Energy Costs

Chart of the price of one kW/hour

There has been a lot of discussion about energy around me lately, some of it quite emotional. One thing that struck me is that people generally don’t realise how cheap energies like electrical power and fossil fuel are. One question that came up during lunch yesterday was if from a price standpoint, biking was even cost effective.

First let us consider the price of energy. In Zürich, daytime electrical power costs CHF 0.185 per kiloWatt/hour (kW/h), a litre of diesel fuel costs CHF 1.86, and contains 37.3 mega Joules (mJ), which is ≈10.36 kW/h, which brings us to a price in around CHF 0.18 per kW/h. Now, let’s consider fuel for a human, in the form of a Mars bar. A pack of 6 × 45g Mars Classic is CHF 2.7, which is conveniently CHF 1.0 for 100g. The energy content of 100g is 1896 kilo Joules (kJ), which is ≈0.53 kW/h, so the energy price is CHF 1.9 per kW/h, basically ten times more expensive. One reason for this is that we typically use a lot of energy to create food.

The energy consumption of a bike is 1.62 kJ/(㎞ × ㎏), let us assume the bike, the rider and the stuff moved is 100㎏. So the energy consumption is 162 kJ/㎞, which gives us 0.045 kW/h/㎞. The swiss railways has a energy efficiency of 0.082 kW/h/㎞ per passenger. So from an energy standpoint, the bike is still more efficient than the train (although at a lower speed), and given the cost of the swiss railways, also cost effective: 100g of mars bar is sufficient for more than 10㎞. Clearly energy is not an important factor in either biking or public transportation.

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