Renewable energy for the future of our planet

From integrated solar and wind power management to new forms of wave energy, from the revival of hydroelectric power to innovative thermal storage solutions and so-called “energy geostructures”, Politecnico di Torino is a hub of ideas and innovation, which we explored by meeting its leading figures.

Filippo Spertino, professor at the Energy Department of Politecnico, defines electricity as “the highest level vector”. Its versatility is remarkable: it can be converted into any other form of energy, from mechanical to thermal energy, from lighting to powering electronic devices.

“Electricity is the key to decarbonising the economy,” explains Spertino, "but it must be managed intelligently." And that word – “intelligence” – encompasses a whole world. His research group has developed the Photovoltaic Zero Energy Network (PVEN) laboratory, for experimenting with photovoltaic-based networks, electrochemical storage devices and advanced control systems.

A crucial feature of the electrical system is its control, which ensures a balance between demand and generation. In other words, energy must be produced when it is needed, at different stages of the day and night. To achieve this balance, network operators in various countries employ systems that, for every hour of the day, determine the planned and forecast energy requirements and the actual energy: the energy concretely supplied based on these requirements.

Towards a faster and safer transition to electricity. On an April morning, while monitoring with the professor electricity consumption on the Spanish grid operator's website, the energy mix consisted of almost 70% renewables (wind, solar and hydroelectric), 15% nuclear, 1% coal and 8% gas. In Italy, the trend is quite different. Wind and solar power are growing but more sluggishly than elsewhere, while gas remains a major source of energy (about 40-50% of electricity), with significantly higher costs.

The research led by Filippo Spertino is meant to make the switch to electric faster, more efficient, and safer. There are many areas of investigation: just to begin, the differentiation of sources to compensate for the intermittent nature of renewables - such as wind and solar power - still needs a boost. Hydroelectric power plays a crucial role here, with its potential energy storage capacity provided by wind turbines and solar panels.

‘Italy has 6,000 MW of pumping capacity, with the Entracque plant in the province of Cuneo alone providing 1,000 MW,’ explains Spertino. ‘Unfortunately, these facilities are underutilised, when they could be used to store excess energy produced by renewables.’

The key question is not whether solar and wind power will have a future in Italy (and worldwide), but what sort of installations will be favoured. On the ground, or on the roofs of houses and warehouses (which could theoretically be enough to supply all the energy needed, occupying 7% of Italy's territory)? With large power plants or whithin energy communities with small networks based on local exchange and largely on self-consumption?

Energy communities. Politecnico di Torino has always supported energy communities. The first sustainable energy community (CER) was established in Piedmont, in the municipality of Magliano Alpi in the province of Cuneo, with the collaboration of the Politecnico's Energy Center, which had already launched a Manifesto of Energy Communities in mid-2020. Today, there are around 160 CERs in Italy, but the goal is to have thousands by 2030. Building communities with sustainable energy is the essence of sharing resources such as photovoltaics, as well as wind power, biomass, and others, for individual buildings or entire villages. This includes storage and connection to the electricity grid, allowing energy to be drawn or fed in as needed. Beyond the technical aspects, CERs foster a distributed and participatory energy system and encourage the evolution of their members from simple consumers to collective producers and consumers of energy (prosumers). This has significant implications for social and ecological awareness.

With the Photovoltaic Zero Energy Network lab, the research group led by Spertino studies the different energy parameters needed for a proper energy communities performance. The lab has three photovoltaic generators connected to electrochemical storage devices and three virtual users that simulate three households that produce, consume, and exchange electricity.

The team is also leading innovative research into agrivoltaics, which integrates agriculture and solar energy production on the same land, with positive results for agricultural entrepreneurs. Interesting studies are also being carried out on floating photovoltaics, which uses water to cool the panels, increasing their efficiency and reducing evaporation. Wind power is also at the centre of the laboratory's research, focusing on various aspects of converting mechanical energy into electricity, energy production, plus the optimal connection of these plants to the grid, and more generally to the smart grids of the future.

 Are renewables intermittent? Not all of them. The sea provides a relatively constant source of energy: waves. And if you happened to look out from the north-western coast of the island of Pantelleria, you would see, about 800 metres from the shore, an 8-metre by 15-metre hull generating electricity from its pitching motion. This is ISWEC (Inertial Sea Wave Energy Converter), a jewel of technological innovation developed by the MOREnergy Lab (Marine Offshore Renewable Energy Lab) research group of the Department of Mechanical and Aerospace Engineering-DIMEAS, coordinated by Professor Giuliana Mattiazzo.

A gyroscope is housed in the hull anchored to the seabed, which converts the platform's pitching into the rotary motion of an electric power generator to feed into the island's grid. This device has a negligible environmental impact and is suitable for use in various wave conditions, even in enclosed seas. It has no moving parts in the water, is visually comparable to a typical boat due to its low height above the waterline, and does not produce noise that could disturb local wildlife.

