TED.com is a site that is known for very high quality content. Unfortunately on occasion they do get things wrong.

Rob Hopkins in his talk at TED Global 2009 claimed that 1 liter of oil “contains the energy equivalent of five weeks of human labor by 35 strong people” [1]. Now Rob has made a lot of good points and I look forward to watching his lecture when it becomes available, but I can’t let his claim about the energy of oil pass.

First we have to consider the functional usability of the energy. A Prius takes about 5 liters of petrol to drive 100Km and I believe that Toyota is going to improve this in the near future. Let’s assume for the sake of discussion that a hypothetical turbo-Diesel Prius based on the yet to be released new Toyota hybrid drive-train would take 3L of Diesel fuel per 100Km (Diesel engines are more efficient and Toyota is continuing to improve their technology). The Prius weighs about 1300Kg so let’s assume for the sake of discussion that 1L of Diesel fuel can move 1500Kg (vehicle plus driver and cargo) a distance of 33Km.

So the question becomes, how long would it take 35 strong people to move 1500Kg a distance of 33Km? 1500/35 gives a mass of 42Kg per person – any strong person can lift 42Kg with ease (it’s less than the mass of a good Trinitron monitor). 5 * 40 hour working weeks gives 200 hours of work, 33Km in 200 hours means an average of 165 meters per hour. I think that I could carry a 42Kg mass more than 165 meters per hour without excessive effort. If I was allowed to use some form of trolley then I could take it a lot further – I have moved monitors much faster than that while balanced on a wheeled chair!

It seems that the Bicycle Rickshaw [2] is one of the most efficient ways of moving passengers and cargo on roads. According to the reports I’ve heard a 100Kg passenger who comes from a first-world country (and can therefore pay well) will be welcomed as a rickshaw passenger. I think it’s reasonable to assume that a rickshaw driver can transport a passenger more than 33Km in one day. So if you had 35 strong rickshaw drivers working for a day they should be able to transport 3,500Kg of passengers and cargo for a distance that is greater than 33Km as opposed to a hypothetical future-technology Prius which can transport 1500Kg for 33Km while using a liter of Diesel fuel!

Now if we consider the fact that the 1500Kg that the Prius moves is comprised of 1300Kg of car and 200Kg of passengers and cargo we have 1 liter of oil in the Prius moving 200Kg a distance of 33Km vs 35 strong people working for a day and moving 3500Kg the same distance.

According to the Human Powered Transport Wikipedia page [3] someone who is “in shape” can produce 200W of cycling energy for more than an hour – that is 720KJ/hour. I wonder how many hours they could do that for in a day. It seems reasonable that a full 8 hour day of work would comprise at least the equivalent of 4 hours work, so that would be 2.88MJ per day or 72MJ for five 40 hour weeks. Therefore for 35 people it would be 2.52GJ of cycling energy over five 40 hour working weeks!

According to the Wikipedia page on Fuel Efficiency [4] one liter of Diesel fuel contains 38.6MJ of energy. If the energy in one liter of Diesel fuel was converted to motion with 100% efficiency then it might be equivalent to one strong person cycling for 13.4 days.

According to the Wikipedia page on Thermal Efficiency [5] the most thermally efficient engine is the Wärtsilä-Sulzer_RTA96-C [6] which can run at 51.7% efficiency which gives 163g of fuel used per KWh. So the RTA96-C could produce just over 22MJ of usable energy for 1 liter of fuel. That’s about equal to one person cycling for 7.6 days. Also note that the RTA96-C is an engine for a very large cargo ship, smaller engines are much less efficient.

There is no doubt that petro-chemicals are a concentrated source of fuel. I can carry a jerry-can which contains usable energy equivalent to more than 6 months of work by a laborer (according to my rough calculations). But there is no way I could carry enough food to keep someone alive and working for 6 months.

I look forward to watching Rob’s talk when it is available for download, I don’t think that getting one point spectacularly wrong reduces the value of his work. The Transition Towns [7] concept has many benefits to offer, even beyond Rob’s initial plans.