What Makes a Panel Bifacial?
A bifacial solar panel has an active photovoltaic cell layer that can absorb light from both sides. Most use TOPCon or HJT cell technology, which naturally supports a transparent rear surface. A glass-glass construction (glass front and glass rear) replaces the traditional opaque white backsheet, allowing sunlight reflected from the ground or nearby surfaces to hit the rear cells and generate additional electricity.
Manufacturers including LONGi (Hi-MO 7), JinkoSolar (Tiger Neo), and Trina Solar (Vertex S+) all ship bifacial as their standard offering. The premium over a comparable monofacial panel has largely disappeared at scale โ most bifacial modules cost the same as or within 2โ3% of equivalent monofacial products from the same manufacturer.
The Bifacial Gain: What the Data Says
The rear-side gain โ the additional energy generated from reflected light โ is expressed as a percentage of front-side output. NREL field testing and Fraunhofer ISE independent studies give the following ranges:
| Mounting scenario | Rear-side gain | Annual yield uplift |
|---|---|---|
| Ground-mount over white gravel/sand | 15โ25% | 10โ18% |
| Ground-mount over green grass | 8โ14% | 5โ10% |
| Ground-mount over dark soil | 4โ8% | 2โ5% |
| Flat rooftop (ballasted, elevated) | 6โ12% | 4โ8% |
| Tilted rooftop (standard mounting) | 2โ6% | 1โ4% |
| Vertical bifacial (agrivoltaic, fences) | 20โ40% | 15โ28% |
The pattern is clear: bifacial gains are maximised when the rear face has a clear view of a reflective surface. A standard pitched residential roof with tiles directly beneath the panel provides almost no rear-side gain โ the mounting rail sits only a few centimetres above the tile.
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When Bifacial Panels Make Sense
Ground-Mount Systems
This is the sweet spot. Utility-scale and large residential ground-mount systems routinely achieve 10โ15% additional energy production with bifacial panels. White or light-coloured gravel, concrete, or sand albedo (reflectivity 0.3โ0.6) combined with elevated tracker or fixed-tilt mounting (300โ500mm clearance) produces the best results. Many large solar farms now spec bifacial as default and report payback period reductions of 1โ2 years.
Flat Commercial Rooftops
Ballasted flat-roof systems with 10โ15ยฐ tilt and at least 200mm of clearance see meaningful rear-side gains, particularly if the rooftop surface is a light-coloured membrane. BloombergNEF estimates that bifacial adds 6โ9% to the lifetime energy output of a typical commercial flat-roof installation.
Agrivoltaic and Vertical Installations
Vertical bifacial installations โ panels mounted portrait at 90ยฐ โ are growing rapidly in agrivoltaic contexts (solar over farmland) and as agricultural fencing. Both faces see full sky exposure at different times of day, producing a flatter daily generation curve that aligns better with morning and evening energy demand.
When Bifacial Panels Do Not Pay Off
A standard residential pitched-roof installation with conventional close-mount racking gets minimal rear-side gain. The glass-glass construction does add weight (approximately 20% heavier than glass-backsheet alternatives), and some installers prefer lighter glass-backsheet bifacial variants.
For these situations, the practical advice is: buy bifacial because it is now the standard product and costs essentially the same โ but do not pay a premium specifically for the bifacial feature if you have a standard tilted roof.
The Glass-Glass Durability Advantage
Beyond energy yield, bifacial glass-glass panels offer a durability benefit independent of the rear-side gain. Glass rear surfaces are significantly more resistant to PID (potential induced degradation), UV yellowing, and moisture ingress than plastic backsheets. Long-term degradation studies by Fraunhofer ISE show glass-glass panels losing 0.3โ0.4% output per year versus 0.4โ0.6% for glass-backsheet equivalents. Over 25 years, that compounds into meaningfully more total energy.
Calculating Your Bifacial Gain
PV simulation tools including PVsyst and Aurora Solar now incorporate bifacial modelling. The key inputs are:
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- Mounting height (clearance above ground/roof surface)
- Ground albedo (reflectivity) โ typically 0.10โ0.20 for standard roofing, 0.25โ0.35 for light concrete, 0.6+ for snow
- Row spacing (for ground-mount arrays)
- Local diffuse fraction of solar radiation