In March 2024 I was at a conference on information technologies during which a person from REE stated that in the future we will not be able to take the security of electricity supply for granted. This person did not explain the reason for such a statement, but I do not think he was thinking of a catastrophic blackout like the one we suffered last April 28,2025 in Spain. From the context of the workshop, it is possible that he meant that, in an electricity system based exlcusively on renewable generation, there may be times when the available generation will not be able to cover all demand without bringing down the entire electricity system. In any case, this hypothetical situation is related to what some consider to be, if not the cause of the blackout, at least its framework. I´m refering to the lack of inertia in the electric system.
For years, research articles have been published characterizing inertia and studying how it has been decreasing as the penetration of renewable energies has increased. This hasn´t not only occured in Spain, but also in all countries that are introducing renewable energies in a significant way. The famous 50 Hz of the grid, which we see on the nameplates of any domestic device, have their origin in the rotation of the rotors of the alternators of hydroelectric, thermal and nuclear power plants which, thanks to their mass, have the inertia that allows them to compensate for sudden and transient variations in frequency. As these types of generators lose ground in electricity generation, physical sources at 50Hz also disappear, and the system becomes more vulnerable to inestabilities that can alter this frequency. Redeia itself acknowledge the risk this situation poses to the electricity system´s balancing capacity in its 2024 Consolidated Management Report. This should lead us yo believe that the transition to an electricity system based only on renewable energy can not consist only of installing more and more renewable generation capacity.
Renewable energy sources, both wind and photovoltaic, use electronic power converters. These converters are designed to feed the energy into a well-constituted grid with its expected 50 Hz. They are grid-following converters. For that reason, if they detect that the grid is unstable they disconnect from it. This is what may have happened on April 28 when, according to ENTSO-e, the frequency dropped to 48 Hz. Unlike conventional converters, there are others capable of generating synthetic inertia, i.e., by means of appropriate devices and control techniques, it is possible for the converters to react within milliseconds to changes in the grid frequency and thus mimic the response of a generator with natural inertia. In this way, renewable generation could contribute to grid stability. Such converters can also achieve the same effect with batteries, so that the batteries would not only store the renewable surplus, but also contribute to grid stability. But for such converters to be developed commercially, they need to be covered by regulations. The European Union launched the procedure in 2022 to initiate the revision of the corresponding grid codes, but it is a process that takes years until each country finally integrates them into its regulations. It will also be necessary to modify the regulations so that batteries can have access to all the services available on the market.
It should not be forgotten that demand can also contribute to grid stability. In Spain, the active demand response service (SRAD) has already been activated four times, through which the system operator requests the disconnection of the loads of those consumers who voluntarily participate in the service and who receive remuneration in exchange for their flexibility. But the conditions for participation leave out many potential participants. It is necessary to lower the minimum power or allow the aggregation of consumers and increase the frequency of auctions to facilitate the incorporation of more power to the service. It seems that all these ideas are already on the table and could be a reality soon. Along the same lines, the announced capacity market could play an important role in the stability of the system. In this market, generation, storage and demand will be able to participate. It seems that aggregation will be allowed, which could open the door for small consumers, such as domestic consumers, to take advantage of the flexibility of their demand for their own benefit and for the benefit of the system.
“The Active Demand Response Service (SRAD) is established as a specific balancing product provided by the electricity demand of the Spanish peninsula electrical system to address situations where a shortage of upward tertiary regulation reserve is identified.”
Finally, to transform the electrical system, in addition to all of the above, new lines will have to be laid in the most saturated areas and grid monitoring improved. Simply filling thousands of acres with panels and wind turbines isn’t enough. And an important question remains: how to finance all of this.
In 2022, the European Commision launched one of its most ambitious initiatives: the Smart and Climate Neutral Cities Mission for 2030. In this mission, 112 cities were selected from among 377 candidates to lead the transition to climate neutrality and achieve it by 2030, 20 years before the global target set for the entire continent in the European Green Pact. Among them are 7 Spanish cities: Madrid, Barcelona, Valencia, Seville, Valladolid, Vitoria and Zaragoza.
The Mission introduced a results-oriented logic, with the Climate City Contracts (CCC) as a central tool to articulate three pillars necessary to achieve this transformation: political commitment, technical roadmap and integrated financial mechanisms.
