Alternatively-fuelled vehicles (AFVs) are any that run on something other than just petrol or diesel. The term covers a multitude of other energy sources, from batteries to vegetable oil. Even electric vehicles come in a variety of forms, including hybrids - like the Toyota Prius - and pure electric plug-ins, like the Nissan Leaf.
To help navigate this complicated landscape, and to set out the terminology we’ll be using throughout our series of posts on AFVs, here’s a brief description of each of the main types:
Hybrid Electric Vehicle (HEV)
This is a vehicle powered by a traditional internal combustion engine (ICE) – either petrol or diesel – as well as an electric battery. The battery is charged using excess energy from the ICE, as well as by reclaiming the car’s kinetic energy when it brakes. The electric powertrain allows a hybrid to achieve much better fuel economy, and therefore lower emissions, than a traditional ICE vehicle.
The most popular HEV is the Toyota Prius – a petrol-electric hybrid. It can do 94mpg and produces just 70g CO2/km, compared to 52mpg and 124g CO2/km for the average new petrol car.
Battery Electric Vehicle (BEV)
This is a vehicle powered entirely by an electric battery that is charged by plugging it in. These vehicles emit no CO2, although CO2 is of course emitted when producing the electricity that charges them.
The most popular BEV in the UK is the Nissan LEAF, which can travel up to 155 miles on a single charge.
Plug-in Hybrid Electric Vehicle (PHEV)
This is a vehicle that has both an ICE and a plug-in electric battery. At any time, it can be running on the battery alone, on the ICE alone, or on a combination of the two, like a HEV.
The UK’s most popular model is the Mitsubishi Outlander PHEV, which can do the equivalent of 157mpg and emits 41g CO2/km.
This category also includes ‘range extended’ versions of BEVs, such as the BMW i3 REx. These are BEVs fitted with an additional, small petrol engine to generate electricity when the battery’s charge is too low. The i3’s range extender increases its range on a single charge from 125 miles to 206 miles.
Hydrogen Fuel Cell Vehicle (FCV)
This is an electric vehicle that uses a hydrogen fuel cell, instead of a battery, to generate electricity. FCVs emit no CO2 – only water – although most of their hydrogen comes from natural gas, and CO2 is emitted in the production process. They generally have lower overall energy efficiency than BEVs, but a much greater range. Refilling a hydrogen tank also takes much less time than recharging a battery.
Only two FCVs are currently available in the UK: the Hyundai ix35 FCEV and the Toyota Mirai. The Honda Clarity is also due to go on sale this year. All three models can go more than 300 miles on a single tank of hydrogen.
Some vans and even heavy goods vehicles (HGVs) have been converted to dual-fuel vehicles, running on both diesel and hydrogen.
Compressed Natural Gas (CNG) and Liquefied Petroleum Gas (LPG) vehicles
These are vehicles powered by gas – either natural gas (which is mostly methane) or LPG (which is mostly propane). They are generally converted from petrol vehicles, and most are dual-fuel; they can run on either gas or petrol. Engines have also been developed to allow HGVs to run on gas – either pure CNG or LPG, or a 50/50 blend of gas and diesel.
Gas vehicles emit less CO2 than petrol ones, and although they also emit methane, their total greenhouse gas emissions are less than petrol and roughly equivalent to diesel. They emit less NOx and other air pollutants than diesel, though, making them cleaner than traditional fuels overall.
The environmental benefits of CNG are even greater when Bio-CNG is used – renewable biomethane gas generated from food and other waste.
Biodiesel and Bioethanol vehicles
These are vehicles that run on biofuels – either biodiesel (made from vegetable or animal oil) or bioethanol (an alcohol made from plants). Bioethanol can be blended with petrol and used to power petrol engines with no modification. Similarly, biodiesel can be blended with diesel to run diesel cars.
Using these blends does not reduce a vehicle’s CO2 emissions; however, CO2 is absorbed from the atmosphere by the plants used to make the biofuels, meaning that net lifecycle emissions are lower.