Poster Sample: Testing Solar Panel Efficiency Under Shading

Type: Academic Poster  |  Subject: Engineering  |  Level: Undergraduate  |  Word Count: ~900 words

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The Brief

Produce a laboratory-based poster testing how partial shading affects the power output and efficiency of a photovoltaic module, for a Level 5 Renewable Energy Systems laboratory assessment.

The Effect of Partial Shading on Photovoltaic Module Efficiency

T. Kowalski, School of Engineering, University of Mereworth

Introduction & Aims

Photovoltaic modules are built from cells wired predominantly in series, so shading even a small fraction of the cell area can disproportionately reduce output, because the shaded cells constrain current flow through the entire string rather than simply losing output in proportion to their own area. Roof-mounted arrays are frequently exposed to partial shading from chimneys, trees, dormer windows and neighbouring buildings, yet installers and students alike often underestimate how severe the resulting loss can be. This bench investigation measured how 25% and 50% shading, with and without an active bypass diode, affects the power output and conversion efficiency of a 50W monocrystalline module, to quantify this effect under controlled laboratory conditions. Because domestic and educational-site installations are increasingly common on terraced roofs with partial obstruction, understanding the practical scale of shading losses has direct relevance to community energy and school solar projects, not just utility-scale arrays.

Methods

• Equipment: a 50W monocrystalline PV module, an adjustable halogen lamp array providing approximately 1000 W/m² of irradiance at the module plane, a digital multimeter and a variable resistive load box for sweeping the current-voltage curve.
• Calibration: irradiance was checked with a handheld solar power meter at the module plane before each run, and module temperature was allowed to stabilise for five minutes under the lamp array to reduce thermal drift between conditions.
• Procedure: the module was first tested unshaded to establish a baseline, then retested with an opaque card mask covering 25% and 50% of its surface area, with the internal bypass diode active in each shaded run.
• Additional run: the 50% shaded condition was repeated with the bypass diode disconnected, to isolate the diode’s protective contribution from the shading loss itself.
• Repeatability: each condition was measured three times in immediate succession and the mean value recorded, to reduce the influence of minor irradiance fluctuations from the lamp array.
• Measurements: maximum power point voltage (Vmp), current (Imp), power output and module efficiency were recorded for each condition by sweeping the load resistance and identifying the peak power point on the resulting curve.

Results

Power output fell from 47.8W unshaded to 34.6W under 25% shading and 21.3W under 50% shading with the bypass diode active, corresponding to efficiency losses from 18.2% to 13.2% and 8.1% respectively. Removing the diode under the 50% shaded condition reduced output much further, to just 9.7W and 3.7% efficiency, confirming the diode’s central role in limiting mismatch losses. Relative to the unshaded baseline, this represents efficiency losses of approximately 27%, 55% and 80% for the 25% shaded, 50% shaded with diode, and 50% shaded without diode conditions respectively. Maximum power point voltage and current both declined progressively with increased shading, consistent with the shaded cells constraining current through the series string.

Discussion

The disproportionate power loss under shading reflects current mismatch: because cells are wired in series, the shaded cells limit current through the whole string unless a bypass diode routes current around the affected section. Without a functioning diode, the shaded cells can also be forced into reverse bias, dissipating power as heat rather than generating it, which creates a hot-spot risk in addition to the larger output loss recorded here. The scale of the drop between the diode-active and diode-disabled 50% shading conditions, roughly a further 11.6W, illustrates how much protection a correctly wired bypass diode provides in practice. From a design standpoint, these findings support specifying module-level power electronics, such as power optimisers, on any array where even partial shading is anticipated during part of the day.

These bench results are consistent with the manufacturer’s stated diode configuration and with the general pattern reported in shading-loss literature, though a laboratory halogen rig cannot fully replicate the spectral distribution and diffuse component of outdoor sunlight. Field verification under real shading conditions, and repetition across multiple module samples, would strengthen confidence in the precise loss percentages reported here.

Conclusion

• Partial shading reduces module power output disproportionately to the shaded area, due to current-limiting effects within the series-connected string.
• Bypass diodes substantially recover lost output and materially reduce hot-spot risk; their function should always be specified and verified as working during installation.
• Panel siting should minimise partial shading from chimneys, trees and adjacent structures wherever practicable, particularly for strings without module-level power electronics.
• Where shading cannot be avoided, module-level optimisers or microinverters may reduce mismatch losses further than a passive bypass diode alone.
• Repeat testing across additional module samples and real outdoor shading conditions would help confirm how closely these bench figures generalise to installed arrays.

Key References: Bishop (1988, Solar Cells); Silvestre et al. (2009, Renewable Energy); MacAlpine et al. (2013, IEEE Journal of Photovoltaics); Woyte et al. (2003, Solar Energy).

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