Currently, the European development and manufacturing of renewable and sustainable technologies are both critical and crucial. The EU-funded H2020 project REGEN-BY-2 demonstrates the manufacturing and testing of an innovative tri-generation technology that can simultaneously provide electricity, heat, and cold. The novel unit mainly operates using two-phase flow, demanding special requirements for individual components, mainly expanders and compressors. However, this technology has not been demonstrated; it is already relevant to identify later user types and investigate their future mechanisms in the heating and cooling demand. This analysis presents the four most important user types and various combinations of these, the joint use cases. The industrial, retail, office, and residential user types are first described in terms of their general characteristics, potential dependence on climate, and daily operation schedules. The results show that office and residential user types lack simultaneous demand for heating and cooling, as they are mainly influenced by seasonal weather conditions. Industrial and retail users, on the other hand, require both heating and cooling throughout the year with only daily variations. A system approach of the tri-generation unit coupled with thermal energy storage (TES) and additional auxiliary units, such as boilers and chillers, seems most promising for later applications. In addition, the availability of potential heat sources to drive tri-generation was verified. Industrial users are not only promising end-users, but also potential heat suppliers with a focus on untapped waste heat. This analysis follows a generalized approach. The next step would be to identify real use cases and examine the dimensioning and adaptation of the tri-generation unit in a complete system concept.

The increasing demand for space cooling poses a major challenge to energy systems and buildings, both residential and commercial applications. Cost-effective and easily deployable solutions are widely needed to tackle this challenge. Heat emitted to the indoor from equipment is critical, particularly cooling units such as refrigerators and freezers. The impact of heat rejected from refrigerators on the indoor climate of small shops and supermarkets have been widely overlooked. This study presents and investigates an innovative and low-tech solution to control the heat dissipation of indoor cooling units, leading to increased comfort and reduced cooling demand. The solution, designed to be installed as a retrofit measure, controls the exhaust air ducting. Thus, it does not provide cooling, but manages the waste heat from refrigerators. This study includes the monitoring of an actual kiosk in Stuttgart, Germany, to meter refrigerators’ power consumption, a lab-scale prototype testing to prove the methodology of the solution and additionally dynamic thermal simulations via TRNSYS18 for different climates to analyze the performance and impact of the novel solution. The prototype showed the effectiveness of the control strategy during the lab-testing. The simulation results for Stuttgart show that controlled heat dissipation can reduce overheating degree hours by up to 97 – Boxed ventilation system can reduce cooling degree hours and accordingly cooling demand in commercial shops – Experimental measurement using lab-scale prototype proves system design and control – Boxed ventilation system is more efficient compared to open exhaust air ventilation

The accelerating global demand for renewable heating, cooling and electricity, driven by climate change and rising living standards, presents both a challenge and an opportunity for sustainable energy transitions. This paper introduces the Initial-Aid Cashback (IAC) model, an innovative business model designed to finance renewable energy solutions, with a focus on space cooling, by leveraging citizen participation and collaborative financing mechanisms. The model incentivizes private investors through discounted energy prices, while system operators benefit from reduced upfront capital requirements and minimised financial risk. Through two case studies, an office building in Romania (small-scale case) and the application of the REGEN-BY-2 technology in a mixed housing–office area (large-scale case), the paper demonstrates the model’s potential to accelerate the adoption of renewable cooling technologies, enhance profitability for operators, and provide attractive returns for investors. The findings highlight the model’s adaptability to diverse stakeholder needs, its scalability, and its role in fostering the clean energy transition (CET). However, challenges such as the need for a minimum number of investors, legal complexities, and trust-building among stakeholders are identified as critical barriers to implementation. The paper concludes that the IAC model offers a promising pathway to integrate citizens and small investors into the CET, while emphasising the importance of supportive policies, clear governance structures, and practical testing to ensure its success.

Urban areas account for a significant proportion of energy consumption and greenhouse gas emissions in the European Union (EU), while hosting 75% of its population. Therefore, they are primarily responsible for the transition towards a clean energy future and the achievement of long-term sustainability goals. However, the current scientific debate on carbon neutrality focuses primarily on larger cities (national capitals or medium-sized cities), whilst the potential contribution of small cities and rural areas to the EU's overall climate neutrality goal for 2050 remains largely untapped. This paper aims to address this gap, providing a dual-dimension evaluation framework to assess the design, implementation and outcomes of climate and energy actions in small municipalities. The first component of this framework provides an overview of municipalities based on self-assessment reports, their climate and energy plans, and an indicator-based analysis. The second component involves a context-based gap analysis conducted to highlight the drivers and barriers to implementing the clean energy transition. Additionally, a questionnaire on envisaged actions was distributed to local administrators of the sample of cities to collect information on how fill the gaps and derive context specific recommendations.Applying the proposed methodology to six pilot municipalities in six different EU countries involved in the LIFE LOCAL GoGREEN project revealed substantial barriers to the clean energy transition. This experience highlights that a lack of financial resources and a lack of motivation among decision makers remain common issues, particularly among small and rural local authorities.

