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Soiling of PV modules is an issue causing non-negligible losses on PV power plants, between 3 and 4% of the total energy production. Cleaning is the most common way to mitigate soiling. The impact of the cleaning activity can be significant, both in terms of cost and resources consumption. For these reasons, it is important to monitor and predict soiling profiles and establish an optimal cleaning schedule. Especially in locations where raining is irregular or where desert winds carry a high concentration of particles, it is also important to know how precipitation and dust events affect the soiling ratio. This paper presents a new model based on environmental conditions that helps the decision-making process of the cleaning schedule. The model was validated by the analysis of five large grid-connected PV plants in Spain over two years of operation, with a total power of 200 MW. The comparison between the model and soiling sensors at the five locations was included. Excellent results were achieved, the mean difference between sensors and model being 0.71%. [ABSTRACT FROM AUTHOR]

Aligned with the goals of achieving higher sustainability in water systems, the minimization of energy costs is a top priority for the operators and owners of such systems. Early research contributions on the rate of energy dissipation due to head losses, defined as energy slope J , demonstrated that this parameter can be optimized so that such cost minimization is achieved. However, an important factor that was not considered in previous research is that water demand might be variable during the lifetime of water systems. Whether due to daily variation patterns, seasonal changes, or long-term water demand growth, variations on the flow rate complicates the determination of the optimized energy slope Jopt that will minimize energy costs. This work addresses this knowledge gap, performing an evaluation of how demand variation impacts Jopt and how deviations from the optimum energy slope affect costs for varying water demands. In addition, this work also provided insights into pipe cost installation terms and pipe cost exponents using real-world data of existing water systems in Spain. Such exponents are very important in the computation of optimum energy slopes. It is hoped that this research will provide practical guidance to designers and operators of water systems regarding the minimization of energy costs, leading to greater sustainability of such systems. [ABSTRACT FROM AUTHOR]

The low energy efficiency of the European building stock is both a social and environmental issue. However, plans and studies on energy retrofitting interventions do not usually evaluate the impact of these measures on households' energy affordability. This paper analyses and compares the effect of alternative retrofitting strategies on thermal energy services' affordability in Spanish vulnerable households. This analysis was carried out by applying the Required Thermal Energy Expenditure model proposed in previous studies to several 2030 residential building stock scenarios, setting 2020 as a baseline. Therefore, this work proposes a methodological approach to assess the impact of the considered energy efficiency interventions on energy poverty in winter (WEP) and summer (SEP) and carries out both a 'social cost' and a cost-benefit analysis. The dwelling's thermal-enclosure retrofitting stands out as a very WEP-reduction and social-cost effective measure. Instead, replacing old thermal systems with more efficient ones would have a higher impact on SEP. Combining both kinds of retrofitting measures could reduce heating and cooling required expenditures by, respectively, 49% and 59%, and decrease the WEP and SEP share, correspondingly, by 35% and 63%. These results might inform policymakers to enhance the targeting and design of energy efficiency programs. [ABSTRACT FROM AUTHOR]

• Advanced climate-resilient energy retrofit technology reduces the use of non-renewable energy in the building sector. • Renewable District Heating as an optimal technology in deep energy renovation strategies. • Sustainable cities and buildings are feasible by Centralised District Heating system powered by biomass. • Key Performance Indicators (KPIs), to achieve nZEB performances established in the European legislations. This paper presents the implementation of a biomass-fuelled District Heating System (DHS), as a part of a deep energy renovation exercise to achieve a climate-resilient campus with minimum carbon dioxide emissions. The case study is carried out for the University of Valladolid, an average-sized university in Spain, with a continental weather climate. Prior to renovation, the different building blocks had a wide-ranging level of fossil fuel consumption for space heating and domestic hot water ranging between 60 and 430 kWh/m2·year. The application of this centralised heating system allows to achieve the minimum threshold for near zero-energy buildings (nZEB) of 100–120 kWh/m2, in accordance with the Spanish Standards. These values correspond to the maximum European indicators for offices in continental weather conditions. Results of this comprehensive study show that 15 out of the 19 buildings reached the nZEB target, due to the proposed strategy. The overall carbon dioxide emissions have dropped by 92.69% as compared to the original fossil-fuel powered boiler, thus bringing carbon dioxide emissions down to 1.57 kgCO 2 /m2·y. Therefore, it is shown that deep energy renovation strategies through renewable energy DHS have the potential of achieving nZEB for universities in continental weather conditions. [ABSTRACT FROM AUTHOR]