“The Climate City Contracts (CCC) are voluntary agreements between cities and the European Commision that looks for collaborate to address the challenges of climate change at the local level”
Three years after its launch, and in the context of the recent Mission Conference1“Building on Cities´Successes: Driving Climate Action for 2030”; held in Vilnius (Lithuania) from May 6-8, which served as a key meeting point for mission cities, their technology partnerts and the European Commision, it is timely to review progress. From CARTIF, as an active partner in several projects linked to the Mission, we have closely experienced this evolution from the initial vision to the current implementations that we can summarize by taking a look at the mission projects in which we work:
NETZEROCITIES(GA 101036519), platform that supports the implementation of the mission, acts as its methodological backbone, providing technical assistance, support to the “pioneer cities” and the development of tools for urban innovation (several designed and developed by CARTIF as technological partner of the project) that are helping to consolidate a common approach for all participating cities, beyond individual projects. In this context, it also highlights the role of CapaCITIES (GA 101056927), of which CARTIF is also part, and which acts as a catalyst to strengthen the institutional, technical and of governance capacities of the cities, replicating the concept of mission implementation platform in national contexts.
In NEUTRALPATH (GA 101096753), project coordinated by CARTIF, we are working with Zaragoza and Dresden to develop Positive Energy Districts (PEDs), capable of producing more energy than they consume as one of the main elements to improve energy efficiency, reduce emissions and therefore achieve climate neutrality. This transformation requires integrated solutions in energy efficiency, renewable energy, storage, digitalization and citizen participation. The project is demonstrating that the neighbourhood scale approach can be not only viable, but replicable, and key to reaching urban climate neutrality.
In ASCEND(GA 101096571) , where CARTIF participates as a partner, we collaborate with the cities of Lyon and Munich in the accelerated demonstration of integrated and scalable urban solutions, also associated with the concept of Positive Energy Districts (PED). Our role focuses on the design of climate impact planning and monitoring tools, enabling cities to make informed and adaptive decisions. ASCEND seeks not only to test technologies, but to orchestrate them in real urban ecosystems, with the ambition to scale.
Finally, in MOBILITIES FOR EU (GA 101139666), coordinated by CARTIF, we collaborate with Madrid and Dresden to demonstrate electric and autonomous mobility solutions, connected to renewable energy infrastructure and smart urban grids such as advanced 5G systems. Our approach combines technology, systemic analysis and business models to accelerate the adoption of clean solutions for mobility of people and goods.
The Vilnius conference has highlighted that the Mission is no longer a promise, but a network of cities in full transformation. From CARTIF, at the forefront of the implementation of the mission, we reaffirm our commitment to this vision: to put innovation at the service of cities and businesses to make them more sustainable, fair and resilient.
These projects are funded by the Horizon Europe research and innovation program.
1 Cities Mission Conference “Harnessing City Successes: Advancing Climate Action for 2030”
In a previous blog post, we talked about the importance of interoperability and how it allows different systems to communicate with each other without barriers. We used the metaphor of the digital Tower of Babel to explain the challenges that arise when multiple technologies, devices and platforms try to share information without common language. In this context, one of the pillars facilitating semantic interoperability is the use of ontologies.
But what is an ontology and why is it so relevant for the digital and energy efficiency world? Let´s explain it in a simple way.
Machine language: how we understand?
To understand what an ontology is, let´s think about how human beings communicate. We do not all speak the same language, and each language has its own grammatical structure, sounds and written symbols. Even within a language, there are dialects and regional variations that can make communication more complex.
Machines and digital systems face a similar problem. Each manufacturer of sensors, devices or software may use its own “language” to represent data. One building´s air conditioning system may report the temperature in degrees Celsius, while another reports it in Fahrenheit. Some devices may call a value “room temperature”, while others simply label it “temp” o “T”. If these systems do not have a common dictionary, communication between them will be difficult or even impossible. This is where ontologies come into the picture..
What is an ontology ?
In the field of computer science and AI, an ontology is a structure that defines concepts and the relationships between them within a specific domain. In other words, it is a way of organising information so that different systems understand it in the same way.
