Energy yield from vertically mounted bifacial solar panels
- Jul 22, 2022
- 16 min read
Updated: Aug 1
This article takes a deep dive into the factors that determine the energy yield of vertical bifacial solar systems, from orientation, albedo and module technology to geometry, shading, climate and temperature. It also examines how vertical PV is simulated and compares those estimates with results reported in peer-reviewed field studies.
Last major update: 31.07.2026.
The vertical PV production pattern: more off-peak energy
Vertical bifacial solar panels have a distinctly different production pattern from conventional south-facing, tilted solar panels. When the panels face east and west, production typically rises quickly in the morning, decreases around the middle of the day, and increases again during the afternoon. This creates two characteristic production peaks at times when electricity demand and electricity prices are often higher than during the solar-rich midday hours.
The graph below shows this daily production pattern using measured data from one of Over Easy Solar’s research installations in Oslo, Norway, where the company is based. On the day shown, the vertical bifacial installation produced significantly more energy during the morning and afternoon than the conventional reference system. The graph illustrates an important feature of vertical PV: annual energy yield is only one part of the performance assessment. The time of day when the electricity is generated may also affect its value for self-consumption, electricity markets and the power grid.
Vertical solar panels can also generate more off-season energy, as seen in the graph below, the annual production profile from one of our research installations close to Oslo. It illustrates how production develops throughout an entire year, and you clearly see that vertical bifacial delivers more energy in the winter months, especially the south-north orientation.
Actual production data from the same installation as shown above, from 2022 and 2023, shown per month for the two different azimuths.
Over Easy Solar has collected production data from several research and commercial installations, and many of them in the Oslo area. Across these installations, measured annual specific yield has typically ranged from approximately 700 to 1,000 kWh per installed kWp. This is a considerable range, even within the same geographical region.
The differences in energy yield for vertical bifacial systems are caused by several interacting factors, including panel orientation, surface albedo, module bifaciality, system geometry, row spacing, local shading, snow conditions, weather and data availability. These factors also help explain why measurements and estimates of vertical solar yield from different projects cannot be compared without understanding how each system is designed and where it is installed. We examine each of these factors in the following.
In order to get a good understanding of energy yield of vertical solar installations, Over Easy Solar has since 2021 been collecting data from 13 different R&D installations, some of them equipped with substantial monitoring equipment. A description of the setups and early findings can be surveyed in Vertical Bifacial PV for Flat Rooftops - Energy Yields from Prototypes and Pilots in Europe (Foss et al., EU PVSEC 2023).
What determines the energy yield of vertical bifacial solar panels?
The energy yield of a vertical bifacial solar installation cannot be explained by location alone. Even installations within the same region can produce significantly different energy yields because the amount of direct, diffuse and reflected irradiance changes with the system design and surrounding environment.
The most important factors include:
The orientation of the panels
The local solar climate and seasonal weather
Annual variations in weather and solar irradiation
The reflectivity, or albedo, of the roof or ground
The bifaciality of the solar modules
The height of the panels and distance between rows
Shading between neighbouring panels
Local shading from trees, nearby buildings and obstructions on the mounting surface, such as pipes, ventilation equipment and chimneys
Snow, soiling and operating temperature
Electrical and operational losses
Annual specific-yield figures are normally based either on measurements from a particular year or on simulations using a typical meteorological year (TMY). An unusually sunny, cloudy or snowy year may therefore produce results that differ materially from the long-term average.
This is why a single figure for “vertical solar yield” is rarely meaningful without knowing the location, measurement period, orientation, system geometry and surrounding conditions.
Panel orientation affects when energy is produced
For vertical bifacial panels, orientation refers to the directions faced by the two module surfaces. An east-west system has one side facing east and the other west, while a south-north system has one side facing south and the other north.
We here show some simulation from our VPV Simulation Engine, which show that orientation has a large effect on the production profile, but only a small effect on total annual yield. At 5% albedo, the simulated annual yield was 748 kWh/kWp for east-west and 747 kWh/kWp for south-north. Albedo, on the other hand, At 70% albedo, the corresponding yields were 939 and 936 kWh/kWp.
East-west panels produce the characteristic morning and afternoon peaks shown in the graph. South-north panels produce more around midday and perform relatively better during autumn, winter and early spring, when the sun is lower in the southern sky. East-west panels produce more during the high-sun months from May to August.
For a deeper comparison with flat roof east-west mounting with conventional solar panels, have a look at the article about east-west solar energy production.
The choice of orientation should therefore consider not only annual energy yield, but also when during the day and year the electricity is most useful.
