Efficient energy storage is necessary for a reasonable transition to sustainable energy sources. This means that we will, in part, have to convert and store sustainably generated electricity in chemical compounds. This says Wiebren de Jong in his inaugural speech as professor at TU Delft on Friday 27 October.
Sun and wind
A lot is expected from energy sources such as solar and wind as part of the ongoing transition from fossil to sustainable energy. Energy and electricity consumption, however, are also often confused in the process. The vast majority of our energy consumption is not electricity, but for example heat use in industry and households and transport fuels. ‘The wind and sun are also – geographically and in time – variable sources and so are difficult to predict,’ points out Wiebren de Jong, Professor of Large-Scale Energy Storage.
Cheap and expensive electricity
This creates a mismatch between electricity supply and demand, resulting in inevitable periods of cheap and expensive electricity. ‘This makes it interesting to create a degree of system flexibility,’ says De Jong. ‘In cheap periods, for example, you could store electricity to use at a later date during electricity shortage. Large-scale energy storage therefore contributes to stability and reduces our dependence on fossil fuels.’
‘Electricity storage can be done in small-scale systems, such as flywheels and batteries, but also in the form of chemical compounds, fuels. For large-scale energy storage, on the other hand, we must convert the electrons from sustainably generated electricity into chemical compounds. And we can also produce quite a few molecules: from a bulk fuel like CH4 to fertilisers and plastics.’
How do we actually get from sustainable electricity to these molecules? The first possibility is the indirect route, a process in which water with electricity is first decomposed into hydrogen. This can sometimes be used directly in industry. ‘But this sounds easier than it really is,’ says De Jong. Moreover, hydrogen can also be combined with CO2 to produce more efficient energy carriers.
‘One example of this is methane gas production. The electricity grid has many possible sustainable supply sources, such as biomass, from which CO2 can be extracted through combustion and CO2 capture. In turn, the CO2 forms the raw material for methane production. Our current gas infrastructure has a significant storage capacity, so that in times of sustainable sources scarcity, methane can be converted into electricity by methane gas turbines.’
‘This is an example of how we look at processes within the Process & Energy department at TU Delft. It involves a smart approach to integrating processes and provides possibilities for upscaling. This is now also possible in our recently renovated P&E lab.’
‘But my research group is also looking expressly into the direct power-to-X route, a process in which electricity is used to convert CO2 into the desired molecules directly via electrochemistry. The core of these molecules forms the electrochemical cell. This electrochemical technology has significant potential due to the facts that the selectivity can be high and the process conditions, especially concerning temperature, are manageable’
Power to X, the direct and indirect way via water electrolysis or not?
‘Various domains are necessary for the successful development of electrochemical energy storage,’ observes De Jong. ‘In Delft we are working on aligning disciplines, varying from materials science, catalysis, electrochemistry, transport phenomena, reactor science, energy technology and process-system-integration to embedding in our national infrastructures via system studies. We call this collaboration the development of the E-Refinery, in which we are looking at the integration of the fluctuating electricity production, CO2 capture, primary conversion, further product separation and purification and transport and product use in various sectors.’
Now or never
‘Our field of study will need to answer questions about large-scale energy storage. Should we pursue the indirect route via hydrogen or is direct electrochemical conversion the way to go? Both routes need to be developed through the entire chain, from material selection to process-system-integration and embedding in our national infrastructures.’
‘However, really large-scale energy storage, on the other hand, means that we will need to convert the electrons from sustainably generated electricity into chemical bonds. And to achieve this, the time-honoured field of electrochemistry, and especially electrochemical engineering, must be put back on the map. A lengthy lack of attention and drive has created a gap between existing knowledge and skills and what is necessary in this area in our society. It is a gap that needs to be bridged through education and research linked to valorisation. We have to bridge that gap before it is too late. It is now or never.’