ISWEC was conceived in 2006 and implemented in 2015, but it is not the only creation of the Laboratory. In February 2023, a second version of the device was installed off the coast of Pantelleria, achieving a peak electricity production of 260kW, while new devices are being developed. They are expected to convert wave motion into electricity through the oscillating motion of a pendulum (PeWEC - Pendulum Wave Energy Converter).

Another prototype developed by MOREnergy Lab is called WEPA (Water Energy Point Absorber). Giuseppe Giorgi, a researcher at MOREnergy Lab, explains: “It consists of a buoy that moves up and down. It has a mooring line connected to the seabed and to a drum inside the buoy. As it moves up and down, the line winds and unwinds around the drum (similar to a yo-yo in reverse), allowing electrical energy to be extracted.”

Although still in the prototype stage, these technologies could soon be developed on an industrial scale as a valuable addition to other sources. Wave energy has different characteristics from other renewable sources. ‘First of all, it is a denser form of energy (water is 1,000 times denser than air), it is more constant and stable than wind energy, it is more easily predictable in the short term, and it is complementary to solar and wind energy,’ continues Giorgi. On islands with no connection to the grid (such as Lampedusa, Giglio, and Pantelleria), wave energy can partially replace diesel generators, for example, and can be easily integrated with solar and wind power.

Offshore wind power but floating. Offshore wind power is another flagship project at MOREnergy Lab, which focuses on floating technologies that are particularly suited to the Mediterranean Sea. Unlike the North Sea, where shallow waters are ideal for fixed turbines, the Mediterranean sea quickly becomes deeper as it moves away from the coast, making floating solutions more viable.

The group is also developing innovative concepts such as vertical axis turbines, which rotating blades designed differently from traditional turbines. These could offer benefits in terms of maintenance, as the generator can be installed at the base of the tower instead of high up in a nacelle, reducing maintenance costs.

A promising area of research also concerns hybrid platforms that combine wind and wave energy on the same structure. Potential benefits include greater stability of the floating platform and complementarity of electricity production between the two sources, which could reduce the need for storage.

Hydroelectric power represents the well-known history of renewable energy, yet is still evolving. Paolo Vezza, Professor of hydraulics at Politecnico's Department of Environmental, Land and Infrastructure Engineering-DIATI, emphasises the importance of this energy source for Italy. Hydroelectric power constitutes approximately 40-45% of national production from renewable sources, positioning the country as the fourth largest producer of hydroelectric energy within the European Union, thanks to the presence of the Alps and Apennines mountain ranges.

The working principle of hydroelectric plants is apparently simple: water is stored in artificial reservoirs or taken from natural watercourses and collected in loading tanks. From the reservoirs or tanks, penstocks carry the water downhill, where the difference in height causes it to turn turbines and generate electricity. Although the general layout is always similar, each plant is unique, with customised technical solutions that tell the extraordinary story of hydraulic and electrical engineering over the last century. Vezza observes: “It is a stroke of luck to already have large hydroelectric plants in place, but it is much less so to build them", given how powerful and costly they are. Now is the time to innovate and update their operating systems, also in light of the environmental context.

When snow and rain are scarce. Climate change is radically altering the hydrological cycle, with significant implications for hydroelectric power generation. Rising temperatures mean that, in addition to the inevitable melting of glaciers, some of the water that used to fall as snow now falls as rain, due to the rise in the freezing point. The hydrological regime is changing, with more intense and concentrated rainfall. "If the snow melts earlier, as is happening now, there will be less water available in the summer. This means that peak hydroelectric production for plants without reservoirs may be brought forward by one or two months compared to the past,’" explains Vezza.

Another alarming figure concerns average rainfall nationwide: comparing average rainfall over the last 30 years with that recorded between 1921 and 1950, there has been a downward trend, with a difference that now stands at 19%, meaning that almost a fifth of the water that used to fall from the sky no longer does so.

New hydroelectric power is more eco-friendly. In 2029, the concessions for large plants will expire, and plans are necessary for the future of this vital energy source. Politecnico is therefore working on a vision for "new hydroelectric power” that can generate renewable energy while also being environmentally sustainable and resilient to climate change.

The hydroelectric power of the future, as we are envisioning and promoting it, will be more attentive to its impact on aquatic ecosystems, with innovative management solutions that allow for revamping and increased energy production,’’ explains Vezza. The key challenge of this adjustment will be to modulate production based on water availability and the ecological processes underlying the river ecosystem. "The current regulatory change governing the release of Ecological Flow (DE) from hydroelectric intakes represents a unique opportunity which, combined with the renewal of concessions, allows us to propose the revamping and upgrading of climate-resilient and environmentally compatible plants," says Vezza.

Large dams, in this new form that pays much more attention to the integrity of the rivers that feed them, will certainly continue to play an essential role in the national electricity system, both for energy production and conservation. This will be achieved through pumping stations that can store water in reservoirs as potential energy, using surplus energy from sources such as wind and solar power.

