I like this:
If anyone's wondering, the equation ER/EI is "energy return" divided by "energy invested" (more info here), the point being that the oil (and coal and gas) we extracted in the past was easy to get at, so the energy return was large compared to the energy invested.
Today, the EROEI (as it's more commonly known) ratio is a lot lower, as we go for difficult-to-get fossil fuels, such as polar oil and tar sands, and is falling as each year goes by. That means that there's less energy for the human race to live on, just as demand is rising. I expect you don't need me to tell you that means trouble...
So now you know one of the incentives for us buying a wood - it grows renewable fuel for us!
So what's the EROEI for a chainsaw? Well, we've only burned about 12 litres of petrol so far, which might move a small car 120 miles or so, and contains in the region of 500MJ of energy. That fuel has enabled us to cut 10 tonnes of wood (at a conservative guess, it could be a lot more), which once seasoned could yield about 150,000MJ of energy. I think that's a better return than burning it in a car! I think I'll go and burn some more tomorrow...
p.s. More info on Peak Oil is available at PowerSwitch UK, which I helped set up a few years ago. Other good sites are The Oil Drum and EnergyBulletin.
Thursday, 31 January 2008
I like this: