“Electric grids are becoming a bottleneck to clean energy transitions. Delays in investments and reforms would put the 1.5 °C goal out of reach.” This is in substance the warning issued by the International Energy Agency (IEA) in its report “Electricity Grids and Secure Energy Transitions”: stalled spending on grids is slowing the rollout of renewable energy and could jeopardize efforts to limit climate. To achieve energy and climate goals, over 80 million kilometres of grids should be added or refurbished by 2040, the equivalent of the entire existing global infrastructure – hence, the call to policy makers to prevent grids from becoming a “bottleneck”. As IEA Executive Director Fatih Birol put it last October: “It’s like you are manufacturing a very efficient, very speedy, very handsome car, but you forget to build the roads for it.” To meet the net-zero emissions target by 2050, the agency estimates that electricity usage must increase 20% faster over the next decade, with predictions suggesting that wind and solar will account for over 80% of this growth. But this is where the challenges begin.

Two of the major issues hampering the penetration of renewables are directly tied to the grid architecture itself. One stems from the fact that to integrate the growing share of self-generation, we are essentially asking the current infrastructure to work differently from how it was originally designed. “A bit like water, whose pressure needs to be higher at the source for it to run into the pipes, the voltage must be higher at the energy source, for the electricity to reach the consumer. But with distributed energy production, and consumers turning into prosumers, we now also need it to carry the electricity in the opposite direction,” explains Dominique Roggo, lecturer and researcher at the University of Applied Science in Turku, Finland.

Another challenge arises from the use of alternating current (AC) as the standard for the existing grid, while renewable energy systems such as wind and solar, along with electric vehicles and many other modern devices, primarily use direct current (DC). “Just think that if you have PV modules on your roof, the energy they produce must undergo four different conversion stages, before it reaches its application each of them implying energy losses of around 5%,” points out Roggo. Not only does conversion from DC to AC and back to DC lead to power losses, which are further compounded by long-distance electricity transmission, but the overall efficiency and reliability of the power system are diminished as well. This is why integrating DC grids into the main electricity network is now a key focus for researchers.
Supporters of this “paradigm shift” argue that it would significantly improve flexibility, security and reliability of the power system, but also acknowledge multiple challenges. Project manager at the Spanish technology centre CIRCE, Montserrat Lanero Martinez coordinates Tigon, a European project developing innovative solutions to achieve a more efficient energy system. “Due to the high proliferation of renewable energy sources, DC grids have become significantly more attractive in the past few years,” she says. “However, the transition from an AC- to DC-based system architectures requires the rapid advancement of equipment based on power electronic converters.”
Crucial to maximising the integration of renewables into the grid, these devices are basically aimed at converting the electrical energy from AC to DC or vice versa. Scientists and experts place high hopes on them, and believe that especially their new generation could play a pivotal role. “Currently, grid operators limit the share of renewables with variable supply such as solar and wind, because they struggle to estimate how much of them will be available. In this regard, for instance, new generation converters could pave the way for a 100% renewable energy penetration,” explains Isaac Portugal, IEA Energy analyst. Yet, the conventional ones still suffer from significant voltage limitations, which is why a new and most advanced generation of DC to DC silicon-carbide (SiC) converters was developed by Tigon’s partner CEA. “The ones that we are testing in our demo sites are expected to achieve energy efficiencies over 98% at higher frequencies over 80 kHz,” says Montserrat Lanero. “This increase in frequency results in a more than 1000-fold increase in the transformer's power density, allowing for smaller equipment.”
Also aimed at reducing environmental impact and Europe’s energy dependency are so-called “solid state transformers” (SST), advanced power electronic devices used to connect different voltage levels and frequencies. More importantly, they help maintain grid stability and performance by improving the management of “active and reactive flows,” the energy flowing to and from prosumers. “Solid state transformers are a key technological enabler for decentralised energy supply systems,” explains Lanero. “Not only do their features facilitate the integration of next-generation smart grids, but they also increase their reliability by shielding them from disturbances that may occur on the main power grid.”
This is why her project is also developing a SST prototype, which will then be integrated into real life scenarios, ahead of possible replication in other EU cities. Along with a metro line in Sofia, Bulgaria, a residential district in Naantali, Finland, will serve as a niche market for analysing rollout and replicability of some Tigon’s solutions. “Here the project aims at testing so-called ‘hybrid DC-AC smart-grids’ – grids resulting from the interconnection of several microgrids, which are all connected to the main AC grid,” explains Roggo, who collaborates on the tests with the Finnish University of Turku. “The idea is to experiment different voltages to transfer the energy from building to building, initially using AC, but if it proves safe, cheaper and more efficient, in the medium term also using DC.”
As microgrids are smaller, self-contained, and controllable networks within the larger power grid, “the main challenge is designing the entire system to work together seamlessly,” confirms Portugal: “While they aren’t a one-size-fits-all solution, they can be extremely useful in certain situations, particularly by facilitating the connection of distributed assets like storage, electric vehicles, and renewables at lower voltage levels on the consumer side.” Before being replicated in Finland and Bulgaria, Tigon’s solutions will be validated in its French and Spanish pilots, which have also worked on their development. “For DC technologies to evolve from promising solutions to commercially available options, there’s still a need for demonstrations,” concludes Montserrat Lanero.
By Diego Giuliani

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