Contributing to the ambitious European goal of becoming the first carbon-neutral continent by 2050 requires coordinated efforts across all levels of governance. However, small and rural communities often struggle to keep pace and are disadvantaged by a number of factors including limited access to financial resources, technical expertise, and the use of planning tools such as decision support systems (DSTs), datasets, and geographic information systems (GIS). This study presents findings from the LIFE22-CET LOCAL GoGREEN project (2024–2026), which supports six small municipalities located in Bulgaria, Croatia, Slovenia, Italy, Germany, and Spain in their clean energy transition. A common methodological framework was co-designed and shared with the municipalities to guide the development of local case study profiles through structured Self-Assessment Reports (SARs). The SARs provided valuable insights into local energy and climate planning, enabling the identification of key challenges and opportunities. The final comparative analysis revealed a generally fragmented planning framework, a widespread absence of long-term strategic vision, and limited multi-level cooperation. Moreover, the adoption of DSTs, GIS, and structured data analysis in local planning remains minimal. Despite focusing on a limited number of cases, the study offers relevant considerations for policy-makers and stakeholders aiming to support the energy transition in rural and small communities across Europe in a more inclusive and effective way.

Achieving Europe’s mid-term decarbonization targets by 2030 is an ambitious challenge for local authorities. However, small and rural municipalities face significant barriers, including structural, institutional and economic challenges. To facilitate the achievement of this ambitious goal, it is essential to strengthen local administrative capacities through targeted support. This is indeed the main objective of the European LIFE22-CET LOCAL GoGREEN project, which is aimed to accelerate the clean energy transition in six small communities across Bulgaria, Croatia, Slovenia, Italy, Germany, and Spain. In particular, it supports them in developing strategic actions in five priority areas: sustainable transport and e-mobility, energy efficiency in buildings, renewable energy expansion, land-use planning for carbon sequestration, and waste-to-energy solutions. This is achieved through a range of activities, including stakeholder engagement, local capacity building, providing analytical tools for energy planning, conducting pre-feasibility studies, and developing roadmaps and action plans. This paper presents the groundwork for the preparation of action plans and feasibility studies by the pilot cities, i.e. the characterization of the state of the art from an energy and planning perspective. It focuses on the analysis of the self-assessments carried out by the pilot cities, the database of their current climate and energy plans and programmes, and the definition of a common set of key indicators to characterize their planning performance. The results obtained so far show a two-speed behavior in the planning practices of small municipalities across Europe, with lagging municipalities able to learn and adopt good practices from the leading examples in the project in horizontal mainstreaming.

The energy sector is currently under enormous transition, moving from fossil fuels to renewable energies and integrating energy efficiency measures. This transition can hold opportunities for new and innovative energy systems. This study presents an energetic and economic assessment of an innovative tri-generation unit working with a two-phase thermodynamic cycle. The tri-generation unit is driven by heat and is capable of providing heat at lower level, cold, and electricity to end users. The use cases—residential, day-use offices, commercial retail, and manufacturing industry—are integrated in a dynamic simulation model, indicating the operation mode of the unit. The results show that the tri-generation unit is able to provide heat and cold with an Energy Utilization Factor of 35% to 68%, depending on the use case. Solar thermal has a limited to potential to supply the unit with heat, due to the high temperature of 180 °C and the required unit operation at nighttime. The economic comparison indicates that the driving heat must be as low as possible and that savings through self-consumption is most relevant.

The European construction sector is one of the areas with the highest potential when it comes to reducing annual energy consumption. Facing many challenges to achieve ambitious energy efficiency objectives, this sector aims to proceed by applying successful training initiatives and supporting policy instruments. For this reason, the creation of BUILD UP Skills, an EU Initiative to improve the qualification and skills of Europe’s building workers, acted as a springboard to stimulate the demand for energy efficiency skills. Furthermore, focusing on the continuing education of craftsmen and other on-site building workers, this initiative is home to most of the projects presented during the Sustainable Energy Skills in the Construction sector workshops 1.0 and 2.0 and 3.0, presented at SP2020, SP2021 and SP 2022, respectively. Consisting of nine Horizon 2020 projects—PRO-Heritage, TRAIN4SUSTAIN, INSTRUCT, BUSLeague, the nZEB Roadshow, SEEtheSkills, ARISE, BUS-GoCircular and nZEB Ready—the objective of the third edition of the workshop was to share expertise, lessons learned, and developed methodologies on energy efficiency skills competencies, and qualifications across the building design, operation, and maintenance value chain.

