Energy consumption and cost, a comparison with human power 

I summarize the average daily energy consumption per person and the associated costs in US. All numbers are approximate to give a sense of magnitude. Please correct me if the magnitude is wrong. For ease of comparison, all energy units are in kWh, kilowatt hour. 

To compare with human metabolic energy consumption and muscle power output, our metabolic energy consumption is roughly 100 watts, with a daily consumption of about 2 kWh. Our sustainable muscle power output is less than 100 watts. Assuming a 8 hour workday, human muscle power out is less than 1 kWh daily.

The prices of natural gas, gasoline and electricity per kWh in US are roughly 3, 6, and 12 cents. The average daily consumptions per person are 100, 30 and 10 kWh for natural gas, gasoline and electricity respectively. From the above numbers, natural gas is the cheapest and most consumed energy source while electricity is the most expensive and least consumed energy source. This is consistent with our intuition.

Overall, energy is extremely cheap. The total average daily energy cost, calculated from the above numbers, is only 6 dollars. The amount of energy consumption is higher than 170 human power output. This means we are hiring more than 170 human labours for 6 dollars. In other words, the value ofour daily work, from the energy perspective, worth less than 5 cents. It is the employment of this extremely cheap energy source that we enjoy our energy intensive lifestyle, such as frequent long distance travels.

Many of us make more 500 dollars a day, which is 10,000 times of  5 cents, the price of our energy output. This extreme ratio is the reason why we enjoy such an affluent lifestyle. In a society where energy is scarce, our affluent lifestyle will also end.