by TigPil » Sat 13 Jan 2007, 21:34:22
$this->bbcode_second_pass_quote('SchroedingersCat', '
')1.026 kWh of electricity?
See what we're facing? The EROEI of all of these (except humans) is dropping. Coal was 20:1 in the late 70's. What is it now?
Imagine a future where humans are the power source because of the EROEI. Treadmills, manual labor, etc.
I recently saw that pre-fossil fuels it took 6 farming families to support one non-farming family (like a teacher). Essential services will rule quite soon.
EROEI of wind generated electricity and solar power has been improving for the last 30 years. Only non-renewables start from a high EROEI and drop as the resource becomes harder to extract. Ways of harnessing renewable energy tend to improve with technology since they involve capturing an existing energy flow ultimately derived from the sun. If you think of photosynthesis as a very inefficient biofuel system then we have been exploiting it throughout human history with greater and greather efficiency. Improvements in crop types since 8000 BC have yielded greater output in final food products. The energy of draught animals is also ultimately derived from photosynthesis. Windmills and sailing have also existed for hundreds of years and have experienced gradual improvements in that time.
So the problem isn't that the EROEI of everything is dropping and will go to 1. The problem is given the high EROEI we currently get from fossil fuels and the lower EROEI (but still greater than 1) of other sources of energy, how do we manage the transition from one source to another.
As for pre-industrial societies, the percentage of the labor force not engaged in agricultural labor was betweeen 5% and 20% so the support ratio could be as bad as 19:1 and as good as 4:1. The variability was mostly a function of the surplus produced by different crop types and different regional fertility levels (e.g. growing rice in the river basins of southern China was more efficient than growing wheat on the Nile was more efficient than growing rye in Scandinavia). This also changed over time so agriculture in England was more productive in 1800 than in 1100 and more productive in 1100 than in 100.
As I mentioned in another post in this thread, the introduction of New World crops and the rise of scientific agriculture led to much improved crop yields and started to shift the balance well before any fossil fuels were used for agriculture. In England by 1830 only 25% of the population was engaged in agriculture for a support ratio of 1:3. There have been some other basic innovations since then that owe nothing to mechanization, fossil fuel based fertilizers or pesticides. I would guess that this would make it possible to have a 1:10 support ratio even with 0 industrial energy production so only 10% of the population would have to work in agriculture. This is 5 fold drop from the current employment ratio. But since electricity generation won't completely disappear either, we may retain productivity rates that are higher and an even better than 1:10 support ratio.