Most bifacial plants are designed as monofacial plants with a gain percentage added at the end. That shortcut hides three risks: undersized DC conductors, rear-side shading from the structure, and a yield number the lender will not accept.
This guide covers bifacial solar design in 2026 as a set of engineering decisions. It does not walk through software screens. For that, use our PVsyst bifacial gain modeling tutorial.
Quick answer. Bifacial solar design in 2026 means designing for two light sources. Read the module’s bifaciality and rear-side rating. Size DC circuits for the higher current. Raise and space rows so light reaches the back, keep the structure out of the rear view, and model albedo by season. Each choice changes yield, cable cost or code compliance.
TL;DR
- Bifaciality differs by cell type. Use the datasheet value, not a generic one.
- IEC 61730-1:2023 defines rear-side test irradiance levels of 135 W/m² and 300 W/m².
- Bifacial current must be in the NEC 690.8 maximum-current calculation. The 2026 NEC makes this explicit.
- Height, GCR and structure shading decide most of the rear gain.
- In India, projects commissioned from 1 June 2026 under net-metering or open access need ALMM List-II cells.
What changed for bifacial solar design in 2026?
Three things moved. Module ratings now follow defined rear-side test conditions. The US electrical code made bifacial current explicit. India tightened what cells may go into covered projects.
| Area | 2026 position | Design impact |
|---|---|---|
| Module rating | IEC 61730-1:2023 rear-side irradiance conditions | Compare datasheets on the same basis |
| US code | 2026 NEC 690.8 requires the highest Isc value | Larger conductors and fuses |
| India procurement | ALMM List-II for cells from 1 June 2026 | Module shortlist narrows |
| Yield reports | Bifacial inputs are reviewed in detail | Albedo and height need evidence |
How do you read a bifacial datasheet?
Start with bifaciality. It is the ratio of rear-side to front-side performance, measured under the procedures in IEC TS 60904-1-2:2019. A peer-reviewed review in Solar reports 65 to 75 percent for PERC. Some TOPCon and heterojunction (HJT) cells exceed 90 percent (MDPI Solar, 2025).
Next, find the rated rear-side conditions. IEC 61730-1:2023 sets bifacial nameplate irradiance (BNPI) at 1000 W/m² front plus 135 W/m² rear. Bifacial stress irradiance (BSI) is 1000 W/m² front plus 300 W/m² rear (Solar Tech Collective, 2026).
Datasheets often print power and current at several rear gains. Record which row you used, and use the same row for every module you compare.
Common trap. Comparing one supplier's front-only STC power with another's BNPI power. The BNPI figure is higher by design. Compare like with like.
How do bifacial modules change DC current sizing?
Rear light adds current. If the circuit calculation ignores it, conductors and overcurrent devices can be undersized.
Under NEC 690.8(A)(1), the simple method multiplies module short-circuit current (Isc) by 1.25. For the 2026 NEC, the code-making panel noted that bifacial modules “may have higher max current values depending on application. For this simple method, the highest value is required” (Solar Tech Collective, 2026).
SolarAPP+ shows one practical approach for residential permits. It applies the 1.25 factor, then a mounting factor of 1.05 for flush mounts or 1.30 for tilted mounts (SolarAPP+ Knowledge Base).
| Step | Monofacial (A) | Bifacial, tilt mount (A) |
|---|---|---|
| Datasheet Isc | 10.74 | 10.74 |
| × 1.25 irradiance factor | 13.43 | 13.43 |
| × 1.30 SolarAPP+ tilt factor | n/a | 17.45 |
Example values from the SolarAPP+ article. Your AHJ and code edition decide the method.
That is a 30 percent jump in maximum circuit current. It can push a string circuit to the next conductor size or fuse rating. NEC 690.8(A)(1) also allows an engineered method by a licensed professional engineer. Confirm which method your AHJ accepts.
How high and how far apart should bifacial rows be?
Rear gain depends on how much reflected light reaches the back. Two levers control it: height above ground and row spacing.