• The Stanford Energy System Innovations plan is adapted to a university in Valencia. • Waste heat recovery from a large data centre is used to heat campus buildings. • A polyvalent heat pump that can simultaneously provide cooling and heating is used. • Thermal energy and emission savings of more than 64% in three campus buildings. • The findings help to promote similar studies in Mediterranean universities. In this research work, the Stanford Energy System Innovations action plan is adapted to the decarbonization of the Universitat Politècnica de València, of the Mediterranean coast of Spain. Special focus is dedicated to waste heat recovery from a data centre located on campus with an almost constant cooling demand throughout the year, amounting to a yearly 1,661,020 kWh. To recover the waste heat generated by the data centre, a method for assessing thermal performance of the system is presented, which is implemented by selecting a 300 kW polyvalent heat pump (capable of easily switching from water-to-water to air-to-water working modes). It can simultaneously provide cooling and heating to a set of strategically identified buildings on the campus: the university data centre and three buildings located nearby that currently use the university's central natural gas boilers for heating. A thermal storage system is designed to balance the cooling and heating needs. The results lead to potential thermal energy savings of more than 254,106 kWh/year, and a consequent reduction in CO 2 emissions of at least 64,035 kg/year, supporting the decarbonization of the Vera campus. The outcomes of the study can help to design similar research projects applied to large data centres in Mediterranean cities. [ABSTRACT FROM AUTHOR]

The definition of the term gastronomy encompasses both the knowledge of food and its handling, preparation and consumption. Beyond a sense of cultural identity and tradition, gastronomy also represents a pole of tourist attraction. This is the case of Galicia, a region in north-western Spain. Within this framework, local dishes, which include distinctive elements of the Atlantic diet, have gained popularity. This research delves into the sustainability of 60 Galician recipes by performing a hierarchical cluster analysis to study their carbon footprint, the energy return on investment ratio and cost. The life cycle assessment methodology was followed to account for the carbon footprint and the energy return on investment ratio of the recipes. The scope was bounded to the cradle-to-fork phases through the life cycle: production of the ingredients, transport, and meal preparation. The functional unit selected was one serving of a Galician meal. The results suggest that the recipes could be classified into three main groups according to the presence of a greater or lesser amount of animal-based products. Cluster 1 comprises 10 meat recipes. Cluster 2 encompasses 31 recipes rich in fish with some vegetables and moderate consumption of red meat and dairy products. Cluster 3 includes 22 vegetable-based recipes. The higher the portion of animal products in the recipes (mainly red meat), the higher the costs and carbon footprint and the lower the energy return on investment ratio. Conversely, plant-based recipes tend to reduce greenhouse gases emissions and increase cost competitiveness and energy efficiency indicators. Based on this study, the food service could promote eco-labelling that support and certify restaurant menus. This research could also provide transformative climate education for sustainable food for consumers, giving advice to improve food-based dietary guidelines in Spain. • Analysis of the carbon footprint, energy consumption and cost of Atlantic recipes. • Recipes can be classified into three hierarchical dietary clusters. • Cluster 1 comprises meat recipes with low energy return on investment ratio and high carbon footprint and economic cost. • Cluster 2 comprises recipes rich in fish with vegetables and moderate meat. • Cluster 3 includes low-cost and low-carbon vegetable-based recipes. [ABSTRACT FROM AUTHOR]