Returning to the language analogy, an ontology is like a multilingual dictionary with clear grammatical rules. It not only establishes equivalences between concepts belonging to different languages, but also establishes the relationships between them. For example, if an ontology says that “room temperature” and “temp” means the same thing, a system using this ontology will consider both expressions as equivalent. Moreover, an ontology allows inferring new information from the knowledge that is already defined in it. That is, it not only stores data, but can also use it to infer things that weren´t explicitly written down.
To fix the concept of ontology let´s imagine a house, in which we could define:
Relationships: a door conects rooms, windows are in walls, a bathroom is a type of room….
With all this described and well formulated, an artificial intelligence could answer questions such as, can a window be on the roof? or can there be more than one door in a house?
Ontologies help machines reason about information, allowing them to understand concepts in a more structured way, and not just as loose data. In fact, ontologies are often used in intelligent search engines, robotics, chatbots, etc.
Ontologies and semantic interoperability
As mentioned in our previous post, interoperability has several dimensions: technical, syntactic, semantil and organisational. In this case, ontologies play a crucial role in semantic interoperability, ensuring that systems understand and interpret information in the same way.
Imagine a platform that manages the energy efficiency of a smart building. It receives data from multiple sensors and systems: lighting, air conditioning, electricity consumption, air quality, etc. If each of these devices uses a different way of representing the information, without an ontology to standardise this data, it would be a chaotic to try to process and analyse it in a unified way.
The use of a pre-established ontology will allow this platform to recognise that “temperature sensor”, “thermometer” and “internal climate” are related, ensuring that the information is processed in a consistent and homogeneous way.
“An ontology is a structure structure that defines concepts and the relationships between them within a specific domain”
Ontologies in everyday life and energy efficiency
Ontologies are not only a exclusive concept on digital world. In our everyday life, without knowing, we use similar structures to organize information. For example:
In a supermarket, products are organised into sections: fruits, dairy products, meat, bakery etc. This scheme helps us to find what we are looking for quickly.
In a library, books are classified by genre, author and subject, making them easier to find.
In the medical field, there are classification systems for diseases and medicines so that health professionals speak the same language.
In the field of energy efficiency, ontologies are essential to develop services that turn buildings into smart buildings capable of self-managing and optimising their consumption. By using a common ontology, different systems can exchange information without misinterpretation, allowing lighting, HVAC and other devices to work together efficiently.
In addition, ontologies allow reasoning (drawing conclusions), which facilitates the development of decision support systems to optimise energy use, reduce waste and improve the operational efficiency of buildings.
There are several projects in which CARTIF analyses and applies standard ontologies to ensure that data from different buildings are understandable and reusable in advanced digital solutions, such as the DEDALUSand DigiBUILD projects. In both projects, the use of ontologies allows the information to be unified, thus facilitating the generation of joint building automation and control strategies and decision making based on real data. Furthermore, the use of ontologies allows the different systems being developed in these projects to “speak the same language”, which means that they can easily exchange information and understandeach other, even if they have been designed by different entities or for different functions.
Through the use of ontologies, we incorporate a new technological enabler that allow us to build a more digital and sustainable future, where information flows without barriers and where buildings are truly intelligent, thus contributing to the decarbonisation and sustainability of the planet.
Spain is positioned as a global referent in the energy transition thanks to its ambitious energy and climate change policies. According to the report by the International Energy Agency (IEA), Spain aspires to achieve climate neutrality by 2050, with 100% renewable energy in the electricity mix and 97% in the total energy mix. This will only be possible by adopting renewable energies, improving energy efficiency and boosting electrification. However, green hydrogen will also play a crucial role, especially to decarbonise sectors such as industry and transport, as well as to store surplus renewable energy, reducing energy waste (curtialment).
In fact, green or renewable hydrogen is consolidating as a crucial energy vector to reach the decarbonisation of the Spanish energy system. With 20% of European electrolysis projects announced, Spain leads the way, followed by Denmark (12%) and Germany (10%). These three countries could generate more than 40% of Europe´s low-emission hydrogen by 2030.
Hydrogen, the most abundant chemical element in the universe, is not found in its pure state in nature and must be produced. Its sustainability depends on the method of production. Green hydrogen is produced by electrolysis powered by renewable energies, without generating polluting emissions, making it an indispensable ally in meeting global climate targets.
