[Paper Review] Agrivoltaic Farm Design: Vertical Bifacial vs. Tilted Monofacial Photovoltaic Panels

Rehan Younas, Hassan Imran+2 more|arXiv (Cornell University)|Oct 2, 2019

Photovoltaic Systems and Sustainability17 citations

TL;DR

This study proposes east/west (E/W) vertical bifacial photovoltaic (PV) panels for agrivoltaic (AV) farming, demonstrating they enhance spatial homogeneity in daily sunlight distribution compared to standard north/south (N/S) fixed-tilt panels. For Lahore, E/W vertical bifacial systems achieve ~5% higher land productivity at slightly lower PV density than standard solar farms, with resilience to soiling losses, though performance degrades at higher densities due to mutual shading.

ABSTRACT

An unprecedented demand for Food, Energy, and Water (FEW) over coming decades require integrated FEW innovations with least environmental footprint. Collocating solar photovoltaic (PV) technology with agriculture is a promising approach towards dual land productivity that could locally fulfil growing food and energy demands. This 'agrivoltaic' (AV) solution can be highly suitable for hot and arid climates where an optimized solar panel coverage could prevent excessive thermal stress thereby increasing the crop yield and lowering the water budget. One of the concerns with using standard fixed tilt solar array structure that faces north/south (N/S) direction for AV farming is the spatial heterogeneity in the daily sunlight distribution for crops and soil water contents, both of which could affect crop yield. Dynamic tilt control through a tracking system can eliminate this problem but could increase the system cost and complexity. Here, we investigate east/west (E/W) faced vertical bifacial panel structure for AV farming and show that this could provide a much better spatial homogeneity for daily sunlight distribution relative to the fixed tilt N/S faced PV structure implying a better suitability for monoculture cropping. By modeling PV energy and crop yield under varying density (row to row pitch) for PV arrays and shade tolerances for crops, we show that E/W vertical bifacial panels can provide ~5% better land productivity as compared to N/S faced fixed tilt panels for Lahore (31.520N, 74.358E) when PV array density is slightly lower than that of a standard solar farm. In contrast, when PV arrays are denser than the standard, land productivity for E/W vertical bifacial panels degrades due to mutual shading. These results, together with high inherent resilience to soiling (dust accumulation) losses for E/W vertical bifacial panels, indicate their attractive prospects for AV applications.

Motivation & Objective

• To address spatial heterogeneity in sunlight and soil moisture distribution caused by standard north/south (N/S) fixed-tilt PV arrays in agrivoltaic systems.
• To evaluate the suitability of east/west (E/W) faced vertical bifacial PV panels for monoculture crop production under varying PV array densities.
• To compare land productivity between E/W vertical bifacial and N/S fixed-tilt PV systems under realistic climatic and crop conditions in Lahore.
• To assess the impact of mutual shading and soiling losses on system performance across different PV array densities.
• To identify optimal PV array density for maximizing dual-use productivity in agrivoltaic farming using vertical bifacial technology.

Proposed method

• Modeling daily solar irradiance distribution across crop rows using a 3D ray-tracing approach for E/W vertical and N/S fixed-tilt PV configurations.
• Simulating crop yield response using crop-specific shade tolerance thresholds under varying daily PAR (photosynthetically active radiation) exposure patterns.
• Quantifying land productivity as the combined energy yield (kWh/m²/year) and crop yield (kg/m²/year) per unit area.
• Analyzing mutual shading effects by varying row-to-row pitch (density) of PV arrays and calculating inter-row shading losses.
• Incorporating soiling loss estimates based on panel orientation, with E/W vertical panels assumed to have lower dust accumulation due to self-cleaning potential.
• Conducting comparative simulations for Lahore (31.520°N, 74.358°E) under standard and high-density PV array configurations.

Experimental results

Research questions

• RQ1 How does the spatial distribution of daily sunlight vary across crop rows when using E/W vertical bifacial PV panels compared to N/S fixed-tilt panels?
• RQ2 What is the optimal PV array density for maximizing land productivity in agrivoltaic systems using E/W vertical bifacial panels?
• RQ3 How does mutual shading affect energy and crop yield when PV arrays are denser than standard solar farm configurations?
• RQ4 To what extent do soiling losses differ between E/W vertical bifacial and N/S fixed-tilt PV systems in arid climates?
• RQ5 What is the relative land productivity gain of E/W vertical bifacial PV systems compared to N/S fixed-tilt systems under realistic crop and climate conditions?

Key findings

• E/W vertical bifacial PV panels provide significantly better spatial homogeneity in daily sunlight distribution across crop rows than N/S fixed-tilt panels, reducing microclimate variability.
• For Lahore, E/W vertical bifacial systems achieve approximately 5% higher land productivity than N/S fixed-tilt systems when PV array density is slightly below standard solar farm levels.
• Land productivity with E/W vertical bifacial panels degrades when PV array density exceeds standard solar farm levels due to increased mutual shading.
• The inherent resilience of E/W vertical bifacial panels to soiling losses enhances their long-term performance and suitability for arid and dusty environments.
• The improved light distribution and reduced shading heterogeneity make E/W vertical bifacial panels particularly suitable for monoculture crop systems.
• The study confirms that vertical bifacial PV systems can simultaneously support high crop yields and stable energy generation with minimal environmental footprint in hot, arid climates.