Quick answer
Bifacial Solar Panel A bifacial solar panel produces electricity from light hitting both its front and its back, using cells that are active on both sides behind a glass or clear rear cover.
The extra energy comes from light reflected off the ground or roof below. It depends on how bright that surface is and how high the panel sits, so the gain is large on raised ground mounts and small on panels flush with a roof.
Quick facts
The key facts about bifacial solar panel, with sources:
- Opposite
- Monofacial: a panel with an opaque backsheet that collects light only on the front
- Share of modules made
- About 68% bifacial in 2025, projected about 85% by 2036 1
- Key spec
- Bifaciality factor: rear-side efficiency ÷ front-side efficiency, measured at STC 1
- Example bifaciality
- 80 ± 5% (Trina Vertex N TSM-NEG19RC.20) 2
- Measured gain in an NREL field test
- 6.1% (PERC) and 7.6% (heterojunction) more energy than monofacial twins 4
- Best fit
- Ground mounts, carports, pergolas, trackers over light-coloured surfaces
Key takeaways
- A bifacial panel has a clear back, so light bouncing up from below also makes power.
- The gain depends on the site: how bright the surface is and how high the panel sits.
- NREL measured 6.1% to 7.6% more energy in a raised field test. Flush roof mounts gain far less.
- The wattage on the label is front-side only. Rear gain is a separate, site-dependent number.
- Bifacial fits ground mounts, carports and pergolas best. On a normal roof, choose on front-side specs.
What "bifacial" means
"Bi" means two and "facial" means face. A bifacial panel works on both faces. A normal panel, called monofacial, has a solid white or black sheet on the back, so only the front makes power.
Two things make a panel bifacial. The cells must collect light on both sides. And the back cover must let light through, so it is glass or a clear plastic sheet.
Glass on both sides gives the common name "glass-glass" or "dual-glass" panel. You can often see light through the gaps between the cells.
Where the rear-side energy comes from
Sunlight that misses the panel lands on the ground, gravel or roof below. Some of it bounces back up. A monofacial panel wastes that light. A bifacial panel turns some of it into current.
The share of light a surface reflects is its albedo. Fresh snow and white roof membranes reflect a lot. Grass, dark shingles and asphalt reflect little.
Height matters too. A panel a metre or more off the ground lets light reach its whole back. A panel a few inches above a roof shades its own rear.
Most cells made today already work on both sides. The ITRPV roadmap notes bifacial cells are also used in ordinary one-sided panels.
The REC Alpha Pure-RX is one example: its data sheet lists "bifacial REC heterojunction cells" behind a black backsheet, so it is sold as a one-sided panel 3. The clear back is what makes a panel bifacial.
Sources: [1]
Types: bifaciality depends on the cell design
| Cell design | Bifaciality factor reported by ITRPV (2025 survey) |
|---|---|
| Heterojunction (SHJ) | Highest of the group; expected to rise above 90% |
| TOPCon | Between SHJ and PERC; expected to reach up to 85% |
| PERC | Expected to improve to a maximum of 73% |
| Back contact | Lowest, 68% in 2025, projected 80% by 2036 |
Sources: [1]
Two ways bifacial panels are built
Glass-glass. Glass on front and back, often with a thin frame or none. These are common on solar farms and carports. They tend to be heavy, so check the data sheet weight.
Transparent backsheet. Glass on the front and a clear plastic sheet on the back. These weigh less but still pass light to the rear of the cells.
Worked example: reading the bifacial table on a data sheet
Trina’s Vertex N TSM-NEG19RC.20 data sheet (a utility-scale glass-glass panel) lists front-side ratings plus a second table "with bifacial gains" at a 10% rear-to-front light ratio 2.
| Line on the data sheet | Value | What it means |
|---|---|---|
| Peak power, front only (STC) | 590 W | The nameplate rating everyone quotes |
| Power bifaciality | 80 ± 5% | The rear cells are about 80% as good as the front |
| Irradiance ratio (rear/front) | 10% | An assumed condition: the back gets one tenth of the front’s light |
| Total equivalent power | 637 W | 590 × (1 + 0.10 × 0.80) ≈ 637 W, an 8% gain |
The 637 W figure only holds when the back really gets 10% of the front’s light. Your site sets that ratio, not the panel. On a panel close to a dark roof the ratio is lower, and so is the gain. Ask your installer what rear light their production model assumed.
What a real field test measured
NREL (now the National Laboratory of the Rockies) runs a bifacial test field next to matching one-sided panels. Over the test period, bifacial PERC made 6.1% more energy and bifacial heterojunction 7.6% more.
There was a catch. NREL saw the bifacial gain trend slightly down over three years. From 2019 to 2022 its bifacial panels lost about 3% of power on average, against about 1% for the one-sided ones. NREL lists possible causes such as glass-glass build and how the cells were doped, and calls for long-term data.
