Automatic solar shading is one of the highest-ROI KNX automations in European residential construction. Preventing summer overheating reduces cooling load by 30–40% while maintaining the view during non-critical sun angles. Done correctly — with sun position tracking, wind safety, and rain protection — it runs completely without occupant interaction and outperforms any manual blind management.

Sensor comparison

Three sensors dominate the EU KNX market. The **Elsner P04-KNX** (combined sun/wind/rain/temperature, ~€280) is a single bus-powered device covering all four measurement channels in one flush-mounted outdoor unit. It measures sun intensity on three axes (south, east, west), wind speed via ultrasonic anemometer, rain via optical sensor, and ambient temperature. One cable run, one KNX device address. The **MDT Wetterstation WS-HEL01.01** (three-axis sun, Beaufort wind scale, ~€320) is similar but lacks rain detection — pair it with a separate MDT rain sensor (SCI-SR55.01). The **Theben LUNA 120 KNX** (~€120) measures only dawn/dusk illuminance — no wind, no rain, no sun direction. It's suitable only for simple on/off shading based on overall brightness, not sun-tracking.

Sun tracking logic

Sun position (azimuth and elevation) changes throughout the day and across seasons. A blind on a south-facing facade should be lowered only when the sun's azimuth is between approximately 120° and 240° (sun is in front of the facade) and elevation is above 15° (sun is high enough to cause glare or heat load). In ETS6: configure the MDT sun logic block or use a Home Assistant solar position helper (available natively in HA). Map facade angle per blind group — a villa with south, south-east and south-west exposures needs three separate sun-angle zones. The Elsner P04 sends KNX sun intensity per axis directly — no azimuth calculation needed; if the south axis exceeds the configured lux threshold (typically 30,000–50,000 lux), the south facade blinds activate.

Wind safety

Textile blinds and roller shutters are damaged by wind above 45–60 km/h depending on the product (always check the manufacturer's rated wind class). Configure the wind speed threshold as a KNX parameter: when any anemometer reading exceeds the threshold, all blinds retract immediately and are blocked from lowering for 10 minutes after wind drops below the threshold. The 10-minute hold prevents rapid cycling during gusty conditions. In ETS: wind alarm telegram (1 bit, TRUE = wind alarm) → binary object in MDT blind actuator → "go to upper position + block". Priority 2 (wind safety) must override Priority 3 (sun automation) and Priority 4 (manual) in the actuator's priority chain.

Rain detection

Rain on a fabric roller blind causes staining and mould if the blind is rolled up wet. Rain alarm (from Elsner P04 optical sensor or MDT separate rain sensor) triggers: all fabric blinds retract, manual override is blocked for 30 minutes after rain detection clears. Venetian blinds (aluminium slats) can remain in position during rain — rain protection is primarily for textile products. Configure rain alarm as Priority 2 alongside wind, with a 30-minute release delay.

Slat angle optimisation

Venetian blind actuators (Gira 2060 00, MDT JAL-0810.02) control both the position (DPT 5.001, 0–100%) and the slat angle (DPT 5.001, 0–100%, where 0% = fully open, 100% = fully closed). For optimum sun shading: lower the blind fully (position = 100%) but set slat angle to a partially open position (50–70%) that blocks direct sunlight but maintains diffuse daylight and partial view. The optimal slat angle for a given sun elevation is: slat angle = 90° − (sun elevation + facade offset angle). ETS6 logic blocks or a HA template sensor can calculate this dynamically. The actuator sends physical stop feedback (DPT 1.001) when the blind reaches the end position — always wire this back to a status GA to confirm position.

Conflict resolution

The priority chain in KNX blind actuators (MDT, Gira, Schneider) handles conflicts: Priority 1 = safety (alarm). Priority 2 = wind/rain protection. Priority 3 = sun automation. Priority 4 = manual operation. Priority 5 = time/scene. Manual override (Priority 4) wins over sun automation (Priority 3) — but only for a configurable duration. Set a 2-hour manual override timeout: after 2 hours without further manual input, automation resumes. This prevents the common problem of a user pressing the blind switch in the morning and the automation staying blocked all day.

Our recommendation

The Elsner P04-KNX is the most complete single-sensor solution for EU residential projects. It covers sun intensity (three axes), wind speed (ultrasonic, more accurate than cup anemometers), rain detection, and ambient temperature in one bus-powered KNX device. Installation requires one outdoor cable run and one KNX address — the most cost-effective weatherstation option for projects up to 20 blind groups.