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AbstractRoughly 97% of the European Union (EU) building stock is not considered energy efficient, and 75–85% of it will still be in use in 2050 (Artola et al., Boosting building renovation: What potential and value for Europe? 2016). Residential buildings account for around two thirds of final energy consumption in European buildings. The rate at which new buildings either replace the old stock or expand the total stock is about 1% per year. Similarly, the current renovation rate of existing buildings in the EU is about 1–2% of the building stock renovated each year. Renovation strategies on building levels need to be derived from a combination of energy efficiency upgrades to buildings and the use of renewable energy to decarbonize the energy supply, on a district or city scale. IEA EBC Annex 75 subtask D2 focuses on promoting cost-effective building renovation at district level combining energy efficiency and renewable energy systems, by focusing on the business models that can make implementation possible. This paper intends to provide an overview of the business model archetypes that can support the development of district demand and/or supply of energy-efficient building renovations and/or renewable energy solutions by targeting various types of stakeholders. It builds upon existing literature to gain insights into the current distributed energy business model landscape. Further, implementation strategies are identified that focus on a holistic evaluation of the expected energy and CO2 performance of the site and optimized infrastructure investment pathways.

Quantification of spatial and temporal changes in forest cover is an essential component of forest monitoring programs. Due to its cloud free capability, Synthetic Aperture Radar (SAR) is an ideal source of information on forest dynamics in countries with near-constant cloud-cover. However, few studies have investigated the use of SAR for forest cover estimation in landscapes with highly sparse and fragmented forest cover. In this study, the potential use of L-band SAR for forest cover estimation in two regions (Longford and Sligo) in Ireland is investigated and compared to forest cover estimates derived from three national (Forestry2010, Prime2, National Forest Inventory), one pan-European (Forest Map 2006) and one global forest cover (Global Forest Change) product. Two machine-learning approaches (Random Forests and Extremely Randomised Trees) are evaluated. Both Random Forests and Extremely Randomised Trees classification accuracies were high (98.1-98.5%), with differences between the two classifiers being minimal (<0.5%). Increasing levels of post classification filtering led to a decrease in estimated forest area and an increase in overall accuracy of SAR-derived forest cover maps. All forest cover products were evaluated using an independent validation dataset. For the Longford region, the highest overall accuracy was recorded with the Forestry2010 dataset (97.42%) whereas in Sligo, highest overall accuracy was obtained for the Prime2 dataset (97.43%), although accuracies of SAR-derived forest maps were comparable. Our findings indicate that spaceborne radar could aid inventories in regions with low levels of forest cover in fragmented landscapes. The reduced accuracies observed for the global and pan-continental forest cover maps in comparison to national and SAR-derived forest maps indicate that caution should be exercised when applying these datasets for national reporting.

An aerosol reactor was tested for the thermal reduction of ceria as part of a solar thermochemical redox cycle for producing H2 and CO from H2O and CO2. The design is based on the downward aerosol flow of ceria particles, counter to an argon sweep gas, which are rapidly heated and thermally reduced within residence times of less than 1 s. When operating in the temperature range of 1723–1873 K and at oxygen partial pressures between 5 × 10–5 and 1.2 × 10–4 atm, reduction extents of small particles (Dv50 = 12 μm) approached those predicted by thermodynamics. However, heat- and mass-transfer effects were found to limit their conversion when the ceria mass flow rate was increased above 100 mg s–1. This reactor concept inherently results in separation of the reduced ceria and evolved O2(g), operates isothermally throughout the day, and decouples the reduction and oxidation steps in both space and time for potential 24-h syngas generation.

Optimization models can support decision-makers in the synthesis and operation of multi-sector energy systems. To identify the optimal design and operation of a low-carbon system, we need to consider high temporal and spatial variability in the electricity supply, sector coupling, and environmental impacts over the whole life cycle. Incorporating such aspects in optimization models is demanding. To avoid redundant research efforts and enhance transparency, the developed models and used data sets should be shared openly. In this work, we present the SecMOD framework for multi-sector energy system optimization incorporating life-cycle assessment (LCA). The framework allows optimizing multiple sectors jointly, ranging from industrial production and their linked energy supply systems to sector-coupled national energy systems. The framework incorporates LCA to account for environmental impacts. We hence provide the first open-source framework to consistently include a holistic life-cycle perspective in multi-sector optimization by a full integration of LCA. We apply the framework to a case-study of the German sector-coupled energy system. Starting with few base technologies, we demonstrate the modular capabilities of SecMOD by the stepwise addition of technologies, sectors and existing infrastructure. Our modular open-source framework SecMOD aims to accelerate research for sustainable energy systems by combining multi-sector energy system optimization and life-cycle assessment.

