I've commented several times on the ongoing struggle of the Cape Wind project off Nantucket to get past local opposition to the "environmental profile" of the proposed offshore wind turbine array. The battle has taken another twist, with the prospect of a Congressional amendment regulating the proximity of wind turbines to shipping lanes. Rather than playing another riff on my frequent anti-NIMBY refrain, it occurs to me that part of the problem here arises from a fundamental misunderstanding of the nature of renewable energy. In a nutshell, the inherent properties of fossil fuels have spoiled us and made it difficult to grasp the compromises associated with other energy sources.
This is an extension of some of the ideas in a recent posting on geothermal energy. A couple of probing responses forced me to do some homework I should have done previously. It turns out that our civilization uses quantities of energy on roughly the same order of magnitude as the entire energy flux generated by the molten core of the earth. That sounds counter-intuitive, but it makes sense when you consider that fossil fuels are really--as we've heard so many times--concentrated sunlight. When you unpack that cliche, you realize that by consuming in a century or two the results of millions and millions of years of gradual, inefficient-but-cumulatively-monumental energy storage processes, we are able to "live large"--to use energy on a planetary scale without having to collect it concurrently from the sun and the earth.
That might sound very abstract, but it has a profoundly practical effect. It means that replacing a meaningful fraction of our energy supply with renewable sources--those tied in real time to the sun, the wind, and the earth's own heat--will fundamentally change our relationship with energy. We're accustomed to sourcing our energy far from where most of us live, in oil fields, gas wells and coal mines all over the world--but typically distant from urban concentrations. The portion we're used to seeing around us is just distribution infrastructure--power lines, gas stations, and the occasional pipeline or refinery. Renewable energy on a large scale will change that situation utterly. We will go from a world of energy-at-a-distance to energy-all-around-us.
Consider wind turbines. A state-of-the-art turbine generates between 3 and 5 Megawatts of electricity, when the wind blows. A natural gas-fired power plant, on the other hand, generates anywhere from 500 to 1000 MW, and can do so around the clock, more than 90% of the year. Replacing fossil fuels with wind, in this instance, means building 800 or so structures, each taller than the Statue of Liberty (ground to torch.) If we wanted to replace all of the fossil fuels used in US power generation, it would require over 300,000 of these installations.
Nor am I singling out wind. Do the math for solar, geothermal, wave power, or anything else you like, and you'll see that, to have a material impact at the scale the human race uses energy, we will need lots of them, everywhere. Biofuels? Great stuff, but plan on devoting a lot of land to them. How much? Well, replacing the entire global output of petroleum would require around 5 billion acres, at current yields. This works out to about half of all land currently under cultivation. By comparison, drilling in ANWR and offshore Florida is quite unobtrusive, because those nasty old hydrocarbons are still the most concentrated forms of energy around, other than Uranium.
Now, you might read this as an attempt to make renewable energy look impossible, or at least extremely unattractive. Far from it. It's meant as a reality check. Opting to make renewables a major part of our future energy supply requires setting aside our tender sensibilities and being confronted on a daily basis with the real-world foundation of the energy-consuming pyramid atop which we sit. Unless, of course, the goal is only enough renewable energy to make us feel good, but not enough to matter.