Sources: [4]
Where bifacial panels are used
Large solar farms, often on trackers that follow the sun, are the main market. The ITRPV roadmap says about 68% of panels made in 2025 were bifacial.
At home, they suit raised structures. Think ground mounts, solar carports, pergolas and awnings. Glass-glass panels on a pergola also let some daylight through.
On a data sheet, look for "bifacial", "dual glass" or a table titled "electrical characteristics with bifacial gain".
Sources: [1]
Benefits and limits of bifacial panels
Benefits
- More energy from the same footprint when the back gets light; 6.1%–7.6% in NREL’s field test 4.
- Glass backs resist moisture better than some plastic backsheets.
- Look good from below on carports and pergolas.
- Most new cells are already bifacial, so the extra cost is mainly the clear back.
Limits
- Little gain when mounted flush on a dark roof.
- Glass-glass versions are usually heavier.
- Gain is hard to predict without a site model.
- NREL saw faster power loss in its bifacial panels over three years 4.
- Racking rails and junction boxes can shade the back.
Limits to keep in mind
The biggest limit is the mount. On a pitched roof the panels sit a few inches above dark shingles. Little light reaches the back, so most of the gain is lost.
Weight is next. Check the roof can carry glass-glass panels; see panel weight and roof loading.
Shade still matters on both faces. Rails, posts and wiring under the panel cast shadows on the back.
What drives the cost of bifacial
HyreSolar does not publish panel prices. For bifacial, the cost drivers are the clear back, heavier glass, and taller racking that lets light reach the rear. A ground mount or carport costs more to build than a flush roof mount. Our cost per watt guide explains how to compare.
Judge value by energy, not watts. Ask for yearly kWh with and without rear gain, and compare the cost of each kWh.
Lifespan counts too. DOE cites a Berkeley Lab finding that average panel life reached 25–35 years in 2025. Read each maker’s warranty for its yearly loss rate.
Sources: [5]
How a bifacial system is designed and installed
A licensed installer and electrician do the work. Design matters more than for one-sided panels.
- The installer measures the site: surface color, available height and shade from below.
- They model yearly kWh with a rear-gain setting, and show you the number without it too.
- They choose racking that keeps rails and boxes out of the rear light where possible.
- They draw plans and apply for building and electrical permits; carports may need a structural review.
- They apply to the utility to connect, called interconnection.
- Crews build the structure and mount the panels. An inspector checks the work.
- The utility grants permission to operate.
Caring for bifacial panels
Keep the surface below bright and clear. Tall weeds or stored items under a ground mount block the light the back needs.
Watch monitoring and compare months year to year. A light-colored surface that gets dirty or covered will cut output.
Keep the front glass clean of heavy dirt. Our panel cleaning guide covers safe methods.
Warning signs and when to call a pro
Call a licensed installer or electrician for any of these. Do not touch the panels or wiring.
- Cracked front or back glass, including fine spider cracks.
- Output falling faster than the warranty’s yearly rate.
- Moisture or haze inside a glass-glass panel.
- Rust or loose bolts on a carport or ground-mount frame.
- Wires hanging under the array, where people walk or park.
Safety rule
Carport and pergola arrays put live wiring within reach. Keep children and tools clear, and leave all electrical work to a licensed pro.
Standards and rules that apply
Product listing. UL says the NEC, IBC and IRC require PV products on or near buildings to be certified by a Nationally Recognized Testing Laboratory. The panel safety standard is UL 61730-1 and -2, harmonized with IEC 61730.
Structures. Carports, pergolas and ground mounts are structures, so your city or county may require structural plans as well as electrical ones. In South Carolina, the SC Building Codes Council lists the 2021 codes as in force.
Glass products. A bifacial panel built into a roof or canopy as the roof covering may count as building-integrated PV. UL says the 2021 IBC and IRC require BIPV roofing to be listed to UL 7103.
Bifacial vs monofacial
| Bifacial | Monofacial | |
|---|---|---|
| Rear cover | Glass or clear backsheet | Solid backsheet (white or black) |
| Collects light from | Front and back | Front only |
| Rated power on the label | Front side at STC, plus an optional bifacial-gain table | Front side at STC |
| Weight | Glass-glass versions are usually heavier; check the sheet | Usually lighter |
| Strongest use | Raised ground mounts, carports, trackers | Flush roof mounts, where the back sees little light |
| Field result (NREL) | +6.1% to +7.6% energy; faster loss in years 1–3 4 | Baseline |
Misconceptions
- Myth Bifacial panels make twice the power.
- Reality The back only gets reflected light. NREL measured 6.1% to 7.6% more energy on a raised test field 4.
- Myth The bifacial wattage is the real rating.
- Reality The nameplate is front-side power. Bifacial rows on a data sheet assume a rear light ratio you may not have.
- Myth Bifacial is always worth it.
