Tilted bifacial panels usually produce more annual electricity. Vertical east–west panels can produce more valuable electricity when their morning and afternoon output matches higher prices or on-site demand. With a fixed export price, higher output earns more. With time-based prices or self-consumption, compare the value of each hour’s generation, then subtract the cost of each layout.
How the Layouts Compare
This comparison covers fixed-tilt bifacial panels facing the equator and vertical panels with one face pointing east and the other west. Both layouts use light reaching either side, including direct sunlight, diffuse light and ground reflections.
| Factor | Tilted bifacial panels | Vertical east–west bifacial panels |
|---|---|---|
| Position | Panels face south in the Northern Hemisphere or north in the Southern Hemisphere; the tilt is selected for the site. | Panels stand at 90° to the ground, with their two faces pointing east and west. |
| Daily output | Output generally peaks around solar noon. | Clear-day output commonly has morning and afternoon peaks, with lower output around solar noon. |
| Annual energy | An optimized layout generally produces more electricity per installed kW. | The difference depends on location, shading, ground cover, spacing and module characteristics. |
| Potential financial advantage | More electricity to sell at a fixed price or supply to daytime loads. | More generation outside the midday peak, potentially matching higher prices or different operating hours. |
IEA-PVPS research supports the general energy advantage of optimized equator-facing bifacial layouts over vertical installations. It does not establish one percentage difference that applies to every site.[1]
What Field Tests Actually Found
Sandia National Laboratories began monitoring bifacial test arrays in Albuquerque, New Mexico, in 2016. Its Prism Solar test installation covered five orientations and two ground covers. Ordinary gravel had a reflectivity of roughly 0.20–0.25; white-rock areas reached approximately 0.55–0.60.
The first-year analysis found that south-facing bifacial panels tilted at 15° over white gravel produced the highest energy yield. East–west vertical panels showed the highest bifacial gain and performed similarly to latitude-tilted monofacial reference modules—not necessarily tilted bifacial modules.
That distinction matters when comparing proposals: the largest percentage gain from using both sides does not mean the highest total output. The report also warns that small, short test rows benefit from surrounding unshaded ground, so their results should not be transferred directly to a dense commercial array.[2]
When Vertical Power Is Worth More
A business that buys expensive electricity during sunny morning or afternoon hours may save more by using vertical-panel output on site. A midday-heavy factory load may favor tilted panels instead. High evening electricity prices help only while sunlight remains: vertical panels cannot supply an after-dark peak without storage.
For exported electricity, check the actual contract. A low wholesale market price does not automatically reduce revenue under a fixed export tariff. Likewise, vertical panels only reduce curtailment losses if their output avoids the periods when that particular connection is restricted. IEA-PVPS identifies curtailment and negative prices as risks that need project-specific financial analysis.[3]
If vertical panels produce 15% less electricity, each generated kWh must be worth about 17.6% more to match the tilted layout’s annual electricity value. This is a mathematical break-even point, before differences in installation and operating costs—not a claim that vertical panels normally lose 15%.
A Transparent 10 kW Example
The following calculation uses assumed production, self-consumption and prices. It is not a measured installation, a local tariff quotation or a yield forecast. Both systems have 10 kW of front-rated DC capacity and no battery.
| Input or result | Tilted | Vertical |
|---|---|---|
| Assumed annual generation | 13,500 kWh | 11,475 kWh |
| Assumed share used on site | 35% | 60% |
| Electricity used on site | 4,725 kWh | 6,885 kWh |
| Electricity exported | 8,775 kWh | 4,590 kWh |
| Assumed value of self-used electricity | CNY 0.85/kWh | CNY 0.85/kWh |
| Assumed export price | CNY 0.32/kWh | CNY 0.32/kWh |
| Annual electricity value | CNY 6,824.25 | CNY 7,321.05 |
Annual electricity value = self-used kWh × avoided electricity price + exported kWh × export price.
Under these assumptions, vertical produces 2,025 kWh less but delivers CNY 496.80 more annual value, an increase of about 7.3%. Its higher self-consumption is an input that a site model must demonstrate—not an automatic benefit of standing panels upright.
If both systems export every kWh at CNY 0.32, tilted earns CNY 4,320 and vertical earns CNY 3,672. Tilted then leads by CNY 648. Neither calculation establishes payback: installation, maintenance, financing, taxes and equipment replacement still need to be included.
Site Conditions That Can Change the Result
Ground Cover and Module Choice
Ground reflectivity changes with moisture, vegetation and snow. A model should use realistic seasonal conditions rather than assume a permanent white surface. There is no universal rule that increasing reflectivity by 0.10 adds a fixed percentage to annual generation.
Module bifaciality is another separate input. For example, the Tongwei TWMNF-66QD product page states a mass-production bifaciality of 90 ±5%. That rating does not mean 90% more annual electricity. The actual contribution depends on how much light reaches each face.
Snow and Ground Clearance
Vertical mounting can reduce snow accumulation on the module surface, but snowbanks can still shade the lower part of the modules. IEA-PVPS research covering locations above 60°N highlights the potential of vertical and bifacial systems while stressing snow-aware layouts and climate-specific foundations. It does not support a universal snow-loss guarantee.[4]
Land and Roof Constraints
Compare both kWh per installed kW and kWh per usable square metre. Wide vertical rows may preserve machinery access, but fewer panels may fit on the same plot. Farm layouts also need crop-specific shading checks; no single yield-loss percentage applies to all crops.
On roofs, the structure, wind exposure, clearances and rear-side obstructions can determine which layout is practical. A bifacial module mounted close to an opaque roof has limited rear-light access, regardless of its laboratory rating.
What to Request Before Ordering
Ask for two designs using the same site boundary, comparable modules and clearly stated DC and inverter capacities. The comparison should include:
- Time-matched energy data. Use 12 months of hourly or 15-minute consumption, matched to generation and tariff periods. Separate self-use, exports and curtailed electricity.
- A bifacial-capable model. Include both faces, row shading, mounting obstructions, seasonal ground reflectivity, temperature and inverter clipping.
- Comparable costs. Itemize foundations, racking, wiring, land, cleaning and replacements. If a layout also replaces a fence, credit only the fence cost it genuinely avoids.
- Installation limits. Check the selected model’s mounting instructions and electrical limits in its product documentation. Have qualified engineers assess wind loads, foundations, roof capacity and any glare risk.
After installation, review interval output rather than only the annual meter total. Separate outages, export restrictions and snow-covered periods from normal operation before judging whether the layout met its forecast.