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• Mechanisms to encourage clean energy in Spain from 2005 to the present are analyzed. • FiT and FiP mechanisms can be effective in promoting new renewable projects. • Experience suggests that excessive support can jeopardize the entire market. • A transitional retribution scheme has proven to be effective if correctly supervised. This research paper delves into the central mechanisms implemented in Spain to foster the adoption of clean energy projects. The study scrutinizes various mechanisms established from 2005 onwards, evaluating their efficacy in achieving the desired outcome of supporting clean energy project implementation. The aim is to comprehensively assess the associated costs, effectiveness, and attainment of renewable energy objectives stemming from implementing diverse support schemes. This paper explores the effectiveness of feed-in tariffs and feed-in premium mechanisms in promoting the integration of new renewable energy generation into the power system. However, the Spanish experience suggests that exhaustive planning control is imperative to prevent excessive support costs that could jeopardize the entire market and cause a significant rise in final energy costs. The research studies the support schemes and associated market distortion and presents the roadmap from regulated tariffs to a "total market" for wind and solar energy. The findings demonstrate that, under proper supervision and planning, a transitional retribution scheme effectively promotes renewable energy plant integration. Finally, the analysis examines the need to regulate the excess benefits that non-emitting power sources receive in a marginal price market, as this can lead to market imbalances and a substantial increase in final costs. These plans serve as a crucial tool in achieving the decarbonization objectives of the European Power System. [ABSTRACT FROM AUTHOR]

• Pioneer Spain: first country to include in grid code the synthetic inertia capability. • Synthetic inertial response of a PV inverter studied based on the Spanish grid code. • Analyzed the role of power plant controller in the dynamic response of the facility. • PV system able to contribute to frequency control providing an inertial response. As the large-scale integration of renewable energy grows, inertia in power systems is reduced, which causes the rate of change of frequency to increase and worsens the frequency nadir during disturbances. There is, therefore, an urgent need to accelerate the development of international standards and regulations that require solar PV systems and other renewable installations to also contribute to stability in the network by emulating inertia. Spain is a pioneer in this field: it is currently the only country that includes the synthetic inertia technical requirement in its grid code. In this context, the present paper analyzes the synthetic inertial response of a PV system model that forms part of an actual PV power plant in Spain under two scenarios, according to its grid code: i) when measurements are conducted at the power conversion PV system level and hence only its control algorithms are executed; and ii) when measurements are conducted at the power plant level and the power plant controller also influences the response of the entire installation. Among its aims, this paper seeks to thoroughly assess the response of an actual PV power conversion system that has the capability of actively contributing to frequency regulation in a network and to critically analyze the suitability of having a power plant controller when the PV facility contributes to power-frequency control by means of an inertial response. The results reveal, at the power conversion PV system level, that the inertia emulation module significantly reduces the response times of the installation to changes in frequency -by more than 68% in the worst case under frequency increases, and by 73% under frequency decreases, thus contributing to more rapid power-frequency regulation in the network. However, at the power plant level, the power plant controller disturbs the PV power conversion system's behavior and causes the opposite effect: response times increase -up to more than 7% in the most unfavorable case when the inertia module is enabled. [ABSTRACT FROM AUTHOR]

Decreasing greenhouse gas emissions plays a crucial role in the Europe energy transition and the production of hydrogen using electricity from renewable sources (green H 2) contributes significantly to this objective. As the renewable energy production capacity grows, the impact of green H 2 is likely to increase. In the case of the Iberian Electricity Market (MIBEL), no quantitative studies have so far tested the viability of the H 2 growth plans. This paper fills this gap through a novel mathematical programming model, which integrates H2 generation into the MIBEL. The model reveals a mismatch between the sustainability goals and the expansion plans of renewable and green H 2 for Spain and Portugal. [Display omitted] • Mathematical Programming to analyse green hydrogen production in the MIBEL. • Influence of the electricity market on hydrogen production and prices. • Generating green hydrogen is preferable to hydro pumping. • Green hydrogen integration might entail additional emissions. • MIBEL hydrogen strategy must be revised to achieve sustainability. [ABSTRACT FROM AUTHOR]

