I often wonder if when most cars go all electric, they’ll start including a gallon or two diesel tanks that you might fill once or twice a year, like your windshield washer fluid. Sounds odd that you would need to add diesel to a plug-in electric vehicle but actually makes a lot of sense when you consider the laws of thermodynamics – virtually all electric buses carry a small 5 gallon diesel tank to run the diesel heaters.

An all electric car in cold climates would have much longer range if it relied on a small, efficient diesel heater to provide warmth to the batteries when starting, heat the interior and provide defrost. Diesel is widely used to heat homes – although we call untaxed diesel – heating oil.

While it’s true that an electric car that burns diesel for heat isn’t 100% carbon free, adding a diesel heater to electric cars could reduce carbon emissions by reducing required battery sizes and electricity consumption due to cold battery losses. Diesel heater consumption in an all electric car would be tiny compared to fossil automobiles – as your just heating not moving the car with diesel.

Electric cars could also contain a reversing valve in the air conditioning system to pump heat into the car in cold weather – and that’s more efficient than resistance heating. The problem with heat pumps in a car is you are limited in where you can pump heat from on a cold day – even a large radiator and very high refrigerant compression might not be sufficient to raise temperatures sufficiently without generating heat from the electricity which is very energy intensive. Maybe you can recover waste heat from the motors and battery but there is less than you might think – and as electric cars improve waste heat will only decline.

So I’m thinking low sulfur diesel might be the way to go for heating electric cars in cold climates.