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Country & City

  • Germany
  • Stuttgart

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The aim of the SCHOOL OF THE FUTURE project was to design, demonstrate, evaluate and communicate shining examples of how to achieve the high-performance building of the future with a focus on school buildings. One of the project’s demonstration sites was the Solitude-Gymnasium, which is located in the north-west of Stuttgart, the capital of the federal state Baden-Württemberg (south-western Germany).

The secondary school consists of five buildings with a mix of central and side corridors. Overall, a gross floor area of 9918 m² (heated area: 8924 m²) has been refurbished in the project. The school has around 710 students and 60 employees. The existing buildings have been constructed during different phases between the 1960s and the early 1990s.

Before the renovation, the school consisted of several solid constructions with high-energy consumption – the main building, the science building, the big pavilion and the gym. Some interventions to address this had already taken place prior to this project: the boilers and the south-facing windows of the big pavilion were replaced, and the roofs of the main building and the gym were refurbished.



The total energy demand for the Solitude-Gymnasium in Stuttgart amounted to 175 kWh/m²/yr for monitoring consumption before the refurbishment. The monitored values following the end of the project were 125 kWh/m²/yr, which was higher than expected. The main reason behind this is the use of the gymnasium as a shelter for refugees, which led to an increase in the energy consumption that could not have been foreseen by the project. Excluding the gym, the monitored energy consumption after the refurbishment is 77 kWh/m²/yr.

The reduction in energy consumption following the refurbishment and use of energy sources with lower primary energy factors led to an annual reduction of 605 MWh in the final use of energy and 935 MWh in the use of primary energy. This represents more than 50 % of the use of primary energy before the refurbishment. Accordingly, CO2 emissions are down by 55 tonnes, which is a reduction of 60 % from before the refurbishment.

Financial & Economic

Financial & Economic
Encountered barriers

Several solar renewable energy installations were planned for the gymnasium. Due to shading, space limitation or structural restraints, only one photovoltaic installation was realised.

The photovoltaic system consisting of 30 modules and a total power of 7.65 kWp was installed on the main building. The modules are oriented east-west with a tilt-angle of 10 degrees.





The gym has been used as refugee accommodation so the usage profile of the predicted energy savings for the gym could not be achieved.


Initially solar thermal installations were planned on the roof of the gym. During the planning phase for the heating system, the economic analysis showed that the solar thermal collectors would decrease the full load hours of the micro CHP installation. Due to the counter-productive effects on the efficient work of the micro CHP, the solar thermal plants were not installed at the site.


The heating system could not be changed completely because of the existing gas boilers dating from 2004, but the additional installation of a CHP unit seemed possible and economically feasible. Although there are examples of refurbishments available, every retrofit brings new challenges and many results from previous projects cannot be used.


Space limitations or structural restraints can prevent the implementation of efficiency measures in the refurbishment of buildings. In this case it was the installation of the initially planned additional photovoltaic panels and the heat recovery in the gym. 


On the south facade of the gym a photovoltaic plant had been planned with a total power of 24 kWp with 164 m². The project was tendered in 2014 but the outcomes of the tender were way off budget and the profitability was not given. In the end the photovoltaic system could not be realised.


The refurbishment measures implemented included:

Energy efficiency in buildings

  • Retrofitting the building envelope
    • Intensive retrofitting plan for the building envelope: walls, roofs, and windows (triple-glazed)
  • Building integrated renewable energy sources
    • Photovoltaics
  • Building services (HVAC and lighting)
    • Mechanical ventilation system with heat recovery

Energy systems integration

  • Cogeneration (CHP)
  • Building energy management system
    • Installation of sensors to monitor daylight, temperature, humidity and CO2 as well as meters to measure the operating hours of electrical lighting

The investment cost for the interventions was EUR 1 340/m², which makes a total of over EUR 13 m. Due to this high investment cost, the payback period according to the design data exceeds 30 years.

SRT data