Since 20 years or so, we assist, mainly under the pressure of sustainability imperatives, to the emergence of new political regulations of the relations between the societies and their environment and more precisely of the social uses of natural resources. These new modes of regulation, empirically noticeable, are characterised by a joint movement of rearticulating sector-specific policy logics, redefining territorial perimeters and pertinent regulation scales as well as of redefining and redistributing resources use rights. This article has for objective to identify and document these different modalities of questioning the existing logics (sectors, institutional territories and property rights) of the public action, then to propose the concept of functional space as an analytical tool allowing to account for alternative formatting of the public action on the one hand and as conceptual framework which could underlie a new political steering of the public action in favour of sustainability on the other hand.

Abstract The buildings and construction sector is responsible for nearly 40% of the total greenhouse emissions (GHG). Considering 50% of the building stock that will exist in 2050 is yet to be built and most of it will be devoted to housing; the sector is a determinant and transformative force to strengthen sustainability, reducing CO2 emissions and environmental degradation worldwide. Most of the increase in construction and housing is set to occur in developing countries and mainly in cities in Asia and Africa. This global picture places new housing programs in the rapidly urbanising regions as potential agents of sustainable transformation, with positive outcomes for both communities and the environment. Investing in sustainable housing has significant and real value in reducing emissions, confronting climate change, and generating better planned, inclusive, and sustainable cities. The holistic benefit achieved with the implementation of carbon neutral and carbon negative technologies is often scattered, and an integrated view of it would be a key tool to support the development of sustainable housing programmes. Considering that technologies to decarbonize and render the construction sector more sustainable have already been developed, there is a need to contrast their applicability to different countries and contexts in order to verify their functionality and identify gaps for improvement. The recent decade has witnessed a significant improvement at the global level with regards to the application of the concept of sustainability to the built environment, this being demonstrated by the multiple sustainability ratings and frameworks being developed to certify building performance. Their adoption has been critically important in most regions in the so-called Global North, where countries have started enforcing them at a normative level. While these tools’ accuracy and comprehensiveness could be disputed, their importance in promoting a systematic standardisation of the adoption of sustainability measures in the built environment is endorsed. Nevertheless, the diffusion of such tools and frameworks across rapidly urbanising middle and low-income countries has been so far extremely limited. There are myriad reasons why this is the case: tools based for high-income country contexts, their complexity, the need for accurate data and specific capacity for their adoption and diffusion, the lack of contextual relevance with regards to the specific market, culture and behavioural dynamics, and more. The following paper aims at demonstrating the value of shifting toward sustainable building practices by a comparative analysis of existing global tools and certifications and their applicability to low and middle-income countries undergoing a rapid urbanisation process. It proposes a three-phased multi-stakeholders methodology. The outcome of these three phases is combined, providing a more appropriate definition of effective and operative guidelines and tools for sustainable housing in rapidly urbanising middle and lowincome regions.

Abstract Proper water management plays an essential role in the performance and durability of Polymer Electrolyte Fuel Cells (PEFCs), but it is challenged by the variety of water transport phenomena that take place in these devices. Previous experimental work has shown the existence of fluctuations between low and high current density levels in PEFCs operated with wet hydrogen and dry air feed. The alternation between both performance states is accompanied by strong changes in the high frequency resistance, suggesting a cyclic hydration and dehydration of the membrane. This peculiar scenario is examined here considering liquid water distributions from neutron imaging and predictions from a 3D two-phase non-isothermal model. The results show that the hydration-dehydration cycles are triggered by the periodic condensation and shedding of liquid water at the anode inlet. The input of liquid water humidifies the anode channel and offsets the membrane dry-out induced by the dry air stream, thus leading to the high-performance state. When liquid water is flushed out of the anode channel, the dehydration process takes over, and the cell comes back to the low-performance state. The predicted amplitude of the current oscillations grows with decreasing hydrogen and increasing air flow rates, in agreement with previous experimental data.