Mr. Sens, you talk about the relevance of the entire fuel life cycle. Why is this perspective so important? Isn't it enough for the car to be locally emission-free?
Marc Sens: No, that's not enough if we take the goal of global CO₂ reduction seriously. In Germany and Europe, we often have a very narrow debate that focuses almost exclusively on vehicle efficiency – i.e., “tank-to-wheel” or, at best, direct electricity use. But that only represents a fraction of the reality. If we want to defossilize the transportation sector as quickly as possible, we need to think globally and consider the entire chain: Where does the energy come from, how is it transported, and what is the economic cost of bringing it to the user? The IAV analysis shows that the supposedly most efficient way on paper is often not the fastest or cheapest way to defossilization in reality.
You are referring to the dominance of battery electric vehicles (BEVs). It is commonly said that charging electricity directly into the battery is unbeatably efficient. E-fuels, on the other hand, are often referred to as the “champagne of the energy transition” – too precious and inefficient for mass transportation. Are these descriptions accurate?
Marc Sens: Even though I can confirm that direct electricity use is the most efficient method and must definitely be pursued further, the image of synthetic fuels as “champagne” is incorrect and hardly stands up to comprehensive scrutiny. Based on publicly available data, we can currently assume that the global transport sector, including the maritime and aviation sectors, will require approximately 42,500 terawatt hours (TWh) of energy in 2035. Even if we exclude the maritime and aviation sectors and make the very optimistic assumption that 25 percent of the global vehicle fleet will be fully electrified by then, and also fully exploit the potential of biofuels, i.e., use all the predicted biofuel potential for road transport alone, there will still be a huge gap in energy demand that will have to be covered by fossil fuels.
According to our calculations, this amounts to around 19,000 TWh in road transport alone. How can we best close this gap? Either we introduce only purely battery-electric vehicles to the market from today onwards and try to meet the increasing demand for electricity from renewable sources, or we rely in parallel on synthetic fuels, which would have to be introduced to the market as quickly as possible. Since we surely agree that a sudden or even very rapid transition to purely battery-electric mobility is absolutely unrealistic in a global context for many reasons, there is no way around renewable fuels if we want to rapidly defossilize the transport sector.
What do the aforementioned 19,000 TWh mean for the required infrastructure?
Marc Sens: That's the crux of the matter. If we want to make this amount of energy available to the transport sector in the form of synthetically produced fuels – and we have to if we want to replace fossil fuels – we're talking about gigantic dimensions of installed wind and solar power plants. To meet this demand with synthetic fuels such as methanol, we would need an installed capacity of either approximately 50,000 GW of PV systems or approximately 20,000 GW of wind turbines in favorable regions such as North Africa (MENA). By way of comparison, Germany currently has an installed capacity of renewables from wind and PV that is only a fraction of this – around 200 GW. So we are talking about a factor of several hundred here. This shows that we will have to import this energy. And energy is much easier and cheaper to transport as a liquid in ships than electricity over thousands of kilometers of high-voltage lines that do not yet exist.
Let's stick with efficiency. Critics argue that too much energy is lost in the production of e-fuels. In your study, you compare different paths: direct electrification, hydrogen, ammonia, methanol, and methanol to gasoline. Which one wins?
Marc Sens: If you look purely at the physics from the wind turbine to the wheel, direct electricity use naturally wins out with a remarkable efficiency of around 72 to 73 percent. No one disputes that. But this electricity must be available exactly where and when it is needed. And many studies, at least, doubt whether we will ever be able to cover the entire energy demand in Germany or Europe exclusively with locally generated renewable electricity. As soon as we start talking about importing renewable energy from regions rich in sun and wind, such as MENA, we must definitely consider renewable fuels. This is because transporting electricity over long distances is technically complex or involves significant losses. And then the question arises: which of the many chemical energy carrier options under discussion makes the most sense?
To get to the bottom of this question, it is worth looking not only at the usability of the energy source, but also at its entire life cycle. Hydrogen, often touted as a panacea, is extremely difficult to transport over long distances when it cannot be transported via pipelines. Since transporting it in gaseous form over long distances makes little sense, it must be liquefied, cooled, and pressurized. In the end, the “well-to-wheel” hydrogen path only achieves an efficiency of around 16 to 17 percent. This efficiency describes the proportion of energy generated by the wind turbine or solar panel that ultimately reaches the wheel of a vehicle with a combustion engine. Methanol and ammonia perform better in this respect, with efficiencies of around 20 to 21 percent. That may not sound like much, but it makes a significant difference in a direct comparison.