Wind power is one of the most important renewable energy sources worldwide. However, integrating these technologies in electricity markets faces challenges due to the intermittent wind speed, resulting in potential imbalances within power grids and subsequent inefficiencies. Traditional approaches for modeling the uncertainty simulate fixed wind power values in operational and planning models, which work well for the short term but are inadequate for medium-term decision-making due to lower forecasting accuracy and the inability to differentiate the imbalance risk faced in each simulated value. This paper proposes a novel methodology for incorporating wind energy imbalance risk into medium-term generation planning models. For this, we first simulate realistic wind power scenarios and perform a fitting distribution process to characterize the hourly wind power behavior. Then, we model the imbalance risk using quadratic-uncertainty cost functions for each simulated value. Subsequently, we conduct a temporal aggregation to reduce the computational burden, preserving the conceptual framework of the imbalance risk modeling. Finally, we propose a medium-term generation planning model that includes the imbalance risk model and the temporal aggregation strategy. Our approach is evaluated in a real-size case study formed by Spain, Portugal, and France's electricity markets, demonstrating accurate wind power imbalance risk modeling and lowered planning costs. • A new methodology to include wind energy imbalance risk in generation planning models. • Introducing a fitting process for modeling the distribution asymmetries of wind power. • Proposing a temporal aggregation method for efficient imbalance risk modeling. • The methodology is validated in Spanish, Portuguese, and French electricity markets. [ABSTRACT FROM AUTHOR]

The increased penetration of renewable energy sources (RESs) as an effective mechanism to reduce carbon emissions leads to an increased weather dependency for power and energy systems. This has created dynamic operation and degradation phenomena, which affect the lifetime estimation of the assets operated with RESs. For the reliable and efficient operation of RES it is crucial to monitor the health of its constituent components and feature selection is a crucial step for building robust and accurate health monitoring approaches. In this context, this paper presents a probabilistic feature selection approach, which probabilistically weights and selects features through a heuristic and iterative process for an improved asset lifetime estimation. Power transformers are key power grid assets and they are used to demonstrate the validity and impact of the proposed approach. The approach is tested on two different photovoltaic power plants operated in Spain and Australia. Results consistently show that the proposed feature-selection approach reduces the prediction error and consistently selects relevant features. The approach has been applied to transformer lifetime estimation, but it can be generally applied to assist in the lifetime estimation of other components operated in RESs. Part of the studies presented here as well as source codes are all open-source under the GitHub repository https://github.com/iramirezg/FeatureSelection. • Probabilistic feature selection approach for improved asset lifetime estimation. • Integration of environmental features for improved renewable-operated asset lifetime. • Systematic and robust feature weighting methodology. • Improved transformer lifetime estimation including sensor and environmental data. • Validated on two real photovoltaic power plant case studies. [ABSTRACT FROM AUTHOR]

