This beautiful 5,543-square-foot home on the coast of Kavarna, Bulgaria has been designed to perfectly match the angle of the summer equinox sun.

Created by Ignatov Architects, the compact, energy-efficient design makes the home 90% more energy efficient than a similar home without upgrades, which also gives it Passive House status.

The home is built right into the hillside, allowing it to work with its natural surroundings. A green roof provides natural insulation and frees up lawn space, minimizing energy loss and maintaining a comfortable indoor temperature.

The wall of glass on the front wall of the home is inverted, keeping sun from entering the home in the middle of summer. In the winter, the low angle of the sun hits the patio swimming pool and reflects into the house to provide natural lighting. A roof oculus allows a single ray of light to shine into the home, acting as an annual calendar as it shines in different spots according to the season.

The home also has a wastewater treatment unit, natural ventilation and recovery system, and rooftop solar panels. Additional heat is provided from an underground heat pump or solar hot water panels installed for the pool.