That's surprising. Methanol, a hydrocarbon, is more efficient than pure hydrogen?
Marc Sens: Yes, especially for logistical reasons. Methanol is liquid at room temperature and also has a very high volumetric energy density compared to hydrogen. This means that methanol can be transported much more efficiently. And even though the carbon for the production of carbon hydrogen must be obtained via direct air capture, the liquefaction of hydrogen consumes so much energy that, in the end, the production of methanol is still less energy-intensive. Finally, it should be noted that many ports already have a methanol infrastructure in place, as it is one of the most traded basic chemicals. Ammonia has similar efficiency levels to methanol, but is highly toxic, which makes it difficult to use in the automotive sector. Hydrogen also has the additional problems of extreme volatility and high infrastructure costs.
So when we look at road transport, I strongly advocate taking a pragmatic approach: methanol is relatively easy to handle and, compared to pure hydrogen, actually has better overall efficiency when you consider the entire chain from production in the MENA region to the wheel in Europe. The disadvantage of the “methanol-to-gasoline” process, where we have an additional process step, is the drop in efficiency to around 13 percent. One advantage of gasoline produced from methanol in an additional process step is the complete utilization of existing infrastructure and the drop-in capability with fossil fuels. However, the low efficiency leads to a significant increase in the installed PV and wind capacity required. Considering speed and costs, this is rather difficult.
In your documents, you mention the “asymmetry” in infrastructure financing. What do you mean by that?
Marc Sens: This is an aspect that is often overlooked in political discussions. When expanding electromobility, the costs for the massive grid expansion, intermediate storage, and, in some cases, the charging infrastructure are passed on to the general public, i.e., electricity customers. Grid fees are rising, and taxpayers are ultimately subsidizing the expansion. The situation is different with synthetic fuels: the investments for the production facilities in the desert or the tankers must be paid for directly by the companies and, ultimately, by the users via the price per liter at the gas station.
This distorts competition. If we were to honestly factor the economic costs of grid expansion into the electricity price for electric cars, or conversely, if the government were to subsidize the infrastructure for e-fuels in the same way as the electricity grid, the cost comparison at the “pump” would look different. This would make the champagne of the energy transition significantly cheaper.
There are calls to reserve e-fuels primarily for air and sea transport, as these sectors are difficult to electrify. Passenger cars should be electric. Do you see it differently?
Marc Sens: I think this prioritization is at least worth considering. For technical reasons, it makes perfect sense, but less so from the point of view of possible financing, especially for a rapid ramp-up. Consider price sensitivity: in aviation, fuel costs account for a huge proportion of operating costs. Kerosene currently costs around 50 cents per liter. Synthetic fuels will initially be significantly more expensive, certainly around 1.50 to 2.00 euros per liter. That would instantly triple ticket prices for flying, at least.
Motorists, on the other hand, are already used to prices of €1.80 and more per liter at the gas station, a large part of which is tax. The willingness to pay is therefore much higher in road transport. That is why I believe that we should not withhold synthetic fuels from road transport, but rather enable faster scaling. The faster we are here, the sooner it will also be available to air transport at lower costs. China is doing exactly that: it is investing heavily in green methanol, which is also to be used in road transport. In the future, the many range extenders and PHEV vehicles sold in China may be powered by green methanol.
You warn against making political decisions about technology. But despite all assurances to the contrary, isn't it already too late for combustion engines in Europe?
Marc Sens: Ideology is a poor guide in physics. If we commit ourselves politically to a single path, we deprive ourselves of the flexibility to respond to market changes and, above all, of speed. But that is exactly what we need if we want to reduce the CO2 contribution of road traffic as quickly as possible. My appeal is therefore: let us listen more closely to the engineering sciences again. If the efficiency of a system has been physically exhausted, then that's the way it is. We should agree on the path that enables the fastest and most cost-effective defossilization – globally, not just within the EU borders.
We are currently seeing that the pure BEV strategy is stalling because customers are experiencing a number of disadvantages in everyday life and the expansion of the infrastructure is not keeping pace. A hybrid vehicle that runs on electricity in everyday use and is powered by green methanol, for example, on long journeys could be the bridge we need for the coming decades.