This paper proposes the first application of a split-range control technique on a concentrating solar collector to improve an absorption plant production. Solar absorption plants have solar power availability in phase with cooling demand under design conditions. Thus, it is a powerful cooling technology in the context of renewable energy and energy efficiency. These plants need control systems to cope with solar irradiance intermittency, reject irradiation disturbances, manage fossil fuels backup systems and dump closed-loop thermal-hydraulic oscillations. In this work, control techniques are proposed and simulated in an absorption plant in Spain. The plant consists of a concentrating Fresnel solar collector connected to an absorption chiller. The objectives are to operate with 100% renewable solar energy and avoid safety defocus events while reducing temperature oscillations and control actuators effort. Firstly, the current available plant controllers are defined, then two modifications are proposed. The first modification is a split-range controller capable of manipulating both flow and defocus of the Fresnel collector, the second modification is a PI controller to substitute the original chiller on-off controller. The results compare, through validated models, the different control systems and indicate that using both proposed controllers reduces 94% of the sum of actuators effort and 43% of the integral of absolute set-point tracking error compared to the plant's factory pre-set controllers. The suggested controllers increase 66% of energy production and 63% of exergy production. Besides, the split-range technique can be extended to any concentrating solar collector control. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper presents a model for optimizing the life cycle economic and environmental impacts of a hybrid renewable energy and battery storage system – as energy supply technologies (EST) for off-grid farms. Micro-hydropower and photovoltaics represent the primary renewable energy (RE) sources, with batteries and a diesel generator considered as possible back-up systems. A modified Non-dominated Sorting Genetic Algorithm II (NSGA-II) was developed and applied to a case study farm in Southern Spain and provided different EST solutions to optimize a design based on economic (life cycle costing or LCC) and environmental (life cycle assessment or LCA) constraints. The results highlighted that cases with a strong dependence on batteries could achieve minimum costs and lower impacts for climate change and energy resources (non-renewable fuels). In contrast, the optimal system for minimizing the consumption of material resources (metals/minerals) resulted in higher fuel use, which was up to 25% more expensive. The optimal EST solutions used up to 37% of the total energy generated; however, the results were sensitive to energy production-demand distributions. This methodology can help identify the most cost-effective solutions with the lower environmental impacts for decarbonizing the agricultural sector. [Display omitted] [ABSTRACT FROM AUTHOR]

• Energy Communities analysis and review in Europe and, more specifically, in Spain. • Promoting energy poverty reduction and cooperation through Energy Communities. • Real case study focused on reducing energy poverty in the city of Getafe (Spain). • Selection of public buildings to implement energy community in two neighborhoods. • Significant electricity bill reductions for energy poverty households. Advancements in renewable energy technologies, a growing awareness of the need for sustainable energy solutions, and the emergence of new business models in the energy sector, have contributed to the growth of Energy Communities. Public entities can find in energy communities today an opportunity to tackle energy poverty, to increase the cooperation among citizens and to empower them to be a more active player within the energy sector. This paper analyzes energy communities in Europe and focuses specifically on Spain; considering the three beneficial aspects previously mentioned. It aims to obtain ground truth about the applications of these new citizens' arrangements. A citizen-led initiative at the city of Getafe (Madrid, Spain) is included and discussed in detail. This case study focused on reducing energy poverty of its participants. An energy community was designed and implemented as a collective PV solar self-consumption infrastructure. The roofs of various public buildings in the two case study neighborhoods were selected for locating the PV installations. Real metered data were used to evaluate the solution. A public building was selected for the energy community, considering generation on roof and dwellings proximity. The results provided that out of the 77% PV generations could be used to contribute to the demand of 100 residences; while the resulting 23% would provide approximately 60% of the energy demand of the public building. The setting up of the Energy Community not only had the technical part but also included workshops seminars and information sessions, to ensure that people prone to benefit and maximize its impact. [ABSTRACT FROM AUTHOR]

Marine renewable energies can play a key role by reducing the dependency on fossil fuels and, therefore, mitigating climate change. Among them, it is expected that wave energy will experience rapid growth in the upcoming decades. Thus, it is important to know how wave climate will change and how suitable the wave energy converters (WECs) will be to the new wave conditions. This paper aims to evaluate the capability of four different WECs—a WaveRoller type device (WRTD), Atargis, AquaBuoy and RM5—to extract wave energy on the Northwest coast of Spain (NWCS). The analysis was performed using the high-resolution wave data obtained from the Simulating Waves Nearshore (SWAN) model over the near future winters (2026–2045). The energy output (P E), the power load factor (ε), the normalized capture width (NC w) and the operational time (OT) were analyzed. According to these parameters, among the devices that work for intermediate-deep waters, Atargis would be the best option (P E = 1400 ± 56 kW, ε = 55.4 ± 2.2%, NC w = 35.5 ± 4.1% and OT = 84.5 ± 3.3%). The WRTD would also be a good option for shallow nearshore areas with P E = 427 ± 248 kW, ε = 12.8 ± 7.4%, NC w = 48.9 ± 9.6% and OT = 88.7 ± 18.9%. A combination of Atargis and WRTDs is proposed to make up the future wave energy farms on the NWCS. • Dynamical downscaling using SWAN to simulate near-shore wave conditions. • Wave energy converters suitability is analyzed in the context of climate change. • Atargis is the most suitable device to future sea conditions in intermediate waters. • WaveRoller type devices can constitute future wave farms for shallow waters. [ABSTRACT FROM AUTHOR]

