Collectors

The use of solar thermal applications to support district heating networks and industrial processes is becoming increasingly important. Higher operating temperatures, larger collector fields, and highly varied load profiles require tailored solutions for components and systems. The group focuses on developing and testing new concepts as well as analyzing and optimizing the hydraulic behavior of collector fields. A central topic is the stagnation behavior of solar thermal systems and its impact on their long-term operational reliability and economic efficiency. Evaporation of the heat transfer fluid in the collectors can cause damage to temperature-sensitive components in the collector circuit and lead to additional costs. The group has many years of experience in analyzing stagnation states and developing strategies to minimize related risks. A key area of focus is the development of novel collectors that significantly reduce temperatures in the solar loop and enable inherently safe, steam-free operation. Two promising and ongoing concepts in this regard are the control of two-phase heat transport in gravity-driven heat pipes and the use of solar absorbers with temperature-dependent optical properties (thermochromic coatings).

Integrating thermal and hybrid photovoltaic-thermal (PVT) collectors into the building envelope enables architecturally attractive solutions and cost savings through synergy effects. This is a key requirement for greater acceptance and successful implementation of solar technologies in construction practice. Integration into buildings, or the solar activation of the building envelope, demands innovative designs: In addition to system performance, construction, building physics, and design aspects must also be considered. In cooperation with the construction industry, architectural and planning offices, we develop solutions for the façades of residential and non-residential buildings, as well as concepts for transforming roofs into large-area solar collectors. Systemically, the focus is on using the building envelope as a heat source for heat pump systems. Current topics such as serial construction and renovation, as well as the Building Information Modeling (BIM) methodology, are also addressed in the development process.

Hybrid photovoltaic-thermal (PVT) systems can simultaneously generate heat and electricity from solar radiation, achieving very high area-specific efficiency. Although this principle has existed for nearly 50 years, it is currently experiencing a revival due to the rapid market growth of heat pumps and photovoltaics. PVT systems can contribute significantly to CO₂ reduction in various applications. The group focuses on developing uncovered modules and systems for efficient integration into heat pump-based energy supply systems. We benefit from the expertise of other working groups in the Solar Energy Systems and Photovoltaics departments. Another focus lies in the development of practical tools for designing and evaluating these systems.

In most cases, solar thermal energy alone cannot fully meet the heat demand of buildings, neighborhoods, or industrial processes. However, it can be very effectively combined with all fossil and renewable heat technologies, offering significant untapped potential for conserving resources and reducing greenhouse gas emissions. As energy solutions become increasingly multivalent, the integration of solar thermal systems plays a crucial role. The group aims to minimize system complexity and increase system efficiency through system-oriented development of components, interconnections, and control strategies. To achieve this, hardware-in-the-loop methods are employed, and real systems or their components are simulated and analyzed using digital twins.