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Difference in collector plane radiation between 'with tracking' and 'without tracking'


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I have done a comparison on gain over tracker plane radiation for a horizontal single axis east-west tracker between 'with back tracking' and 'without back tracking'.

in the case of 'with back tracking', the radiation gain on collector plane is 18.3% over Global Horizontal Irradiation(GHI) and for the case of 'without backtracking', gain is 27.7% over GHI.

As per PVsyst report, the Near shading loss for 'without backtracking' case is 9.9%, out of which 5.6% accounts to beam loss and the rest to diffuse and albedo.

Similarly for 'with backtracking' case, the Near shading loss is 3% which is due to diffuse and albedo (almost same as 'without backtracking' case).

My question is , if shading due to beam component is adjusted in 'with backtracking' case, the net gain on collector plane over GHI should be (27.7-5.6) equal to around 22%, but PVsyst report shows only 18.3% gain over GHI.

Kindly clarify which parameter makes the difference in gain on collector plane over GHI between 'with back tracking' and 'without backtracking'.

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The "Back-tracking" strategy and the "shadings" strategy are usually relatively equivalent, as you intercept the same tube of light.

What you loose as shadings with the latter case, you loose it as incidence orientation loss with the Backtracking.

Now this equivalence is not strict. It may be slightly different according to other parameters (like GCR, axis tilt, number of trackers, etc).

I don't understand well your statement.

See our FAQ Which gain can I expect from Backtrackintg strategy ?

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Thanks for your reply.

can u please let us know, in PVsyst, when we simulate single-axis east west tracker without shading scene , why shading loss is not accounted, whereas in fixed tilt simulation, shading loss is accounted by PVsyst even without shading scene (with unlimited sheds option).

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  • 3 weeks later...


Net gain estimation using PVsyst for HSAT

I had done HSAT simulation for the location Veltoor in Telangana –India. The coordinates of the location are 16.443° N, 77.865° E.

HSAT Specifications are as below:

Axis Tilt 0°

Pitch 4m

Axis azimuth 0° (South)

Collector bandwidth 2m

Tracking range -45° to +45°

Following are the net gain estimations using PVsyst v 6.38 for this location.

Parameters With Shading scene Without Shading scene

With Backtracking Without Backtracking With Backtracking Without Backtracking

Gain over GHI 22.6% 27.0% 22.6% 27.0%

Near shadings: Irradiance level loss 2.6% 5.7% 0% 0%

IAM loss 1.9% 1.7% 2.2% 2.0%

Shadings: Electrical loss 0% 5.2% 0% 0%

Net gain 18.1% 14.4% 20.4% 25.0%

In the attached comparison, GCR is 48.9%, axis tilt is 0°and number of trackers are 120 which are maintained same in all four cases.

In the attached comparison, the net gain calculated after deducting shadings due to irradiance level loss, IAM loss and Shadings: Electrical loss are different in all four cases.

Based on your previous reply, does that mean generation estimation for HSAT option using PVsyst without shading scene is invalid

Please let us know, from the attached comparison, which option is more reliable and correct.

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It doesn't make sense to simulate a tracking array without defining the 3D shading scene.

- Without backtracking the shade cannot be neglected of course.

- With backtracking there is always a shading loss on the diffuse part (see How is calculated the Shading Loss on diffuse with tracking systems ?. Normally with recent versions, PVsyst will prevent you to run a simulation with backtracking and without defining the 3D scene.

Now for the irradiance yield (including linear shadings), both strategies are usually rather equivalent.

The electrical losses present in the not-backtracking system may do the difference (especially with narrow trackers, here with only 2 modules in the width).

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