Power-to-hydrogen explained

Take electricity, water and an electrolyzer. Get hydrogen.

Without diving into the chemical process of how an electrolyzer works, the process of converting electrical power to hydrogen is actually pretty simple. You power an electrolyzer with electricity and the electrolyzer uses this energy to split water into oxygen and hydrogen. If you use electricity from renewable energy sources the hydrogen is considered green hydrogen and, in fact, carbon-neutral. The hydrogen can then be used at a later point to deliver energy.

The upside of this: Once the electrolyzer is installed, the entire process is relatively cheap, water is widely available, hydrogen is easy to store and transport, and pretty versatile.

The downside: Power-to-hydrogen is really inefficient. When storing energy in a battery around 15-30% of the energy is lost. Storing energy in hydrogen 55-70% of energy is lost.

Hydrogen can provide (a lot of) flexibility

So why bother with power-to-hydrogen if it is so inefficient? Well, for one hydrogen can provide flexibility. Something that is extremely useful with an ever growing share of intermittent and seasonal renewable energies.

• Short-term flexibility: Electrolyzers are quick to start up. Thus, they can be switched on in times of excess electricity supply to stabilize the grid and lower the need for curtailment. Vice versa, in times of low production hydrogen can be converted into electricity fairly quickly. Today, it is mostly natural gas power plants that provide this flexibility.
• Transfer energy between seasons: Hydrogen is cheap to store in large quantities and unlike batteries does not lose energy over time. In Germany, for example, energy demand is 30% higher in winter than in summer. Energy supply from renewables, however, is 50% lower. Hydrogen could be used to level this, transferring the abundant clean energy from summer into winter.

Hydrogen is easy to transport

While a pipeline is by far the most efficient and cheapest way to transport hydrogen, it can also be transported by ship to bridge long distances and transfer energy between regions that are not connected by a pipeline. This quality is useful for many applications:

• Detached power production: Depending on a range of circumstances it might be extremely expensive to connect offshore wind power plants to the electricity grid. In such cases hydrogen can serve as an energy carrier. Power is converted to hydrogen directly at the wind power plant and can then be transported to the mainland on ships.
• Bridging large distances: In some regions supply of renewable energies exceeds demand by a margin. Whereas other regions consume a lot more than they could generate from renewables. Converting power to hydrogen provides a means of transporting energy between these regions.

Hydrogen can replace fossil fuels

Some processes are difficult to electrify. In other cases existing machinery is geared to burning natural gas. Hydrogen can come to the rescue in these cases:

• Industry: Hydrogen can be used in various processes that currently rely on natural gas. This stretches from the production of fertilizers to steel.
• Fuel: Hydrogen can be used in transport to replace fossil fuels. Either entirely with engines and turbines that can run on hydrogen or mixed with natural gas in engines that were actually built for pure natural gas.
• Heat: Lastly, hydrogen can also be used in heating either mixed with natural gas or on its own. This use case could also utilize existing infrastructure initially built for natural gas.

In practice power-to-hydrogen is yet to be scaled

But despite all those use cases, converting power to hydrogen is not quite common practice (yet). However, in a scenario aligned with the Paris-agreement, the IRENA expects hydrogen production to grow substantially over the coming decades. From a mere 3 EJ in 2030 to more than 6-fold in 2050 (19 EJ).

In line with this projection more and more projects using hydrogen to integrate sectors have been kicked-off in recent years.

Reducing curtailment of wind and tidal energy

The Surf’n’Turf initiative is based in Orkney, UK. Here, electricity from wind and tidal energy is converted into hydrogen. The hydrogen is then used in two ways. On the island of Eday, where the wind turbine is located, the hydrogen provides electricity when the wind turbine cannot meet local demand. On the other hand, the hydrogen is shipped to the mainland where it is used to heat ferries in the port of Kirkwall and as fuel for vehicles. 

In this case, many advantages of hydrogen come to the fore. It provides flexibility to reduce curtailment and supply clean electricity when renewables do not cover demand. On top, it enables the transport of clean energy without a grid and can be used as a substitute for fossil fuels in heating and transport.

Striving for 100% renewable energy in mobility and heat

The SmartQuart project is a joint project of gridX and 9 other parties and is backed by the German Ministry of Economic Affairs. The project was kicked off in January 2020 and aims to build three smart and self-sufficient districts. One of the districts is located in the town of Kaisersesch and dubbed the hydrogen district.

In Kaisersesch renewable energy is used directly to charge EVs and supply multiple buildings and industry with electricity and heat. Production in excess of demand is converted into hydrogen in a 10 MW electrolyzer. The hydrogen produced thereby is used in a CHP as well as multiple fuel cells as follows: 

• Energy-source of heat: Hydrogen is used in combined heat and power units to produce electricity and supply the district with heat.
• Energy-source of electricity: Hydrogen is burned in fuel cells to produce electricity in periods of low supply from renewables.
• Energy-source for mobility: The district is equipped with a hydrogen fuel station to supply buses of the local transport system with clean energy.

Furthermore, the hydrogen is stored in liquid organic hydrogen carriers (LOHCs). LOHCs are compounds that can absorb and release hydrogen. Once absorbed by a LOHC, hydrogen can be transported to serve for the above mentioned ways as a source of heat and electricity as well as various other applications.

Similar to the setup in Orkney, hydrogen in Kaisersesch provides a way to store and use otherwise curtailed renewable energy and link mobility, heat and power.

Power-to-hydrogen is a part of the energy transition

Power-to-hydrogen can help to decarbonize energy. Used to store energy, hydrogen can stabilize the grid and serve as a medium to transport energy between seasons. The ease to store and transport hydrogen also makes it possible to transfer energy between continents. Lastly, it can also serve to integrate sectors and replace fossil fuels in processes that are difficult to electrify.

But power-to-hydrogen’s contribution to the energy transition should not be overestimated. Green hydrogen production is expected to grow to 19 EJ by 2050. In the same year global energy consumption is expected to total 351 EJ. This means that green hydrogen is estimated to cover just 5.4% of global energy demand in 2050 – a substantial share but not quite the pillar of a clean energy system.

The inefficiency of converting power to hydrogen remains the biggest drawback. Other methods are more efficient by a factor of 3-5 and are thus preferable in many cases. So in conclusion – despite a wide range of use cases and many promising projects – power-to-hydrogen is not the “eierlegende Wollmilchsau” of the energy transition but rather a complement to electrification and an increase in renewable energy capacity.