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Comparing backtracking HSAT at diff. timestamps with Fixed Tilt Arrays of corr. tilt & orientation


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I am comparing the hourly simulation outcome of a backtracking HSAT (+45, -45) at different hours for a day with the hourly simulation results of different fixed tilt arrays with equivalent tilt, orientation and system configuration for the corresponding hours of the year.

System details: 3600 REC 320Wp modules - total 1152kWp; 1 ABB 1000kW inverter; 4m pitch; 30 x 1.97m wide 118m long arrays. All loss factors are kept equal for HSAT and FT arrays.

It is seen that the backtracking HSAT has zero shading (electrical) losses for all hours of the day, whereas the corresponding fixed tilt systems are subjected to shading losses.

For instance, I am referring to the hourly simulation result for the two systems for 7:00 am March 31 :

Backtracking HSAT is at a tilt of the 15degrees, -90 azimuth and inverter output power is 256569W with zero electrical shading loss.

The corresponding fixed tilt array with 15 degree tilt and -90 azimuth gives an inverter output of 177123W with 67672W of power lost due to electrical shading effect.

Despite the similarities in the system details, why does the fixed tilt system suffer shading losses, whereas the HSAT with a backtracking tilt angle of 15 degree and -90 azimuth is not subjected to any electrical shading loss at the same hour in the same day?

Hope someone can help me understand the reason for the disparity in these simulation results.



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It is indeed the definition of the Backtracking strategy to avoid mutual shadings. It does that by adjusting the plane tilt (phi angle) according to the sun's position.

If you don't have near shadings you don't have electrical shading losses of course.

Now I don't know how you evaluate the plane tilt during operation: this will highly depend on the sun's position.

However if you construct the same system with fixed tilt, you should have exactly the same shading situation for the same plane tilt and same sun's position.

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