Tired of your heating system fighting against free solar heat coming through your windows? I’ve created a blueprint that automatically reduces your thermostat temperature based on predicted solar heat gain through glazed surfaces.
What It Does
This automation intelligently adjusts your thermostat temperature downward by 0-2°C based on how much solar energy will enter your room through windows. It uses the Forecast.Solar integration to predict solar heat gain and proactively reduces heating to avoid overheating while saving energy.
The automation evaluates solar forecasts hourly and applies graduated temperature reductions:
- High solar gain: -2.0°C reduction
- Medium solar gain: -1.0°C reduction
- Low solar gain: -0.5°C reduction
- Negligible solar: No adjustment
Key Features
Predictive behavior: Switches from today’s to tomorrow’s forecast at a configurable hour (useful for slow-response systems like underfloor heating)
Smooth transitions: Only adjusts when needed (≥0.5°C change) to avoid constant thermostat fiddling
Customizable thresholds: Configure sensitivity based on your specific window area and glass properties
Multi-window support: Can combine multiple window orientations using template sensors
Prerequisites
- Forecast.Solar Integration (available in HACS)
- An
input_numberhelper (min: -5, max: 0, step: 0.5) to store the automation state
Setup
The blueprint requires you to configure Forecast.Solar for your windows:
- Declination: 90° for vertical windows
- Azimuth: Your window orientation (N=0°, E=90°, S=180°, W=270°)
- Watt peak power: Calculate as:
window_area_m² × glass_g_value × 1000- Example: 10m² of triple glazing (g=0.55) = 5,500 Wp
Then configure the three threshold values based on your room’s maximum daily solar gain potential.
Use Cases
This blueprint is perfect for:
- Rooms with large south/west-facing windows that get significant solar heat
- Underfloor heating systems (use earlier tomorrow-switch time)
- Reducing energy consumption while maintaining comfort
- Preventing afternoon overheating in sunny rooms
Import the Blueprint
Or copy the YAML directly from the source code.
Example Configuration
For a living room with 10m² of triple-glazed windows (g=0.55):
- Max daily potential: 5.5 kWp × 8 hours × 0.001 = ~44 kWh (theoretical)
- Practical max (accounting for weather): ~25 kWh
- High threshold: 20 kWh (80%)
- Medium threshold: 12 kWh (48%)
- Low threshold: 6 kWh (24%)
- Tomorrow switch: 16:00 (for standard radiators) or 14:00 (for underfloor)
Tips & Tricks
If you have windows facing multiple directions, create separate Forecast.Solar sensors for each orientation and combine them with a template sensor.
Start conservative with thresholds and adjust based on observed comfort levels over a few weeks.
For underfloor heating systems with 4-6 hour response times, set the tomorrow switch time earlier (14-16h).
