Have you ever wondered what a world where renewable energy storage is efficient and affordable would look like?
One of the challenges society must address to achieve effective decarbonization is increasing the generation and penetration of renewable energy. Despite the progress made, the intermittency of sources such as solar and wind, jalong with the need to optimize complex systems, limits the potential of these energies. Furthermore, energy storage technology developers face high risks when testing new devices in changing environments which can limit the insights gained.
At CARTIF, we have a multi-system test bench that allows us to store these surplus potentials in different formats: batteries, hydrogen and heat. In addition to evaluating the transformation chain in each case, we can characterize its behaviour in response to variations in demand, assessing its dynamic behaviour.
It is designed to replicate real-life energy scenarios, offering a unique environment where companies can confidently validate strategies and devices. We highlight some of its features:
Advanced technology: Includes PEM fuel cell, AEM electrolyzer, electric batteries, and hydrogen storage in metal hydrides.
Realistic simulation: Ability to emulate energy generation and demand profiles when interconnected with a data acquisition system.
Intelligent control: Incorporates a multi-level control system that optimizes operations in real time and allows for long-term analysis.
How can energy companies maximize the efficiency of its systems?
Here is where our test bench enters in game. These are some of the key advantages:
Accelerated innovation: Mathematical models have been developed to scale and visualize the performance that would be achieved with larger installations.
Risks mitigation: It allows for a reduction in the risk of technological scaling, as new technologies can be validated and development costs can be reduced by anticipating potential errors.
Superior energy efficiency: Through tests simulating its operation in the residential sector, up to 90% of the generated energy surpluses have been utilized, reducing peak demand, installed base power, and dependence on the electrical grid by up to 50%.
Regulatory compliance: The information extracted can also be used to ensure compliance with environmental and safety legislation.
CARTIF Multi-system Test Bench
Why you should be interested on this solution?
The energy sector is immersed in a critical transition to clean energy sources. The decisions you make now could determine the success of your projects in the coming years. Our test bench offers you the security and flexibility you need to lead this revolution.
Join the transformation! If you are an energy company looking to optimize resources or a developer needing to validate your products, this test bench is for you.
Discover the power of controlled innovation. Maximize your systems, reduce risks, and lead the way toward a sustainable energy future.
Contact us and take the next step toward technological excellence!
Luis Ángel Bujedo.Industrial Engineer. He works on energy efficiency and integration of renewable energy in buildings and industrial processes, especially on photovoltaic applications, monitoring and control of solar facilities and identification of cold facilities.
Three problems, one only answer: water-energy-food nexus
This year we´ve experienced situations as diverse as a widespread blackout that left us without power and basic services for several hours; a period of intense rain that, while providing sufficient water, also caused flooding in certain regions, and heat waves that have led to fires and droughts affecting forests and farmland.
If all these events are causing a huge headache for us, who live in a socially and technologically developed country with the capacity for prevention and response, it is logical to assume that in other contexts with far fewer possibilities, their impacts will be exponentially more damaging.
A clear example of this is the African continent, which, despite having a vast array of natural resources, constantly faces energy, food, and resource management challenges. To make matters worse, its current and future economic and demographic development only exacerbates these problems, as greater social growth implies greater demands for electricity, water, and food.
Everything is connected (even it seems it doesn´t)
When we experience a drought, our minds often focus on the lack of water for drinking or irrigating crops. However, a drought can also mean less hydroelectric production and, therefore, more pressure on the grid and electricity prices. If harvests are reduced due to lack of water or extreme heat, food production plummets and, consequently, food prices skyrocket. If a power outage prevents water from being pumped or food from being stored, the problem worsens.
This web of interdependencies is no coincidence. Water, energy, and food form an interconnected system where any change in one element can trigger effects on the others. That’s why the approach known as the Water-Energy-Food Nexus Methodology (or WEF Nexus Methodology) has been promoted for years.
Graphical representation of the Water-Energy-Food Nexus. Clean Energy Solution Center, Clean Energy Ministerial (2011)
What is the NEXO approach?
NEXO proposes, like many other theories, that the best way to address challenges related to natural resources is to move away from traditional silo thinking (understanding each resource as an individual entity, separate from the rest) and instead approach them in an integrated manner, understanding them as complex and interconnected systems in which acting on one will affect another, either negatively or positively. This systemic methodological approach analyzes how water, energy, and food interact with each other, while also including the influence of other associated factors such as the economy, demographics, climate change, and so on.
Rather than thinking “how do we improve agriculture?” or “how do we guarantee the electricity supply?”, the NEXO approach leads us to ask how we can guarantee sustainable access to all three resources simultaneously, without harming any and maximizing joint benefits. This approach allows us to anticipate conflicts, optimize resources, and make more balanced decisions in highly complex contexts.
Model to understand (and to decide better)
But of course, understanding and predicting these relationships is not easy. How do you measure the impact of a new dam on agricultural production? What effect does an increase in fuel prices have on water use in a region? How does urban growth influence food security?
To answer these questions, we need to study how these relationships have worked in the past. This is achieved through real historical data that feeds models: tools that digitally represent the relationships between the different elements of the system. These models draw on historical values to simulate different future scenarios, allowing us to analyze the effects of different political or strategic decisions. They do not seek to offer a single answer, but rather to create a framework for evaluating alternatives and making informed decisions.
