All-electric – is the diesel bus really history already?

Guest article by Christian Marquordt, Author at Urban Transport Magazine

Public transport buses

Anyone who follows what type of buses public transport companies order these days must be rubbing their eyes in disbelief. The news is that orders are being placed almost solely for electric buses with alternative drives that use either batteries or a fuel cell to operate. There is hardly any mention of new diesel buses for public transport. If they do exist, then as hybrid buses which recover electric energy during braking or travelling downhill. This is then stored in batteries or ultra-capacitors (ultracaps) and can be used to accelerate from the next bus stop. So even these hybrid buses are “semi-electric”. Stadtwerke Bonn operates almost 60 hybrid buses out of a combined fleet of 200 vehicles, and reports that hybrid buses consume 14 per cent less diesel fuel.

It comes as no surprise then that some bus manufacturers no longer market ICE public transport buses. They include, in alphabetical order, BYD (China), Ebusco (Netherlands), Van Hool (Belgium), VDL (Netherlands) and Yutong (China).

Daimler Buses (Mercedes and Setra) has also announced that in 2024 it is converting its Mannheim works into an electric-only bus manufacturing plant, at a cost of several million euros. For a brief interim period, diesel buses for public transport will still be made at the Ligny-en-Barrois works in France.

The bus industry is also working on making vehicles lighter in order to improve their range. Non-existent weight requires no momentum and consumes no energy.

The case for battery-electric buses

One obvious advantage of battery-electric buses is that the technology has existed for over 15 years and that it currently powers buses worldwide. Not only is it tried and tested, but operating a battery-electric bus nowadays comes with no risks involved.

How far a battery-electric bus can travel before recharging varies. It depends for example on the type of batteries installed and the vehicle’s weight. The battery cells’ chemistry also plays quite an important role. At present, almost all buses operate with lithium-ion batteries. However, intense research is currently taking place on sodium-ion batteries. These will store more energy and soon be market-ready. The industry is also exploring solid-state batteries which will also store more energy. Among some battery-electric bus manufacturers there is already talk of realising a range of 1,000 kilometres in the not too distant future. A number of bus models have already exceeded 500 kilometres during testing on multiple occasions.

As yet, the ranges manufacturers quote for their buses still vary greatly. While this figure is influenced not least by battery specifications, some manufacturers are also more cautious than their competitors about how far their buses will travel.

A battery-electric bus is around 1.5 times the price of a diesel bus, which means that state funding is a necessity.

The case for fuel-cell buses

A bus which produces its own energy from an electrochemical reaction involving hydrogen and the oxygen in the atmosphere has two main advantages over a battery-electric bus. The first is its range. Before it needs refuelling it can cover distances a battery-electric bus cannot possibly yet achieve. A fuel-cell bus can already manage an entire shift from early morning to late evening and back to the bus depot without refuelling. The other advantage is that a fuel-cell bus takes about as long to fill up as a diesel bus. The manufacturers quote around ten minutes.

How much a fuel-cell bus costs to operate is difficult to answer. The key issue is where the hydrogen it uses comes from. Hydrogen produced by electrolysis is of course more expensive. However, some transport companies operate in the vicinity of chemical plants where hydrogen is an inevitable by-product which used to be disposed of simply by flaring. Hydrogen sourced this way is extremely cheap and from an environmental perspective using it makes more sense than destroying it.

But even when hydrogen is produced by electrolysis, it is generally accepted that the fuel costs are roughly the same as for a diesel bus. Regionalverkehr Köln put its first two fuel-cell buses into service in 2011, and the hydrogen price quoted then was 33 cents per kilo.
In terms of purchase price, battery-electric and fuel-cell buses are roughly the same.

Special case: a battery-electric bus with a range-extending fuel cell

The limited range of battery-electric buses has resulted in the market offering a combined battery and fuel-cell solution. This type of bus always runs on its batteries, which in turn are constantly charged by a fuel cell. The result is a respectable range of around 400 kilometres. The recently unveiled Mercedes-Benz eCitaro REX is an example of this drive system.

Coaches

The story is altogether different for coaches, which do not return daily to the depot and are not always near a charging point on their travels. The current range of an electric drive does not cover a journey, especially over a long distance. This is where diesel engines still have an edge. A number of battery manufacturers are already promising a 1,000-kilometre battery range, which is why one can dare forecast that diesel engines no longer really have a future even in coaches.