannot calculate it.

[spelland74]

Thanks Andre. I guess this will be something to look forward to in the future version.

[deblynn]

Hello, I'm writing with a follow-up question to the earlier conversation. Can you define 2 separate trackers, at two different elevations, with no backtracking specified, and get an estimate of shading losses without backtracking? If those shading losses are linear (not according to strings), will the energy estimate be comparable to a backtracking system? (though I realize diffuse losses and IAM factor will be different). If there are only 2 trackers, I recognize that only one tracker will be shaded at a time, so the shading loss will be half the impact on a large array.

I am trying to figure out a way to use PVsyst to answer the question: how much elevation difference between trackers (E-W) is acceptable in terms of the magnitude of shading/backtracking loss? I would like to set up a simple 3D layout to test this, but I am not sure if it will work.

Thanks for any insights!

-Debbie

[deblynn]

A further follow-up. If I placed two multi-row back-tracking arrays next to each other, but with an elevation difference, could I still use the linear near shading loss between the two as a proxy for the impact of elevation? And if I modified the pitch of the back-tracking arrays, could I look at whether changing the backtracking settings helps with the shade impacts of the elevation difference?

Sorry, I know this is complicated.

-Debbie

[sneakypete92]

Hello,

I'm looking to simulate a similar scenario to the one Debbie described above.

I'd like to model a N-S axis tracker with a trans-axial slope (tracker sheds are on a sloped hill) and includes backtracking. I understand that at the time of the above posts (~July 2015) there was no functionality for shed-to-shed slope and backtracking with N-S axis trackers =. Has there been any development or updates? Is there a work-around way to model this scenario?

~Pete

[itaisuez]

Hi,

I'm looking to see if the issue of modeling trans-axial slopes has been addressed for N-S trackers. I understand that it will be very complicated to implement a backtracking algorithm that ensures that there is no row to row shading in this scenario, but that would be preferable for understanding these potential losses.

I'd like to model tran-axial slopes or row height differences assuming they are all backtracking like they would if the terrain were flat. As an additional note, does Helios 3D output an array layout that allows PVsyst to consider the height of each individual panel or row? Is it a true 3D model that PVsyst can use?

Thanks in advance for your help,

~Itai