• A DCE is conducted to assess households' willingness to insulate their homes. • Determinants for the adoption of façade thermal insulation are identified. • The investment cost required in the existing building stock is below the obtained WTP. • The required subsidy level is lower than the grants set by existing aid programs. • Increased tax rebate has greater incentive effect than soft financing. This paper assesses Spanish households' willingness to thermally insulate their homes and the drivers that influence such a decision-making process. Stated preference data were collected through a discrete choice experiment (DCE). The final sample of 191 respondents and 1,145 observations was analysed by the use of a mixed logit model, weighing the factors that encourage homeowners to carry out façade energy renovations or not. The model enables the quantitative estimation of renovation adoption rates depending on the households' characteristics and public support instruments in place. The results show that homeowners are extremely interested in increasing the thermal insulation of their homes. The actual investment cost required in the existing building stock is lower than the obtained willingness-to-pay. Furthermore, it was found a relevant effect of a variety of household features on renovation choice (income, age, heating system, etc.), which should be contemplated in the energy efficiency policy design. Additionally, a case analysis is performed which comprises 3 household categories. The results reveal that the required subsidy level is different in each case, sometimes even unnecessary, although all of them lower than the grants set by existing aid programs. Thus, to reduce the free-riding effect, a closer perspective would enable targeted support mechanisms towards each household category. Moreover, the policy performance can be improved by combining subsidies with other measures such as low-interest loans or increased tax rebates, which could contribute to improving the cost effectiveness of the public expense associated with direct grants. Overall, an increased tax rebate is preferred to soft financing, although the influence of the latter increases in low-income households. [ABSTRACT FROM AUTHOR]

Residential end-uses represent a significant share of final energy consumption and material stocks. However, approaching sustainability of the residential sector merely as an environmental technical problem is insufficient. Home is the center of daily life providing essential functions to people. Household metabolism is not a matter of the sum of individual behaviors, typologies of buildings, or energy uses stripped out of context, but the system that emerges from the historical combination of these elements and the functions it performs. The residential sector comprises both families (units of organized individuals) and dwellings (within municipalities/urban forms). To analyze these dynamics, we draw upon practice theory and Multi-Scale Integrated Analysis of Societal and Ecosystem Metabolism (MuSIASEM) illustrating with data from Sweden and Spain in 2015. The objective is to establish an interdisciplinary framework for analyzing the sustainability of the residential sector. We also present a list of possible measures and their trade-offs in diverse dimensions: energy carrier consumption and greenhouse gas emissions, materials, floor area, human activity, social organization and institutions, finance and desirability. Even though the inclusion of all variables in a single model is not feasible, the holistic understanding of household metabolism can help build coherent anticipation scenarios by selecting plausible hypotheses. Ultimately, this allows making profound transformations to sustainability. • Sustainability of the residential sector must be approached in an interdisciplinary way. • We provide an exhaustive review of measures and their trade-offs. • Energy, materials, emissions, social organization and desirability play a role. • The boundary of the residential sector moves when functions are addressed in services. • Social practices and household units affect performance and layout of dwellings. [ABSTRACT FROM AUTHOR]

Buildings are one of the most important energy consumers worldwide and heating requirements are usually achieved using fossil fuels. This situation poses a risk to achieving the objectives for emissions reduction in existing buildings and electrification, based on heat pumps. It is one of the most feasible solutions to achieve emissions reduction objectives. Current research analyzes the potential for decarbonization of heat pumps and uses the Spanish scenario as a novel case study, where 8.5% of carbon dioxide emissions into the atmosphere came from the residential sector, with 66% of the energy consumption associated with cooling and heating. Using EnergyPlan the potential of decarbonization using heat pumps or heating systems in existing buildings and installing this technology in new buildings is analyzed. Results show a reduction of 8.43% in total emissions and prove that the proposed methodology can be extended worldwide as a solution to reduce emissions and improve energy efficiency in existent heating systems in buildings. Moreover, the integration of electrical climatization systems allows increasing the renewable electricity share in the grid or electrical vehicles integration, among others. [Display omitted] • Heating in existing buildings using Natural Gas difficult decarbonization. • Building heating systems decarbonization poses a risk to achieve 2050 objectives. • EnergyPLAN to study potential of heat pumps for heating decarbonization in Spain. • Results show 8.43% greenhouse gases reduction and include an implementation roadmap. • The methodology and solution can be applied worldwide in existent and new buildings. [ABSTRACT FROM AUTHOR]

