Next Generation Energy

A primary concern about global energy supplies in this generation has been security and stability. Domestic, second generation biofuels have been touted as a thermodynamically feasible alternative possessing superior security to foreign oil. If one's perspective is that the world is made of geopolitical actors only, then this might be correct. But behind the politics and boundaries, there is a physical environment that has the final say in what will or will not work.

To get some perspective on the global distribution of energy resources, let's forget about politics for a moment. I'll use a broad brush and some raw data to paint a picture of what energy resources are available, a picture rather different from the one it seems that most politicians see.

Insecure biofuels

The production of biofuel is not simply just the industrial process that some will portray it as. It is an agricultural process and therefore also an ecological one. The successful delivery of second-generation biofuels depends on much more than discovering the right cellulose catalyst, it also depends on the successful provision of sunlight, well-timed water delivery, viable seeds, a reasonably pest-free environment, sufficient fixed-nitrogen and phosphorous, etc. And if you ask any farmer, providing all of these consistently year after year isn't trivial. In fact, if you define energy-security as making sure that our energy supply is immune to disruption, there is no way biofuels will be secure. Recall the "Dust Bowl" that devastated American agriculture? What about the recent epidemic depopulation of pollinators, with bee colonies across the US unpredictably crashing? Or the ecological instability inherent to massive monocultures, painfully demonstrated by the impending (and historic) breakdown of modern banana agriculture?

My point is that, thermodynamics aside, securing biofuels would mean securing the extraordinarily elaborate and dynamic system that supports its production: the global ecosystem. And not only is this impossible to do, we, as a species (even if we're not good at anything else), seem to be experts at doing the exact opposite; and the disruptions we cause seem to be growing in magnitude. So as well intentioned as my second-generation-catalyst-searching chemical-engineering friends are, it's important to remember that reliable biofuels production is much more than a chemical-engineering problem.

So in an abstract sense, why is this so? I would argue that the energy stored in biofuels represent a "highly processed" form of energy (this is clearly not a technical term). Biofuel energy is "highly processed" because it started from the Sun (along with the rest of the 99% of the energy we observe on Earth) and required a very elaborate pathway to get into the plant tissues that we distill into diesel. The energy itself traveled directly from the sun to the plant's leaf where it was used to split a water molecule and fix some carbon. This doesn't sound very elaborate. But setting up "the machinery" to execute this procedure, namely keeping the plant alive, is. As described earlier, it involves supplying water, pollinating flowers, moving seeds, fertilizing soil, keeping pests out, etc. And (skipping some details) all of these processes takes more energy from the Sun. So in fact, the fixation of energy in the plant tissue requires that the Sun's energy be captured and harnessed in a large number of ways, creating a production process that is convoluted, complex, and prone to disruption.

The next generation of generation

For the next generation, we should try to get away from "highly processed" fuels (fossil fuels are just plant tissue that's been "processed" even more), since "processing" leads both to inefficiencies in the energy-capture process and heightened sensitivity to disruption in the supply chain. Since almost all of the energy available on Earth comes from the Sun, we should probably think about how close and how simply we can connect ourselves to that power source.

Never removed: Solar

The plot above is my very simple estimate of how much solar energy reaches the surface of the Earth without being reflect by clouds in your average year (its units are in Watts per square meter). To generate this plot, I combined information about the variation of Earth's orbit, changes in length of the day, the angle of incoming solar radiation and average cloud cover (conservatively assuming that total cloud cover reflects 85% of the Sun's rays) over the course of a year [Spencer, 1971, Hartman, 1994, Mitchell and Jones, 2005]. (This and the next two maps are all equal area projections, so the "amount" of energy pictured {area x intensity} is the actual amount of energy available).

Such a coarse analysis is instantly revealing about the distribution of energy available to photovoltaic and [probably more importantly] solar-thermal generation. There is strong variation in the potential for using direct solar power, suggesting that if we have trouble making solar work in New York State, this may not mean solar is impotent, but maybe that we should move our power plants. Some of the distances between high solar potential and high energy consumption seem large, but note that DC electric current can be economically transmitted several thousands of miles. We're also already shipping liquid fuel all the way from the Middle East where the solar potential is excellent. It's not inconcievable that we could switch it from oil to hydrogen generated by electrolysis. In the map, the Asian Subcontinent (where demand is currently exploding), the Australian Outback and Sahara desert also look like prime regions for generation. For not unrelated reasons, these latter two are also places where land is relatively cheap and large solar-thermal installations that export energy could probably be profitable.

Once removed: Wind

Wind is driven by air masses that are unequally heated by the sun. The wind fields that I am about to refer to are driven by differences in heating between the middle-latitudes and the poles. In this sense, the energy available to us is only "once removed" from the Sun's rays and virtually impossible to disrupt significantly.