Higher rows let light spread under the module and reduce the dark band near the lower edge. Wider spacing, meaning a lower ground coverage ratio, lets more sunlight reach the ground between rows. Both cost money: taller posts and more land.
| Lever | Effect on rear irradiance | Cost side |
|---|---|---|
| Higher module edge | More even rear light | Longer posts, higher wind moment |
| Lower GCR | More lit ground between rows | More land, longer cables |
| Brighter ground | More reflected light | Gravel or membrane cost, upkeep |
| Portrait or horizontal module orientation | Changes self-shading pattern | Racking and tube design |
There is no single best height. Run the yield model across two or three heights and price each, then pick the one with the lowest cost per kWh. On raised farm arrays the trade-off changes again, as we explain in our agrivoltaics engineering guide for India.
Does the mounting structure shade the rear side?
Yes. Torque tubes, purlins, rails and junction boxes all sit behind the module. On a single-axis tracker, the torque tube is the largest object in the rear view, which is one reason torque tube and foundation design affects yield as well as structure.
Design responses include:
- Two-in-portrait layouts that leave a gap over the torque tube.
- Module clamps and rails kept off the active rear cell area where the racking allows.
- Cables tied along structural members, not hanging across the module back.
- A structure-shading loss entered in the yield model, not left at zero.
For tracker layouts, see the single-axis tracker glossary entry and our guide to tracker yield studies.
How should albedo be modeled?
Albedo is the share of sunlight the ground reflects. It drives rear gain more than any other site input.
Ground cover changes through the year. Dry soil, wet soil, grass, crop and gravel all reflect differently. Use monthly albedo values where you have evidence, and state the source for each.
Do not borrow a high albedo from a brochure or a snow site. A bankable report shows where every albedo value came from. The PVsyst tutorial linked above covers the validation checks lenders apply.
What do Indian projects need to check?
For Indian projects, module choice is also a compliance decision. Under MNRE’s ALMM order, net-metering and open-access projects commissioned from 1 June 2026 must use List-I modules with List-II cells (Energetica India, 2025).
That narrows the bifacial shortlist to modules built with listed cells. Our article on the ALMM List-II commissioning deadline covers the timing rules. Check the live ALMM list on the day you freeze the BOQ.
Bifacial design checklist
- Record bifaciality and the rated rear-side condition from each datasheet.
- Compare modules on the same rating basis.
- Size DC circuits with bifacial current, per the code edition and AHJ.
- Model two or three heights and GCRs, then compare cost per kWh.
- Enter structure shading as a real loss.
- Use sourced, seasonal albedo values.
- In India, confirm ALMM List-I and List-II status at BOQ freeze.
- Write every bifacial assumption into the design basis report.
How Heaven Designs helps
Bifacial design ties together the layout, the electrical calculations and the yield model. Our solar ground mount design service covers layout, structure and DC design for bifacial plants. Our reports service prepares PVsyst studies with stated bifacial inputs.
We do not guarantee a yield figure or lender acceptance. We document the inputs so your reviewer can check them.
To see a sample PVsyst report and drawing set, download design samples. To discuss a project, get a project quote.
FAQ
What is a good bifaciality factor in 2026?
It depends on the cell type. A peer-reviewed review reports about 65 to 75 percent for PERC and above 90 percent for some TOPCon and HJT cells. Use the value on the datasheet you are buying, because it varies by product.
Do bifacial modules need bigger cables?
Often, yes. Rear-side light raises circuit current, and the NEC maximum-current calculation must include it. In SolarAPP+‘s method, a tilt-mounted bifacial module’s maximum current is 30 percent higher than the monofacial result. That can change conductor and fuse sizes.
Are bifacial modules worth it on rooftops?
The gain is lower on flush-mounted roofs, because little light reaches the rear. SolarAPP+ uses a 1.05 factor for flush mounts against 1.30 for tilted mounts, which reflects that difference in current. Tilted racks on bright membranes do better. Model the specific roof before deciding.
What albedo should I use for a bifacial yield study?
Use measured or well-sourced values for the actual ground cover, by month where possible. Avoid a single generic value. Reviewers will ask for the source of each albedo input.
Does ALMM apply to bifacial modules in India?
ALMM applies by project type, not by module type. If your project is covered, bifacial modules must be on ALMM List-I, and from 1 June 2026 most covered projects also need List-II cells. Check the MNRE order for your project category.