In this paper, the energy benefits of switchable insulation systems (SIS) are assessed when applied as shades for windows as well as dynamic insulation for exterior walls of residential buildings located in European countries including Belgium and Spain. A series of analyses is performed for detached houses and apartments representing common Belgian residential buildings to determine the energy performance of SIS when deployed to windows and exterior walls and operated using simplified rule-based controls. The analysis results indicate that SIS-integrated windows can achieve significant energy savings for both dwelling types in Belgium, including the elimination of any mechanical cooling and a reduction of up to 44% of heating energy end-use. Moreover, the results show that SIS can offer even more energy efficiency and thermal comfort benefits when deployed to both windows and exterior walls for residential buildings. These energy efficiency benefits are higher, especially for reducing heating needs, for the milder climates of Belgium and Spain. However, it should be noted that the energy performance of SIS could be affected substantially by windows' orientation and occupants' behavior. [ABSTRACT FROM AUTHOR]

The energy performance of a building located in La Roca del Vallès, close to Barcelona in Spain designed under the near Zero Energy Building (nZEB) and Net Zero Energy Building (NZEB) criteria was investigated. The aim was to introduce entropy generation rate as a magnitude to describe energy efficiency in buildings. This was achieved by studying the energy and entropy balances using a commercial energy performance simulation software for different scenarios proposing different efficiency conditions. The annual energy and entropy flow balances cancel. Entropy generation was due to heat losses through the envelope, sun irradiance, appliances, lighting and occupation of the building. The building designed following nZEB criteria was compared with the same building with poorer energy performance. The first one generated 45,834 kJ K−1 while the second one generated 79,985 kJ K−1. This is an important result because with a single magnitude, entropy generation, we combine the impact of all energy transformations taking place in the building. Sun irradiance is found to be the most important entropy generation source: a building with sun irradiance can generate nearly 3.4 times more entropy than a shadowed building. Finally, we evaluated the generated entropy ratio between the transferred entropy to the environment in terms of Gouy-Stodola theorem and the cumulated entropy that contributes to building degradation. Although cumulated degradation entropy is well below the threshold of building collapse, practical degradation effects in the building were shown. Entropy balance of a building from energy transformations in the building. [Display omitted] • Evaluation of energy and entropy balance of buildings in terms of Gouy-Stodola theorem. • Introduction of entropy generation as a magnitude to describe energy efficiency in buildings. • Relationship between entropy generation and building degradation. [ABSTRACT FROM AUTHOR]

• The study fills a gap in literature by breaking down the energy rebound effect. • The Spanish economy is taken as a case study. • The Direct Rebound Effect explains around 10% of the total effect. • Indirect Rebound Effect values range between 1.2% and 1.8%. • Economy-wide Rebound Effect values range from −4.51% to 128.45%, with no clear trend. The rebound effect caused by energy efficiency improvements demands greater attention from energy policymakers as it represents an important obstacle to energy consumption reduction measures. Despite the emerging literature about the rebound effect, no studies to date have managed to break down it. To do so, this study introduces the disruptive innovation of replacing the Logarithmic Mean Divisia Index method used in previous literature with Structural Decomposition Analysis. Based on Input-Output tables, a re-spending model allows us to assess the Indirect Rebound Effect for 14 productive sectors. Finally, Structural Decomposition Analysis enables us to determine the Economy-Wide Rebound Effect caused by energy efficiency improvements. As far as we are aware, no other study to date has done so. Spain is used as a case study for the 2000–2014 period. Major findings indicate that total rebound effect varies from nearly to 10% to around 50%. The part of rebound explained by Direct rebound effect is around 10%. Indirect rebound effect shows values between 1.2% and 1.8%. Finally, Economic wide rebound effect varies from −4.51% to around 40% but without showing a clear trend for the period considered. The novelty of this study is that it attempts to break the overall rebound effect down to the direct, indirect, and economic wide rebound effect by combining the Cobb-Douglas production function and decomposition techniques. [ABSTRACT FROM AUTHOR]