• 2050 low-carbon economy pledge and Spanish photovoltaic investment plan. • Photovoltaic spatial allocations minimising unpredictable variability. • Impact of wind energy investments on the optimal photovoltaic spatial allocation. • Allocation of photovoltaic and wind investments minimising supply–demand mismatch. • Assessment of the current photovoltaic investments in Spain. After a period of stagnation that lasted until approximately 2018, Spain has established an ambitious investment program in photovoltaics, derived from the pledge to switch to a carbon-free energy system by 2050, the sustained cost decreases of the technology, and the excellent irradiance values over its territory. This paper implements an additional criterion for the spatial allocation of these investments based on minimising the energy variability generated because of weather intermittency. The analysis is based on hourly data for the years 2005–2020 (inclusive), in various locations homogeneously spread throughout Spain. Subtracting the deterministic daily and annual irradiance cycles to estimate the variability of the random component is discussed. Failing to do that yields significantly higher and distorted values for solar energy variability, resulting in low investment proportions when combined with other energies, like wind. The first results show that a straightforward, equally-weighted allocation of investments is suboptimal. It is also shown that investing in low-irradiance locations contributes to reducing overall variability. Secondly, the study analyses overall power variability minimisation conditional on a given wind investment weight. It is found that the impact is significant spatially, and that proportions of wind energy above 10% increase aggregated variability across all levels of aggregated power generated. Nevertheless, investment proportions in wind energy below 10% reduce the overall combined variability significantly due to the negative correlation between wind and solar irradiation. The third point addressed is the minimisation of the mismatches between renewable energy supply and aggregate electricity demand. The optimal proportion for solar and wind investments becomes close to 50% in this case. However, this proportion tilts towards solar investments if variability minimisation is also considered. Finally, the current spatial distribution of photovoltaic investments in Spain is analysed, and it is shown that there is room for improvement. It is also found that the current ratio between wind and photovoltaic energy may not be optimal, and that it would be advisable to increase proportionally more photovoltaic energy. [ABSTRACT FROM AUTHOR]

This paper evaluates a parametric analysis towards compliance with the nZEB standard, which in Spain is defined by the latest update of the Technical Building Code. This regulation is critically assessed regarding its ability to promote the concept of cost optimization, promote renewable energy sources and minimize primary energy consumption in the residential sector. To this end, a virtual building was defined and multiple designs were evaluated using DesignBuilder software. A set of 170 alternative scenarios was established and parametrically evaluated for five cities representing the five climatic zones of inland Spain (Bilbao, Burgos, Seville, Madrid and Almeria). The results were evaluated focusing on cost-cost effectiveness and primary energy consumption values for the different scenarios, evaluating them in relation to the minimum requirements set by the regulation. The great potential of photovoltaic energy is highlighted, which allows negative values to be obtained for the two Equivalent Uniform Annual Costs due to the cost avoided through self-consumption. This fact makes the optimal designs tend to electrification, specifically through air and ground source heat pumps. It is worth mentioning that the new Code has only established a minimum target for renewable self-consumption in the residential sector, which should be reinforced in future updates. [ABSTRACT FROM AUTHOR]

