Achieving sustainable biowaste management is a key challenge for cities worldwide. In this context, biowaste valorization is an indispensable option for managing unavoidable biowaste and reducing the associated methane emissions. Several innovations that enable biowaste valorization are technologically mature. However, their implementation is still limited in most cities around the world. Therefore, it is essential to better understand the different pathways towards implementing biowaste valorization. This paper presents a case-study of two countries at different phases in their transition to biowaste valorization: Sweden as a case at a mature phase and Greece as a case at a formative phase. We apply the Technological Innovation Systems framework to investigate how innovation systems for biowaste valorization develop and associated path-dependencies. Our findings show that various path-dependence lock-ins can occur at different transition phases. Our empirical insights suggest that a focus on the diffusion of certain mature innovations can support the growth of biowaste valorization systems. However, it can also lead to path-dependence lock-ins that influence the systems’ resilience to shocks. We thus recommend decision-makers to pursue balance between the rapid diffusion of mature innovations for biowaste valorization and parallel support for experimenting with more radical innovations to harness the systems’ resilience to shocks.

Heating and cooling activities account for nearly half of the European Union's total energy use, yet only 23 % of this demand is met by renewable sources. As reliance on fossil fuels declines and waste suitable for incineration diminishes, alternative renewable and excess heat (EH) sources become essential. In Sweden, approximately 4.7 TWh of industrial EH is recovered annually, contributing 12 % of available EH and 9 % of the district heating (DH) supply. Despite projections that EH utilisation will rise from 22 TWh in 2015 to 33 TWh by 2050, lowtemperature levels and economic viability challenges have limited Urban Excess Heat (UEH) integration into DH systems. This study develops a spatial-techno-economic optimisation framework to support long-term UEH integration in DH networks. The framework, composed of three open-source tools for spatial network optimisation, long-term planning, and short-term operational optimisation, was applied to the City of Stockholm's DH system, where over 80 % of buildings are DH-connected. Results indicate that UEH sources within a 5-km radius of primary DH pipelines have the highest feasibility for integration. Economic analyses revealed that investment sensitivity is highest with fluctuations in electricity prices, emphasising the cost implications of energy markets on UEH feasibility. Scenarios with varying grid temperatures demonstrated that lower temperatures improve UEH uptake but require adaptive network designs for efficiency. Iterative linking of long-term and highresolution operational models highlighted differences between cost-optimal plans and operational realities, suggesting refinement needs. This framework offers robust pre-feasibility insights for stakeholders, enhancing strategic planning for sustainable urban heating across municipal and regional levels.

The valorisation of urban biowaste can contribute to a circular and sustainable resource management. However, biowaste valorisation is not inherently sustainable. This study employs the Sustainable Development Goals (SDGs) to investigate the sustainability implications of biowaste valorisation. A narrative literature review provided an overview of the current scientific knowledge on interactions between biowaste valorisation and selected SDG targets. Then stakeholder interviews yielded insights into such interactions in a national context. Our findings show the potential for 19 synergies and 11 trade-offs between biowaste valorisation and 20 selected SDG targets that are addressed in detail. Although the synergies outnumber the trade-offs, different context-dependencies influence the nature and strength of the interactions. We highlight three types of context-dependencies relating to governance. This study informs the scientific community and decision-makers on planning for sustainable biowaste valorisation that addresses context-dependencies. The insights can guide countries and cities at early transition stages towards biowaste valorisation.

Urban sustainability is a key locus and focus of global climate action due to the high resource consumption, population density and tradition of innovation and investment. An assessment of the effectiveness of urban climate actions is necessary to assure goals are met and negative effects on surrounding regions, under-served populations, and the wider landscape are minimized. This study defines and builds a qualitative, descriptive mapping of two specific measures from Stockholm’s 2030 climate action plan that have impacts both within and outside of the metropolitan Stockholm area. We include both descriptive analysis and quantitative calculations to assess the magnitude of the impacts. Climate, land, energy, and water impacts are considered. 

Replacing fossil oil in the district heating system with bio-oil was evaluated through comparing the fossil oil reference scenario, a bio-oil from fast pyrolysis of food waste scenarios, and a tall oil pitch scenario. It was found that using fast pyrolysis bio-oil from food waste resulted in the most CO2e emissions. Fossil oil had the highest land use impact. It was found that tall oil pitch had the highest energy demand for production. Fossil oil had the highest water impact. The spillovers associated with the measure were found to occur mostly within Europe, with some in the US and China. 

 It was found that, when implementing bio-energy carbon capture and storage (BECCS) within the system limits defined in the study, negative emissions would have the greatest climate impact. The emissions due to transporting the CO2 to its storage location were found to be negligible. The land use impacts due to storing the CO2 were found to be negligible. It was found that there is a tradeoff between power generation and carbon sequestration. The energy needed to inject the CO2 into its storage location was quantified. Finally, the water impact due to the CO2 storage was found to be negligible, though water consumption due to adding the carbon capture unit could increase, depending on the technology used. 

 This study is part of an academic partnership and exchange between UC Berkeley in the USA and KTH in Sweden. 

