A bifacial solar panel has solar cells that collect light on both faces: sunlight on the front, and light reflected from the ground or roof onto the back. Datasheets for these panels print a second, bigger wattage, and retailers advertise rear-side gains of up to 30%. On a raised frame over pale gravel or a white roof membrane, some of that extra power is real.
On a typical South African home, though, the panels sit flat against a pitched tile or IBR roof, a short distance above a dark surface. The back of the panel sees very little light. This guide explains how the rear-side gain works, what independent research measured, why your roof probably won't deliver the datasheet figure, and why that doesn't mean you should avoid bifacial panels.
Key takeaways
Most 585W to 630W home panels sold in South Africa are already bifacial dual-glass panels: 17 of the 18 listings in SolarGuide's Q3 2026 price index were.
Rear-side gain depends on how much light reaches the back. That takes height above the surface, a light-coloured surface beneath and space between rows. A flush-mounted pitched roof has none of the three.
NREL field tests measured annual energy gains of about 6% for bifacial PERC and 9% for heterojunction panels on raised single-axis trackers. That's the favourable case, not a home roof.
Bifacial panels cost no more per watt than the alternatives in current SA listings. Compare panels on their front-side rating and treat any rear-side gain on a roof as a bonus, not a design figure.
How a bifacial panel works
A conventional (monofacial) panel has an opaque white backsheet behind the cells. A bifacial panel replaces it with glass, or a transparent backsheet, and uses cells that can convert light arriving from behind. The current n-type TOPCon panels from Jinko, Trina, JA Solar and Canadian Solar all use 2.0mm heat-strengthened glass on both faces.
The bifaciality factor
Bifaciality is how well the back of the panel converts light compared with the front, measured at standard test conditions. A bifaciality of 80% means the rear produces 80% as much power as the front would from the same light.
Panel
Bifaciality (from datasheet)
Jinko Tiger Neo JKM605-630N-66HL4M-BDV
80% ± 5%
Trina Vertex N TSM-NEG19RC.20
80% ± 5%
JA Solar JAM72D40 575-600/LB
80% ± 10%
Canadian Solar TOPBiHiKu6 CS6.2-66TB
80% (advertised as "up to 85%")
Manufacturer datasheets, checked on 22 October 2026.
NREL gives typical module bifaciality by cell type as 0.65 to 0.80 for p-type PERC, 0.75 to 0.90 for n-type PERT and 0.85 to 0.95 for heterojunction (HJT). Today's TOPCon panels sit around 0.8.
Bifacial gain is about light, not the panel
Bifaciality is fixed by the panel. Bifacial gain depends on the site. NREL models the total light a bifacial panel uses as the front irradiance plus the rear irradiance multiplied by the bifaciality. So, roughly:
Rear-side gain ≈ bifaciality × (light on the back ÷ light on the front)
If the back receives 10% as much light as the front, an 80%-bifacial panel gains about 8%. If the back receives 2%, it gains under 2%. That's our simplification of NREL's model, and it ignores mismatch and shading losses, which reduce the gain further.
What the datasheet "bifacial" wattage means
Bifacial datasheets add a second set of ratings, and this is where most of the confusion starts.
Jinko lists 668W to 696W "BNPI" ratings for its 605W to 630W panels. BNPI means 1,000W per square metre on the front plus 135W per square metre on the back. For the 625W panel that is 690W, about 10% more.
Trina lists BNPI ratings on the same basis (676W to 704W for its 610W to 635W panels), plus tables at 5% and 10% "backside power gain". Its datasheet claims "up to 10%~20% additional power gain from back side depending on albedo".
Canadian Solar lists power at 5% and 10% backside gain, and adds a footnote that the gain "depends on mounting (structure, height, tilt angle etc.) and albedo of the ground".
JA Solar lists ratings at a 10% "irradiation ratio" (rear light equal to 10% of front light), for example 648W for its 600W panel.
One South African retailer, Solar Shop, describes the Trina 630W as providing "up to 30% additional energy gain from the rear side".
These are claims under stated test conditions, not predictions for your roof. Every one assumes the back of the panel receives a meaningful share of the front's light, typically 10% or more. Whether your installation gets anywhere near that is a question of mounting and surface.
