Gothenburgs "first" electric bus

It might be unfair to call this a vanity project, but the new route 55 which started last week is being promoted as Gothenburg's first electric bus. It is not, because there were a few trolleybus routes running until the early 1960s. It is a hybrid, with charging points at each end of the route, using an overhead supply and a pantograph on the roof of the bus. Charging takes about five minutes. It runs on electricity on the flat sections of the route in the centre of the city, which makes it quiet and emission-free when running on its batteries, but the engine starts up as soon as it hits a slope.

This probably takes battery power as far is it will go. The underlying problem with batteries is the poor energy density, both in terms of mass and volume - they are bulky and heavy and can not store enough energy. They are also expensive due to the use of materials which are relatively scarce. The technology will ultimately be seen as a dead-end.

Road transport fuels must have a high energy density. Hydrogen fails because it does not liquify at ambient temperatures and can only be stored under great pressure. The same applies to methane. Hydrogen also needs to be used in fuel cells which require costly platinum as a catalyst. This is why short-chain hydrocarbon fuels such as petrol and diesel have persisted.

One possibility which has been proposed is ammonia. It has a good energy density, though not as good as a hydrocarbon. Its great advantages are that it can be liquified no great pressure - less than 10 atmospheres, if I recall, at ambient temperatures and that  the waste products are harmless nitrogen and water. It can be used in fuel cells, and has been experimentally, but for some reason the technology seems to have been neglected.