Bifacial Solar Panels: Technology, Benefits, and Installation Considerations

Bifacial solar panels capture sunlight on both the front and rear surfaces of the module, distinguishing them from conventional single-sided panels that rely solely on direct irradiance from above. This page covers the core technology behind bifacial panels, the conditions under which they deliver measurable energy gains, the installation variables that determine real-world performance, and the regulatory and permitting considerations that apply to bifacial deployments across US jurisdictions. Understanding these factors helps property owners, contractors, and project developers evaluate whether bifacial technology is the appropriate choice for a given site and application.

Definition and scope

A bifacial solar panel is a photovoltaic module that generates electricity from light incident on both the front glass face and the rear glass or transparent backsheet face. The rear surface collects albedo light — solar radiation reflected from the ground or surrounding surfaces — and routes it through the same cell structure used by the front surface. This dual-capture design is governed by module-level performance standards defined in IEC 60904-1-1, which establishes test procedures for measuring bifacial photovoltaic devices under standard test conditions (STC).

Bifacial panels are produced in two primary structural forms. Glass-glass modules sandwich the cell layer between two panes of tempered glass, providing a transparent rear surface and mechanical durability suited to elevated mounting configurations. Glass-transparent-backsheet modules use a clear polymer backsheet in place of the rear glass pane, reducing weight while still allowing rear-side light collection. A standard monofacial panel, by contrast, uses an opaque white or black backsheet that reflects no usable light and contributes no rear-side generation. For a side-by-side comparison of panel constructions, the solar panel types comparison page provides additional classification detail.

The bifaciality factor — expressed as a percentage — describes how efficiently the rear surface converts light relative to the front surface. Industry-standard bifacial modules typically carry bifaciality factors ranging from 65% to 90%, as stated in manufacturer datasheets evaluated under IEC 61215 for terrestrial photovoltaic module qualification. A module rated at 80% bifaciality captures 80 watts of rear-side power for every 100 watts the front surface would produce under identical irradiance conditions.

How it works

Bifacial panels rely on monocrystalline or polycrystalline silicon cells that are not occluded by rear-side opaque materials. The functional sequence operates as follows:

1. Front-surface absorption: Direct and diffuse solar irradiance strikes the front glass, passes through an anti-reflective coating, and is converted by the silicon cell layer into direct-current electricity.
2. Rear-surface albedo capture: Reflected irradiance from the mounting surface, roof membrane, ground cover, or surrounding structures travels upward through the transparent rear layer and reaches the cell layer from below.
3. Current summation: Front-side and rear-side currents combine within each cell's junction, increasing the total power output relative to a front-only module of identical wattage rating.
4. Inverter conversion: The combined DC output routes through string or microinverter systems — covered in detail on the solar inverter types page — for conversion to AC power suitable for grid delivery or on-site use.

The energy gain attributable to rear-side capture is expressed as the bifacial gain, typically measured in percentage points above the front-only baseline. The magnitude of bifacial gain is site-dependent. White or light-colored surfaces — including white thermoplastic polyolefin (TPO) roofing membranes and light gravel — produce albedo values in the range of 0.5 to 0.8 on a 0-to-1 scale. Standard dark asphalt surfaces produce albedo values near 0.1 to 0.2. The National Renewable Energy Laboratory (NREL) publishes albedo data and bifacial modeling resources through its PVWatts and SAM tools, which project developers use to estimate site-specific bifacial gain before procurement.

Mounting height above the reflective surface also influences rear-side irradiance. Ground-mount and elevated racking configurations generally yield higher bifacial gains than flush roof mounts, because low-clearance installations block the angular spread of reflected light reaching the rear cells.

Common scenarios

Bifacial panels appear across residential, commercial, and utility-scale deployments, though site conditions determine where the technology delivers meaningful advantage.

Ground-mount arrays represent the highest-performance scenario for bifacial technology. Light-colored ground cover — white gravel, bare sand, or snow — combined with single-axis or dual-axis tracker racking (discussed further on the solar tracker systems page) can produce bifacial gains of 5% to 30% above the front-only baseline, according to NREL modeling studies. The elevated mounting typical of ground arrays ensures unobstructed rear-side exposure.

Commercial flat-roof installations benefit from bifacial panels when the roof membrane has a high-reflectivity surface. TPO and PVC white membranes are common in commercial construction and carry albedo values that materially increase rear-side yield. Flush-mounting limits this gain, so elevated ballasted racking systems are frequently paired with bifacial modules in commercial projects.

Carport and canopy structures create a scenario in which the rear surface faces upward (toward direct sky irradiance) and the front surface faces downward toward the parking surface or occupied area. This inverted configuration is detailed under solar carport installations and can yield significant rear-side gains when the structure is designed for it from the outset.

Residential rooftop installations on dark asphalt shingles with low panel clearance are the scenario where bifacial panels offer the least incremental gain over monofacial alternatives.

Decision boundaries

Selecting bifacial panels over monofacial modules involves a structured evaluation of site, cost, and regulatory factors.

Albedo threshold: Sites with ground or surface albedo below 0.2 — measured or modeled through NREL's albedo datasets — are unlikely to produce bifacial gains large enough to offset the price premium associated with glass-glass bifacial modules.

Mounting clearance: Rear-cell irradiance diminishes sharply when panel-to-surface clearance falls below approximately 0.3 meters. Installation designs must account for this in racking specifications, which are subject to structural review under the International Building Code (IBC) and local amendments enforced by the Authority Having Jurisdiction (AHJ).

Permitting implications: Bifacial glass-glass modules weigh more per unit than standard glass-backsheet panels — typically 2 to 4 kilograms more per module for a 60-cell equivalent format. This additional dead load must be declared in structural calculations submitted during the permit process, as addressed in the solar installation permits and approvals framework. AHJs applying IBC Section 1603 require dead load documentation for all roof-mounted equipment.

Electrical code compliance: Bifacial systems are subject to the same National Electrical Code (NEC) Article 690 requirements as monofacial systems, covering DC circuit sizing, rapid shutdown, and grounding. Because bifacial modules can produce rear-side current under conditions not reflected in standard STC ratings, string sizing calculations should account for the maximum potential combined output. The solar installation safety standards page covers NEC 690 compliance requirements applicable to all photovoltaic installations.

Economic threshold: The cost differential between bifacial and monofacial panels narrowed substantially as bifacial module production scaled through 2022 and 2023, with bifacial modules representing the majority of new module shipments globally according to Wood Mackenzie and BloombergNEF market analyses. Project-level financial modeling using NREL's System Advisor Model (SAM) can quantify whether the projected bifacial gain justifies any remaining cost premium in a specific deployment context. Broader financial analysis tools are summarized on the solar energy system ROI calculator guide page.

Warranty and degradation: Bifacial glass-glass modules typically carry linear power warranty terms of 25 to 30 years, with annual degradation rates specified at 0.4% to 0.5% per year in leading manufacturer datasheets — rates consistent with performance data published in NREL's Photovoltaic Lifetime Project.

References

• IEC 60904-1-1 – Photovoltaic Devices: Measurement of Bifacial PV Devices
• IEC 61215 – Terrestrial Photovoltaic Modules: Design Qualification and Type Approval
• National Renewable Energy Laboratory (NREL) – Bifacial PV Modeling and PVWatts Tool
• NREL System Advisor Model (SAM)
• National Electrical Code (NEC) Article 690 – Solar Photovoltaic Systems (NFPA 70)
• International Building Code (IBC) – International Code Council
• NREL Photovoltaic Lifetime Project – Module Degradation Research