The scale of green solutions

For someone who’s long identified himself as an environmentalist, the rise in recent years of the profile of environmental issues, particularly climate change, is heartening. Much of this attention is the result of Al Gore’s An Inconvenient Truth, which concludes, as much of the more optimistic reporting on the subject does, with solutions and steps to avert the prospect of catastrophic global climate change.  An often overlooked but absolutely critical aspect of any of these “greener” ways of doing things is an investigation of the way they scale. Two questions that need to be asked of any proposed solution:

1. Is the idea feasible on a large scale?
2. If implemented on a large scale, how does the overall benefit compare with the magnitude of the problem that the solution purports to address?

We do need to constantly look for ways to lower energy use, to create less waste, to reduce the release of toxics to the environment. An abiding quest to green and re-green our lives should become a universal American value, in much the same fashion that thriftiness was admired during the depression, or that discount shopping was admired in the 1990s. But at the same time, we must be careful not to fool ourselves: there is a real prospect that, if we do not consider the scale of the problems and potential solutions, we’ll stop short, that metaphorically we’ll change a lightbulb and recycle a soda can and think we’re done.

Consumption of energy is the biggest part of greenhouse gas emissions, which is the biggest environmental problem facing us today. Almost universally, in the popular press, there is a widespread lack of awareness of scale involved, which is both understandable and frustrating. It is frustrating because figures on overall energy consumption are unambiguous and readily available from the Department of Energy, yet understandable because the numbers involved are so huge. Large scale energy consumption is measured in quads, or quadrillion BTUs. The United States consumes roughly 100 quads, or 100,000,000,000,000,000 BTUs, of energy per year. The outline of the flow of this energy is brilliantly presented in this graph from the DOE. On average, this amount of energy consumption is equivalent to a power consumption of 3.3 trillion watts.

As a very crude¹ (but illuminating) approximation, suppose that every American, all 300 million of us, turns off a lightbulb and reduces our power consumption by 100 watts. In this approximation, we imagine a bulb which had been on 24/7/365 to now be off. All total, we’d save 30 billion watts. Sounds like a large number, doesn’t it? It’s the output of 30 Gigawatt-sized power plants. Certainly admirable. But it’s just 1% of our overall 3 Terawatt power consumption.

Petroleum constitutes roughly 40% of our energy consumption, to the tune of 865 million gallons per day.²³ This turns out to be 10000 gallons per second;  it takes our country about a minute and 40 seconds to burn through a million gallons of oil. Keep this scale in mind the next time you hear about a great way for our country to save a million gallons of oil: wonderful, but hardly the whole solution.

Of this oil, each day we burn 388 million gallons of gasoline and 175 million gallons of diesel fuel.⁴⁵ It is contemplating these figures that lead us into question 1 above: how feasible are any of the alternate fuels touted as replacements for gasoline?

For the moment, I will just address biodiesel. To make biodiesel, vegetable oil is combined with an alcohol and a strong base to produce a liquid that is similar to petroleum-based diesel fuel. There are serious questions as to the energy efficiency of this whole process, which I will not address in this post. As a reasonable approximation, suppose one gallon of vegetable oil can be turned into one gallon of biodiesel.

The entire annual US production of vegetable oil is about 2.9 billion gallons.⁶  If all the vegetable oil produced over the course of a whole year were converted into biodiesel, it would displace about 5 days of gasoline and petro-diesel use.

I’ve seen (but can’t find at the moment) a figure that roughly 10% of our vegetable oil production ends up as waste vegetable oil. So if we converted an entire year’s supply of  used french-fry oil, etc., to biodiesel, we’d keep our country motoring for about 12 hours and 22 minutes.

This is why I’m more than a little skeptical when conversion to bio-diesel is taken as evidence that someone or some organization has “gone green.”  To replace all our motoring fuel with bio-diesel, we’d have to scale up production by a factor of 70. Even if we set a more modest target of replacing a quarter of our motor fuel with biodiesel, we’d need to produce 18 times as much vegetable oil as we do today. In this context, discussion about whether one method of producing biodiesel is, say, 20% more efficient than another method, or whether one type of biodiesel-burning engine is, say, 30% more efficient than another is really irrelevant. What’s relevant is the scale.

I’ll close with one final calculation that puts the scale in perspective. Just looking at gasoline, 388 million gallons per day is equivalent to 1.3 gallons per person per day. We can see that it makes sense: it’s what you get if everyone drives 30 miles per day. We tend not to think of the volume of gasoline that we consume because we don’t see it: it goes from a tank underground through a hose to a tank under our car. But aside from water, there’s nothing for which each and every one of us consumes that’s on that scale. For a family of four, 1.3 gallons per day is 36 gallons per week: imagine this volume of vegetable oil, every week. Sound absurd? That’s what the bio-diesel solution would be.

1. Crude because it mixes primary energy–like coal and gas–with electricity, which is good for order of magnitude, but keep in mind that only a third of the heat value of the primary energy makes it into electricity. [↩]
2. 1 barrel is 42 gallons [↩]
3. Equivalent to the volume of Lipsette Lake every two days. [↩]
4. distillate fuel oil=diesel [↩]
5. plus 68 million gallons of jet fuel [↩]
6. See Table 6 of any of the reports. Note that production of oilseed and production of vegetable oil are different things; only part of the weight of the oilseed is oil. Here I use a specific gravity of 0.9 to convert from metric tons to gallons, so about 7 pounds per gallon. [↩]