When the UK government canceled its plans to electrify rail lines running through Wales, the Midlands and the north of England and cut the electrification of the Great Western rail network, it prematurely ended the rail investment program, considered one of the largest in the country since the Victorian era. But now the government and train manufacturers are hoping that hydrogen could be an alternative to electrifying British railways.
Hydrogen Trains
Hydrogen trains have already replaced dirtier diesel engines in Germany, and some rail companies believe the UK will follow suit by 2022. Investments are still needed to introduce new technologies. But they can be an important step towards reducing the carbon footprint of railways.
Currently, only a third of the UK's rail network is electrified, and few additional tracks have been converted over the past few years. As the government stops electrifying the grid, it faces a dilemma: How to eliminate diesel trains that produce carbon dioxide and other harmful pollutants?
The current strategy is to buy bimodal trains that can switch to diesel when they get out of the way without electricity. But this does not solve the problem as such.
If electrifying the rest of the network seems too expensive, one possible alternative would be to generate electricity on board the train. One way to do this is to use fuel cells that combine hydrogen gas with oxygen from the air to produce electricity and water. Hydrogen can carry more energy than batteries of the same weight, which means that fuel cell systems can be lighter. In addition, they take less time to refuel than batteries to recharge and do not have the same high environmental costs to manufacture.
Hydrogen gas must be compressed in tanks, which are usually located on the train roof. But adding a regenerative braking system to charge an extra small battery will reduce the amount of hydrogen needed to power the train.
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The high cost of installing overhead lines means that hydrogen trains are likely to be a more economical way to electrify rail lines with relatively little traffic. It also makes sense to experiment with hydrogen trains to spot any unexpected problems. However, widespread use will require significant investment in hydrogen production and storage. Since very few railways have been built on hydrogen, it is unclear whether they can save money by eliminating the electrification of large lines, whether an economy of scale will work.
A better solution may also be the development of hybrid dual-mode trains that can switch between electricity from overhead wires and fuel cells. This is better suited for rail networks that run through bridges and tunnels.
Another problem with hydrogen fuel cells is that fuel is now produced from methane (natural gas) using a process called methane steam reforming, which also produces high yields of highly toxic carbon monoxide. It can be converted to carbon dioxide, but then hydrogen fuel will still contribute to greenhouse gas emissions.
Pure hydrogen
An environmentally friendly way of producing hydrogen is through electrolysis, when an electric current is passed through the water. In theory, you could use excess wind (and possibly solar) energy to generate that electricity and make hydrogen a renewable energy source. The problem is that electrolysis plants are unlikely to be economical if they are not running for most of the day. This would mean that when there is no excess wind to power them, they will need regular electricity from the grid, making the process very expensive (and not necessarily renewable).
The second alternative is the use of a "thermochemical" production method, which involves the interaction of water with sulfur and iodine in the presence of heat. The good news is that this method will become economical over the next ten years, thanks to the development of generation IV nuclear power plants. These high temperature small modular reactors are being developed in China, USA, Canada and Japan, but not in the UK or Europe.
Despite all the restrictions on the use of hydrogen as a transport fuel, as more and more countries (in particular, Japan) conduct further research in the field of hydrogen economy, its cost will decrease. Hydrogen may even replace natural gas in main gas pipes, which will also help reduce the cost of using it for transportation.
Ilya Khel