There is a greater sense of urgency than ever before to find more sustainable, secure, cost-effective and ethical ways to source and store energy. As we look to replace fossil fuels, renewable energy sources such as solar, wind, hydro, tidal and hydrogen have taken centre stage. But the perceived volatility of these sources, and the time taken for them to come onstream, is driving some decision-makers to reconsider the backwards step of drilling, mining and fracking for carbon-intensive fossil fuels.
With sustainable, secure and cost-effective new energy sources within our reach, governments and businesses should look to increase the ease, reliability and efficiency of energy generation and reject any calls for the protracted reliance on fossil fuels.
The hydrogen rainbow
For some time, hydrogen has been seen as a key part of the solution. After all, it is the most abundant chemical element and accounts for around 75pc of the mass of the universe. Hydrogen atoms are found in water, plants, animals and natural gas, but it rarely exists on its own as a gas. It needs some form of extraction process to produce sufficient quantities to fuel industry, vehicles or homes. Most processes used to manufacture hydrogen involve some level of carbon—in terms of both input and output. This has given rise to the idea of the ‘hydrogen rainbow’, which uses a colour code to differentiate the different manufacturing methods by their carbon intensity. At the current count there are at least ten shades in an increasingly crowded rainbow, but the three that most people will be familiar with are a more muted palette of grey, blue and green.
Clearly, as it emits zero carbon and uses energy from renewable sources, green hydrogen is most likely to deliver decarbonisation targets and also protect against the supply volatility of the current fossil-dependent energy markets.
The hunt for hydrogen efficiency
Compared to traditional batteries, hydrogen stores energy much more densely and can refuel vehicles faster, but historically it has proved quite inefficient to produce, store and transport. A kilogram of hydrogen holds 39kWh of energy—the thermodynamic minimum net energy required to form hydrogen from water. However, the actual amount of energy needed to create that kilogram varies by manufacturing process and is typically higher.
Conventional thermochemical processes for manufacturing hydrogen require very high temperatures of 500–2,000°C. This itself requires a great deal of energy is less energy-efficient than other processes, such as electrolysis.
Electrolysis uses electricity to split water into hydrogen and oxygen inside an electrolyser unit, of which there are different types that operate in different ways. These include polymer-electrolyte-membrane (PEM), alkaline and solid-oxide electrolysers. Despite being more efficient than other thermodynamic processes, at 70–80pc efficiency, electrolysis still loses 20–30pc of the energy used during the conversion. So, there is an ever-increasing need for new technology to improve efficiency. That is where plasma comes in.
First of all, let us remind ourselves what plasma is. It is an electrically charged—or ionised—gas, which is sometimes described as the fourth state of matter. Plasma occurs naturally in lightning, sparks from static electricity and the aurora borealis. It is used in television and display screens, fluorescent lighting and even arc welding.
Green hydrogen production from applying the ‘plasma effect’ is the core feature of an innovative UK-developed technology called tetronics hydrogen plasmolysis (THP).
THP involves applying highly concentrated electrical energy to water under the high temperature and pressure gradients arising from the plasma arc.
Compared with current benchmark electrolysis technologies, including PEM cells, THP offers a step-change in performance and delivers considerable energy efficiency improvements in terms of kWh/kg of hydrogen.
Over the summer of 2022, Tetronics built a first-of-its-kind THP system and ran a series of hydrogen production trials funded by the UK’s Department of Business, Enterprise and Industrial Strategy (Beis).The system took plasma-based hydrogen production beyond the scale achieved by previous laboratory researchers, thanks to the integration of its patented plasma torch technology. The work demonstrated the benefits of plasma-assisted hydrogen production by achieving high hydrogen yields with a lower electricity demand than comparable electrolysis systems.
The feasibility test showed that a specific gross energy requirement of 36–40kWh equivalent per kg of hydrogen was achieved using a water-based electrolyte. This is approximately a 10pc improvement in efficiency beyond the theoretical minimum and as much as a 40pc improvement over the reported commercial performance of PEM fuel cells.
This snapshot of the efficiency advantages THP technology has over other hydrogen production methods points to a competitive, energy-efficient, green hydrogen supply solution based on a unique and inventive assembly of proven technologies. What is more, THP has the advantage of being scalable—requiring a smaller footprint than other electrolysis plants—and is suitable for remote, off-grid locations, which in turn reduces transportation costs and losses that might occur. It promises to make a major contribution to reducing our dependence on fossil fuels.
Peter Keeley-Lopez is the senior process applications engineer, Tetronics.
This article is part of our special Outlook 2023 report, which features predictions and expectations from the energy industry on key trends in the year ahead. Click here to read the full report