Africa has a real laboratory: ONEPlanET case
The ONEPlanETProject, of which CARTIF is a key partner and a key element, was born from this approach. As part of the Horizon Europe research program, ONEPlanET began in November 2022 and will hold its final event next October in Cape Verde. Its main objective is to contribute to sustainable development in Africa by creating a common WEF Nexus modeling framework, which allows for the simulation and evaluation of different policy and resource management alternatives. To this end, three river basins have been chosen as case studies: the Inkomati-Usuthu Basin (South Africa), the Bani River Basin (Mali-Ivory Coast), and the Songwe River Basin (Tanzania-Malawi).
The initial stages consisted of an in-depth study of the case studies, organizing in-person workshops with local stakeholders (NGOs, policymakers, universities, etc.). The more technical sections then began, involving the characterization of the specific models for each pilot, the collection of data to feed them, and the development of the models themselves and their visualization tools. Currently, work is focused on the presentation and accessibility of the results. To this end, two avenues have been designed: an online tool aimed at technical users and a board game to raise awareness among broader audiences about the challenges of the nexus.
CARTIF has participated in every stage of the project: from workshops with local organizations and data collection to the creation of the models and the development of the two results visualization options.
A tool to understand the present and design the future
Although ONEPlanET is being developed in Africa, the NEXO approach and the modeling tools it promotes are replicable anywhere in the world and at any scale, provided the required data are available. In an increasingly interdependent global context, marked by climate change, resource pressure, and growing uncertainty, understanding how water, energy, and food interact is more urgent than ever.
Because the challenges of the future and the present don’t come in watertight compartments. And neither should the solutions.
By now, we’re probably all tired of hearing every kind of theory—some quite colorful—about the causes behind the April 28th blackout. But what has received far less media attention is the set of technical solutions that made it possible to restore power to a peninsula with over 50 million people. That’s precisely the focus of the following paragraphs.
Although an official report already outlines the causes of this blackout in our electrical system, one word echoes across the entire chain of missteps: frequency. In electrical terms, frequency refers to the rate at which alternating current switches polarity (from positive to negative and back), and it must always remain constant—50 Hz in the Iberian Peninsula—since the entire grid infrastructure is designed to operate under that non-negotiable condition.
That frequency, however, has become a point of media debate, sometimes used to criticize renewable energies, and other times to advocate for the unchecked use of fossil fuels. Yet there’s one renewable source—less flashy, quieter, but vital—that plays a key role in frequency control: hydropower.
Just like other technologies such as nuclear plants or gas turbines, hydropower generates electricity through synchronized rotation of mechanical components, which allows it to contribute directly to maintaining the system’s 50 Hz frequency. On the other hand, technologies like solar photovoltaics and wind—while essential to the energy transition—lack this direct regulatory capability and are also highly sensitive to frequency deviations due to their power electronics. It’s a vicious cycle.
But what truly made hydropower a star after the blackout was its black start capability—the ability to start an electric facility without relying on the grid. Only a few plants in the system have this feature, and in Spain, most of them are hydroelectric stations with reservoirs. Thanks to their design, they can start their turbines using only auxiliary batteries or diesel generators, harnessing the pressure from stored water.
That’s exactly what happened after the “electrical zero” of April 28. Plants such as Aldeadávila, Ricobayo, or Riba-roja d’Ebre started operating autonomously, injecting the first kilowatts into a completely dark grid. Spain’s transmission system operator, Red Eléctrica de España (REE), coordinated these plants to create small “electrical islands,” where both frequency and voltage were stabilized before rebuilding the interconnected grid from there.
In this scenario, the challenge wasn’t just to generate electricity again, but to ensure power quality—primarily meaning keeping frequency and voltage within very specific margins. To achieve this, power systems rely on balancing mechanisms such as primary, secondary, and tertiary regulation, each reacting at different time scales to generation-demand imbalances.
The first step was to activate primary regulation, which responds immediately to frequency deviations. Here, the islanded hydropower plants were able to autonomously maintain stable frequency within their sub-networks. Once stabilized, secondary regulation (AGC) was activated from REE’s control center to fine-tune the frequency to its nominal 50 Hz, supporting the primary regulation. This phase was enabled by remote communication and the fast response capability of hydropower turbines.
As more zones regained voltage, hydropower plants increased output or transferred load to other technologies, such as combined-cycle gas plants. This process released reserves through tertiary regulation, which also activated pumped-storage plants—like Estany Gento in the Pyrenees—that acted as giant batteries, providing extra support over the following hours and days.
In short, the April 28 blackout not only tested the resilience of Spain’s electrical system—it also highlighted the strategic value of hydropower. In today’s context of electrification and energy transition, it’s becoming increasingly clear that we need flexible technologies capable of modulating output, storing energy, or responding to demand.
At CARTIF, we are actively working in this direction through European projects like D-HYDROFLEX andiAMP-Hydro, which aim to modernize existing hydropower stations through hybrid systems and intelligent control. The goal: to provide these facilities with greater flexibility, efficiency, and stabilization capacity, contributing to the development of a more robust, sustainable, and future-ready electric system.
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.