This resource offers a viable solution for storing renewable energy and decarbonising difficult sectors such as industry and transport. At CARTIF, we have carried out an exhaustive analysis using advanced energy models to explore how this vector could be implemented in different future scenarios. To do so, we have used tools such as LEAP and other prospective methodologies that allow us to assess economic, social and environmental impacts.
Context and objectives
The main objective of this analysis is to know the possibilities of integrating renewable hydrogen in Spain as a key strategy for achieving climate neutrality by 2050. This study is based on three fundamental scenarios that describe different development trajectories:
Trending: represents a trend development of the energy system without the application of additional masures since 2019.
PNIEC Objective: considers the policies and objectives set out in the National Integrated Energy and Climate Plan (PNIEC)
Ambitious: proposes a high penetration of the renewable hydrogen, alligned with the goals of the European Hydrogen Roadmap.
This analysis also includes a comprehensive approach to assess economic, social and environmental impacts, thus allowing for the identification of barriers and opportunities for the energy transition in Spain.
To carry out this analysis, a simulation model was developed in the LEAP tool, capable of projecting both energy demand and generation over long-term time horizons. The model combines:
Socioeconomic projections, including variables such as PIB an population evolution.
Historical data on energy consumption and generation, essential to establish a base year reference
Specific scenarios that include different hydrogen penetration levels.
Key technologies integration such as electrolysers and hydrogen storage in salt caverns.
In addition, differnt national and international energy policies were evaluated, such as the Spanish Hydrogen Roadmap and the European Union´s vision of a “Clean planet for all”, as well as emission restrictions and reaching a certain percentage of renewables by 2050.
In the baseline scenario, where energy policies for demand reduction and decarbonisation aren´t considered, total energy demand in Spain would increase by 7% between 2020 and 2050. This growth is due to an increase ithe electrification of key sectors, following the trend observed so far. The PNIEC Objective scenario contemplate a much more significant improvement in energy efficiency and, above all, transitions from very energy intensive technologies to less energy intensive options (e.g. buses) or electricity consuming alternatives (e.g. heat pumps), using 40% less total energy in 2050 compared to the baseline scenario. In addition, there is a higher electrification (an increase of 26.6% between 2019 and 2050). In the scenarios that include hydrogen, electricity consumption in electrolysers is increased in exchange for decreasing the use of fossil fuels in the overall energy system.
Evolution of the system demand by sector on the different scenarios (TWh)
In terms of electricity sector supply, scenarios with hydrogen storage manage to reduce the renewable energy that cannot be harnessed due to lack of demand, known as curtailment, by up to 68%, allowing for greater efficiency in the use of renewable energies and avoiding oversized investments in installed capacity. This is mainly due to hydrogen´s ability to act as a energy storage vector, transforming surplus renewable generation into hydrogen that can be stored and used in periods of high demand or low renewable production. In addition, hydrogen systems such as electrolysers and fuel cells also improve the flexibility of the electricity system, enabling more efficient integration of intermittent sources such as solar and wind. These technological advances also reduce reliance on non-renewable sources during periods of high demand, consolidating a more sustainable energy system.
Results summary
In terms of emissions, in the baseline scenario CO2 equivalent emissions increaseslightly until 2050 due to limited electrification and continued dependence on fossil fuels.
The PNIEC objective scenario reduce emissions by 30% between 2019 and 2050, partially meeting climate objectives. A 100% renewable electricity grid is reach, although with a large investment. However, the 90% emission reduction target compared to1990 is not reached due to emissions caused by energy demand from other sectors.
Similar to the case of costs, in the basic hydrogen penetration scenario, emissions are reduced slightly, but not significantly. In the ambitious hydrogen scenario, thanks to a high penetration of electrolysers and energy storage, a 90% reduction in emissions is achieved, in line with the climate neutrality proposed by the PNIEC.
Emissions evolution (M ton. Co2 eq.)
Conclusions
The integration of renewable hydrogen into the Spanish energy system is essential to reach climate objectives and decarbonise key sectors such as industry and transport. The results of this study highlightthat:
It is essential to incorporate energy storage technologies, such as hydrogen, to maximise the use of renewable energies and reduce the losses and cost overruns associated with curtailment.
