eroie
eroie is the amount of energy you get out of a system divided by the energy you invest in creating, running, and disposing of it. bigger is better of course. i argue that low eroie things are useless. currently in this category are solar cells, windmills, corn ethanol, etc. it has been argued that it doesn't matter what the eroie is as long as it's more than 1.0. cause then you can reinvest the energy and get as much as you want out. heh. this argument fails for a number of reasons. the first is that the energy you invest is of one form. usually oil. and the energy you get out is another form. say electricity. you can use electricity instead of oil to build stuff. but not as efficiently. which drives down your eroie. and if it's already low then it might go below 1.0. and then you're screwed. the other major reason the argument fails is because your system has inputs other than energy. like for example there are only so many places suitable to build windmills. you can't just build arbitrarily more.