The following activities will be performed through the four Subtasks, as categorised in the Work Plan:

Subtask A: State-of-the-art and operating environments in different regions

With 57% of the total solar heating capacity in operation globally (link), thermosyphon systems top the list of the world’s most used solar thermal technologies. Due to their mass production in China, thermosyphons are likely to maintain their dominance in the solar hot water market throughout the 2020s.  At the same time, photovoltaic solar panels are increasingly being utilised for water heating both in off-grid environments (e.g., PV2Heat systems) and in grid-connected systems where there is an economic incentive for self-consumption of the electricity (e.g., PV diverters).    

Another general trend that will be investigated is the move to ‘smart’ and advanced systems — a trend where the hot water market is a relative laggard as compared to other building energy systems. This subtask will focus on the state-of-the-art of the solar hot water market, regulatory frameworks, and funding schemes as well as the development trends of these two technologies in different regions around the world.

This subtask aims to get the detailed data related to solar hot water installations globally, including the operating environment, trends, best practices, current regulations, and the major technical and non-technical barriers to adoption. The findings and results of this subtask are closely interlinked with subtask B and C.  


The main objective of Subtask A is to

  • Collect the data on regional hot water load and review installed technologies, common back up fuels used and to get a broad knowledge and understanding of SHWs.
  • Identify the best solar technologies for SHWs in different regions and their barriers to adoption (technological, economic, social).
  • Review system configurations for best practice
    • Thermosyphon
    • Smart tanks
    • PV hot water (PV2Heat & PV diverters)
    • Other emerging and ancillary components for the above
  • Identify the technical and economic potential for each technology/ system design in relevant regions around the globe

Specific objectives of Subtask A are to

  • Prepare a wholistic literature review of available solar technologies used for solar hot water systems, with focus on the identified dominant technologies of thermosyphon and PV2Heat. 
  • Get market feedback/needs on versatile, best practice, SHWs designs
  • Document possible SHWs configurations for best practice in each region
  • Evaluate the new systems (including smart components/ control) economic potential and benefits for end users and countries emission target plans.


  1. 1. Data collection, barriers, and solutions for widespread adoption

Collection of SHWs installed in each region and their types (thermal or PV collectors devoted to water heating). The first part of this activity aims to collect and collate data to understand each region’s needs and boundaries and further analysis for what can be done to improve the current systems (from technical, economic, and environmental perspectives). The second part focuses on a detailed understanding of the current installed systems drawbacks and technical/non-technical barriers to investigate possible solutions to increase solar technologies adoption in future HWs and provides a collection of success stories and beneficial market conditions for SHWs.

  1. 2. Thermosyphon systems: System configurations for relevant regions

Compare different designs for thermosyphon systems (direct, indirect, open, closed, heat pipes) for their potential in different regions. Identify techno-economical peak performers for region specific boundary conditions like water quality, dust, sea water atmosphere, frost conditions etc., reducing CAPEX and OPEX (little to no maintenance) and increasing lifetime.

      A. 3. PV systems: Components for electrical to thermal energy conversion

Compare the various components associated with PV for solar heating from the performance and capital cost perspectives in each region. Although heat pumps can get a high COP and payback in a short period of time (relative to the system lifetime), PV resistance heating is more popular in Africa due to the low capital cost. This may include a review of PVT systems.

Subtask B: Thermosyphon hot water systems

Since solar thermosyphon systems represent the majority of installed SHW systems, this subtask focuses on how these systems may be improved going forward through better design and management, as well as the potential for performance improvements, and durability & reliability improvements. Finally, since the key aim for solar installation is to ‘move the needle’ for GHG reductions, this subtask has also set several deliverables relating to how thermosyphon installations impact GHG with respect to overall country-specific and global emissions targets.

This subtask will have a particular focus on how thermosyphons can be modernized via new technologies, which include: temperature/flow monitoring, mechanical and passive temperature/flow control, smart tanks, IOT, and AI. All of these provide opportunities for manufactures and system designers/installers to obtain better durability, reliability, convenience and reducing the system cost and reduce the ongoing costs (conventional fuel). Another key aspect of this subtask will be to investigate durability and reliability of these systems, accounting for their relatively poor track record in GN SEC regions. Finally, the subtask will also investigate the potential of new technologies to save energy and reduce GHG emission as compared to conventional systems.


