Designing Solar Simulator Optics for Irradiance Uniformity and Spatial Class with TracePro

Solar simulator optical design requires a useful illuminated area with controlled spatial variation, an appropriate spectrum, and suitable angular illumination. A bright central spot alone does not satisfy that specification. TracePro can help engineers compare the lamp, collector, homogenizer, and test-plane geometry before committing to an optical bench. The most useful model connects its outputs to the measurements planned for the completed instrument. [1]

Start with the test requirement

Define the test area, working distance, irradiance target, wavelength range, and allowable angular spread before choosing an integrator. Record whether the instrument will test a small cell or a larger module; an optical layout that illuminates one may vignette the other.

IEC 60904-9:2020 classifies photovoltaic solar simulators using spectral match, spatial irradiance non-uniformity, and temporal instability. These are separate criteria. A favorable ray-traced irradiance map is useful design evidence, but it does not establish the complete classification of a physical simulator. Use the standard’s applicable measurement procedure and edition when setting acceptance requirements. [2]

Represent the lamp and collector

Model the emitting region as an extended source. For an arc lamp, use manufacturer or measured spatial, angular, and spectral information where available. A point source may hide collector aberrations, clipping, and sensitivity to lamp position. Document approximations so the team can see which conclusions depend on uncertain inputs.

Include the collector aperture, obscurations, mechanical stops, and relevant reflective or transmissive surfaces. TracePro supports source and optical-property definitions for this type of Monte Carlo analysis. Use wavelength-dependent data when spectral losses matter; a single broadband reflectance value can conceal a filter or coating limitation. [1]

Build the homogenizer around the required field

A fly’s eye integrator uses lenslet arrays and relay optics to superimpose contributions across the target. Its performance depends on the source, lenslet geometry, clear apertures, spacing, and downstream optics. Increasing lenslet count is not a universal guarantee of better uniformity.

Compare candidate pitches, focal lengths, array spacing, and condenser geometry while tracking transmitted power and the illuminated boundary. Inspect whether individual channels are clipped or whether source structure remains visible in the field. Treat diffraction or coherent interference separately when those effects are relevant; a geometrical ray model alone cannot establish them.

Evaluate spatial uniformity consistently

Use a receiver covering the specified test area and retain the same region of interest for every variant. TracePro provides irradiance maps and related analysis outputs. Choose a sampling grid that can be related to the intended measurement aperture and scan positions, rather than optimizing the appearance of a displayed map. [3]

Report the spatial non-uniformity definition, receiver area, grid, and any excluded edge region alongside the result. Keep these settings fixed during comparison. An apparent improvement caused by coarser averaging or a smaller evaluation area is not an optical improvement.

Increase ray count and repeat selected runs until sampling variation is small enough to support the design decision. There is no universal ray count that makes every map reliable. Pay particular attention to sparsely sampled edge regions and small differences between otherwise similar designs.

Check spectrum and angular content separately

A spatially uniform total-irradiance map can still conceal wavelength-dependent variation. Trace representative wavelength bands with appropriate source weights and material data when the spectral requirement calls for it. Compare band-specific outputs using a documented normalization.

Also inspect the angular distribution reaching the test area. A design may gain uniformity by accepting a wider range of directions. Whether that trade is acceptable depends on the device and test method. Surface irradiance and angular intensity describe different quantities; choose reports or exported ray analysis that answer the actual requirement.

Test alignment and plan verification

Vary source position, lenslet decenter and tilt, relevant separations, and receiver location over tolerances supported by the proposed hardware. Rank sensitivities using the same performance measures as the nominal model. Do not assume the lamp or one particular lens is always the dominant adjustment.

Before building, agree on a verification plan covering warm-up, operating conditions, measurement geometry, and instrument calibration. Compare the prototype with the model under matching conditions, then investigate discrepancies in source data, surface properties, alignment, and sampling. This creates a useful design-to-test loop without treating simulated class margins as measured certification.

Develop your solar simulator model

Download a free TracePro trial to compare solar simulator optical layouts using your source data, target area, and uniformity requirements. Bring the proposed measurement method into the model early so optical decisions remain connected to the eventual hardware test.