The plot below is a mapping of annual average near-surface winds that I generated using publicly available reanalysis data [Trenberth et al., 1989]. The first two things that jump out are the red patches in the Northern Hemisphere and the ring of red around Antarctica. These are regions with high annual average winds, places where one might expect lucrative wind-farming. Although, my first caution would be that the high-wind regions off the coasts of Japan, North America and Europe are really only this strong in the winter and are much less energetic in the summer, a major problem when the AC's go on and power demand spikes.

However, the ring of wind over the Southern Ocean around Antarctica is very steady and very powerful all year round; it would make the perfect wind farm if we could figure out a cost-effective way to tap into that energy. I am aware of some work to design tradition windmills that can float far out at sea, however these may be susceptible to rapid deterioration in such a high-energy and corrosive environment.

What might hold potential for this region is some interesting recent work on oscillating resonators that can be used for power generation (sorry I couldn't find a link). The idea behind this technology is to use something that looks like a flag or a guitar string that will vibrate in the wind. This vibration can be turned into electricity and then transmitted or stored. What's nice about these technologies for use in this region is that they have no gears of pulleys, and their only moving parts just vibrate or wave in the wind, so intuition would suggest that they're less susceptible to corrosion. I'll also point out that salt water is a good medium for generating hydrogen by electrolysis and there's no shortage of that in the Southern Ocean (just in case you'd prefer to transport a high-energy-density liquid fuel rather than run cables to your wind farms).

Twice removed: Ocean currents

The Sun powers the wind and the wind drives surface currents in the oceans, so ocean currents can be thought of as "twice removed" from the Sun. The circulation of the ocean is complex, but one of the most obvious features of the surface flow are known as "western boundary currents" (see my plot below). The strong, concentrated currents run along the western edge of almost all ocean basins, returning water towards the poles that the wind has pushed towards the equator [Pedlosky, 1998]. The intuitive way that I think about this is that the Sun's energy is "focused" by the atmosphere and ocean into this narrow, highly energetic current (analogous, perhaps, to how a magnifying glass can be used to focus sunlight into a narrow, energetic beam). Unlike biofuels, the mechanisms of this conversion are simple and depend only on the shape and rotation of the Earth (things that even we humans would have a hard time disrupting).

The plot above shows approximately the global distribution of these currents. Again, I've plotted publicly available data [Carton and Giese, 2007]. While the speed of the water is slower than the speed of air, remember that water is very heavy and so even slowly moving water can hold a tremendous amount of energy.

Until recently, there was no technology that was good at extracting energy from these currents. However over the last decade, Prof. Alexander Gorlov has developed a remarkable "low-head" turbine. "Low-head" refers to the ability of the turbine to effectively generated power even when the flow does not exert a large amount of pressure on the turbine's blades (this is quite different from standard hydro-electric turbines that require dams to be built to increase the pressure of the flow). Gorlov has argued that these turbines represent the breakthrough needed to tap into the energy of these western boundary currents [Gorlov, 1998]. It seems that Gorlov's group is now working for the South Korean government to install 3,600 MW of capacity (a nuclear plant might be 1,000 MW) using tidal flows through restricted channels.

Vision for the future

Biofuels seem unwise. The supply chain of nuclear power is not yet a closed cycle, and may never be, so visions of sustainability that rely on it might be trusting our capacity to innovate too much. Carbon sequestration may mitigate climatic change while fostering economic development. However, if one is thinking about the time-scales in which hydrocarbon resources might be exhausted, then it seems inevitable that we'll eventually turn to these relatively basic and minimally "processed" forms of solar energy. Moreover, given recent technological advances (solar-thermal, resonating oscillator and low-head turbine technologies) it seems like it may be in our own financial and security interest to do so sooner rather than later. The quantities of energy available from these sources are mind-boggling (they're often measured in petawatts), all we need to do is find the political maturity, will-power and cooperation needed to tap into them.

References

[Carton and Giese, 2007] Carton and Giese (2007). A reanalysis of ocean climate using SODA. Monthly Weather Review.

[Gorlov, 1998] Gorlov, A. M. (1998). Helical turbines for the gulf stream: Conceptual approach to design of a large-scale floating power farm. Marine Technology, 35.

[Hartman, 1994] Hartman, D. L. (1994). Global Physical Climatology. Academic Press.

[Mitchell and Jones, 2005] Mitchell, T. D. and Jones, P. D. (2005). An improved method of constructing a database of monthly climate observations and associated high-resolution grids. International Journal of Climate, 25.

[Pedlosky, 1998] Pedlosky, J. (1998). Ocean Circulation Theory. Springer.

[Spencer, 1971] Spencer, J. W. (1971). Fourier series representation of the position of the sun. Search, 2.

[Trenberth et al., 1989] Trenberth, K., Olson, J., and Large, W. (1989). A global ocean wind stress climatology based on ECMWF analysis. Tech. Rep. NCAR/TN-338+STR, National Center for Atmospheric Research.