(This is Part 9 of a series. Go back to Part 8.)
As Alex Kirby tells us, "Global water consumption rose sixfold between 1900 and 1995—more than double the rate of population growth." In addition, humanity's water requirements continue to grow—"as farming, industry and domestic demand all increase."
So far, humans have been doing a short-term fix on this by drawing their water from underground aquifers—aquifers that were formed over countless millennia and now are being drawn down in a few decades. We're eating our seed corn, to mix metaphors, and water tables in the U.S., China, India, Russia and West Asia are all dropping.
Agriculture already uses 70% of all the water consumed worldwide—and, with the exception of biodiesel from algae, we may not want to put further strains on earth's fresh water supply with biofuels. Let's remember, earth's fresh water supply has to supply not just us humans but also all land-based life, including both plant and animal life.
For a similar reason, hydropower may also become less important as time goes on. Long-term, as the planet becomes hotter and drier, water will likely become way too precious to divert to water-intensive energy from hydropower, except in relatively token amounts.
Some optimists point to desalinization as the key to humanity's future water supply. Maybe. But desalinization has huge drawbacks itself—in addition to leaving huge amounts of brine, desalinating water requires huge amounts of energy.
Ah, there's our old friend energy again. Water is connected to climate change is connected to energy is connected to the financial system is connected to geopolitics and on and on. It's all connected now, and the entire system will most likely have to be solved as a whole if it is to be solved at all. That is, the entire human enterprise will probably have to shift to some kind of sustainable basis if, long-term, human and other life is to continue on planet earth.
What about energy from fusion? Humanity has pursued the dream of controlled power from atomic fusion—the same reaction that powers the sun and the hydrogen bomb—for over 50 years now. And yet any practical application still seems at least 50 years away.
A speculation: Not only will controlled fusion be solved at some point, but the day may even come when a fusion generator is no larger than a battery. But that time, I imagine, is way, way off and is probably more in the realm of science fiction than serious prediction.
And I must admit to a bias about something. All the fuels that we’ve considered so far are all really just stored sunlight. It’s true about petroleum and it’s true of biofuels. Even with ethanol from cellulose or biodiesel from algae we have a very complex process to turn the plant into fuel. Moreover, photosynthesis converts only 3% to 6% of the available sunlight into usable energy—compare that to solar cells which can now operate at 20% efficiency in capturing the energy in sunlight.
Why not harvest sunlight more directly then?
This brings us to what are probably the two most promising candidates for a deep solution to humanity’s energy challenges—wind and solar. Let's now take a look at them in terms of their long-term potential.
Wind, I must say, has some mighty advantages as a sustainable fuel: Except for the manufacture of turbines, it is almost completely clean. It is completely renewable. It does not take precious water. It's EROI is quite good. And its cost, though not yet competitive without subsidies, continues to drop with each passing year. Yes, wind can be intermittent, but the development of better batteries should take care of that.
Combining solar and wind is also a fruitful idea. The days that are bad for wind—bright, clear, sunny—are good for solar, and vice-versa. Experiments in Spain and elsewhere have demonstrated that this combination can provide remarkably stable supplies of energy.
What could really make a difference is when the electricity grid goes global, which can only be a matter of time. A think tank called The Global Energy Network Institute is exploring this idea. What this means is that direct current (DC) transmission lines would cover the globe, taking energy anywhere it's being produced to anywhere on the planet where it's needed.
This scheme would use DC power instead of AC power because DC power can travel extremely long distances with very low loss of power. Thus energy being generated by wind farms in Siberia, North Dakota or offshore, for example, could be gathered and sent anywhere on the globe that needed energy. Similar considerations could apply to solar-generated power.
Wind will certainly make a great contribution to the planet's sustainable energy needs. But let's remember, even wind is a two-step conversion: first sunlight to wind, and then wind to electricity. It's inherently less efficient than a one-step process. For that reason, long-term, wind may not become humanity's primary sustainable energy source.
That role will almost certainly go to solar power.
(This is the end of Part 9. Go to Part 10.)
—jim sloman, 3.22.07
|