Albedo has a major effect on vertical bifacial yield
Albedo is the proportion of sunlight reflected by the roof or ground. Because vertical bifacial panels receive light on both sides, reflected irradiance can make a substantial contribution to production.
In the Oslo simulations, increasing the assumed albedo from 5% to 70% raised the annual specific yield by approximately 25% for both orientations:
Orientation | 5% albedo | 70% albedo | Increase |
East-west | 748 kWh/kWp | 939 kWh/kWp | 25.5% |
South-north | 747 kWh/kWp | 936 kWh/kWp | 25.3% |
The effect is particularly visible during spring and summer, when more solar radiation reaches the mounting surface and can be reflected towards the modules. The horizontal reference system is unchanged between the two scenarios because a horizontal panel has effectively no view of the surface beneath it in this model.
An albedo of 70% represents a highly reflective surface and is included here to demonstrate the sensitivity of vertical bifacial yield to surface conditions. Actual albedo depends on the roof material, vegetation, moisture, dirt and snow, and may vary considerably during the year.
For a deeper discussion of vertical solar panels and the role of albedo, see our article about Vertical solar panels and albedo.
Module bifaciality affects how much reflected light becomes electricity
Bifaciality describes how efficiently the rear side of a solar module converts light compared with the front side. A module with 95% bifaciality can produce almost as much power from light reaching the rear as from the same amount of light reaching the front.
This matters particularly for vertical PV, where both sides of the module contribute significantly to production. The benefit of a reflective roof or ground surface will therefore be greater for a module with high bifaciality than for one with a less efficient rear side.
Typical bifaciality values vary by cell technology:
Solar cell technology | Typical bifaciality |
HJT | 90 to 95% |
TOPCon | 70 to 85% |
Back-contact, or BC | 50 to 75% |
These are indicative ranges. Actual bifaciality varies between manufacturers, module designs and product generations.
Bifaciality is also important when comparing results from different vertical solar installations or research studies. Two systems with the same location, orientation and albedo may still achieve different yields if they use modules with different rear-side efficiency. The energy yield from a TOPCon vertical bifacial module can be up to 13% lower compared to a HJT module, just because of bifaciality.
Panel height, row spacing and self-shading
The geometry of a vertical solar installation affects how much direct, diffuse and reflected light reaches the modules. One useful measure is the pitch-to-height ratio, or P/H ratio: the distance between panel rows divided by the panel height.
Over Easy Solar’s rooftop system has a P/H ratio of approximately 2. This relatively compact geometry allows substantial capacity to be installed on a limited roof area, but row-to-row shading must be included in the yield calculation. Vertical agrivoltaic systems typically have a higher P/H ratio because the rows are spaced farther apart to preserve agricultural access and reduce shading.
Wider spacing generally increases specific yield in kWh/kWp by reducing mutual shading and improving access to reflected light. Closer spacing can reduce yield per installed kWp, but may allow more capacity and total production to be installed on the available surface.
Self-shading can also come from the product itself. Parts of the mounting structure may block light, particularly at low sun angles. Module design is equally important. On a vertical module, a conventional frame can permanently shade the first row of cells along the lower edge. Depending on the electrical cell layout and bypass-diode configuration, this narrow shadow can cause a much larger loss than its physical area suggests.
A reliable yield model should therefore represent the actual row spacing, module height, mounting structure and module design, rather than treating the installation as an unobstructed vertical surface.
Location, climate and local shading
Vertical PV yield depends strongly on local solar conditions. Latitude affects sun height and seasonal variation, while cloud cover influences the balance between direct and diffuse irradiance. These factors can change both annual production and the relative performance of different orientations. To get a quick overview of the effect of location and other factors, Over Easy Solar has launched a VPV Energy Yield Portal, which presents simulated data for selected locations around the world.
Vertical panels often benefit from low sun angles, particularly during mornings, afternoons and winter months. In summer, when the sun is high, horizontal or tilted systems may receive more direct irradiance around midday. The annual result therefore depends on how solar energy is distributed across the day and year, not only on total irradiation.
Local shading can also have a major impact. Mountains and terrain may block the sun at low angles, while nearby trees, buildings, parapets, chimneys, pipes and ventilation equipment can reduce production during specific hours or seasons. This type of shading is highly site-specific and should be assessed separately from the broader climate and horizon data used in standard simulations.
Yield also varies from year to year. A measured annual value represents the weather conditions of that specific year, while simulations normally use long-term weather datasets to estimate a typical year. Actual production may be higher or lower because of unusually sunny, cloudy or snowy conditions.
