The objective of this Task was the assessment of performances and relevance of combined systems using solar thermal and heat pumps, to provide common definition of performances of such systems and to contribute to successful market penetration of these new systems.

Other objectives were needed to reach the main one where international collaboration was definitively needed to make it possible within a 4 years framework, mainly:

  • Defining performance figures of a combined solar and heat pump solution
  • Defining assessment and test methods of such systems
  • Analysing monitored data on such systems
  • Developping component models or integrating existing ones into a system model
  • Simulating various systems under common conditions
  • Providing guidelines of good practice to the market and stakeholder
  • Providing authorities with relevant information on the interest of such systems.
  • Staying close to the market and bringing independent information and knowledge to the actors on this market along the duration of the Task.

The scope of the Task considered solar thermal systems in combination with heat pumps, applied for the supply of domestic hot water and heating in family houses.

Project manager and participating countries

Finland, Germany, Switzerland (Operating Agent) and UK,

and from SHC: Austria, Belgium, Canada, Denmark, France, Germany, Italy, Spain, Sweden, Switzerland and the United States.


The Annex was structured into the following tasks:

Task A Solutions and generic systems – Collection of information on monitored
projects and about 20 monitored installations, which will be evaluated. A map of
possible system configurations has been sketched and a new way to describe system
configurations has been proposed, so that different types of installations can be
more easily understood.
Task B Performance assessment – Discussions of a common seasonal performance
factor definition that would embrace both solar and heat pump performance. This
could be the basis for an international standard definition. Five technical laboratories
are committed within the Annex to define a common testing procedure for a system
combining solar collectors and a heat pump, typically in the range of 5-10 kW and
4-20 m2 of collectors for a single-family house.

Task C Modelling and simulation – Dealing with simulation tools and methods.
Initially, existing models for components of a system were recognised.
There is a need for validation of a solar collector model, including condensation and
ice formation on the absorber surface, often needed when solar collectors are used
as the heat exchanger with air for a heat pump. Transient heat pump models for
both air and ground sources are also needed. A reference case has been discussed,
and resulted in an extension with TRNSYS simulations and comparisons of the welldocumented
case of SHC Task 32.

Task D Dissemination and market support – Preparation of the newsletters to be
issued every year, the final handbook of the Annex, the website and the Annex logo.

Publication and result

The deliverables of the Annex were:

  • A survey of the market in 2010 was responded to by more than 80 companies.
  • Four generic categories of SHP systems have been proposed and used throughout the Annex period, and taken over by several other teams in research projects.
  • An energy flow chart solution was developed and used by all 32 Annex projects.
  • Definitions of all performance indicators (from COP to SPF+) are now available and form a basis for a future EU standard.
  • A simulation framework was developed from previous IEA work and proved to be a great tool for comparing SHP systems.
  • Laboratory testing procedures for any SHP system have been developed and used and described.
  • 32 systems in the field were monitored by several teams, and 20 have been reported with a common reporting format.
  • Not surprisingly, a high variance of SPFs was observed and the reasons why explained. The management of the store is one of the important ones, together with the overall control strategy and the temperatures of heat distribution systems.
  • Validated models are now available for many SHP configurations.
  • A comparison of different configurations with the same framework was produced and shows what solar heating can contribute (or not) to heat pump systems.
  • The final report from the project, in the form of a handbook, is of high scientific and technical quality.
  • An economic analysis model to enable systems to be compared has been developed, and will be included in the handbook as Chapter 8. 
  • S + HP systems are now considered as “standard technologies”, although there is still some work to be done to arrive at optimum high performing solutions.
  • All categories of systems can deliver SPFs of 5.0 or more if solar energy is also used, provided that careful designs and control strategies are applied.


IEA SHC Task 44

Reports are available at Annex 38 Publications