Cutting emissions — it all depends on where you find your fuel

An American driver looking to escape the winter chill by driving from New York to Florida would use about 150 litres of petrol to traverse the 1600km in a Chevrolet Impala.

Switch that gas guzzler for an electro-neating electric vehicle and the equation changes. A Tesla Model S travelling the same distance would need the power generated by about 70 cubic metres of natural gas, 130kg of coal or 33 minutes of blades spinning on a giant wind turbine to make the same journey. As electric cars slowly become a bigger part of the global vehicle fleet, questions about fuel efficiency are going to become more important. While multiple variables can affect electric vehicle energy consumption, a Bloomberg New Energy Finance analysis illustrates some ballpark estimates to give drivers a better picture of what’s happening underneath the bonnet.

Coal

Taking that 1600km road trip in an electric vehicle that needs 33 kilowatthours of energy to travel 160km, like a Tesla Model S, would require about 130kg of coal to be burned at a power plant. Modern coal plants convert only about 35 per cent of the fuel’s energy into electricity, and about 10 per cent of that electricity could be lost as it travels along power lines.

Even with all those losses, the electric vehicle road trip is still better for the climate than driving a petrol-powered car. Burning that much coal would release about 310kg of carbon dioxide into the atmosphere, compared with 350kg from the 150l of petrol. Even though coal tends to emit more pollutants than oil for the amount of energy it generates, the efficiency of the electric vehicle, which recharges its battery every time it brakes, more than makes up the difference.

Natural Gas

Natural gas power plants are more efficient than coal, typically converting about half the fuel’s energy into electricity, and they are also much cleaner. A gas power plant producing the same amount of electricity would emit just 170kg of carbon dioxide for the 1600km journey.

Solar

When it comes to charging electric vehicles with solar power, size matters. A typical 10-kilowatt rooftop array would need about seven days to create enough electricity for a 1600km journey, as clouds and darkness mean it only operates at about 20 per cent of its capacity on an average day. Scale up to a photovoltaic power station, though, and it would take a matter of minutes, not days. At a modest-sized solar field, the average daily output would produce enough electricity for a 1600km drive in less than four minutes.

Wind

Wind is a similar story, with different sizes of turbines producing different amounts of electricity. Take the Vestas V90-2.0 MW, an 80-metre tall behemoth. Just one of these turbines — and wind farms are usually planted with dozens of them — is capable of producing enough electricity to power a

1600km trip every 33 minutes.

Hydro

At full capacity, a big hydro plant like New Zealand’s Clyde Dam would churn out enough power for the 1600km trip in less than three seconds.

Calculating carbon emissions from wind, solar and hydro can be tricky. None of them emit any carbon dioxide in the course of producing electricity on a daily basis. But unless they’re paired with adequate energy storage — and most existing renewable generation isn’t — carbon-emitting generation may be needed to make up for them whenever the sun isn’t shining, the wind isn’t blowing or the lakes are low.