Paper and Leaves Both Cut Solar Panel Output, but Paper Blocks More Light in Ugandan Field Test
Shading is one of the most stubborn enemies of solar power, and in tropical cities it often arrives in the most ordinary forms: a fallen leaf, a scrap of paper carried by the wind, dust washed against a panel after rain. A new open-access study published in Discover Energy on 21 September 2026 set out to quantify exactly how much these everyday materials matter, comparing paper and Ficus lyrata leaves as shading layers on a small photovoltaic panel in Kansanga, Makindye Division, Kampala, Uganda. Over 80 days of measurements, the researchers found that both materials sharply reduced the panel’s electrical output, but paper proved the more damaging of the two, blocking more of the incoming solar radiation despite being far thinner than the leaves.
The experiment centered on a TOP SOLAR monocrystalline module with a rated maximum output of 40 W, 36 solar cells, an open-circuit voltage of 25.04 V, and a short-circuit current of 2.05 A. The panel was mounted on a fixed stand in an open area, oriented toward the sun, with unshaded conditions serving as the baseline control. The team then applied one, two, and three layers of paper and of Ficus lyrata leaves directly to the panel surface, taking care to keep placement and coverage consistent between tests. Measurements were taken between 9:00 a.m. and 5:00 p.m. under clear weather conditions, using a digital multimeter for voltage and current, a solar power meter for irradiance, and a digital thermocouple thermometer for cell and ambient temperature. Power output was calculated as the product of current and voltage, and efficiency was computed from power output relative to solar irradiance and panel area.
The unshaded panel set a clear benchmark. Its average voltage was 24.85 V, its average current 1.22 A, its average power production 30.24 W, and its average efficiency 12.61%. From that baseline, the effects of shading unfolded in a steady, layered progression. Under leaf shading, average power output fell from 15.28 W with one leaf layer to 7.45 W with three, while efficiency dropped from 5.70% to 2.90% and average current declined from 0.64 A to 0.32 A. Paper shading produced still deeper losses: average current fell from 0.43 A to 0.21 A across one to three layers, power output dropped from 10.35 W to 4.80 W, and efficiency sank from 4.21% to just 1.88%.
The pattern held across intermediate layers as well. With paper, average current reached 0.43 A, 0.30 A, and 0.21 A for one, two, and three layers respectively, while leaf shading yielded gentler declines of 0.64 A, 0.43 A, and 0.32 A. Efficiency under leaf shading stepped down through 5.70%, 3.93%, and 2.90%, compared with 4.21%, 2.68%, and 1.88% under paper. Average power fell to 15.28 W, 10.10 W, and 7.45 W under one, two, and three leaf layers, and to 10.35 W, 6.93 W, and 4.80 W under the corresponding paper layers. In every comparison, the paper-shaded panel performed worse than the leaf-shaded one.
What makes this result physically interesting is that the materials differ in the opposite direction when it comes to thickness. The leaves averaged 0.39 mm, 0.75 mm, and 1.17 mm for one, two, and three layers, while the paper layers measured only 0.10 mm, 0.19 mm, and 0.29 mm. Despite being several times thicker, the leaves transmitted more usable light, likely because their internal structure allows partial light penetration, whereas paper is comparatively opaque. The authors attribute the greater losses under paper to this lower light transmittance, which blocks a larger fraction of incident radiation from reaching the photovoltaic cells.
The statistical analysis reinforced the hierarchy of harm. Correlation analysis found stronger associations under paper-shaded conditions (r = 0.63) than under leaf shading (r = 0.58). Regression models told a similar story: paper shading explained 35.3% of the variation in panel efficiency (R² = 0.35, p < 0.001), while leaf shading explained only 9.1% (R² = 0.09, p = 0.06), a result that was not statistically significant. For power output, paper shading accounted for 14.4% of the variation and leaf shading for 12.8%. Analysis of variance confirmed that the paper-shading model was statistically significant (F = 13.83, p < 0.001), and coefficient analysis showed that a single layer of paper had the largest individual effect on efficiency (β = 0.52, p < 0.001).
