Dr. Andreas Bohren

Substituting fossil fuels with renewable energies will not be feasible without a notable expansion of seasonal energy storage. Seasonal thermal energy storages (STES) are expected to contribute significantly to this goal. The project SwissSTES systematically analyses STES potentials such as available and unused cavities, geothermal probe or pit storages and it develops novel STES technologies together with a systemic action and implementation plan for Switzerland. The highly interdisciplinary consortium brings together all relevant stakeholders from science, industry and society to promote the spread of STES in Switzerland. In this context, technical innovations but also social, legal and economic aspects play an important role. Furthermore, regional case studies pave the way for future pilot and demonstration projects throughout Switzerland.

What options are there for implementing well-integrated solar systems that are also suitable for listed buildings (special architecture or historic interest)? What technologies are available for this, what do they cost compared to "ordinary" solar energy systems, and do they deliver the same yield? These questions were investigated by SPF on behalf of the Office for Energy and Transport of the Canton of Graubünden. As a result, a catalog of available solar technologies was published, which is also made available online here (in German).

Thermal stratification is an important parameter in the energy evaluation of storage tanks. The electrical energy consumption in a heat pump system can be up to 40 % lower with a well stratified storage tank than with a poorly stratified thermal energy storage.

In the StorEx project, SPF introduced stratification efficiency as a key performance indicator and at the same time a method for measuring it, which has already become established in Switzerland.

An alternative to this is the measurement of the storage tank according to the EN 12977-3 standard with a subsequent simulation with a calibrated model.

In order for the «thermal stratification» to become a generally, or internationally, recognized characteristic value for thermal storage tanks with a clearly defined measurement procedure, it is important that these two procedures are investigated in a comparative measurement. This is the aim of this project.

Numerous studies predict a strong increase in the cooling demand of buildings. However, for both economic and ecological reasons, electricity consumption must not increase in proportion to the cooling demand. New, efficient cooling solutions are therefore required.

Together with the University of Applied Sciences of Northwestern Switzerland (FHNW) and the Lucerne University of Applied Sciences and Arts (HSLU), we are working on the development of the CoolShift cooling concept. In this concept, waste heat is not released during the day, but with a time delay at night into a much cooler environment. The heat generated during the day is temporarily stored in the thermally activated building mass or in heat storage tanks. The heat is released via PVT collectors or unglazed solar absorbers made of metal or plastic, which are also used to harvest solar energy at daytime.

Experimental characterisation of components and mathematical modelling of components and overall systems are used to create a basis for dimensioning CoolShift cooling systems.

In the project HiPer-PVT we have developed a glazed (covered) PVT collector with a high electrical and a high thermal efficiency. Thanks to an overheating protection mechanism becoming effective at approximately 100 °C, this collector can be easily integrated into a thermal system. The concept of the overheating protection is that once the absorber reaches a predefined maximum temperature, it is brought into contact with the cover glass via a thermally activated lifting mechanism. This increases the heat losses and limits the stagnation temperature.

The are no universal guidelines or thresholds for reflected sunlight in the public space. In this project, physical parameters for an objective description and quantification of a «discomfort glare» from reflected sunlight are elaborated. Furthermore, the scattered reflection (bidirectional reflectance distribution function, BRDF) of several glass types and other materials of the building envelope is measured in order to generate an extensive database. This database can help to evaluate the «discomfort glare» from solar installations and other surfaces of the building envelope already in the planning phase. New materials or surfaces can be compared with standard materials of the database in order to assess their effect concerning glare from reflected sunlight.