Datasheet BNPI rating (135W/m² on the back)690 W
At 5% backside gain (Trina table, 625W panel)656 W
Front-side STC rating625 W
Three ratings for one 625W bifacial panel (Jinko and Trina datasheets, checked 22 October 2026)
What independent research measured
NREL, the US Department of Energy laboratory since renamed the National Laboratory of the Rockies, ran bifacial panels on single-axis trackers in Golden, Colorado. Its 2019 results showed annual energy gains of 6% for bifacial PERC and 9% for heterojunction panels compared with monofacial panels. Its sensitivity modelling put the range at 4% to 8% for PERC and 6.5% to 11% for HJT, for ground albedo between 0.15 and 0.30.
Those trackers hold panels high above open ground, which is the favourable case. NREL's other findings explain why roofs do worse:
Surface colour has a big effect. For a single panel at standard conditions, NREL's chart shows rear irradiance of roughly 70W per square metre over asphalt, about 130 over soil, about 165 over concrete and about 430 over a white EPDM roof membrane. Dark surfaces reflect little.
Rows shade each other's backs. In an array, rear irradiance on interior rows fell by about 50% compared with a single module.
Height matters. In a close-mounted rooftop mock-up over a white roof, rear irradiance across the middle of the panel at 0.15m clearance was roughly a quarter of what it was at 0.6m.
Figures read from NREL's published charts; treat them as approximate.
Why a flush-mounted roof gets little benefit
Put those findings together and a typical South African home roof is close to the worst case for bifacial gain:
Low clearance. Pitched-roof rails typically hold panels close to the roof covering, nearer NREL's 0.15m case than its 0.6m case.
Dark surfaces. Charcoal concrete tiles, dark IBR sheeting and weathered roofs reflect little light. NREL's lowest data point, asphalt, is closer to them than white membrane is.
Panels block their own light. On a flush mount the panels cover the roof that would reflect light onto their backs, and adjacent panels shade the gaps.
The back faces the roof, not the sky. Little diffuse skylight reaches the rear of a panel lying parallel to the roof.
We haven't found a measured annual bifacial gain for flush-mounted pitched home roofs in the research above, so we won't invent one. Our reading of the evidence is simple: plan on little or no rear-side gain on a flush pitched roof, and don't accept a quote that adds datasheet bifacial watts to its yield estimate for one.
Where bifacial panels do pay
The rear side earns its keep when there's space and light beneath the panels:
Ground mounts on a farm or large plot, raised well above pale gravel, sand or dry grass.
Carports and pergolas, where light paving underneath and an open structure let light reach the back. Our solar carport cost guide covers what these structures cost.
Tilted frames on flat roofs, especially over a white or light membrane, with enough row spacing to avoid self-shading.
Vertical or fence-style mounts, where both faces see the sky directly.
If you're planning one of these, ask the installer to model the bifacial gain with a tool such as PVsyst or NREL's SAM using your actual height, row spacing and surface, rather than using the datasheet figure.
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Bifacial panels use glass on both sides, so it's reasonable to worry about weight. The datasheets show it's less of an issue than it sounds:
Panel
Construction
Size
Weight
Weight per m²
Jinko Tiger Neo 605W to 630W
2.0mm glass front and back
2,382 × 1,134mm
32.4kg
12.0kg
Trina Vertex N 610W to 635W
2.0mm glass front and back
2,382 × 1,134mm
33.0kg
12.2kg
Canadian Solar TOPBiHiKu6
2.0mm glass front and back
2,382 × 1,134mm
32.8kg
12.1kg
Canadian Solar HiKu6 460W (monofacial PERC)
3.2mm glass front, backsheet
1,903 × 1,134mm
24.2kg
11.2kg
Weights and dimensions from manufacturer datasheets and the Sustainable.co.za specification page, checked on 22 October 2026. Weight per square metre is a SolarGuide calculation.
Two thin sheets of glass weigh about the same as one thick sheet plus a backsheet. Per square metre of roof, the glass-glass panels above are only about 1kg heavier than the monofacial panel. The bigger change is panel size: a 33kg, 2.38m panel is harder to handle on a roof and puts its load on fewer fixing points.
Whatever the panel, the installer should check that the roof structure can carry the array and that the rails and clamps sit within the clamping zones in the manufacturer's installation manual. Glass-glass panels have their own approved clamping positions, set out in that manual. For space planning, our roof space guide shows how much area each panel size needs.
