Each facade fin is a semi-transparent photovoltaic glass panel. Two physical effects fight each other as the glass gets clearer:
P = G0·sin(elev) · cosθ · η_cell·(1 − VLT) · A
θ = angle between sun ray and fin normal
cosθ = cos(elev + tilt) (both fin and sun rotate in the same vertical plane)
VLT = fraction of visible light the glass lets through
- Fin tilt — rotates the panel normal about a horizontal axis, changing the incidence angle θ. Because both the sun's ray and the fin normal live in the same vertical plane, the dot product collapses to the clean identity cosθ = cos(elev + tilt): a fin tilted to exactly cancel the sun's elevation (tilt = 90° − elev is the closest this slider range allows) faces the sun most directly.
- Sun elevation — models the time-of-day sun path. Available irradiance is approximated as G0·sin(elevation), so a low sun near the horizon delivers far less power even at a favourable incidence angle.
- VLT (visible light transmittance) — the fraction of light that passes straight through the BIPV glass to light the room instead of being absorbed by the embedded cells. Raising VLT directly lowers electrical efficiency η_eff = η_cell·(1 − VLT): the panel cannot be maximally transparent and maximally opaque-absorbing at the same time. The trade-off chart on the canvas plots both curves against VLT at your current tilt/elevation so you can see the crossing directly.
- Tint hue — a cosmetic dichroic-coating colour (real BIPV glass ships in bronze, blue, gold and graphite); it does not change the physics here, only the building's appearance, which is exactly the point of the trade-off.
Drag the sun icon in the cross-section panel to change elevation directly, or tick "Animate day cycle" to sweep it automatically. The two presets show the extremes: steep, dark, sun-facing fins maximise generation; near-flat, highly transparent fins maximise how much daylight reaches the interior.