By 2030, seventy percent of the energy supply in the Netherlands must come from renewable energy sources such as solar and wind. The integration of these large numbers of variable, renewable energy requires technological innovations to prevent fluctuations in the energy supply. After all, renewable energy sources are highly dependent on weather conditions. The FlexH2 project (Flexible Offshore Wind Hydrogen Power Plant Module) of the GROW consortium looks at how wind energy can make a consistent contribution to the energy supply.
“If we want to increase the proportion of wind energy, an interim stopgap has to be built in between the generation of wind energy and its eventual use to help balance the system,” explains Dongsheng Yang. He is involved in FlexH2 as an assistant professor in Electrical Energy Systems at Eindhoven University of Technology (TU/e).
Hydrogen as a stopgap
Within the FlexH2 project, green hydrogen acts as that stopgap. “We can quickly scale up offshore renewable energy generation and convert a significant portion of it into hydrogen. That way, we can store that energy. Moreover, that hydrogen can be used as industrial feedstock or converted into other forms of gas or fuel which people can use safely at home to cook and to heat their homes. In this way, we can use more sustainable power without further burdening the electricity grid.”
The Netherlands plans to raise offshore wind energy between 38 and 72 gigawatts by 2050. However, the Dutch electricity grid currently has a total capacity of around twenty gigawatts. The possibility of converting hydrogen into gas is therefore a good alternative for using this sustainably generated electricity.
Getting those huge amounts of generated electricity to the mainland, and converting it into hydrogen once there is quite a chore.
Transportation of huge amounts of energy from sea to land
One of the biggest challenges is transporting huge amounts of energy to the electrolysers on land. “You have two ways to move the power that’s generated at sea. As alternating current (AC) or as direct current (DC). AC technology is generally more mature and relatively cheaper. However, for long-distance energy transportation from wind farms located far offshore, AC technology will no longer be efficient anymore as the electric power transmission capability of the AC cable will be greatly reduced due to capacitive charging,” Yang explains.
With DC technology, long-distance transmission is not a problem. But, a complicated power conversion system is needed to convert wind power to high-voltage DC, which is more expensive than that for an AC alternative. And installing such power conversion equipment far from shore is already anything but cheap. “If we can make the DC conversion stations more compact, that would be the best option. But it will take a lot of breakthroughs before that happens.”
The difference between alternating and direct current
The name says it all: with direct current the voltage is constant, with alternating current the voltage changes fifty times per second between positive voltage and negative voltage. The entire Dutch energy network operates on alternating current. It comes out of the wall socket at 230 volts. Direct current is, for example, the current we use for our smartphones. That is why it comes with an adapter, which converts the alternating current from the wall socket into direct current.
Direct Current grid
Yang sees a DC offshore power grid, which all those wind turbines are directly connected to, as the best solution. “That way, we can transport the energy as direct current to the mainland,” he says. The combination of new DC transmission technology with grid-forming wind turbines has never been done before in actual practice. This poses a lot of technical risks. From the science side, we look purely at the technology, but at FlexH2, industry is also taking a look. Without their involvement, we would overlook many things, such as fault-handling, black start, etc.”
A lot of pressure
When scientists started researching the topic ten years ago, many people did not believe that renewable energy would take a leading role. “Back then, a ten percent share was already seen as a lot. Ten years later, there are times when there is more renewable than regularly generated energy in the Dutch electricity grid. But we are still behind schedule when it comes to combatting global warming. That adds a great deal of pressure.”
As a result, Yang also sees that many industry partners are actively seeking solutions. The fact that TU/e works so closely with partners from this sector is one of the main reasons why he was so keen to work at the university. “The research topics I work with have a high technology-readiness rating. This means that the results of the research can be put into use in a relatively short period of time. The idea that I can really make a difference with my research motivates me enormously.”
“We are still behind schedule when it comes to combatting global warming. That adds a great deal of pressure.”
Dongsheng Yang
Accelerating the energy transition
The FlexH2 project is a good example of this. Shell is the main driver of the research project. In addition to TU/e, General Electric, ABB, VONK and Delft University of Technology are responsible for the electrical engineering innovation side of things. Shell, Van Oord, TKF, TNO and DNV are contributing their expertise in areas such as hydrogen electrolysis and system balancing.
In August 2023, Yang hopes to have a dem of the FlexH2 project ready. “This is very important, so all parties involved can see what technology we are developing. My biggest motivation is that the research I’m doing really contributes to accelerating the energy transition.”
Collaboration
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