Green v blue hydrogen

The debate over the merits or otherwise of hydrogen as an energy vector continues to run and run, with one focus being the choice between green and blue hydrogen. A good overview article in the Athropocene magazine looked back to an article last year co-authored by Schalk Cloete, a Research Scientist at Sintef in Norway. It said that Blue hydrogen, where natural gas is converted to hydrogen, with CCS to reduce emissions, has significant cost and emissions advantages over green hydrogen, produced using renewable power. According to the research paper, the key issue was the capital under-utilisation involved in using electrolysers part time to make hydrogen from variable output renewables.  

The Sintef study considered ‘Green H2’ scenarios, where hydrogen could only be produced via electrolysis using surplus renewable power, and mixed scenarios, where ‘Blue hydrogen’, produced using natural gas with CCS, was also available for deployment. In addition to the conventional Steam reforming CCS approach, it also looked at a case where Gas Switching Reforming (GSR) plants were also available for deployment. GSR is a novel flexible power and hydrogen production technology designed for the economic integration of higher shares of variable renewables. But it still used CCS.

The study found that more renewables were needed in the green hydrogen cases than in the mixed green hydrogen/fossil CCS cases. And in terms of cost, the study found that, though green hydrogen can help integrate higher shares of wind and solar, this strategy brings ‘considerable costs’ due to capital under utilization of the expensive electrolysers and, in some cases, the extra transmission links needed: 

*When electrolysers are co-located with demand, costly transmission network expansions are required to transmit wind and solar production peaks to the electrolysers.

*When electrolysers are co-located with wind power, the low utilisation of the expensive electrolysers and the large hydrogen transmission and storage capacity required to handle intermittent hydrogen fluxes inflate system costs.

*When conventional CCS power plants are deployed, the model chooses to operate these plants under baseload conditions to maximise the utilisation of expensive CCS infrastructure, limiting VRE deployment.

*Flexible power and hydrogen production from GSR can integrate more wind and solar, but the associated intermittent hydrogen production increases hydrogen transmission and storage costs, reducing the positive impact of this novel process. 

As can be seen, the trade-offs are quite complex. Dealing with variable renewables adds to the cost, and, on balance the study concludes that, in a mixed Green and Blue hydrogen system, ‘flexible power and hydrogen production with CCS offers substantial benefits to a future energy system with high VRE shares. In addition, it produces large quantities of clean hydrogen to decarbonise sectors other than electricity’. So it sees Blue Hydrogen playing a key role. 

There are however some issues here. Why go for a mixed green and blue hydrogen system? In a Green hydrogen only system, power shortfalls due to the variable inputs from renewables can be balanced by using power produced using hydrogen made earlier from renewable surpluses and stored ready for the lulls. That might mean that the electrolysers are only used part time, although that’s not necessarily the case if the hydrogen storage capacity is high enough. It’s the hydrogen storage option, whether in salt caverns, tanks or other formats, which takes the sting out of variability. Alternatively, in a Blue Hydrogen only system, the variations in renewable are met by ramping the gas CCS plants up and down, reducing their efficiency- although allegedly not so much in the case of GSR. But you still have to have CCS- and that only partly cuts CO2 emissions. 

It may be that, in reality, we will have a mixed Green and Blue hydrogen system for a while, since the emphasis at present is on Blue hydrogen, which is seen as cheaper for the moment. It is true that, as the study says, ‘hydrogen produced from electrolysis will always be more expensive than the electricity used to produce it, whereas natural gas can be converted to hydrogen at a significantly lower cost than it can be converted to electricity’.  But, with the CCS costs included, the balance may change- green hydrogen should be competitive with blue hydrogen by 2030, if not earlier. As it is, this study assumes that CCS is viable on a large scale, including the transport of CO2 over long distances to suitable wells offshore. And that electrolysers wont get cheap and flexible! Whereas, GSR allegedly will be- despite so far it being an undeveloped technology. In fact, the whole analysis seems a bit of a tautology- if GSR is very flexible (more so than electrolysers) then of course it would help deal with variable renewables. 

Given all these uncertainties, it is hard to identify optimal mixes in the various transient mixed systems that might emerge, and certainly it is odd to use this type of analysis to downplay the green hydrogen option, and to lend support to the use of fossil gas!  

Not so UK electrolyser pioneers ITM Power, who in a paper in the Fell Cell Bulletin  recently flagged up an interesting new angle: ‘Hydrogen derived from water electrolysis neither results in oxygen depletion nor increases the atmospheric concentrations of water vapour and CO2’. Conversely, in addition to the associated CO2 production (even given CCS), ‘the use of hydrogen derived from fossil fuels (with or without carbon capture and storage, CCS) depletes the oxygen resource and increases water vapour emissions to the atmosphere, which enhances the rate of global warming’.

The paper’s authors, Marcus Newborough and Graham Cooley, add that, in addition to avoiding direct warming, ‘the long-term objective should be to stabilise, or even increase slightly, the concentrations of atmospheric and aquatic oxygen, and possibly speed up the decay of atmospheric methane. Clearly the production-and-use of hydrogen derived from fossil fuels contravenes this objective, and should cease without delay’. 

The implication is that we should go for zero carbon green hydrogen straight away and not mess around with Blue hydrogen/CCS. Sadly however, we seem to be going the other way: the UK’s Industrial Strategy Challenge recently supported a series of Blue hydrogen/CCS projects.