Viewing convection as a solar farm phenomenon broadens modern power predictions for solar photovoltaics

Abstract

Heat mitigation for large-scale solar photovoltaic (PV) arrays is crucial to extend lifetime and energy harvesting capacity. PV module temperature is dependent on site-specific farm geometry, yet common predictions consider panel-scale and environmental factors only. Here, we characterize convective cooling in diverse PV array designs, capturing combined effects of spatial and atmospheric variation on panel temperature and production. Parameters, including row spacing, panel inclination, module height, and wind velocity, are explored through wind tunnel experiments, high-resolution numerical simulations, and operating field data. A length scale based on fractal lacunarity encapsulates all aspects of arrangement (angle, height, etc.) in a single value. When applied to the Reynolds number Re within the canonical Nusselt number heat transfer correlation, lacunarity reveals a relationship between convection and farm-specific geometry. This correlation can be applied to existing and forthcoming array designs to optimize convective cooling, ultimately increasing production and PV cell life.

Technoeconomic Analysis of Changing PV Array Convective Cooling Through Changing Array Spacing

“…However, convection varies significantly for PV plants with the identical module dimensions but varied plant configurations-suggesting that the full array geometry is responsible for flow behavior and relative cooling [8], [16]. To account for these effects, we employ a length scale L Λ based on the 3-D lacunarity to quantify the heterogeneity of solar arrays as canopy flows [17], [18]. As further described in Section VI, L Λ characterizes the space through which flow is able to move in a solar array as a measure of "gappiness" based on the full plant geometry [19].…”

“…As further described in Section VI, L Λ characterizes the space through which flow is able to move in a solar array as a measure of "gappiness" based on the full plant geometry [19]. Embedding this parameter as the length scale in Re allows for a Nusselt number correlation of potential PV cooling Nu = f (Re, P r), which encompasses all the unique physical characteristics present in solar arrays [18]. This Nusselt number correlation was derived from operating field data, wind tunnel measurements, and numerical simulations and is shown in the following equation [9], [18]:…”

“…Fit coefficients found in this study of a = 0.09, m = 1/5, n = 1/12, and b = 1.91 resulted in a logarithmic relation with the coefficient of determination over R 2 = 90%. The works [9], [16], and [18] include more of the detailed heat transfer analysis used to determine the Nusselt number relationship used in this article. With this relation, a given PV plant canopy and flow configuration could estimate convective cooling through solving for h and use this value for h in existing thermal models to more accurately calculate power production.…”

“…For example, lacunarity has been used to assess surface roughness for material manufacturing, quantify damage on regions in the brain affected by neurological disease, and even characterize large-scale canopies such as heat islands in urban environments and effects of deforestation [25], [26], [27], [28]. We can also consider PV arrays as a type of canopy, where flow is able to pass through and around the pattern-like rows of heated objects in space [18]. The method used here to ascribe lacunarity values to a theoretical PV array is adapted from forest canopy research as described in [17] as an expansion on the box-counting technique introduced by Plotnick et al [29].…”

“…The following GitHub repository contains MATLAB code for calculating PV array lacunarity given geometric array parameters as written and employed for [17] and [18]. 1 The associated README file describes the necessary function calls and dependencies and contains all the relevant/necessary geometry values and author/contact information.…”