The main objective of Subtask B is to

  • Evaluate thermosyphon systems in terms of their technical and economic potential to ‘move the needle’ on renewable energy targets.
  • The potential for improving performance of thermosyphons:
    • Convenience
    • Durability and reliability
    • Energy saving & carbon reduction calculation and testing
  • Investigate emerging installation requirements (such as aesthetics)

Specific technical objectives of Subtask B include:

  • Design SHW system using various thermal options (i.e., SHWs-without Aux heater, with Aux heater, and with smart component)
  • Components comparative analysis with conventional systems.


B.1. Report of thermosyphon system potential

Investigation of the status of conventional thermosyphon systems and what ‘smart’ technology (including mechanical controls) in the market. This will include a detailed categorization of the current thermosyphon systems and their functional advantages and potential for levelized cost reductions. It will also include a summary of technical specifications and requirements for advanced technologies in different regions (new systems).

B.2. Survey of failure modes and effects and suggestions

As was recommended and discussed during out Task Development Workshops and in consultation with EACREE and SACREE leaders, an important deliverable in this subtask will be a survey of the failure modes and effects.  The aim of this work will be to collate and draw conclusions from common problems that often occur in installed systems, particularly in African nation. This will be contrasted with system failure modes in other locations.   

B.3. Report on durability and reliability improving research and technical results Investigation on current durability & reliability problems faced by users, industries in different regions (especially the GN SEC regions).

A critical research item within this deliverable is to solve durability & reliability problems such as thermal shock, overheat, leak, and freezing (in evacuated tubes and flat plate systems). Therefore, this subtask will provide durability and reliability improvement suggestions (design tool or control strategies).

B.4. Report on energy-saving & GHG reduction methods along with current and future trends

Investigation on current energy-saving & GHG reduction calculation and testing methods available in different regions.

A report will be created to capture the various assumptions, calculation, and testing methods that go into GHG reductions. This report will also quantitatively analyse the energy-saving & GHG reduction performance data of typical thermosyphon systems in different regions. GHG reduction estimates will be made based on current installation and these future trends (out to 2030).

Overall, this subtask will document how the current installed systems are helping the current emission targets and how the new/emerging technologies can help accelerate these targets.


Subtask C: Solar Photovoltaic Hot Water

Objective of Subtask C

The main objective of Subtask C is to evaluate the environmental, social and economic implications of the increased deployment of solar photovoltaic diverter and PV2Heat technologies. In regions in which the technology can be demonstrated to have clear benefits, the objective will then be to promote international free trade and encourage the development of a market structure which will enable the deployment of these devices in line with the county’s Nationally Determined Contributions (NDCs). This will be done principally by:

  • Educating policy makers about benefits of solar photovoltaic diverters.
  • Harmonization of product standards (reducing trade barriers).
  • Achieving representation with buildings standards (including environmental building standards).
  • Developing calculation methods which would enable the technology to have representation in Net Zero roadmaps.

Scope of Subtask C

The focus of this Subtask will be direct heating of domestic hot water using power from solar photovoltaics (with some examples shown in Figure 1 below). Heating technologies considered will be immersion/resistive element/s and/or air source heat pump/s. The subtask will consider off-grid systems (often referred to as PV2Heat), rooftop PV diverter devices and grid-connected hot water cylinders. The focus (in relation to the standards harmonization work) will be on domestic scale systems (residential rooftop thermosiphon equivalents).

This Subtask will focus solely on domestic hot water systems for core activities and deliverables, but experts may also consider multi-purpose applications where domestic hot water may be combined with other heating applications, if they are important in their regions/operating environment. In all cases considered in this subtask, potable domestic water heating supply shall be present.

This Subtask will not consider solar power used for cooling which is being considered as part of Task 65. This Subtask will also not consider the use of hybrid solar collectors, although hybrid solar thermal systems will, in a sense, be dealt with within Subtask B. In collaboration with other TCPs/Tasks, other PV-powered hot water devices may be given consideration, including: showers, cooking, washing and district heating electric boilers.

Given the scope of the Subtask, there is anticipated to be co-operation with the PVPS, HPT, and the Smart Grids TCPs.


C.1 Expert Network(s), Expert Questionnaire / Interviews and Case Studies

STC1 will develop an expert network of stakeholders active in the technology space. This will include government officials, manufactures, academics, standards, and trade associations. This will be formalized via an expert directory located on the SHC website.

During this phase, the Subtask leaders will undertake/facilitate questionnaires, interviews and focus groups to determine the stakeholder perception of the technology (for example trade barriers, technological challenges, and deployment opportunities). 1-page case studies will be developed to showcase different use cases in each of the IEA regions (Africa, Asia Pacific, Central & South America, Eurasia, Europe, Middle East and North America).

