Po-Nien Bob Lu's Online Journal

Your car is greener than your pet. Oh really?

Yeah it is about this article:

How green is your pet? - environment - 23 October 2009 - New Scientist

While almost all the numbers here are arguable, I'm more skeptical about converting the energy consumption of a gasoline vehicle to the equivalent amount of land usage. The numbers in this article just don't add up.

Firstly, we have to remember that the converting the energy consumption of a gasoline vehicle to the equivalent amount of land usage, or so called "eco-footprint" is purely speculative. If we were talking about bio-diesel or ethanol, we would be able to run some more realistic number. But for conventional cars, the truth is, in case you didn't know, that you CAN'T just grow Gasoline (at least not yet)!

Let's assume all the numbers regarding the energy cost of keeping pets are relyable, and use these numbers to examine the alleged eco-footprint of Toyota Land Cruiser. According to the article, it takes 13.4 m^2 of land to generate 1000 g of cereals, which equals to 600 g of dry weight. Let's then assume that this dry weight is all sugar (starch, fiber, they are really all sugar, so this assumption should not be too far from fact). A gram of sugar can produce 4 Kcal, which equals to 4 x 4.2 = 16.8 Kjal, or 1.68 x 10^4 J. Combine all these, it takes 13.4 m^2 of land to generate 600 x 1.68 x 10^4 = 1.008 x 10^7 J. In other words, 7.52 x 10^5 J per M^2. If we then convert it to per hectare (10^4 M^2), it will be 7.52 x 10^9 J per hectare. And yes, that is 7.52 gigajoules.

Again, according to the article, it takes 55.1 gigajoules for a Toyota Land Cruiser to run 10000 miles. If we divide the number by 7.52 gigajoules per hectare, we will get 7.33 hectares, instead of 0.41 hectares mentioned in the article, as the eco-footprint of the Land Cruiser.

So what's wrong? Turns out in Robert and Brenda Vale's calculation, one hectare of land can produce approximately 135 gigajoules of energy per year, which is almost 18 times higher than the result I calculated, based on the numbers they gave us!

I have to admit that while solar and winds power is still a joke by the aspect of energy efficiency, there might be more energy efficient way to generate fuel from land. Corps with higher energy content like corn and soy bean can be an answer. The technology of converting stems and leaves into bio-fuel is also promising. However, the idea that we can realistically generate fuel EIGHTEEN times more efficient than growing corps from land is just...... can I say BS?