ᐅ Underfloor heating with an air-to-water heat pump. House gets too warm when the sun is shining.

Hello everyone,

I have a general question.

We moved into our new build four months ago. The living area on the ground floor has three large floor-to-ceiling windows facing south. We have underfloor heating and an air-to-water heat pump.
It provides a really comfortable temperature inside the house, but we have a problem – whenever the sun is shining in winter, even if it’s -2°C (28°F) outside, the temperature suddenly rises to 24°C (75°F) in the living room. It gets uncomfortably warm in here, and the underfloor heating can’t be turned down quickly.
Should we assume that the large floor-to-ceiling windows are responsible for the heat gain? A photo of the south-facing side of the house is attached.
What would you do – always lower all the blinds as soon as sunlight is forecast? That seems quite annoying...
We have motorized blinds controlled by Somfy. Would you consider buying a sensor that automatically lowers the blinds at a certain temperature?

Thanks in advance for your replies.