Bifacial gain cannot be assigned from the mounting label alone. A tracker over natural ground, a canopy above parked vehicles and a close-mounted roof expose the module rear to different scenes. Their forecasts need different geometry, obstruction and operating assumptions.
Answer: Bifacial gain by mounting type requires a site-specific comparison with a declared energy reference. Fixed racks, trackers, roofs and canopies change rear illumination, shading and output constraints. Mounting labels do not supply reliable annual percentages. Compare matched cases using the actual module, geometry, surface and losses, then evaluate delivered energy and verified costs together.
SurgePV publishes this guide and sells solar software. This is a desk review of primary modeling documentation and a laboratory example. No first-hand audited projects, comparative software test or universal gain benchmark is claimed.
Start with a matched energy comparison
Use bifacial gain to define the percentage:
Gain = (evaluated energy − reference energy) / reference energy × 100%
Identify the period and electrical boundary: array DC, inverter AC or delivery meter. A rear irradiance percentage is not automatically a delivered-energy percentage. Bifaciality describes the module’s rear/front response under reference conditions; it does not determine outdoor illumination.
If the reference is monofacial, specify its front rating and configuration. A tracker-bifacial versus fixed-monofacial comparison combines two changes. It does not isolate the contribution of the rear face.
Compare mounting types by their modeling requirements
The useful comparison is what each structure permits or obstructs, rather than a table of unsourced annual ranges.
| Mounting type | Rear-side question | Evidence to collect | Important comparison constraint |
|---|---|---|---|
| Fixed-tilt ground mount | Which sunlit ground and sky areas reach the rear? | Clearance definition, pitch, table width, tilt, ground reflectance and structural shading | Keep site/module capacity and reference geometry declared |
| Single-axis tracker | How do moving rows change ground shade and rear exposure? | Axis height, rotation limits, tracking/backtracking behavior and torque-tube layout | Compare rear contribution using the same tracking reference |
| Pitched rooftop | How much of the rear is blocked by the roof and rails? | Actual roof gap, module/roof slope, rail layout and roof surface | Respect usable roof area and compatible mounting |
| Flat rooftop | Does the roof/ballast/adjacent-row scene match the model? | Membrane condition, table arrangements, clearance, ballast and obstructions | Preserve structural, drainage and access constraints |
| Carport | What do beams, vehicles and surrounding pavement obstruct? | Canopy dimensions, beams, columns, occupied-space assumptions and surface | Do not assume an empty reflective area all year |
| Elevated agrivoltaic array | How do crop cycles and access change the scene? | Crop/ground assumptions, seasonal obstruction and machinery clearances | Retain agricultural and structural requirements |
| Vertical array | How are the two productive faces defined and modeled? | Orientation, row separation, terrain and time-resolved illumination | Declare the reference face and supported geometry |
| Floating array | What do floats, water and supports expose to the rear? | Float arrangement, surface assumptions and equipment environment | Keep thermal and rear-light effects separate |
The table is a review checklist, not an engineering recommendation or promised yield ranking.
Fixed racks: ground reflection is only part of the scene
Evaluate three layout inputs: albedo, clearance and row spacing. Add rear structural obstruction and irradiance nonuniformity. Surface reflectance does not equal the radiation reaching the module rear.
PVsyst’s bifacial procedure distinguishes ground albedo from other project-albedo inputs and documents structural shading and mismatch assumptions. Use the correct field and its source. Do not replace measurements with a surface-color photograph or extrapolate one favorable season into a full year.
Define height explicitly: bottom-edge clearance for a tilted table differs from tracker-axis height. A higher structure can change rear exposure, but it also changes structural design and cost. No universal height provides a guaranteed gain or financial optimum.
For a simple regular row convention, GCR = row width / row pitch, with the same dimension convention on both sides. The earlier article inverted this relationship. Software conventions can differ; record whether width is the sloped table dimension or a specified projection before importing a value.
Wider spacing changes module density as well as shading. Evaluate total site energy and cost, not just gain per module. Use the broader bifacial design guide as a related design topic; this page’s purpose is to review mounting-specific evidence and comparisons.
Trackers: separate tracking benefit from bifacial benefit
A tracker changes front illumination and the rear scene throughout the day. Its geometry, control settings and obstructions must be part of the input record. Do not assume every tracker ships with the same rear-aware algorithm or that a particular controller setting adds a universal percentage.
