In order to judge the viability of an energy source, it is necessary to run a full balance sheet on it, which includes the full energy costs of discovery, extraction, processing and supply, including any infrastructure that needs to be emplaced if it does not already exist for these tasks. The viability of the source is then the sum of the above, subtracted from the total energy contained by that source. As in any book-keeping exercise (or business plan, for that matter), if the net difference is significantly in the black the proposition is probably viable, or otherwise a non-starter, and not to be bothered with. As we teeter on the edge of Hubbert's Peak - the peak in oil production - beyond which extractable resources will become more limited in supply and hence inexorably more expensive, we need to know just how much oil, gas, coal and uranium the world might grasp, ignoring the unattainable resources that lie beyond its fingertips, requiring so much energy to extract that it is simply not worth the effort, and might even shift the net energy profit into the red.
A good example is the resource available in the "oil sands" of Canada, which do not actually contain oil but bitumen. I have heard it said apocryphally that to extract one barrel of oil from such "tar sands" uses the energy equivalent of one barrel of oil. It is not quite that bad, since only two barrels worth are required to extract three barrels of oil from the bitumen ("tar"), which must be processed in a fairly energy intensive manner to yield "oil". If the supply/demand ratio falls far enough, this may yet become a worthwhile option, but it is sobering to note that older, conventional oil reserves can provide 20 times the energy expended in its extraction, and newer ones about 8 times - still a pretty good deal. If Peak Oil is already with us, "Peak Gas" is not scheduled to arrive until around 2100, and we hear that there are 300 years worth of coal left. Of course, these figures refer to current rates of use, and if we substitute these other fuels for oil, there will be a shift forward in their "Peak Production".
So goes an argument based on simple common sense. It is actually worse than this, however, because it is the best, the richest veins of coal or uranium for that matter, as I have commented previously, that will be extracted first. Of course it will: on level economic grounds, clearly the energy used in the extraction and processing costs money (the debit side of the balance sheet) to be offset against the credit side of providing a rich (high energy) fuel primary source. As the best is used up, so increasingly poorer coal and uranium must be dug, and this ultimately to the point when it is no longer viable to do so, and the net energy that may be obtained from the material is exceeded by that demanded for its extraction.
Even if we were armed with full "projections" in our energy business plan, and we knew the timing of the production peaks, and then their production "tails" matched against extractive energy costs, the ball nevertheless rolls down in the same direction. Once resources are used they cannot be restored - ever - and this is the brutal truth of Hubbert's analysis. Although in a common sense overview this is obvious, we still seem surprised in our dawning acknowledgement of the fact of the situation.
If this is the case for non-renewable primary energy sources, then we might find a brighter future for "renewables" which by definition are inexhaustible and will not peak, then tail-off and finally run out. I am all in favour of renewables in principle, but (e.g. my previous postings on Wind, Biohydrogen, Biofuels) I do not believe we can compensate for the loss of the concentrated forms of fuel we have come to rely on by these far more dispersed forms of energy. Whatever course we chart, there is no alternative initial step to devising strategies to use less energy in the first place, particularly in terms of transportation, which uses 54 million tonnes of the total 67 million tonnes of oil (equivalent) consumed annually in the U.K. alone; 12 million tonnes of that being burned by the aviation industry (this will have to stop!). I estimate that by localising our society into smaller communities of say up to 20,000 population (simply on the basis that this number could live in an area of about two miles square and could get around mostly without cars) supplied mainly by local farms, we could cut our use of transport fuel by 90%. This would put us down for only about 5 million tonnes of fuel annually, from the 54 million we presently use, which is an enormous saving.
It is estimated by the Oxford Environmental Change Institute that about 50% of space heat for buildings could be saved through more thermally efficient materials and design. CHP energy schemes are more efficient than separate large scale heat and power production, and if applied locally further losses by national distribution systems (e.g. the "national grid" for electricity distribution) are avoided. Even on a national level, it would be more to the point to burn natural gas directly to provide heat (which delivers up to 90% of the energy contained in the primary fuel), rather than first converting the gas to electricity and using that as a heat source (which recovers only about 35% of the fuel's energy overall).
Having made these demand savings, we are then asking far less from renewables, which may, in a combination of localised (CHP, micro-hydroelectric, wind) production methods, along with larger scale production, e.g. sea-power (wave power; stream power turbines, which probably would still need a grid network as they are impractical on a small scale), provide a significant proportion of what we finally discover we actually need. But so far there is no all-out commitment to any such intention, not even at the level of coherent government policy on the production and use of energy. If we are at the peak of oil production, with the other fuel peaks to follow suite, surely it makes sense to use some of the resources that we still have available to us in a serious effort to investigate the possibilities that renewables might provide, rather than continuing to burn oil profligately until we hit a wall of resource depletion, which will furnish an impassable barrier to achieving the sustainable future use of our resources which really is the only way forward.