How green are electric bikes?
The message that electric vehicles are the zero-emissions transport of the future is impossible to ignore. We’re beaten over the heads with a constant stream of news that tells us internal combustion engines (ICE) are filthy while electrics are the utopian future.
Plans are already in place to pull new petrol and diesel cars and vans from sale by 2040, a date that could yet be brought forward to 2035, and while there’s no such deadline for motorcycles, it’s clear which way the wind is blowing. But does the data actually back up the messaging?
While an electric bike emits nothing from its nonexistent tailpipe, that’s just a small part of a vehicle’s whole-life emissions cycle. Add complexities like how electricity is produced and what is emitted during manufacturing and the picture is far murkier.
The hidden emissions
Although motorcycle-specific data is hard to come by, there’s a bank of info on electric cars that suggests electric bikes might not have the advantage you’d expect.
In 2018 the European Environment Agency compiled a report – Electric vehicles from life cycle and economy perspectives – which gives insight into the issues. Most importantly, it concluded that BEVs (battery electric vehicles) emitted 1.3 to two times as much greenhouse gas (GHG) during the production process as petrol equivalents.
The report said: "GHG emissions from raw material and production LCA [life cycle assessment] phases are typically higher for a BEV than for its ICEV equivalent. This is related to the energy requirements for raw material extraction and processing as well as producing the batteries."
Warming the planet
With the electric vehicles considered for the report, the batteries alone accounted for around 40% of the greenhouse emissions in the production stage. On bikes, that percentage is likely to be higher as there’s simply less raw material in a motorcycle, making the battery a more significant chunk of the total.
According to figures in the EEA report, the batteries accounted for between 16% and 26% of cars’ total weights, while on electric bikes the batteries account for perhaps twice that much. For instance, Harley-Davidson’s LiveWire has a total weight 249kg, of which the battery is 113kg. That’s 45% of the whole bike.
Once production is finished electric vehicles don’t emit greenhouse gasses directly, but there are still emissions from electricity production. It varies from one place to another – in nuclear and hydro-electric-powered Sweden, electrics are estimated to emit the equivalent of 9g/km of CO2 while in Latvia, where electricity comes mainly from coal, it was 234g/km.
A study published in the journal Nature Sustainability found that even when electricity comes from poor sources, they do break even after a long time on the road. Large electric cars typically start to emit less than their petrol equivalents after around 44,000km.
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Small vehicles need 70,000km to reach that point because their batteries account for a greater proportion of their production emissions and their petrol equivalents.
Given that on an electric motorcycle the battery accounts for a larger proportion of the raw materials by weight, it will take even more miles before an electric bike’s overall emissions drop below the lifetime output of a petrol bike.
And there’s the sticking point. Battery cars make sense on the basis that the average car will cover 15,000km per year and last 12 years – giving a lifetime mileage of 180,000km. Given the smaller distances that motorcycles tend to cover, and that the electric bike break-even point may be north of the 70,000km needed for a small electric car to overhaul a petrol one, it’s far from clear that electric bikes are the true green option.
Electric will win in the end
While there are endless arguments for and against the switch to electric vehicles, a 196-year-old scientific theory means they will win the day.
Putting aside variables like how electricity is produced, the emissions from battery production and losses in storage and charging, electric motors have an advantage because they’re not heat engines and as such they’re not subject to ‘Carnot’s rule’.
Established by French physicist Sadi Carnot in 1824, the rule shows that a heat engine (anything that converts thermal energy to mechanical energy) has a maximum efficiency that can’t be exceeded. For petrol engines, Carnot’s rule puts that maximum at about 70%.
Even the most advanced petrol engines manage around 50% , but electric motors aren’t limited by Carnot’s rule. That means they can operate with efficiency levels of 95% or more. As improvements are made in reducing emissions from battery production, the pendulum will inevitably swing in favour of electric even bikes.