A separate article, Vertical solar panel yield by location, presents examples of comparable simulations for different cities and explain the Over Easy Solar VPV Simulation Engine in more detail.
Snow and soiling
Vertical panels are less prone to direct snow accumulation than tilted or horizontal modules, which can help maintain production after snowfall. At the same time, snow on the roof or ground can increase albedo and boost the irradiance reaching both sides of a bifacial module.
The net impact depends on snowfall, temperature, wind, system geometry and how long the snow remains. To learn more, read the blog article about Vertical solar panels and snow.
Vertical mounting also changes soiling behaviour. Dust, pollen and other deposits are less likely to remain on an upright surface, but local conditions still matter. Pollution, bird droppings, nearby vegetation and limited rainfall can all reduce production, and should be included in performance assessments where relevant.
Module temperature and system losses
Solar modules are rated at a cell temperature of 25°C, but they operate considerably hotter in direct sunlight. In full sun, module temperature is commonly around 25°C above ambient temperature. With an air temperature of 35°C, a rooftop module may therefore operate at around 60°C, while poorly ventilated, close-mounted systems in hot climates can exceed 70°C.
As temperature increases, power output decreases. Modern HJT and TOPCon modules typically lose around 2.4% to 2.9% of power for every 10°C increase in cell temperature, while some older crystalline-silicon modules are closer to 3.5%.
A joint study by the Institute for Energy Technology and Over Easy Solar found that the Over Easy system has particularly effective heat transfer. The median measured heat-loss coefficient, called the U-value in the PVsyst thermal model, was 55 W/m²K. By comparison, using the PVsyst default value of 29 W/m²K would overestimate module temperature by approximately 5 to 10°C.
The energy delivered by the system is also reduced by cabling, module mismatch, shading, downtime, degradation and inverter conversion losses. Inverter sizing matters as well: an oversized inverter may operate less efficiently at low power, while an undersized inverter may clip the highest production peaks. This is discussed in more detail in our article on selecting the right inverter size for a flat-roof solar system.
What recent field studies show
Published and peer reviewed field measurements of vertical bifacial PV remain limited, and results depend strongly on the test conditions. Meaningful comparisons require information about module bifaciality, albedo, orientation, mounting geometry, reference-system design and measurement period.
Starting in the North: Field measurements in Trondheim, Norway
A one-year study at SINTEF’s Alpha Centauri test facility in Trondheim compared single rows (no row-to-row shading) of vertical bifacial modules in east-west and south-north orientations with a bifacial module facing south at a 44° tilt. The modules had a bifaciality of 65%, and the roof albedo used in the analysis was 0.13. (Dimd et al., 2024, Full paper on ResearchGate)
Configuration | Measured specific yield |
Vertical south-north | 793 kWh/kWp |
Vertical east-west | 714 kWh/kWp |
South-facing, 44° tilt | 905 kWh/kWp |
In other words, the south-north vertical module produced about 12% less than the steeply tilted reference, while the east-west module produced about 21% less. The study covered July 2022 to June 2023 and found that diffuse irradiance was particularly important for the vertical bifacial configurations. For those interested in flat roof solar solution, we can add that similar weather conditions would have likely yielded about 650 kWh/kWp for a conventional flat roof system with 10 degree tilt in east/west configuration.
The bifaciality of the modules was relatively low. Using a simplified correction from 65% to 95% bifaciality, Over Easy Solar calculates that the same vertical east-west installation would have produced approximately 879 kWh/kWp. For comparison, the VPV Simulation Engine from Over Easy Solar with comparable parameters, estimates an expected specific yield of 768 kWh/kWp for a Typical Meteorological Year (TMY).
Continental Europe: Circling in on 800-1200 kWh/kWp
Scientific literature containing full-year production measurements from vertical bifacial PV systems in continental Europe remains surprisingly limited. Many studies rely mainly on simulations, short measurement periods or small experimental setups. The available field data nevertheless indicate that annual specific yield will often fall somewhere between approximately 800 and 1,200 kWh/kWp, depending strongly on location, module bifaciality, ground reflectance and, not least, the design of the mounting system.
One of the most informative recent studies comes from Foulum in Denmark, where Victoria et al. in Energy Nexus, 2025, compared two co-located 44.4 kWp systems using identical bifacial modules. One system was mounted vertically, while the other faced south at an inclination of 25 degrees. Over one year, the vertical system produced approximately 734 kWh/kWp DC, compared with 999 kWh/kWp for the tilted system.
