Letters to the Editor
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Very well, so there's enough gross energy coming in.
Okay, so we've established that at 7,500 exajoules of technically-exploitable renewable energy per year, there's enough to replace current energy use by a couple of orders of magnitude.
This is really the first and simplest hurdle, but having cleared it, we can talk intelligently about the rest of them. Questions would include:
How much of that energy is exploitable at $60 per barrel-of-oil-equivalent? How much at $70? How much at $200? How much at $10,000?
Of each of the energy alternatives listed, to what extent are they constrained by other limitations?
For instance, a square metre of solar panel requires a certain amount of exotic metals. How much of those metals exist? Recoverable at what cost? Any area of solar panels will involve transmitting the energy a certain distance to the end user. How much of the energy will be lost in the transmission?
Biodiesel is constrained by the area of land that can be used to grow plants--and on whether that land area can do so year after year, without succumbing to the erosion typical of large-scale agriculture. The recent discussion of Alex Farrell's paper on biomass, I did a rough calculation and figured out that to replace current oil consumption, you'd need a square of land 4,700 kilometers on a side. Is there enough water? How much fossil-fuel input will be required in the form of fertilizers?
When thinking of the potential of renewable energy to allow us to keep doing what we do, consider the following: For over thirty years (since the OPEC embargo of 1973-1974) we have known that our (the West's) oil supplies are finite. We've been dependent on foreign regimes located in politically-unstable parts of the world. We've had to spend larger and larger sums to pacify those areas enough to keep the oil coming. We've had growing warnings of global climate change. During this entire time, the principles and basic technology of hydrogen, fuel cells, solar panels, wind turbines, nuclear reactors, biomass and geothermal have been known at least since the 1960's. We have had the largest cohort of working-age population (the Baby Boomers) with the most wealth and the most access to education in a period of sustained world peace and the absence of any major disrupting events.
In other words, under thirty years of the best conditions for doing Stuff Other Than Immediate Crisis Management, coupled with a clear need for such long-term innovation, we have not come up with something that could replace our current energy regime--not even close. This, to me, suggests either that such replacements are not practically feasible, and/or we do not have what it takes to figure them out under even the best conditions.
In a more general sense, it may be that civilizations can only get so big and complex before they become incapable of focusing on goals that will allow them to continue.