Current policies need to be strengthened and updated to ensure that the 2050 objectives are met, including incentives for the installation of electrolysers and hydrogen storage.
Increased investment in R&D for the development of hydrogen technologies will improve the economic and environmental sustainability of the system
Good planning of the energy transition towards climate neutrality is very importnat, with parallel efforts on decarbonisation of electricity generation and energy demand, and renewable hydrogen generation.
At CARTIF, we not only develop innovative technological solutions that drive the transition to decarbonised energy systems, but we also provide detailed energy reports and studies such as this one, designed to support institutions and companies in making key decisions for a sustainable future.
Co-author
Pablo Serna Bravo.Industrial Engineer. He has been working at CARTIF since 2023 as a researcher specialising in hydrogen, energy modelling and global energy policy analysis.
The importance of the design tools and green hydrogen optimisation
Green hydrogen is positioning itself as a viable alternative in the context of the transition towards clean and sustainable energy sources. Not only does this energy carrier transform energy without emitting pollutants, but it also has significant long-term storage capacity, which helps to address one of the main problems of renewable energy sources such as solar and wind: their intermittent and seasonal nature.
Due to the several hydrogen applications and the variable nature of renewable sources, the design and optimisation of green hydrogen production, storage and utilisation systems are complex processes especially when applyied to industrial processes, where careful management of the entire chain is necessary to ensure continuous and efficient operation. This is where simulation and optimisation tools plays a crucial role, facilitating the efficient integration of hydrogen into the energy system and enabling optimal decisions to be made based on detailed data and accurate projections.
Need for specialised tools for energy transition
In order to move towards a more sustainable and decarbonised energy system, it is essential to apply dynamic modelling and simulation to optimise both the production and use of green hydrogen in the residential, industrial and heavy transport sectors, as each has different energy demand patterns, requiring the development of specific tools to evaluate multiple scenarios, optimise design and determine the most appropriate control and management strategies.
These tools not only allow the simulation of system behaviour under real conditions, but also help to optimise important parameters such as electrolyser power ratings, hydrogen storage volume and the management of optimal times to consume or storage energy. The application of advanced optimisation algorithms aims to reduce operational and investment costs while maximising the use of renewable energy by ensuring that the best technical, economical and ecological decisions are made.
Functionalities of the developed tool
CARTIF which is a Cervera Centre of Excellence, awarded by the Ministry of Science and Innovation and the CDTI, under the files CER-20191019 and CER-20211002 has developed a tool for the design and optimisation of this type of systems thanks to the CERVERA H24NewAgeproject. It is a platform that enables the design and optimisation of systems for the production and use of green hydrogen in residential and industrial environments by applying dynamic modelling together with Python through an easy-to-use web interface that facilitates access to complex simulations without the need for advanced technical knowledge, contributing to the democratisation of hydrogen technology, allowing users with different levels of experience to interact with complex models and gather useful information for decision-making in the design of their systems. Some of the key points of the tool are:
Simulation of hydrogen production scenarios: Users can simulate a variety of hydrogen production environments, such as industrial processes, industrial cogeneration, residential micro-cogeneration and large-scale power generation.
Optimisation Based on Advance Algorithms: The tool helps to size the optimal size of system components, minimising costs and maximising renewable energy utilisation using advanced optimisation algorithms. It also includes the creation of operational strategies that consider renewable energy availability, hydrogen demand and storage constraints to achieve economical and efficient operation.
Flexibility and Adaptability: Crucial parameters such as geographic location, demand profiles and renewable production technologies can be adjusted through the platform, making it ideal for a variety of scenarios and specific needs. This capability is fundamental for users to assess how their designs would perform in different situations and scenarios, adapting hydrogen production and storage technologies to the particularities of each environment.
Visualization of results: The tool’s web interface makes it easy to visualise simulation results through interactive graphs and tables showing key aspects of the system, such as energy efficiency, operating costs and storage capacity. Users can also compare the results of different scenarios, which is essential for identifying opportunities for improvement and making further adjustments.