This article deals with ongoing attempts to recover heat and greywater at property level, based on an in-depth study of Stockholm, Sweden. We explore different socio-technical development paths from now up until 2050 using a novel combination of on-property technology case-studies, actor studies and system-level scenario evaluation, based on Artificial Neural Networks modelling. Our results show that the more conservative scenarios work in favour of large-scale actors while the more radical scenarios benefit the property owners. However, in the radical scenarios we identify disruptive effects on a system level due to disturbance on wastewater treatment plants, where incoming wastewater can be critically low for up to 120 days per year. At the same time, net energy savings are relatively modest (7.5% of heat demand) and economic gains for property owners small or uncertain. Current policies at EU and national level around energy-efficient buildings risk being counter-productive in cases when they push property owners to install wastewater heat recovery technology which, in places like Stockholm, can create suboptimal outcomes at the system level.

Favorable thermal conditions within buildings are a necessity. Mechanical air conditioning, although effective, contributes a significant percentage of the world's total energy use, which contributes to global warming. In addition, the refrigerants used in air conditioning also contribute to global warming. Passive means to provide thermal comfort have therefore been considered as alternative solutions. Phase-change materials (PCMs) have been considered as one passive cooling option. Although this option achieves a certain degree of effectiveness, especially in warm and dry climatic conditions, its effectiveness in warm humid climates is subdued due to its inability to handle humidity. In the present study, the suitability of a novel passive comfort provision strategy that combines a PCM and a desiccant is assessed. The passive system operates in a cycle of two phases: the moderating phase and the regenerating phase. For the proposed strategy, the regeneration process first involves the external desiccant bed, then night air drying using the regenerated external bed; the dried air subsequently regenerates the internal wall surface. The study involves the modeling of the proposed strategy and simulation of its performance. The simulation results indicate the significant potential for providing satisfactory comfort and health conditions through application of a combination of a desiccant and a PCM.

With increasing heating and cooling demands, decarbonisation of the heating and cooling sectors is key to achieving a carbon-neutral energy system. Using industrial excess heat in heating systems helps offset emissions by reducing the use of fossil fuels. While several studies have analysed the temperature of heat availability, the cost of extending or constructing the heating network and techno-economic feasibility, it is important to consider all aspects together to achieve a comprehensive design of industrial excess heat recovery. This study proposes a method to link an energy system optimisation tool with a spatial analysis tool and an exergy analysis tool to achieve a comprehensive design. An iterative soft link is implemented between the energy system model and the spatial analysis tool for high spatial and temporal resolution. The developed method is applied to a case study of an industrial park in Greece. Scenarios are developed to assess the robustness of the developed method and the system profitability of excess heat recovery. The scenarios indicated that the profitability of excess heat depends heavily on the price of natural gas with the share of excess heat increasing from 10% to 45% with a 20% increase in natural gas prices in cases where heat pumps are needed for temperature boosting. In cases where heat pumps are not needed, excess heat indicates higher system profitability with a share of around 40% and reduces the emissions by around 50 times. The method provides robust results in considered scenarios with convergence within four iterations.

In this paper, the analysis of the diffusion of photovoltaic systems is performed using the Bass model. The historical data of installed rooftop photovoltaics are not enough for the model, as the installation of photovoltaics was almost non-existent; hence data of solar water heaters are utilised to calculate the parameters for the model. The trajectory of growth for solar water heaters in the market presents a congruence for the growth of solar photovoltaics due to inherent similarities in the technologies and their application. India was used as a case study of the application of this borrowing approach in a market where PV is also used to provide electricity to local communities. Data from India's solar water heater market were used, indicating an innovator parameter of 0.00105 and an imitator parameter of 0.12219. The study is significant as it forecasts the diffusion of photovoltaics in the market, which is essential for achieving India's Intended Nationally Determined Contributions goals and Renewable Energy targets. The results indicate that residential rooftop photovoltaic diffusion will tend to present slower in India than in other markets if no additional policies are implemented to foster this market.

This chapter provides an overview of the application of thermal energy storage in industrial scale systems, e.g. steel works, pulp mills, and also power generation and district heating and cooling utilities. The purpose is to illustrate the benefits of integrating thermal energy storage in such processes, from both a technical functional and economical perspectives. Examples of such benefits are resource efficiency, stability of operation, and lowered cost of fuel.

The supercooling effect is deemed to be a crucial issue for thermal energy storage using phase change materials (PCMs). The exploration of promising additives plays a decisive role in effective suppression efforts for suppressing the supercooling effect of a PCM. The present work proposed a potential additive, polyvinylpyrrolidone (PVP), to reduce the supercooling of erythritol, which is the most promising polyol PCM candidate for medium temperature range. PVP with various loadings was dispersed in erythritol to make composites for the proof-of-concept tests. It was shown that the degree of supercooling of erythritol can be reduced significantly from over 64 ? to about 21 ? in the presence of only 1.0 wt.% PVP. Along with the mitigated supercooling effect, the addition of PVP also leads to an increase of the retrievable latent heat during crystallization, from ~187 J/g to ~224 J/g at the same minute PVP loading of 1.0 wt.%, by increasing the crystallinity of erythritol. The PVP-loaded erythritol composites exhibit little sacrifice in latent heat of fusion, i.e., only ~15% loss when the PVP loading reaches 6.0 wt.%. In addition, multiple tests confirmed that PVP can be dissolved in erythritol, thus desirable compatibility was obtained and the composites would have long-term reliability. This proposed additive enables an efficient and cost-effective way for improving the crystallization behaviors of erythritol (and other polyol PCMs) towards real-world applications.