The main activities in Task 55 are grouped in the following Subtasks.

Subtask A: Network Analyses and Integration

(Lead AIT, Austria)

Subtask A focuses on the operation of district heating networks and the integration of solar thermal technologies. It analyses DHC network supply strategies, including: transition strategies from no to 100% solar thermal supply, hydraulics within networks and at transmission stations, heat demand management, storage charging/discharging, control strategies and energy price scenarios as well as potentials and barriers for the integration of solar thermal systems. A main focus of the analyses will further be on return temperatures and their reduction within the district heating network. Technical characteristics of existing, newly integrated and planned SDH and SDC systems of > 0,5MWth up to GWth will be assessed (typical network temperatures, summer/winter load ratio, pressure level, collector fields, seasonal storages, hybrid-technology implementation, hydraulics, control strategies).

Activities in this subtask will be performed in collaboration with other SHC Tasks and Implementing Agreements such as the DHC Implementing Agreement. The IEA DHC will give expert input in Subtask A and reviews publications and major outputs. Also interactions with Subtask B, C and D are given.


  • A-D1.  Assessment of technical requirements of existing and newly integrated large scale SDH/SDC
  • A-D2.  Economic analyses of overall DHC network supply strategies, transition strategies, heat demand and energy price scenarios
  • A-D3.  Analyses of DHC network hydraulics and evaluation of hybrid technologies and possible supply points for large ST plants
  • A-D4.  Overall DHC network control strategies and other measures for increasing solar thermal fractions

Subtask B: Components Testing, System Monitoring and Quality Assurance

(Lead SUNRAIN, China)

Subtask B focuses on system components. It targets tests, performance guarantees, monitoring, and control strategies of main solar thermal system elements. Methods for hybrid elements in in-situ collector tests at existing installations (6 different collector types approx. 2.500m²) as well as methods for simple thermal power and energy performance proofs will be elaborated. Of interest are also validated performance guarantees for key components such as collectors, storages, piping, heat exchangers, etc. The subtask will also provide data on automated monitoring and failure detection software for key components. In a next step, control strategies and self-learning controls will be developed and described. Finally, results from IEA SHC Task 43 on solar ratings and certification procedures will be implemented in Subtask B as well.


  • B-D1.  In-situ collector tests
  • B-D2.  Further development of validated performance guarantees for key components
  • B-D3.  Automated monitoring, failure detection of key components, control strategies and self-learning controls of key components

Subtask C: Design of the Solar Thermal System and of Hybrid Components

(Lead PlanEnergi, Denmark)

Subtask C focuses on the design of solar thermal systems and the integration of hybrid technologies. The subtask elaborates on characteristics of collector array units, large and seasonal storages, hydraulics, and heat pumps within system operations. Large scale collector fields will be simulated and compared to the measurements in Subtask B. If needed, the simulation tool will be corrected. Parameters of seasonal storages will be calculated and guidelines for the design and construction of different storage types elaborated. Hydraulics within systems are sensitive to a variety of parameters. These parameters will be optimized. Piping within large systems will be investigated as well and options for a modular conception and construction for the system.


  • C-D1.  Simulation and design of collector array units within large systems
  • C-D2.  Assessment and design of large scale seasonal storages
  • C-D3.  Optimized hydraulics and piping in large solar systems
  • C-D4.  Modular conception and construction

Subtask D: Promotion and dissemination of SDH/SDC and hybrid technologies in new markets

(Lead Solites, Germany)

Subtask D elaborates economic aspects and the promotion of results from SHC Task 55. Large scale solar thermal systems require sophisticated financing models due to high initial investment costs. Different business models are already in place and facilitate the realization of large systems. The subtask will assist practitioners, architects, system designers and district heating providers in their efforts for the integration of DHC applications. Stakeholders face several economic challenges and risks and will benefit at large from the deliverables of this Subtask. A database will collect information on different system types already in place and their global distribution. Country regulations such as licenses and permissions are also central for business cases of different markets. Moreover, the subtask will assist the other subtasks in the promotion and dissemination of project results, the organization and execution of events, workshops, and trainings.  


  • D-D1.  Business Models of Solar Thermal and Hybrid Technologies
  • D-D2.  Beneficial and challenging environments for SDH/SDC systems including hybrid technologies in new and existing markets
  • D-D3.  Identification and preparation of Best Practise Examples
  • D-D4.  Evaluation of divers global market development and country reports
  • D-D5.  Dissemination of expertise through education and training