 50% of the world's primary energy is used for heating and cooling, both in the civil and industrial sectors. Furthermore, 90% of energy conversions involve heat in some way, making true decarbonisation impossible without addressing the issue of thermal energy. While making domestic hot water production renewable (approximately 10-15% of a building's thermal consumption) is relatively simple through solar panels, the real problem concerns room heating, which accounts for about two-thirds of total thermal consumption. And cooling will also be an increasing issue in the expected warmer future.

Solar thermal energy is a well-established technology. It can cover a large part of a home's hot water demand. The same cannot be said for heating, which requires long-term storage of the heat generated during cold periods. Politecnico's research aims to tackle this issue. The team led by Professor Eliodoro Chiavazzo, from Politecnico's Energy Department, is working on a set of thermal storage technologies. “Purely physical storage is the most traditional technology, such as domestic hot water boilers, but it is not suitable for long-term storage because the energy disperses into the environment over time,” explains Chiavazzo. “A second storage strategy is thermochemical storage, which uses chemical reactions to store heat in potential form.” With the PNRR project “NEST, Spoke 6”, the research group led by Chiavazzo has applied these methods to cement, so that this widespread material can be reused. In this system, “pelletised” cement is dried during the summer using solar energy, and when exposed to water vapour in winter, it releases heat. This allows for “loss-free” storage, in which thermal energy can theoretically be stored indefinitely as long as the cement and water components remain separate.

The third technology is latent storage, which uses phase change materials, mainly paraffins, with innovative heat exchangers that integrate mechanical actuators to accelerate energy transfer processes and thus the charging and discharging phases. During the phase change, just like water when it freezes, heat is released and the material heats up. Conversely, it can also cool down, just like ice, which absorbs heat from the surrounding environment as it melts. With climate change and the increase in demand for cooling, research is also focusing on cold storage. According to climatologists' projections, the cooling power required will increase significantly, creating peaks in electricity demand. Developing cold storage technologies could therefore help to manage these peaks, making demand more flexible.

 We conclude this tour of renewable energy with an innovation that literally transforms urban infrastructure into power stations. Geothermal energy, which we commonly associate with heat pumps installed in buildings for heating or cooling, can be used even more efficiently and in a highly integrated form. It is less known that the same result can be achieved not with dedicated probes, but by using entire buildings as heat exchange elements. These are called “energy geostructures” and are the speciality of Professor Marco Barla from Politecnico's Department of Structural, Geotechnical and Building Engineering-DISEG.

The concept behind this research is the integration of geothermal heat exchangers into civil constructions. The aim is to incorporate heat exchangers into structures in contact with the ground, just as solar panels that are no longer simply placed on roofs but integrated into the building structure. Instead of building specific geothermal probes or wells, structural elements such as foundations, tunnel linings or earth-retaining walls can be used. The technology remains the same: heat exchanger pipes through which a fluid flows, absorbing or releasing heat to the surrounding ground.

One of the most significant projects developed by Marco Barla's team is Enertun, a patent that allows the lining blocks of a tunnel to be transformed into heat exchange units. The system was installed in Turin, near Piazza Bengasi, with a trial section built during the construction of the underground tunnel. The tunnel is now in service and the heat exchanged by the instrumented blocks is used inside the station, in a technical room used by the staff. This type system has also been included in the design of Turin's metro line 2, with the idea of equipping all tunnels and stations with heat exchanger pipes that transform the entire underground structure into a diffused heat exchanger.

 Energy retrofitting. Marco Barla's team also works on the energy retrofitting of existing structures, such as a motorway tunnel on the A26. In this innovative project, the existing concrete lining (approximately 80 cm thick) was partially milled, leaving approximately 30-40 cm. Heat exchanger pipes were installed in the resulting spaces, and new concrete was poured to complete the structure. The heat recovered from the tunnel is used to de-ice the road surface instead of the traditional method of spreading salt, with obvious environmental and economic benefits.

A more recent aspect of the research concerns the use of underground structures and energy geostructures not only for production but also for seasonal energy storage. Professor Barla's team has recently launched a European project called Regenerate, which aims to reuse abandoned underground structures for energy purposes. A concrete example is the disused Turin-Ceres tunnel, which once connected Dora to Madonna di Campagna. Other potentially usable structures include abandoned air-raid shelters and disused industrial tunnels, such as those of the former Fiat factory.

The principle of this application is as simple as it is effective: an abandoned tunnel could be sealed and filled with water that is heated during the summer, using excess heat from industrial processes or solar thermal energy. This heat, stored like a huge thermal battery, could then be used during the winter to heat nearby buildings, creating a small, energy-efficient local district heating network.

These energy retrofitting projects are particularly promising for Italy, considering the wide availability of outdated real estate and infrastructure that could be revalued in terms of energy efficiency. On this topic, Marco Barla coordinates the Georefit project, which involves the Università degli Studi di Perugia, Politecnico di Milano and the University of Milan in a specialised research network. Other Italian universities contributing to this technological frontier include the Universities of Palermo, Naples and Padua, which together form a national centre of excellence in the field of integrated geothermal energy.