• Self-consumption in residential sector is studied under Spanish regulatory framework. • An average-day model versus a whole-year model is benchmarked. • Scheduling household appliances is analysed in a residential building. • Ex-ante and ex-post renewable energy sharing is investigated. Studies on self-consumption in residential use are constantly evolving, and society claims new solutions in response to changes to new paradigms. This paper aims to optimise the sizing of a self-consumption installation for collective self-consumption in a residential building under the Spanish regulatory framework. The study considers the current price volatility in the retail electricity Spanish market and focuses on the techno-economic analysis of self-consumption in a building consisting of 12 dwellings using photovoltaic energy and the possible support of a storage system. The three aspects analysed are the sizing of the self-consumption facility, the use of smart appliances to shift their consumption to more cost-effective times and the sharing of the renewable energy generated by the facility among the consumers participating in the collective self-consumption. This study employs two models, an average-day model and a whole-year model. The techno-economic analysis yields that between the two self-consumption modalities for residential consumption, the modality with surplus simplified compensation is more profitable than the one without surpluses. Finally, the study focuses on sharing the total renewable energy generated among the participants. The results indicate that both ex-ante and ex-post dynamic sharing brings few benefits. [ABSTRACT FROM AUTHOR]

• Evaluation of the most recent Spanish grid code requirements. • A new tool to speed up the commissioning of new solar PV power plants is presented. • The accuracy of the aggregated PV power plant dynamic model proposed is demonstrated. • The aggregated model is shown to be ten times faster than the detailed equivalent. • The aggregated solar PV power plant simulation model approved by the Spanish TSO. Renewable energy and, in particular, solar PV power, will play a crucial role in achieving net-zero emissions scenarios over the coming decades. Increasing the share of renewables in countries' energy mixes is therefore a major challenge that must be urgently addressed. Within this context, the present work proposes an innovative tool that may accelerate the commissioning process of new solar PV power plants, in the form of an aggregated simulation model to assess a power plant's responses under the technical requirements established in the Spanish grid code. Our analyses, based on the comparison of the proposed model with a detailed model -both representing the same installation, show, from a quantitative and qualitative viewpoint, the accuracy and usefulness of the dynamic simulation model proposed. The aggregated model is shown to be ten times faster than the detailed equivalent, while the errors encountered in the simulation responses of both models are below 0.1% in all cases. It must also be noted that the present paper has allowed for the introduction, in the most recent version of the Spanish grid code and following approval of the Spanish Transmission System Operator (TSO), Red Eléctrica de España (REE), of this new and advantageous PV power plant model. Finally, it is worth mentioning that this study could form the basis for encouraging other countries to also adopt this model in their grid codes as a new tool to help integrate PV power into power grids. [Display omitted] [ABSTRACT FROM AUTHOR]

The evaluation and comparative analyses of energy conversion technologies are carried out with well-established concepts, like the concept of efficiency. Today, however, new technologies based on renewable energy sources challenge conventional approaches. Accounting for fuel diversity and other inequalities can ensure that comparative analyses result in trustworthy results. This paper aims to address this issue by updating conventional efficiency for more accurate comparative evaluations of fossil fuel energy systems. Specifically, the concept of total efficiency is introduced to account for extraction, processing and transportation of fossil fuels, aspects that are not currently considered in the conventional definition of efficiency. The total efficiency is determined by studying the environmental impacts of these processes and quantifying their energy requirements in terms of additional fossil fuel use. Two case studies in Spain are presented to demonstrate the impact of using the developed method on efficiency estimates. The total efficiency is found to be lower than the convectional efficiency by 21–25% to up to 41%, in the most unfavorable cases. This shows the significant impact of the preparation steps of fossil fuels and represents a fairer comparison between fossil fuels and renewable conversion processes. • Introducing total efficiency for more accurate comparative evaluations of energy systems. • Total efficiency accounts for extraction, processing, and transportation of fossil fuels. • The developed method links environmental impacts to additional fuel input. • Fuel processing decreases the efficiencies of fossil power plants significantly. • Updated tools, like total efficiency, are necessary to achieve future energy sustainability. [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]