• A systematic literature-approach to classify retrofitting is proposed. • An overview of Spain's previous guidelines on residential retrofits is presented. • A review of financial and subsidies mechanisms in Spain to renovate buildings is introduced. • A literature-based matrix on retrofitting actions is presented. • A classification of energy efficiency strategies for retrofitting is proposed. The building sector is responsible for more than 40% of final energy consumption in Europe; consequently, retrofitting existing buildings can significantly contribute to mitigate greenhouse emissions. Nevertheless, although the European Union has introduced relevant policy instruments, up to now the annual retrofit rates are considerably low with an average of 0.2% at European level. Understanding the past would support the success of the new strategies, such as the recent ones launched through the New Green Deal, which reinforces the importance of renovating existing buildings stock, as the main aim of the renovation wave. As a starting point for assessing the main challenges to allocate the Recovery funds, this paper provides a review of Spain's relevant literature to clearly define the characterization of the existing building stock, which actions have been typically considered under the scope of retrofits, and which strategies have been implemented until now, considering both, private and public initiatives and public financial schemes. The present work has a strong focus on energy-related strategies, although other interrelated actions are mentioned, such as accessibility measures and interior refurbishment of dwellings. Differences and similarities within these approaches are presented through the analysis of 27 relevant references of retrofitting actions and 52 references of financial mechanisms. As in Spain 93% of multifamily buildings were constructed prior to the national transposition of the first Energy Performance Building Directive (EPBD), and therefore are in need of deep energy renovations, the retrofitting of multifamily buildings topic has been widely addressed, even though often in a disjointed manner. The study suggests that although historically there have been several recommended strategies, few are conceived as integral actions, only 15% of the intervention packages refer passive and active energy-related measures and renewable energy incorporation. Furthermore, considering the antiquity of the building stock and the advantage of addressing the topic through clusters, only 63% of the resources directly refer these actions to specific clusters among the six distinctive periods, although in most cases focusing their recommendations on buildings constructed before 1980 where the worst energy performance buildings are concentrated. Concerning public financial and funding instruments, the research illustrates that there has been a substantial increment of programs over the last years promoting energy-related measures, renewable energy and other complementary aspects such as accessibility and interior renovations, mainly for older clusters. Nevertheless, the funds constitute only 8% of the necessary declared investments, which along with the dispersion between the different procedures and the complexity of the processes, have significantly reduced the global impact of these actions without generating robust and oriented market dynamics. Despite the several resources found, both financial instruments and guidelines tend to describe in more detail strategies related to heating demand and consumption and not delve into other relevant actions for warmer climates, fact associated both to the dynamics coming from other countries, and to a vision of the past in which people do not consume refrigeration. This clear focus on heating loads rather than cooling could present limitations for warmer regions in the near climate-change future. [ABSTRACT FROM AUTHOR]

Industrial waste heat recovery shows significant potential for increasing energy efficiency in industry. However, to design strategies that exploit this potential, it is necessary to have data about the quantity and characteristics of industrial waste heat flows. This information is not always readily available and many companies do not even have a systematic record of these energy flows. Hence, bottom-up methodologies to estimate that recovery potential by means of key transfer figures are useful tools within this field. In the present article, four different methods are applied to determine the industrial waste heat recovery potential in the Autonomous Community of the Basque Country (northern Spain), an energy-intensive industrial region with large energy dependency from the outside. Besides, the analysis of the economic viability of the industrial waste heat recovery is essential, because it determines the final adoption of energy efficiency measures. For that aim, the authors develop an easy-to-apply bottom-up methodology to carry out an assessment for the economic potential of the estimated industrial waste heat at different temperature levels. This method is applied to 129 companies, whose potentials are characterized and discussed. The obtained results show that, for waste heat streams above 400 °C, more than 90% of the studied companies present payback periods below five years. For those industries with waste heat temperatures below 200 °C, the ratio decreases to around 40%, still a noticeable value. The estimations show a significant opportunity to implement solutions to recover this wasted energy, especially in the iron and steel sector and the petrochemical industry. The development of public policies that encourage these measurements would be also beneficial. • Evaluates the techno-economic potential of industrial waste heat recovery. • Lack of assessments of IWH recovery potential at local, regional or national scales. • 13%–16% of the primary energy consumption might be recovered. • For streams above 500 °C, almost all the companies present viable recovery potentials. • Iron and steel and petrochemical sectors present positive economic perspectives. [ABSTRACT FROM AUTHOR]