However, the measured result cannot be interpreted as a clean comparison between vertical and tilted orientation. The researchers found that steel components in the experimental mounting structure shaded the east-facing side of the vertical modules. This is clearly visible in the measured daily production profile, where the morning peak is much lower than predicted, while the afternoon peak is considerably closer to the modelled result. The structural shadows would also have caused mismatch between cells and module substrings, making the electrical loss larger than the directly shaded area alone might suggest.
The researchers had modelled annual production of 914 kWh/kWp for the vertical system and 1,048 kWh/kWp for the tilted system, a difference of approximately 13%. The tilted installation came reasonably close to its expected yield, while the measured vertical output was about 20% below its modelled value. The study therefore illustrates the consequences of using a mounting system that was not fully optimized for vertical bifacial modules. The accompanying graph shows this particularly well and helps distinguish losses caused by the vertical orientation from avoidable losses caused by the structure itself.
A Swiss study by Baumann et al. provides a more relevant reference for vertical PV on rooftops, for an installation put into operation in 2017, actually the world's first rooftop vertical installation. A 9.09 kWp vertical bifacial installation on a green roof in Winterthur produced 942 kWh/kWp of AC electricity over one year. The authors compared this with approximately 1,000 kWh/kWp as a typical annual yield for south-facing PV in the region, although they did not operate a complete co-located reference system for the full year.
The Swiss experiment also demonstrated how strongly the surface below and around the modules can affect production. Parts of the system were installed above a conventional green roof with an albedo of approximately 0.09, while other modules were placed above a brighter surface with an albedo of approximately 0.21. During a four-month detailed comparison, the modules above the brighter surface produced around 17% more energy. Some of this difference may also have resulted from variations in module bifaciality, which ranged from 74% to 93%, but the result still provides clear field evidence of the importance of reflected light.
A third dataset comes from an agrivoltaic pilot in Grembergen, Belgium. Its vertical bifacial system produced approximately 835 kWh/kWp in 2022. The co-located comparison system was a single-axis tracker, which produced 1,245 kWh/kWp and is therefore a more demanding reference than conventional fixed-tilt PV. The vertical modules had a relatively low bifaciality of around 70%, and the rows followed the direction of the agricultural field rather than being oriented precisely east and west. No representative annual albedo was reported. The Belgian result is therefore useful as a real production figure, but less useful for determining the performance of an optimized vertical system.
These scientific measurements range from 734 to 942 kWh/kWp, but all three installations had limitations. The Danish prototype suffered avoidable structural shading, the Belgian system used low-bifaciality modules and a non-optimal orientation, and the Swiss installation used custom modules with varying bifaciality in the very early days of bifacial solar, above surfaces with relatively low reflectance. The published literature therefore does not yet provide a complete picture of what a modern system designed specifically for vertical bifacial PV can achieve.
Commercial experience helps to fill part of this gap, although company statements should be distinguished from peer-reviewed measurements. Next2Sun states that optimized vertical agrivoltaic systems in Germany can reach annual yields of up to approximately 1,200 kWh/kWp, sometimes matching or exceeding conventional fixed south-facing systems. Its newer systems use high-bifaciality modules and mounting structures developed specifically to keep both module surfaces unobstructed.
Taken together, the available evidence suggests that vertical bifacial PV in continental Europe can reasonably produce somewhere around 800 to 1,200 kWh/kWp per year. The lower end is represented mainly by research prototypes with low bifaciality, shading or non-optimal geometry. The upper end reflects optimized commercial systems in favourable Central European locations. The wide range also demonstrates why reliable yield prediction must be based on measurements from many installations, climates, roof surfaces and system configurations rather than on one study or one simulation.
Moving towards the equator: Field measurements in Qatar and Jordan
A study in Doha compared clean vertical east-west bifacial modules with clean south-facing bifacial modules tilted at 22°. The frameless modules had 90% bifaciality, and the measured average ground albedo was 0.45. (Kivambe et al., 2024, Full article on ResearchGate)
The table below converts the monthly average daily specific yields reported by the authors into annual figures for the two complete calendar years in the dataset:
Year | Vertical east-west | South-facing, 22° tilt |
2021 | 2,402 kWh/kWp | 2,479 kWh/kWp |
2022 | 2,259 kWh/kWp | 2,283 kWh/kWp |
Across the full study period, the clean tilted bifacial modules produced approximately 4% more energy on average than the clean vertical modules. During April to August, however, the vertical modules produced 3.8% more on average, and up to 9.2% more during individual periods. The vertical configuration also accumulated less soiling than the tilted modules: The numbers stated in the table above represent modules that were regularly cleaned. Uncleaned tilted modules could show soiling losses as high as 60%, while the vertical bifacial module experienced negligible losses.
