Solar XXI in Lisbon
nZEB Example

Masonry bricks 22 cm thick wall, exterior insulation of 6 cm of expanded polystyrene (ETICS), U=0.45 W/(m K).
Roof slab with exterior insulation of 10 cm (5 cm expanded polystyrene + 5 cm extruded polystyrene), U=0.26 W/(m K).
Double glazed transparent windows with aluminium frame with thermal break, U=3.5 W/(m K).
Increasing the use of direct solar heat gains during heating season: South orientated is covered by windows and PV modules by equivalent proportions. This large glazing area is about 46% of the south façade and 12% of building conditioned floor area. The large glazing area also increases natural light.
Thermal Building Integrated Photovoltaic (BIPV-T) system integrating south building façade is also contributing for the improvement of the indoor climate during heating season in the day time hours, when the heat released in the process of converting solar radiation into power is successfully recovered.
Venetian blinds adjustable by the users were placed outside the glazing to limit direct solar gains in the cooling season.
Ground cooling system provides incoming pre-cooled air into the building using the earth as a cooling source. The system consists of 32 tubes with 30 cm diameter, buried at 4.5 m depth. The ground temperature varies from 13 to 19°C throughout the year, so it represents an excellent cooling source during the summer season.
Natural ventilation is provided due to crosswind and stack effect via openings in the façade and roof level. The façade openings together with adjustable vents on all office room doors provide the cross ventilation, allowing the air to flow from inside to outside and vice versa. In the building’s central hall there is a skylight, which allows for natural ventilation by stack effect (night cooling).
The building lighting system is based on LEDs and presence sensors.
Renewable Energy systems integrated:
▪ CPC Thermal Solar Collectors for indoor heating, area 16m2, 11MWh/year, installed on the roof.
▪ BIPV-T (Façade): 76 PV multicrystalline silicon modules, area 96m2, Installed Peak power 12kW, Productivity 1004kWh/kW.
▪ PV installed on the SolarXXI car parking roof: 100 PV amorphous silicon, area 95m2, Installed Peak power 6kW, Productivity 1401 kWh/kW.
▪ Power Monitoring System integrated, monitoring all spaces in terms of indoor comfort and all buildings energy consumption and generation.
▪ Building Operation Ecostruxure integrated, permits a smart management of the energy consumption.

Building owner


Building type
Project type
Year of construction / major renovation

Construction: 2006
Major renovation: N/A

Total floor area
1500 m²
Construction U-value
nZEB Parameters

The energy nZEB performance of SolarXXI can be considered as a reference year:
▪ Electric consumption: 22 kWh/m2.year
▪ Renewable electricity: 32kWh/m2.year taking into account all 3 PV systems.


The energy nZEB performance of SolarXXI can differ from year to year, especially in regards to the contribution of renewable energy. The data presented are based on monitoring data.

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