Conclusions
Ultimately, tools such as these can be used to evaluate and optimise strategies for the production and use of green hydrogen, facilitating its integration into the energy system and contributing to a more sustainable future. Thanks to access to advanced models and optimisation algorithms, these tools enable informed decisions to be made, resulting in more efficient and resilient systems. A clear example would be the optimal hydrogen storage capacity, the correct estimation of which can avoid unnecessary costs and ensure a constant supply, increasing the operational efficiency of the system. In addition, the ease of use and flexibility offered by these platforms help reduce the technical barriers to adopting green hydrogen, making it an accessible and viable option for a wider range of users and applications. This is key to moving towards an effective energy transition and to fostering solutions that reduce dependence on fossil fuels and support climate change mitigation.
Co-authors
Jesús Samaniego. Industrial Engineer. Since 2002 he has been working at CARTIF in the development of projects within the field of energy efficiency, the integration of renewable energies and in the study of the quality of the electricity supply
I have always been passionate about telecommunications, and the implicit idea of achieving a “connected world”, wired or wireless, where information flows from one end of the globe to the other, regardless of the location and the native way in which each country, city or region tends to communicate. But in the face of this idealisation of a historically and recurrently connected world, there are problems of understanding in this communication. Whether it is because the language is different, because different alphabets or writing is used, or because culturally the rules of language use and the way of communicating differ from continent to continent, the reality is that global communication is a challenge that we continue to face today.
In the era of digitisation and the Internet of Things (IoT), where large volumes of data are now being collected, stored and processed, problems in the communication and unique representation of information are once again becoming apparent. It will be difficult to find data capture devices (from different manufacturers) that provide information using the same format, or that answer using the same question. Such is the problem that there are disciplines, including telematics, that focus on defining and specifying standard communication protocols that apply to different domains. But what if we want to communicate different domains? Despite the existence of standards, the problem persists. We are faced with a Digital Tower of Babel, where the heterogeinity of protocols, representation formats, communication rules and standards once again makes understanding between systems and solutions difficult.
To solve this problem, and of course, in the military and technological sphere, the concept of interoperability was born, understood as the ability of the armed forces of different nations to collaborate efficiently through the integration of systems and communications. This interoperability approach was later adopted by other sectors, such as the Information and Communications Technology (ICT) sector, with the development of systems that required efficient and conflict-free information sharing between different devices and platforms. In this ICT context, interoperability is understood as the ability of different systems, devices or applications to comunicate, exchange and use information effectively and coherently.
“Interoperability. Understood as the ability of different systems, devices or applications to comunicate, exchange and use information effectively and coherently.”
To achieve this interoperability between heterogeneous systems, i.e., systems that speak different languages and represent the information in different ways, we need to cover several dimensions, each focusing on a different aspect of communication and data exchange between systems:
Technical interoperability refers to the ability of different systems and devices to connect and communicate with each other through standards and protocols. This includes hardware, software, networking and communications compatibility.
Semantic interoperability is responsible for ensuring that the information exchanged is understood in the same way by all parties, thanks to the generation of a common vocabulary (ontology). It is about ensuring that systems interpret data with the same meaning, regardless of how they are structured or labelled.
Syntactic interoperability ensures that systems can process and exchange data in a structured way, i.e., that the same data formats and structures, such as XML or JSON, are used.
Organisational interoperability involves the alignment of policies, processes and regulations across organisations to enable effective collaboration. It encompases governance arrangements, security policies and data management.
One of the sectors that will benefit greatly from these interoperability solutions is the building sector, where digitisation and information exchange at all stages of the life cycle offers a springboard for development and competitiveness. Here, the creation of intelligent buildings, highly monitoring and able to anticipate the needs of their users thanks to digitisation and advanced data processing, alowws forbuildings that contribute to the goals of efficiency, decarbonisation and sustainability. In this context, interoperability solutions allows the diverse energy systems (such as lighting,HVAC, air conditioning, etc.) to work together, sharing and processing data seamlessly, regardless of manufacturers or platforms. This helps to optimise building management, reduce costs and improve energy efficiency by enabling systems to work as an integrated ecosystem.
At CARTIF we have been working for more than a decade on energy efficiency projects where interoperability enabling technologies, both technical and semantic, are a key element for obtaining smart, open and highly replicable solutions. Projects such as DigiBuild, DEDALUS and BuildON are examples of how these technologies facilitate the creation of smart and sustainable buildings.
