A major contributor to a building’s energy consumption are windows. They represent the most vulnerable part of the building skin for radiator heat loss and are also responsible for elevated room temperatures in summer due to solar heat transmission. Even though energy-efficient glazing can have a big impact on a building’s energy consumption, it is either optimized to reduce radiator heat loss or to prevent solar heat transmission. Since in intermediate climates both types of energy loss are equally important, we develop within project SUNOVATE a new type of energy-efficient smart window, that autonomously changes its solar heat blocking properties at a pre-defined temperature. Hereby the new technology enables the use of solar heat to heat up a building in winter, which in combination with reduced radiator heat loss reduces heating demand. Simultaneously, the technology enables the blocking of solar heat from entering a building in summer, which keeps the room temperature low and reduces cooling demand.