After nearly three decades in which offshore wind energy pioneers have perfected the commercial viability of turbines on fixed structure foundations, we are on the cusp of a surge in capturing the vast untapped wind resources in harsher and deeper waters offshore – using floating technology. Such resources far exceed future electricity demand in many countries and are worth the pursuit. However, harsher and deeper waters also often imply further offshore, putting cost pressures on energy transmission back to shore.
This raises questions about in what form that captured wind energy could be transmitted to market – as electricity, as hydrogen or indeed, as ammonia. Due to the proximity to shore of current offshore wind projects, that is, less than 200km, “electricity to electricity” has historically been seen as the optimal route to market for the produced energy. But this need not necessarily be so.
As we move further out to sea and transmission losses grow, the trade-off between electricity, hydrogen or ammonia, as the energy carrier, becomes a fascinating question, one that multiple sectors – maritime, oil & gas, renewables – have already started addressing. Solve this puzzle and we can potentially unlock vast volumes of clean energy around the world.
Electricity converted to hydrogen through electrolysis, transport through pipelines or liquefaction and shuttling to shore using tankers are all possible options, though the latter is unlikely to be efficient or cost-effective.
Transmission through pipelines has some attraction, but it is still a technical and metallurgical challenge, which translates into uncertainty and cost. Even if these issues are overcome, after offshore hydrogen is produced and transported by pipeline, there are still two options – use the hydrogen directly in industry and transport or turn the hydrogen back to electricity and plug it into the grid.
Studies of the latter compared with “electricity to electricity” suggest that distance to shore needs to exceed some 300km before the losses in electrolysis and the losses in the reverse process – fuel cell or combined cycle gas turbine – to regenerate electricity are overcome by the losses in electrical cables.
Hydrogen, though much hyped, still has many drawbacks, in terms of its fundamental property to confine, control and prevent destruction of materials, but it remains ripe for research.
The answer is not as simple as adding a fraction of hydrogen into the tried and tested existing offshore natural gas pipelines and then recovering it at the receiving end, because firstly, the permissible fraction of hydrogen in the pipeline is low (c. 15%) and secondly, recovering the hydrogen itself results in losses that make the whole venture inefficient.
A further promising option is ammonia. Electricity to ammonia production, transport and use, is fascinating and the possibilities enhanced through green hydrogen. First, produce hydrogen through electrolysis and then combine with nitrogen in the air to create ammonia, which has many direct industrial applications.
The beauty of ammonia is that worldwide transportation and use is well established and therefore, once produced, offshore infrastructure – ships, ports, industry – is already in place to get it to market.
Moreover, ammonia could become the major tool for decarbonisation of shipping itself, being used to power ships – as its energy content and use are better understood than hydrogen. The icing on the cake is that 2% of global emissions are from ammonia production from hydrogen, derived from natural gas where CO2 is released. Large scale offshore green hydrogen production, from floating wind farms, therefore, has the potential to make a major dent in that, provided costs can be driven down.
Floating wind and hydrogen are a natural combination but not in the simple way it is often portrayed. The contribution green hydrogen can make to produce ammonia, being more versatile in powering of ships, in storage and transmission of energy, makes it the frontrunner to deliver the deepwater energy prize that is floating wind.
· R V Ahilan is CEO of global marine and energy consultancy AqualisBraemar LOC Group