C.2 Systematic International Literature Review + Market Review

Task participants, as a group, will undertake a systematic international literature and market review to determine the current state of the technology. This should be published in peer reviewed journal and will form the evidence for Subtasks 3a, 3b and 3c. Ideally, any gaps in knowledge identified in the literature review would be actively resolved by the Task participants and presented at the SHC conferences.

C.3a Technology / Policy Brief

Based on the results of the Expert Interviews (C1) and Systematic International Literature Review (C2), a Technology / Policy Brief for policy makers will be written and published. This should include issues around energy security, supply chain capacity, latitude effects, resource availability, and current barriers to international trade.

C.3b New ISO Solar Energy Vocabulary

Task participants will make recommendations to the ISO 180 committee to incorporate new Solar Energy Vocabulary related solar photovoltaic diverters.

C.3c Reference Models + Solar Heat Worldwide Chapter

Working closely with the Solar Heat Worldwide (SHW) publication committee, the Task participants should develop a range of standard reference models (environmental and economic) which could be used in future editions of SHW. An initial estimation of the market size should be agreed, based on the best available data, and a chapter on solar photovoltaic diverters should be written for Solar Heat Worldwide. The Task participants should also consider future projections (roadmap) for what proportion of future PV power generation could be directed towards heating domestic hot water in different regions.

C.4 Solar PV Hot Water Technology Harmonisation Strategy

Given the current evidence, the Task participants should develop and agree upon a formal ‘Solar PV Technology Harmonisation Strategy’, which should seek to harmonise international standards and certification. This Strategy should be developed in close collaboration with the ExCo members and international standards organisations.

C.5 Implementation of Solar PV Hot Water Technology Harmonisation Strategy

The final period of the Task should focus on undertaking the initial steps of the Solar PV Hot Water Technology Harmonisation Strategy. This should include the active dissemination of the Technology / Policy Brief to policy makers but may also include: consumer engagement material for civil groups and trade associations, development of regional advocates, regional events and exhibits/presentations at trade shows.


Subtask D: Training and standards

In the past, SHW systems were mainly designed using traditional solar thermal collectors (specifically thermosyphon collector). However, new technologies and smart components are promising to enhance the overall performance and decrease the system capital cost.  This urges the needs to develop new standards to add the new technologies/ configurations and revise the current standards.

This subtask will conclude the task and recommend on the future work needed afterward. 


The main objective of Subtask D is to wrap up the results of previous subtasks and recommend on what is needed to be updated on the current standards (new or revised). The specific objectives of Subtask D are:

  1. Improve and revise the current standards
  2. Propose new standards for PV SHWs
  3. Prepare training materials (workshops) about principle, system sizing and installation.


D.1. Training and status report of selected warranty and certification networks

Develop training for SHW installers and designers, for example, for thermosiphon and PV systems. Additionally, educate decision makers of the importance of these systems to meet the GHG targets.

Qualified installers/engineers are key actors on establishment of a successful market for SWH systems. The need for training will be identified in the following three perspectives:

  • Technological: New technology, installation requirements, design tools, carbon reduction calculation
  • Economical: Benefit of SWH systems, cost performance improvement, economic advantages for installers
  • Social: social awareness, carbon footprint

Training (workshops, webinars, etc.) will be organized for/by installers, engineers, and manufacturers. Relevant experts from the task will be invited.

The training materials developed above will include details on the existing warranty and certifications networks along with some recommendations. The following warranty and certification networks could be considered:

  • Solar Keymark

· Global Solar Certification Network (GSCN)

  • Solar Heating Arab Mark and Certification Initiative (SHAMCI)
  • Other licensing and certification programs (NABCEP, SRCC)

D.2. Standards

Work out recommendations on revision of current standards to add all new technologies and smart components.

Depending on interest of the participants, the following standards could be considered:

Standards for Performance testing and characterizing for Solar Hot Waters

  • Revise ISO 9459 series standards to cover all new technologies

Standards for durability for Solar Hot Waters

  • Thermosyphon systems
  • PV -driven systems
  • Other emerging/enabling components (i.e., Heat pumps, PVT collectors)

Carbon footprint standards of Solar Hot Waters

  • Thermosyphon systems
  • PV-Driven systems
  • Other emerging/enabling components (i.e., Heat pumps, PVT collectors)

D.3. Needs Assessment Report (Training for Solar Energy Practitioners)

Depending on the interest of the participants, and the information collected from previous surveys and reports of the project, a needs assessment will be conducted for solar practitioner training.

D. 4. Report on success stories

Depending on the interest of the participants, a report of the success stories in the various operating environments of the experts will be written as a concluding deliverable of this subtask.