Compare these hypothetical annual meter-boundary outputs:
| Case | Energy | What changes from the prior case? |
|---|---|---|
| Fixed monofacial reference | 100 MWh | Starting reference |
| Tracking monofacial | 120 MWh | Tracking/configuration change |
| Tracking bifacial | 132 MWh | Rear response enabled in the same tracking case |
Tracking-case bifacial gain is (132 − 120) / 120 = 10%. The combined change from fixed monofacial is 32%, not “32% bifacial gain.” The two relative gains compound: 1.20 × 1.10 − 1 = 32%. These are illustrative inputs, not a forecast or field result.
The SAM module model describes rear POA irradiance weighted by module bifaciality and states its infinite-row assumption. Check edge effects and structural details against the selected method. A detailed visual layout does not automatically remove that approximation.
Roofs and canopies: inspect what the rear can actually see
On roofs, document rails, ballast, surface gap and neighboring rows. For canopies, include beams, columns and the expected occupied area. Do not attribute a parking-canopy result wholly to pavement reflectance without checking its full geometry and comparison baseline.
Preserve safety, access, roof loading, waterproofing and equipment mounting requirements when exploring variants. Do not prescribe a clearance simply because it appears in another site’s study.
For additional project context, see the carport design guide. The economic decision still requires current module/rack quotations, delivered-energy estimates and the site’s energy value.
What a real field example can establish
Sandia’s preliminary field example used two bifacial and two monofacial modules on a fixed rack and normalized their outputs to matched front-side reference power. It reported gains of about 7–16% during the short test period, with the lower module showing more gain.
The researchers described torque-tube and equipment obstruction and linked the position difference to low-sun ground illumination. This is useful evidence that rack position and surroundings matter. It is not an annual fixed-mount range, a rooftop prediction or proof that trackers always beat fixed racks.
When using any study, retain its site, period, equipment, normalization, boundary and uncertainty. A daily or seasonal observation cannot be relabeled as an annual benchmark.
Check model applicability before comparing software outputs
PVsyst’s current bifacial-model overview describes rear-irradiance modeling assumptions. Its procedure documents limits for some mixed/east-west fixed-tilt configurations. Inspect the current version and geometry rules before relying on a forecast.
No universal “±15% accuracy” or software ranking follows from one validation study. Accuracy depends on what quantity is tested, the input quality, geometry, period and reference measurements. A ray-tracing method also needs defensible inputs and validation; its name alone is not an accuracy guarantee.
For unusual mounting, record unsupported details and use a qualified reviewer to decide whether another method or independent cross-check is needed. Do not label a workflow bankable without its counterparty’s requirements and accepted evidence.
A mounting-specific acceptance record
Before issuing a customer or investment forecast, retain:
- The reference and evaluated configuration, including what remains fixed.
- The exact module data, rear-response convention and electrical arrangement.
- Height, pitch, structural obstruction and relevant operational/seasonal changes.
- Weather, reflectance evidence and uncertainty/sensitivity assumptions.
- Model/version, geometry limitations and output boundary.
- Delivered energy, loss definitions, verified installed costs and financial assumptions.
- The responsible technical and commercial reviewers and unresolved limitations.
For an as-built review, compare records with the approved layout and use loss analysis to align weather and meter boundaries. A measured-versus-forecast energy difference alone does not isolate bifacial gain.
If evaluating SurgePV’s generation and financial workflow, request a requirements demonstration for the actual mounting arrangement, required rear inputs and exported results. This article does not establish that every listed geometry or rear model is supported.
Frequently Asked Questions
Can mounting type alone predict bifacial gain?
No. Use the actual geometry, weather, reflectance, module response and operating limits with a declared reference and energy boundary. A mounting label cannot establish an annual percentage.
Do trackers always have higher bifacial gain?
No universal ranking follows. Tracking changes front and rear illumination. Compare bifacial and monofacial cases on the same tracking arrangement to isolate rear contribution.
What mounting height should a bifacial array use?
Select a compliant structure for the project and model relevant candidate geometries. Record the height convention, obstructions, structural requirements and costs. No universal clearance guarantees a gain.
Can a field study supply my rooftop gain percentage?
Only a relevant comparison with supported conditions can inform the estimate. Retain the study period, geometry, equipment, reference and boundary. A short fixed-rack test is not an annual rooftop forecast.
How should different mounting options be compared financially?
Use matched delivered-energy cases, current installed quotations, maintenance assumptions and the project energy-value profile. Keep tracking benefits and rear-response benefits distinct. Gain alone does not prove payback.
Sources reviewed September 30, 2026. Numerical worksheets are illustrative; no first-hand site audit is claimed.
Where this fits
This article is part of SurgePV's Solar Technology hub, which works through the topic from first principles to the decisions a project team actually has to make.
