Near Shadings: irradiance loss

What this step does

This loss is the light that the row in front takes from the plane irradiance. When the sun is low, the front row casts a shadow that climbs the module plane, and the direct sunlight on the shaded strip is lost. The rows also hide part of the sky and most of the ground, which reduces the diffuse and ground-reflected light all day. The Model tab's Near shading (row to row) step sets how the shaded fraction and the visible sky are computed.

The math

1. Running total
2. Loss at a timestep

$$E_{after} = E_{before} - E_{row},\qquad E_{row} = \frac{\Delta t}{1000}\sum_i L_i \tag{1}$$ $$L_i = F_{sh,i}\,(B_i + C_i) + (1-F_{sky})\,D_i + \left(1-\tfrac{1}{N_{rows}}\right)G_{gnd,i} \tag{2}$$

where

Symbol	Meaning	Unit
$E_{before}$	the running total of the loss diagram before this row	kWh/m²
$E_{after}$	the running total after this row	kWh/m²
$E_{row}$	the row taken as a loss	kWh/m²
$\Delta t$	the length of one timestep	hours
$L_i$	the irradiance lost at timestep $i$	W/m²
$F_{sh,i}$	the shaded fraction of the module plane at timestep $i$	—
$B_i$	the direct sunlight on the plane	W/m²
$C_i$	the circumsolar part of the diffuse light on the plane	W/m²
$F_{sky}$	the share of the sky diffuse light that still reaches the modules between the rows	—
$D_i$	the sky diffuse light on the plane	W/m²
$N_{rows}$	the number of rows	—
$G_{gnd,i}$	the ground-reflected light on the plane	W/m²

Reading the number

A loss, negative. Rows at a ground cover ratio of 0.5 lose a few percent of the plane irradiance. A higher ground cover ratio and a steeper tilt raise it. A single row, or a rooftop array without rows in front of it, loses almost nothing.

References

1. Appelbaum & Bany 1979, Shadow effect of adjacent solar collectors in large scale systems, Solar Energy 23(6) 497–507

API

loss.near_shading

Symbols follow the symbol registry.