The leaf-side statistics were more nuanced. Correlations between the unshaded panel and panels shaded with one, two, and three leaves were weak (r = 0.04, 0.13, and 0.30 respectively), and the overall leaf-efficiency model was not significant. However, shading with three leaves did show a substantial individual effect on panel efficiency (β = 0.33, p = 0.02), suggesting that heavy leaf accumulation can meaningfully hamper conversion even when lighter coverage does not. For power output, the leaf model was statistically significant overall (F = 3.67, p = 0.02), with two-leaf shading contributing significantly (β = 0.36, p = 0.01), though one-leaf and three-leaf terms did not. On the paper side for power output, the overall model was significant (F = 4.22, p = 0.008), yet none of the individual layer counts—one paper (β = 0.23, p = 0.14), two papers (β = 0.06, p = 0.68), or three papers (β = 0.15, p = 0.29)—independently predicted output.
Those modest coefficients of determination carry an important caveat that the authors themselves emphasize: shading is only part of the story. Even the stronger paper-efficiency model left roughly two-thirds of the variance unexplained, pointing to other environmental factors—solar irradiance, panel temperature, ambient temperature, and wind speed—as substantial contributors to the day-to-day fluctuations in power generation. Collinearity diagnostics supported the reliability of the regression estimates, with variance inflation factors below roughly 2 and condition indices below 10, indicating that the shading variables acted independently rather than muddying each other’s effects.
The physics behind these losses is well established. Because cells within a photovoltaic module are connected in series, the output of the entire panel is constrained by the performance of the most shaded cell, which is why even a small shaded area can cause disproportionate power losses. Current is the parameter most sensitive to shading, since it is directly proportional to the sunlight absorbed by the cells, while voltage is generally more resilient under mild shading. Shading can also force shaded cells into reverse bias, making them behave as loads rather than generators and producing localized hotspots that can damage cells and shorten module lifespan—risks documented in earlier studies of partial shading, including work reporting power losses of 74.42% to 98.97% under complete shading of individual cells, branches, or rows.
Set against earlier research, the Kampala findings fill a specific gap. Prior studies have examined dust accumulation on panels in Nansana, Kampala, shading losses across module types, and modeled shading from obstacles in settings such as northeast Tehran, where southern obstacles caused over 50% energy loss. But few had tested simple, locally available materials like paper and leaves in a tropical field setting. The practical message for solar installers, policymakers, and consumers in similar climates is concrete: common urban shade sources such as litter and vegetation can impose significant energy losses, and managing them through regular panel cleaning, vegetation control, and careful placement away from trees and buildings is essential. The authors also flag directions for future work, including additional shading materials, other photovoltaic technologies such as thin-film and polycrystalline modules, mitigation strategies like maximum power point tracking and bypass diodes in real field conditions, and long-term degradation effects. For now, the study offers a measured, quantified reminder that in tropical cities, the difference between a well-sited, clean panel and one littered with leaves and paper can be measured in watts—roughly 30 W of output versus under 5 W under the heaviest paper shading in this experiment.
Subject of Research: The effects of paper and leaf shading on the electrical performance of a small monocrystalline solar panel in Uganda.
Article Title: Comparative analysis of tree leaves and paper shading materials on solar photovoltaic performance in Makindye, Uganda
Article References: living, O., Baron, M., Mundu, M. M., Judith, A., Uzorka, A., & Peter, J. (2026). Comparative analysis of tree leaves and paper shading materials on solar photovoltaic performance in Makindye, Uganda. Discover Energy, 6(1), Article 68. https://doi.org/10.1007/s43937-026-00186-9
Image Credits: AI Generated
DOI: 10.1007/s43937-026-00186-9
Keywords: photovoltaics, partial shading, solar energy, Uganda, monocrystalline panel, field experiment, energy efficiency, regression analysis, tropical climate, panel maintenance, Comparative, analysis
News Source: Denise Maddox. (October 29, 2026). Paper and Leaves Both Cut Solar Panel Output, but Paper Blocks More Light in Ugandan Field Test. Scienmag.
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