The FlexH2 project will design a novel offshore wind and onshore hydrogen production concept.

Infographic showing 3 types of winpaks and onshore grid connections      

Grid-following wind farms

The electricity in the grid is in the form of Alternate Current (AC); i.e., it is transmitted via a wave that pulsates at 50Hz (i.e., 50 pulses per second).

This frequency is not perfectly 50Hz at all times; it varies in a narrow range around 50Hz in normal operation. In order to inject power into the grid, the wind turbines need to inject the power with waveforms that pulsate at the exact same frequency as the grid.

To do that, a grid-following (GFL) wind turbine “follows” the frequency established by the grid, which acts as a master or metronome that imposes the pattern that must be tracked.

Grid-forming wind farms

A grid-following (GFL) wind turbine “follows” the pattern established by the grid voltage waveform; whereas a grid-forming (GFM) wind turbine “forms” the voltage waveform itself.

A GFM turbine is, therefore, more independent than a GFL wind turbine, in the sense that a GFL wind turbine depends on other equipment to create the voltage waveform.

Nowadays, there are no GFM wind turbines in the market, but they are being researched intensively all across the world. Using GFM wind turbines enables thinking of more compact and efficient offshore substations, among other advantages.


HVAC-based offshore substation

All the wind turbines are connected together via cables. These cables are taken to a central location offshore that is called Offshore Substation. This substation is a collection of electrical equipment, and others, that stand on a platform above the water, whose main function is to collect all the cables and host transformers that will elevate the voltage for high-voltage transmission.

If there is High Voltage Alternate Current (HVAC) transmission, the substation can be relatively small.

To get an idea of weight & size:

Elephant: ~ 5 ton   Football field: 4186m2

HVDC HVAC Difference
Weight 2,000 1,100 45% reduction in HVAC
Footprint 72% 57% 20% reduction in HVAC

HVDC-based offshore substation

For transmission in long distances, it is beneficial to use High Voltage Direct Current (HVDC) instead. Since turbines use AC waveforms, the substation in an HVDC-connected wind farm needs to host equipment to also convert the AC waveform into DC.

That is why, typically, an HVDC-based substation is significantly bigger and more expensive than an HVAC-based substation.

To get an idea of weight & size:

Elephant: ~ 5 ton   Football field: 4186m2

HVDC HVAC Difference
Weight 2,000 1,100 45% reduction in HVAC
Footprint 72% 57% 20% reduction in HVAC

More compact and efficient offshore substation

The FlexH2 project aims to reduce the size of the substation by using a different way of converting from AC to DC waveform. Since the wind turbines are grid-forming instead of grid-following (in a sense, they are smarter) the equipment in the substation can be simpler, and thus it can be reduced in size, price, while increasing reliability and efficiency.


Electrolysis plant

An electrolyser can split the water molecules into its hydrogen and oxygen parts using electricity. The electrolyser needs low voltage and Direct Current (DC) to operate.

Equipment is needed to convert the energy to these specific needs. The typical solution is bulky and requires a lot of materials.

More compact electrolysis plant

In the FlexH2 project, alternative equipment to create the low voltage and Direct Current (DC) is researched: a Solid-State Transformer (SST). The SST has the potential of reducing significantly both the weight and volume.

Nowadays, the biggest electrolysis plants in Europe are typically of some hundreds of MW. When going for even bigger scales (e.g., GW level), space, and volume might become a constraint.

Reducing the weight becomes important as it is an indirect metric of the quantity of materials used. In order to enable a sustainable energy transition, a responsible use of natural resources and materials needs to be encouraged.


Smart allocation of energy to the grid / hydrogen production

Usually, a wind farm is controlled to produce as much power as it is possible given a certain wind condition, and all that power is injected to the grid. In contrast, the FlexH2 system can use the energy to inject into either the grid or the elektrolysis plant to produce hydrogen.

The FlexH2 project is researching a smart way of making this decision; i.e., what should be the operational philosophy of the system. When there is a lot of demand for electricity but not much production, the electricity price is high. The best action in this case is probably to inject a lot of the wind power into the grid.

In contrast, at other times the demand is low, and thus the electricity price is low, and perhaps it is best to use the wind power to produce hydrogen. All in all, the best solution depends on electricity market prices and hydrogen market prices.


Grid connection

When a wind farm starts operating for the first time, energy comes from the grid in order to energize the system and put it into operation. Once the wind farm is running, the power flow reverses and it goes from the wind farm towards the grid.

Reduced grid connection

In the FlexH2 concept, the wind turbines are more advanced than classic concepts. Among other things, they have the capability of energizing themselves and the rest of the system. If desired, the FlexH2 system could be designed in a completely islanded way in a direct generation-to-load concept.

This means that the FlexH2 system could be set up without any grid connection at all. This enables the development of GW scale green hydrogen production systems even in locations where there is no grid network or the grid is extremely congested.

This way the FlexH2 system can help to solve grid congestion, one of the biggest challenges of the energy transition due to the growing connection of renewable sources and electrification of demand (electric vehicles, industries, etc.).

Leveraging these technological innovations, the FlexH2 project can reduce the overall Levelized Cost of Hydrogen (LCOH) for green hydrogen by 0.35 €/kg, therefore providing a cost-competitive solution for the CO2 emission reduction for both the green hydrogen project developers (e.g. private energy company, utility, private investor .etc) and end-users (e.g., industry, mobility, residential user etc.).

The project's outcome will provide the basis for the accelerated development of Power-to-H2 projects in the Netherlands before 2030.