PG here; this is a post from HO's Tech Talk series. This one was originally posted 5 FEB 2006. We encourage you, if you're interested, to look back at the entire extensive series under the tech talk tab up top under the banner.

Often when we talk about different fuels, the fuel itself is considered to be something that can easily be defined. However this is really not always the case, and today I would like to talk a little about types of coal, its content and the product size, and why this can make it a bit difficult to assess EROEI.

For those who wonder what is going on, this is a weekend tech talk, where some underlying aspect of fossil fuel energy is discussed. References to earlier posts are given at the end of this one, and the subjects are usually simplified to get across the basic ideas, within a reasonable amount of space.

Back when my grandfather was mining coal, with a pick and a shovel, he would very carefully separate rock from the coal as he picked lumps out from the solid. The reason for this relates to how he was paid. Before he began to fill a tub with coal, he would place a holder and a token with his mark on it at the bottom of the tub. Thus when it got to the surface, the teller would check that the tub only contained coal, and then would give him credit for the tub. But if the tub contained much stone, from the roof, or from layers of rock within the coal, then the tub would not be counted and my grandfather got no credit for it.