- Reality On a flush roof mount over dark shingles the gain is small. Choose on front-side specs there.
- Myth Any panel with bifacial cells is bifacial.
- Reality A panel with an opaque backsheet is one-sided, even if its cells could work on both faces 3.
Bifacial projects in SC, GA and VA
Size caps matter more than panel type. Georgia Power limits residential renewable systems to 10 kW, so extra kWh from bifacial gain can help within that cap 9. Virginia allows residential net metering up to 25 kW on investor-owned utilities 10.
South Carolina customers who applied after 1 June 2021 use a Solar Choice tariff under Act 62 8. Carports and ground mounts also go through your local building department, which enforces the adopted code edition.
Does bifacial make sense for your project?
- Flush roof mount on dark shingles: little rear light reaches the panel. Choose on front-side specs and price.
- Ground mount over gravel or light soil: the classic bifacial case. Ask for production estimates with and without rear gain.
- Carport, pergola or awning: panels are high and the back is visible from below. See our solar carports guide.
- Flat roof with a white membrane: tilted racking over a bright roof can give real rear gain.
- Next step: compare the cost of each kWh, not each watt, across your quotes.
Related guides
Questions about bifacial solar panel
Are bifacial solar panels worth it on a roof?
Usually not much on a flush-mounted pitched roof. The back sees little light there, so the gain is small. Bifacial panels pay off most when raised over a bright surface, as on ground mounts, carports and tracker systems. On a roof, compare panels on front-side specs and warranty.
How much more power does a bifacial panel produce?
It depends on the site. Trina’s Vertex N data sheet shows 590 W rising to 637 W, about 8%, under an assumed 10% rear light ratio. In NREL’s raised field test, bifacial panels made 6.1% to 7.6% more energy. Darker ground or lower mounting means less.
What is the bifaciality factor?
It is the ratio of rear-side to front-side efficiency, measured at standard test conditions. An 80% bifaciality factor means the back converts light about 80% as well as the front. Heterojunction cells score highest and back-contact cells lowest in the ITRPV survey.
What is a monofacial solar panel?
A monofacial panel collects light only on its front. It has a solid backsheet behind the cells, usually white or black. Most home roof panels have been monofacial. It is the baseline that bifacial gain is measured against.
Is the bifacial gain included in the panel’s wattage?
No. The nameplate wattage is front-side power at standard test conditions. Rear gain appears in a separate table on the data sheet and depends on the site. Make sure any quote shows production with and without that gain.
Do bifacial panels degrade faster?
In NREL’s test field they did. From 2019 to 2022 its bifacial panels lost about 3% of power on average, against about 1% for one-sided twins. NREL lists possible causes, including glass-glass build. Check each maker’s warranted yearly loss.
How high should bifacial panels be mounted?
Higher is better for rear light. A panel a metre or more off the ground lets light reach the whole back. A panel a few inches above a roof shades its own rear. Your installer should model the gain at the height you can actually build.
What surface works best under bifacial panels?
Bright surfaces that reflect a lot of light. Fresh snow and white roof membranes reflect the most. Light gravel and pale soil are good. Grass, dark shingles and asphalt reflect little, so the gain is smaller.
Are bifacial panels heavier?
Glass-glass versions usually are, because they have glass on both faces. Versions with a clear plastic backsheet weigh less. Check the weight on the data sheet and ask whether your roof or carport structure has been checked for it.
Sources
- VDMA, International Technology Roadmap for Photovoltaic (ITRPV), 17th Edition, Results 2025 (June 2026), retrieved .
- Trina Solar, Vertex N TSM-NEG19RC.20 bifacial dual-glass data sheet, version TSM_NEG19RC.20_NA_EN_2022_A (copy filed in a public tender record), retrieved .
- REC Group, REC Alpha Pure-RX series data sheet (US), retrieved .
- Ovaitt, Deline et al., NREL, Bifacial PV: Field & modeling perspectives (NREL/PR-5K00-84268), retrieved .
- US DOE Solar Energy Technologies Office, End-of-Life Management for Solar Photovoltaics, retrieved .
- UL Solutions, Building-Integrated Photovoltaic (BIPV) System Testing and Certification (UL 7103, UL 61730), retrieved .
- SC Building Codes Council, code adoption, retrieved .
- South Carolina Code Title 58 Ch. 40 (Act 62 of 2019, customer-generators), retrieved .
- Georgia Power, Behind-the-Meter Interconnection Summary for Residential Customers (rev. 15 Aug 2025), retrieved .
- Code of Virginia §56-594 (net energy metering), retrieved .
Expert review
Written by the HyreSolar Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Market share and bifaciality trends from ITRPV 17th Edition. Field gains and degradation from the NREL bifacial presentation NREL/PR-5K00-84268. The worked example re-computes the bifacial-gain row printed on the named Trina data sheet; no figure is estimated.
Suggest a correction. We fix errors and say what changed.