The material component of the energy transition

The adoption of new technologies as part of the decarbonisation of the energy system will require a better understanding of the effects on existing plant components, as well as the development of novel materials and coatings. Dr Joy Sumner, reader in energy materials at Cranfield University, calls for more clarity on which technology pathways the UK will pursue to help focus efforts in the right areas.   

Green tech is good for the environment, but not always so good for power generation plant: the transition to alternative, clean technologies often means massive strains on existing components and their materials.

The adoption of biogas and synthetic gases, as well as the use of hydrogen, is critical for decarbonisation in the sector, but will lead to more rapid deterioration of major facilities and additional costs that need to be factored into business plans.

Just as one example, hydrogen is regarded as a relatively straightforward replacement for natural gas, with the potential to reduce our dependence on geopolitical relations (which has implications for enhanced energy security and decoupling from global energy prices).

Hydrogen is particularly attractive as we can make use of much of the existing infrastructure: householders and industry don’t need to install a whole new apparatus. But what do the different chemistry and chemical reactions involved do to the high temperature parts of power generating turbines?

We know, just to begin with, that it means dealing with much larger quantities of water vapour in the stream of exhaust gases. Oxidation can lead to uncertainty over how much metal will be lost, and as some of the most highly loaded and hottest components are exposed in this stream, it is very important to understand what impact this will have on their corrosion.

Another example of how materials could limit the move to green energy relates to storage. With the urgent need to find alternatives to batteries for storing energy from renewables, the use of molten salts is getting more attention.

Systems use the excess solar to heat liquid salts to around 565°C. The salts can even be heated using combusted hydrogen generated in electrolysers in excess wind, for a truly futuristic energy solution.

Like a hot water bottle, this thermal energy is stored over time before the heat is used to produce steam to turn turbine. However, salts of any kind, and molten salts in particular, are very aggressive in terms of their corrosive effects on materials like pipework and storage tanks.

These two, very different examples, show that hard evidence is needed about materials’ degradation to make sure governments and their policymakers, as well as industry, are able to make the best decisions for the long-term on power generation methods. We need to know what the actual effects of green tech are, the different thresholds before damage is caused, and the opportunities for longer, more reliable plant life using new materials and coatings.

New work at Cranfield, for example, is looking at a supercritical-CO2 process, where this CO2 is used at very high temperatures and pressures to drive turbines.

As the supercritical-CO2 is very dense, the energy from burning fuel (gas, biomass, etc) has a high efficiency of conversion into electricity, meaning electricity may be cheaper. It also means the turbine can be very small compared to other power cycles, so the new power plant can fit into small parcels of land and can be put next to existing industrial structures for localised power generation. The CO2 involved can be captured (at levels of 99% purity), and can be transported to be used or stored.

In other words, this power cycle can act as a bridging technology: a means of producing low-CO2 power while other renewable energy sources and storage options are being developed.

However, this cycle still experiences challenges. Here, the turbine is surrounded in CO2 containing small amounts of chemical contaminants that can degrade the materials. It is also essential to find solutions to ensure the plant can withstand the very high temperature and pressure environment generated. Current research is looking at a range of superalloy and ceramic coated samples to provide confidence in this technology as a low-carbon option.

This is where the transition to zero carbon power generation is being held back. There is a lack of clear direction on which technologies to follow, which to put investment into, because of a lack of evidence, which can lead to a cycle of wait-and-see.

We’ve reached a stage where there’s an urgent need for consistency in the message being given to industry on which tech pathways are the right ones for the UK’s future. That means more active conversations and collaboration between universities, industry and government to build a clear, reliable picture.

Otherwise, we remain in situation that is damaging in terms of the general perception of energy providers. We know how much work is going into finding sustainable alternatives, practical means of carbon reduction, and the kinds of long-term solutions that will mean more stability of supplies and more control over prices — but that isn’t what the public sees.

People need to know there is at least a plan in place, with options being worked out in terms of the costs and benefits, so that realistic, workable change is on the way.