Do bifacial panels cost more in South Africa?
In current South African retail, mostly not, because bifacial dual-glass is now the standard format for 585W to 630W home panels. In SolarGuide's Solar Price Index Q3 2026, checked on 26 September 2026, 17 of the 18 panel listings were bifacial. The one exception, a Trina 625W, was listed simply as a "Mono" panel.
Panel type
Example
Price per watt
Bifacial dual glass, 585W to 630W
15 VAT-inclusive listings, Solar Price Index Q3 2026
median R3.30 (R3.13 to R3.52)
Monofacial n-type, 465W
JA Solar 465W black frame, Sustainable.co.za (sold out)
R3.60
Monofacial PERC, 460W
Canadian Solar HiKu6 460W, Sustainable.co.za
R4.03
Panel-only, VAT-inclusive online prices. Price-index figures checked on 26 September 2026; Sustainable.co.za prices (R1,674.95 and R1,855.95, shown as sale prices) checked on 22 October 2026. Price per watt is a SolarGuide calculation.
Bifacial 585W to 630W (median)R3.30
Monofacial JA 465WR3.60
Monofacial Canadian Solar 460WR4.03
Retail price per watt, panel only (Solar Price Index Q3 2026 and Sustainable.co.za, checked 22 October 2026)
This isn't a like-for-like test of bifacial against monofacial, because smaller panels usually cost more per watt regardless of type. But it shows that a buyer in South Africa today isn't paying a premium for the rear side. The monofacial options are mostly smaller or older panels. For a fuller picture of panel prices and sizes, see our solar panel wattage guide.
The verdict
On a flush-mounted pitched roof: bifacial panels are worth buying, but not for the rear side. They're worth buying because they're the mainstream 600W-class n-type panel, they cost no more per watt, and their warranties are as good as any. Expect little or no extra output from the back, and size the system on the front-side rating.
On a ground mount, carport or raised frame over a light surface: bifacial panels can add useful output. NREL measured about 6% to 9% a year on raised trackers. Ask for a site-specific model before you count on any figure.
On any quote: check that the yield estimate uses the panel's front-side STC rating unless the installer has designed and modelled for rear gain. If a quote's kilowatt figure uses the bifacial wattage on a roof, ask why. Our guide to the best solar panel brands in South Africa covers the other checks: warranty, degradation, certification and price per watt.
Alumo, SolarGuide's installation partner, specifies 615W panels for its rent-to-own packages and 655W panels for its subscriptions, and confirms the layout and exact equipment for your roof at the site assessment. Get a free quote with the panel model and yield estimate itemised →
Frequently asked questions
Are bifacial solar panels worth it on a house roof?
They're worth buying because they're now the standard 600W-class panel in South Africa and cost no more per watt. But on a flush-mounted pitched roof, the back of the panel receives very little light, so don't expect much rear-side gain. Size the system on the front-side rating.
How much extra power do bifacial panels produce?
It depends on the installation. NREL measured annual energy gains of about 6% for bifacial PERC and 9% for heterojunction panels on raised single-axis trackers. Manufacturer claims such as Trina's "up to 10%~20%" depend on albedo and mounting. A flush-mounted roof will produce far less than those figures.
What is the bifaciality factor?
It's the ratio of the panel's rear-side power to its front-side power under the same light at standard test conditions. Current TOPCon panels from Jinko, Trina, JA Solar and Canadian Solar quote about 80%. The site's surface, height and row spacing then decide how much rear light the panel actually gets.
Are glass-glass bifacial panels too heavy for my roof?
Usually not because of the glass. Jinko, Trina and Canadian Solar's 2.38m bifacial panels weigh about 12kg per square metre, close to a monofacial panel's 11.2kg. The installer must still check the roof structure and use the manufacturer's approved clamping zones.
Is SolarGuide the installer?
No. SolarGuide is an independent referral partner. Alumo supplies, installs, finances and warrants the systems. We help you compare options and get a free quote. All pricing is indicative and subject to a site assessment and credit approval.
SolarGuide is an independent referral partner. We help you compare options and arrange a free quote — Alumo supplies, installs, finances and warrants the systems. Pricing is indicative, sourced from Alumo’s published catalogue, and subject to a site assessment and credit approval.
