What project owners need to know.
A bifacial solar module is a module whose cells convert light reaching their rear side as well as their front, so reflected and diffuse light from the ground adds to output. How much the rear contributes is described by the bifaciality factor, the ratio of rear-side to front-side performance measured under IEC TS 60904-1-2. In independent 2024 tests by Kiwa PVEL, heterojunction modules averaged about 86.7% bifaciality, TOPCon 75.4% and PERC 69.3%, while the actual energy gain on site depends mostly on ground albedo and mounting.
What makes a cell bifacial
A conventional cell has an opaque rear: the older aluminium back-surface-field (Al-BSF) cell and standard PERC both cover the back with a full layer of aluminium paste. Light that reaches the rear simply cannot get in. A bifacial cell replaces that full layer with a finger grid, so the rear surface is passivated, coated and open to light just like the front.
For p-type PERC, TaiyangNews explained in 2021, this means printing the rear aluminium as a grid rather than spreading paste over the full area, adjusting the rear silicon nitride capping layer and the laser openings, and using pastes designed to print fingers. The n-type designs that now dominate, TOPCon and heterojunction (HJT), are built with passivated, contact-gridded rear sides and are bifacial by construction. Back-contact cells place all contacts on the rear, so their bifaciality depends on how much of that rear is metallised.
- Opaque rear (Al-BSF, monofacial PERC): no rear-side collection
- Bifacial PERC: rear aluminium printed as a grid instead of a full layer
- TOPCon and HJT: passivated rear with a contact grid, bifacial by design
- Module side: a transparent rear, either a second glass (glass-glass) or a clear backsheet
How bifaciality is measured
The test method is IEC TS 60904-1-2, which adds bifacial requirements to the standard I-V measurement of IEC 60904-1. The second edition was published in 2024 and an amended consolidated version followed in March 2026. Each side is measured on its own at standard test conditions while the other side is shielded. According to the PVMET wiki summary, stray light on the non-measured side must not exceed 3 W/m².
Bifaciality is then reported as three ratios of rear to front: short-circuit current (φIsc), open-circuit voltage (φVoc) and maximum power (φPmax). The standard also defines a BiFi coefficient, the slope of power against rear irradiance, and the power at 100 and 200 W/m² of rear light. In the PVMET wiki's worked example, a 400 W module with 75% bifaciality is rated about 427.5 W at 100 W/m² and 455 W at 200 W/m² of rear irradiance. These are reference ratings, not field yield.
- φIsc, φVoc, φPmax: rear-to-front ratios at standard test conditions
- BiFi: power gained per W/m² of rear irradiance
- PmaxBiFi10 and PmaxBiFi20: ratings at 100 and 200 W/m² rear light
PERC vs TOPCon vs HJT: datasheet and test results
Independent testing shows a clear order, and a gap between claims and measured results. In Kiwa PVEL's 2024 PV Module Reliability Scorecard, heterojunction modules averaged 86.7% bifaciality, on a limited number of bills of materials; TOPCon averaged 75.4% across more than 50 BOMs; and PERC averaged 69.3%. Most TOPCon datasheets state 80 ± 10% and most PERC datasheets 75 ± 5%, and PVEL noted that many datasheets give no bifaciality figure at all.
The gap matters. PVEL found that no TOPCon BOM averaged above the 80% datasheet value, and 29% measured below 75%. In one example, a TOPCon BOM measuring 74% instead of its specified 80% lowered simulated energy yield in Las Vegas by 0.8% on a fixed tilt and 0.5% on a single-axis tracker. A 2025 review of 842 bifacial module specifications from 236 manufacturers, in Renewable and Sustainable Energy Reviews, likewise found that HJT modules list higher bifaciality factors than TOPCon.
Why the ground decides the gain
Bifaciality only says how well a module uses rear light; how much rear light arrives depends on the site. 'Albedo is the main factor for differences between monofacial and bifacial,' NREL researcher Bill Marion told pv magazine in 2021, when NREL published measured ground-albedo datasets. Most natural ground has low albedo, while snow, sand, light gravel and artificial surfaces reflect much more.
Albedo is also easy to get wrong. Marion compared satellite-derived albedo from the US National Solar Radiation Database with ground measurements and found differences larger than measurement uncertainty, worth about 1.5% in estimated energy. For Indian projects, that argues for measured or carefully sourced albedo in yield models, along with mounting height, row spacing and tracker type, which shape rear irradiance and its uniformity.
