Objects and shading model
Radiaris calculates shading with real 3D geometry and translates it into electrical loss according to how the modules are connected. This is one of the points where the difference between a quick calculation and a careful one is most noticeable.
Sources of shade
| Source | How it is defined |
|---|---|
| Nearby objects | Chimneys, machines/air conditioning, skylights and rooftop structures, trees, poles and antennas, walls and neighbouring buildings |
| Neighbouring planes | A higher plane shades another (building volume, dormer, upper roof section). It is calculated from the eaves height |
| Between rows | Modules raised on a structure that shade each other |
| Far horizon | Azimuth–elevation profile (see Horizon) |
Objects
Each object is a 3D solid: a polygon or circle with a height. It can rest on the roof (the height is measured from the plane surface: chimneys, skylights, machines) or on the ground (neighbouring buildings, trees, poles, walls). Default heights: chimney 1.2 m, machine 1.0 m, skylight 0.6 m, building 6 m, tree 8 m, pole 6 m, wall 3 m.
Trees are treated as opaque solids (crown cylinder): this is conservative. For each Sun position, the shadow of each face is projected onto the module plane and the covered fraction of each cell is calculated.
Electrical shading model
Partial shading does not reduce production in proportion to the covered area: the current of a chain of cells is limited by the worst-lit one, and bypass diodes bypass substrings. Radiaris offers three variants:
| Model | Criterion |
|---|---|
| Realistic (default) | Generation drops according to the most affected cell in each substring, with bypass diodes: a substring is bypassed if it pays off |
| Optimistic | Generation from the direct component drops in the same proportion as the shaded fraction of the module |
| Pessimistic | If there is shade on the module, its generation from the direct component is 0 (in half-cell modules, only the shaded half) |
It affects the direct and circumsolar components; the isotropic diffuse is reduced by the sky view blocked by the row in front.
Module parameters involved:
- Cell type: half-cell (HC) or full-cell (FC). It is inferred from the name and technology of the module, but you can force it.
- Bypass diodes per module: 3 by default.
- Module orientation: long side in the direction of the tilt (portrait) or across it (landscape).
Parallel strings with different shading
An MPPT can only impose one voltage: if one string is shaded and another is not, the maximum of the set is lower than the sum of the individual maxima. Radiaris calculates this correction with the real I-V curves of the strings, in the hours when they receive different shading.
I-V curves
You can see the I-V curve of a string at a specific moment, with and without shade: it is useful to check the effect and shows the local maxima when there are any. The annual simulation uses a fast model (one loss factor per string) validated against this full circuit.
Optimizers
With one optimizer per module, each module works at its maximum power point, so the shading of one does not limit the others in its string. See Optimizers.
Wiring between rows
With raised modules you can choose how they are grouped into strings:
- Each string runs along one row: the shade on one row only affects its own strings.
- Each string crosses the rows: it has modules from every row; the shaded ones limit the ones in series with them.
How to interpret the loss
The shading loss appears in the loss waterfall. If it is high, try: moving modules to another area, subdividing strings, using optimizers or increasing the row spacing.