A study by Ayadi et al. in Jordan, published as Comparative Experimental Performance Assessment of Tilted and Vertical Bifacial Photovoltaic Configurations for Agrivoltaic Applications, reported a substantially different result despite the site being at a broadly similar latitude to Doha. The vertical east-west system produced 1,288 kWh/kWp, compared with 1,962 kWh/kWp for a south-facing bifacial system tilted at 10°, a difference of approximately 34%.
The studies are not directly comparable. The Jordan study tested complete multi-row systems, where row spacing and structural self-shading affect production, while the Qatar study used isolated frameless modules with little or no array-level shading. The Jordan modules also had a lower bifaciality of approximately 80%, compared with 90% in Qatar, and the Jordan paper did not report the surface albedo. By comparison, the Qatar site had a high measured average albedo of approximately 0.45. The reference systems also differed, with a 10° tilt in Jordan and 22° in Qatar.
Why vertical PV requires a dedicated simulation model
The examples above show why vertical PV yield cannot be estimated from location and module orientation alone. A useful model must calculate direct, diffuse and reflected irradiance on both module sides, while accounting for albedo, bifaciality, row spacing, self-shading, mounting details and local weather.
Over Easy Solar has developed a dedicated VPV Simulation Engine together with the Institute for Energy Technology in Norway. The model has been informed by data from our research installations established between 2021 and 2023, including sites where irradiance, production, albedo - and system geometry could be measured or varied.
The model is used to estimate hourly, monthly and annual production for a defined system and location. It also allows different orientations, surface conditions and layouts to be compared using consistent assumptions.
PVsyst and PV*SOL are useful for conventional PV systems, but their bifacial models rely on simplified row geometry and generalized rear-side irradiance calculations. They handle ground-reflected light, rear-side calculation and structural shading less precisely than is needed for vertical systems. They also cannot fully represent the geometry of an Over Easy Solar VPV Unit, which consists of several small modules. Independent studies have shown that modelling uncertainty is generally higher for vertical bifacial systems than for conventional tilted arrays. The VPV Simulation Engine was therefore developed around the actual product geometry and calibrated against measurements from Over Easy Solar research installations.
So, how much energy do vertical solar panels produce?
There is no single yield figure that applies to all vertical PV systems. For continental Europe, the available evidence suggests that annual specific yield will often fall somewhere around 800 to 1,200 kWh/kWp, depending on location, albedo, module bifaciality, orientation, row spacing, mounting-system design and local shading.
Published full-year measurements currently sit mainly toward the lower and middle part of this range. Reported values include approximately 734 kWh/kWp in Denmark, 835 kWh/kWp in Belgium and 942 kWh/kWp in Switzerland. However, all three systems had identifiable limitations, including structural shading, relatively low module bifaciality, non-optimal orientation or low-reflectance surroundings. The Danish study, for example, modelled 914 kWh/kWp before the avoidable losses caused by the mounting structure.
The upper part of the European range is supported more by simulations and commercial operating experience than by peer-reviewed full-year studies. Next2Sun states that optimized vertical agrivoltaic systems in Germany can reach approximately 1,200 kWh/kWp, using high-bifaciality modules and mounting systems designed to keep both module sides unobstructed.
Measurements from Over Easy Solar installations in the Oslo area have ranged from approximately 700 to 1,000 kWh/kWp, reflecting both the more northerly climate and differences in roof surface, shading, system configuration and weather from year to year.
Further south, considerably higher yields have been reported. In the Qatar field study discussed above, vertical east-west modules produced more than 2,200 kWh/kWp per year, supported by strong solar irradiation, high module bifaciality and a high ground albedo of approximately 0.45. The same study also showed a major operational advantage in a high-soiling environment: tilted modules suffered severe soiling losses when left uncleaned, while the vertical modules remained largely unaffected.
Vertical solar should therefore not be viewed as a technology only for northern latitudes. Its production profile, reduced sensitivity to soiling and ability to use reflected light can also make it relevant in high-irradiation and desert regions. The most useful conclusion is not one universal number, but a broad range that depends on the actual climate and system design. In continental Europe, 800 to 1,200 kWh/kWp is a reasonable range for well-designed installations, while yields above 2,000 kWh/kWp are possible in sunnier regions with favourable albedo and well-designed systems.