- Ground albedo: the largest single driver of rear-side gain
- Mounting height, row spacing and tracker design shape rear irradiance
- Seasonal and surface changes mean one albedo value rarely holds all year
- Use measured site data where possible, not defaults
Bifacial in India's market
Indian utility procurement has moved toward n-type bifacial, glass-glass modules. In April 2026, pv magazine India reported a domestic order worth over ₹430 crore to Ganesh Green Bharat for 630 Wp G12R TOPCon n-type bifacial modules for utility-scale projects. In May 2026, it reported a ₹171.45 crore order to Saatvik Green for TOPCon bifacial glass-glass modules, to be executed by October 2026.
This shapes the whole chain. Bifacial n-type cells need wafers with long carrier lifetime and well-controlled resistivity, because both faces must collect carriers efficiently. As ALMM List-III extends approved-make rules to ingots and wafers, according to PIB, domestic wafer makers will be supplying mostly bifacial TOPCon and HJT cell lines. Wafer quality, not only module design, will set how much of the rear-side gain buyers actually see.
What buyers should check
Treat bifaciality as a specification to verify, not a marketing line. Ask for a third-party bifacial measurement to IEC TS 60904-1-2, check which ratio is quoted (φPmax or φIsc), and run yield models at the measured value rather than the datasheet's upper bound. On the supply side, glass-glass construction changes the encapsulant and lamination choices, which should be qualified rather than carried over from glass-backsheet designs.
This guide is general awareness. Bifacial gain for any specific project should be validated with measured site albedo, independent module test data and a qualified yield assessment.
- Independent IEC TS 60904-1-2 bifacial test report, not only the datasheet
- Which ratio is quoted, and at which tolerance
- Yield model at measured bifaciality and measured site albedo
- Encapsulant and glass-glass build qualified for the cell type
How JRST supports this requirement
JRST works across the silicon chain from high-purity quartz to CZ ingots and n-type wafers, and helps Indian projects set wafer specifications and acceptance tests for the bifacial cell lines they supply. Any project-specific yield or specification question is assessed in a separate proposal and validated with cell makers and test labs.
Discuss your requirement
Mohammed Saif Zaveri connects JRST's industrial content to execution conversations.
As Co-Founder and designated partner of JRST Technology LLP, Mohammed Saif Zaveri works across industrial growth, strategic partnerships, client conversations, equipment strategy, and project pathways for silicon, solar, semiconductor, and advanced-manufacturing opportunities.
This knowledge page is part of JRST's public industrial knowledge base, designed to help buyers move from search terms and early research toward a structured technical-commercial discussion.
View Mohammed Saif Zaveri's profileConnect on LinkedInFrequently asked questions
What is a bifacial solar module?
A bifacial module uses cells that convert light on both their front and rear, built with a transparent rear such as a second glass or a clear backsheet. Light reflected from the ground or scattered from the sky adds to the front-side output.
What is the bifaciality factor?
The bifaciality factor is the ratio of a module's rear-side performance to its front-side performance, each measured separately at standard test conditions. IEC TS 60904-1-2 defines it for short-circuit current, open-circuit voltage and maximum power.
Which solar cell technology has the highest bifaciality?
Heterojunction generally does. In Kiwa PVEL's 2024 testing, HJT modules averaged about 86.7%, TOPCon 75.4% and PERC 69.3%. Back-contact cells vary with how much of the rear is metallised.
How much extra energy does a bifacial module produce?
It depends on the site. Ground albedo, mounting height, row spacing and trackers decide how much light reaches the rear, so there is no single figure. Gains are small over dark soil or grass and larger over light sand, gravel, concrete or snow.
Is the datasheet bifaciality figure reliable?
Not always. Kiwa PVEL found no TOPCon BOM averaging above the 80% datasheet value, and 29% measured below 75%. Buyers should ask for independent test reports and model yield at measured values.
What standard is used to measure bifacial modules?
IEC TS 60904-1-2, which adds bifacial requirements to IEC 60904-1. Its second edition was published in 2024, with an amended version in March 2026.
Why does bifacial matter for wafer makers?
Bifacial n-type cells collect carriers through both faces, so they reward wafers with long carrier lifetime and tight resistivity control. India's domestic wafer chain will largely be supplying bifacial TOPCon and HJT cell lines.
Primary sources and further reading
Last reviewed 2026-10-28. Technical scope, policy eligibility, availability, and commercial terms should be independently confirmed for each project.