for larger vehicles such as heavy trucks, because hydrogen energy storage offers greater range and quicker refueling time. Hydrogen fuel can also be used to power stationary power generation plants, or to provide an alternative to natural gas for heating. Fuel cells Fuel cells present the most attractive choice for energy conversion from hydrogen to electrical power, due to their high efficiency, low noise, and a limited number of moving parts. Fuel cells are of interest for both stationary and mobile power generation from hydrogen. Fuel cells are often considered as part of a vehicle propulsion system. Using a fuel cell to power an electrified powertrain including a battery and an electric motor is two to three times more efficient than using a combustion engine, although some of this benefit is related to the electrified powertrain (i.e., including regenerative braking). This means that significantly greater fuel economy is available using hydrogen in a fuel cell, compared to that of a hydrogen combustion engine. Internal combustion engine conversions to hydrogen Alongside mono-fuel hydrogen combustion, combustion engines in commercial vehicles have the potential to be converted to run on a hydrogen–diesel mix. This has been demonstrated in prototypes in the UK, where their emissions have been reduced by up to 40% during normal driving conditions. This dual-fuel flexibility eliminates range anxiety as the vehicles can alternatively fill up only on diesel when no hydrogen refuelling is available. Relatively minor modifications are needed to the engines, as well as the addition of hydrogen tanks at a compression of 350 bars. Trials are underway to test the efficiency of the 100% conversion of a Volvo FH16 heavy-duty truck to use only hydrogen. The range is expected to be 300 km/17 kg; which means an efficiency better than a standard diesel engine (where the embodied energy of 1 gallon of gasoline is equal to 1 kilogram of hydrogen). Compared to conventional fuels, if a low price for hydrogen (€5/kg), significant fuel savings could be made via such a conversion in Europe or the UK. A lower price would be needed to compete with diesel/gasoline in the US, since these fuels are not taxed as much. Combustion engines using hydrogen are of interest since the technology offers a less substantial change to the automotive industry, and potentially a lower up-front cost of the vehicle compared to fully electric or fuel cell alternatives. However, the non-zero emission