The study investigates the economic feasibility of photovoltaic-powered air-conditioning (AC) systems in thirteen different sunbelt countries. Two different technical solutions have been analysed: (i) hybrid (partially PV powered, grid-connected) and (ii) off-grid (fully PV powered, no grid connection). These two solutions have been studied for three different locations in each country, namely minimum, average and maximum annual global solar irradiation on the horizontal. Lastly, each solution and location has been examined for application in the residential and commercial sector. All solar-based air-conditioning scenarios use high efficiency AC appliances with R290 as refrigerant (Global Warming Potential – GWP of 1) and have been compared against a base-case scenario using AC units with moderate efficiency AC appliances with conventional R410a refrigerant (GWP of 2088) and 100% grid electricity supply. The scope of the study is to identify the economic potential of solar PV cooling technologies. Levelized Cost of Electricity (LCOE) and Net Present Value (NPV) have been calculated for each scenario as part of the comparative analysis. It was found that hybrid photovoltaic-based air-conditioning for a residential house has a financial advantage over grid-based air-conditioning in eleven out of thirteen countries investigated. Exceptions are Ghana and Vietnam. Off-grid photovoltaic-based air-conditioning for residential houses is only economically feasible in five out of thirteen countries, namely Costa Rica, Iran, Grenada, Philippines and Thailand. Hybrid photovoltaic-based air-conditioning for a small commercial building has a financial advantage over grid-based air-conditioning in ten of thirteen countries, except in Colombia, Ghana and Iran. Off-grid photovoltaic-based air-conditioning for a small commercial building is only feasible in China, Grenada, Kenya and Philippines.

The goal of work package D-D5 was to organize four half-day workshops dedicated to the industrial players (manufacturers and installers, consultants, policy makers) in Sunbelt countries. This goal has been exceeded with eleven workshops and trainings organized and conducted for 567 participants over the four years of Task 65. This document lists the individual workshops and trainings as well as gives general information on each of them. Detailed workshop and training agendas can be found in the Appendix.

The goal of the IEA SHC Task 65 “Solar Cooling for the Sunbelt regions” is to focus on innovations for affordable, safe, and reliable Solar Cooling systems for the Sunbelt regions worldwide. Countries located between the 20th and 40th degree latitudes in the Northern and Southern Hemispheres, placed in the Sunbelt, face increasing cooling needs on the one hand and higher solar irradiation on the other a compelling solution.

The goal of the IEA SHC Task 65 “Solar Cooling for the Sunbelt regions” is to focus on innovations for affordable, safe, and reliable Solar Cooling systems for the Sunbelt regions worldwide. Countries located between the 20th and 40th degree latitudes in the Northern and Southern Hemispheres, placed in the Sunbelt, face increasing cooling needs on the one hand and higher solar irradiation on the other a compelling solution.

This document is the final report of activities B4, “Standardized solar cooling kits” of the IEA SHC Task 65, “Solar Cooling for the Sunbelt Regions. The report presents experiences from 11 component and/or system suppliers of solar cooling kits, which adapted/investigated their products/concepts for Sunbelt region conditions. Moreover, several findings on system adaptations for Sunbelt regions are collected and analyzed from manufacturers, equipment providers, solar system providers and researchers.

The goal of work package D-D6 was to identify key stakeholders around the Sunbelt countries. Those stakeholders should be invited to try the technology in demonstration projects. Involvement of stakeholders through one-to-one meetings, workshops, conferences, etc. in their countries. This document describes the identification process, which first involved collecting 90 individuals and organisations from the entire Task 65 observer list. Second, an initial email was sent to 44 individuals and organisations in Sunbelt countries identified from this collection. Third, a second email and questionnaire were sent to 19 individuals and organisations who expressed interest in proceeding. The analysis of questionnaire feedback provided a comprehensive list of topics of interest to stakeholders in Sunbelt countries, Finally, 5 individuals and organisations expressed interest in becoming more involved in the objectives of Task 65.

This is the final report on activity C1, “Design tools and models” of the IEA SHC Task 65 “Solar Cooling for the Sunbelt regions”. The work involved reviewing and adapting tools and models for technical and financial assessment and design for solar cooling and the project phases from pre-feasibility to simulation to monitoring. The main focus is the documentation of the tools and their specific application to provide measured data for validating the tools and the adaptation of selected ones for Sunbelt countries.