CNG – the future-proof alternative
Apart from climate change and the associated need to reduce emissions, the foreseeable finite nature of fossil fuels provides the main motivation for seeking alternative forms of energy to power mobility in the future. Already today, using CNG vehicles makes a significant contribution to reducing the emission of harmful substances in road traffic. However, the potential of CNG has nowhere near been exhausted. CNG vehicles are continuing to build on the head start in the environmental footprint compared with petrol and diesel models with an increasing proportion of biogas gained from renewable materials. The reason is that when biogas undergoes combustion, only as much CO2 is released as the amount previously bound by the growth of the plants themselves. The future-proof nature of CNG grows simultaneously with the biogas ratio. This is because the basic products like energy crops, green waste and other agricultural residues are available as sustainable sources. The same applies to hydrogen, which can also form a component of CNG. If it is generated from wind, solar or hydropower, it too provides a climate-neutral alternative to conventional fuels that is available in unlimited amounts.
Up to now, CNG has been primarily made up of natural gas. The vehicles powered by this fuel meet the strict requirements of the latest emission standards without complex treatment of exhaust gases. However, natural gas is also not available in unlimited amounts. The future-proof utilisation of CNG therefore relies above all on the fact that this fossil raw material can be gradually supplemented and ultimately replaced by sustainably generated energy sources. This process started some time ago. And over the long term it will result in greater independence from imports. It will also optimise the life cycle assessment and increase certainty of supply.
Alongside the natural gas extracted from underground storage reservoirs, biogas can also be produced from renewable raw materials and processed to form CNG. The most important common feature is that the main component and principal energy source of natural gas and biogas is methane. The methane concentration in biogas fluctuates depending on the starting material. This constituent is therefore increased to the standard value for natural gas in a refinement process. Biogas can therefore be used for heating or cooking but also to power automobiles. According to information produced by the biogas sector association – Fachverband Biogas e.V. – pure biogas is already supplied nationwide at 125 filling stations. CNG with a biogas content of ten to 90 percent is available at further filling stations numbering around 100.
SEAT is currently participating in a project to extract biogas from a wastewater treatment plant in the Province of Cádiz located in southern Spain. The SMART Green Gas initiative is a pilot project that is intended to highlight the possibilities of regional and simultaneously sustainable generation of energy for mobility. According to calculations by the operator, the biogas generated from purifying the wastewater from a medium-sized town is sufficient to supply around 300 vehicles permanently with fuel.
Power-to-gas technology is available as an additional supplement or substitute for long-term replacement. This procedure also permits climate-neutral energy production. Hydrogen can be generated using electrolysis from electricity produced renewably for example on wind farms or in solar systems but which cannot be fed into the electricity grid for capacity reasons. Like biogas, hydrogen can be supplied directly into the natural gas grid. However, technical reasons mean that hydrogen blending can only contribute a maximum of five percent. Hydrogen is therefore “methanised” in a second stage. Hydrogen and carbon dioxide are combined to create “synthetic natural gas”. The ideal methane content enables it to be fed into the gas grid without any restrictions. The practical viability of power-to-gas technology is being verified in a number of ways including a project with automobile manufacturer Audi. Since 2013, Audi has been operating a power-to-gas plant in Werlte, Lower Saxony, that produces 1000 metric tons of synthetic natural gas every year – enough to provide 1500 CNG vehicles with climate-neutral fuel to travel some 15 000 kilometres each year.