The Climate in Emergency

A weekly blog on science, news, and ideas related to climate change


Imagining Post-Petroleum

I’m working on a novel set in the relatively near future (decades, not centuries ahead) in a post-petroleum society. As the author, I get to make certain decisions about the world of this novel, and one of the things I’ve decided is that although internal-combustion engines still exist, they are only used for emergency vehicles. Most people walk or use horses or oxen to travel over land and a combination of sails and solar electricity to go by water. My thinking is that the most viable alternative fuels–ethanol, biodiesel, and liquified biogas–would be prohibitively expensive for everyday use.

My logic is that fossil fuel mobilizes dramatically more energy than any sustainable source can yield.

However, I’m not an expert on such things, and I have never encountered a similar guess in anybody else’s writing. Perhaps that’s because few people like the idea of losing fast transportation–although I actually think the change would be a net social good, provided that emergency vehicles and the Internet still exist (which, in my book, they do).

In any case, the book is a novel, a story about people and about ecology, it’s not about economics. I never actually researched my assumptions about my fictional society’s energy economy. And, truth to tell, I am not going to invest the time to do so thoroughly. But how would I go about doing that research? How difficult would it actually be?

The question to start (and maybe end) with is how much land does it actually take to grow the raw ingredients for each type of fuel? After all, the more land the process takes, the greater the opportunity cost involved in growing the fuel instead of, say, food. Although the final cost of the fuel would be the result of market forces I will not even try to predict, the cost in land might be a reasonable rough proxy.


I started with ethanol because it is already used as a fuel and because I knew one of its possible sources–corn–would be easy to get a per-acre figure for. To be clear, there are other ways to make ethanol, some of which, such as wheat straw, are potentially waste products from other endeavors, meaning that the cost in land might be very low but very complicated to calculate. I wanted something simpler.

And actually, it’s simpler than I thought. After some back-of-the-envelope math (literally on the back on an envelope) and online searches, I realized I don’t need to calculate gallons per acre–I need to calculate how much food a gallon of ethanol could have been.

Now, the articles I found on the ecological footprint of ethanol all focused on whether ethanol as it is produced today is a properly “green” fuel. We’re after a slightly different question, so I chose a different angle–I looked up a recipe for corn whiskey. Whiskey is, after all, ethanol.

Turns out, with a recipe that uses only grain, water, and yeast (no sugar or syrup), a five-gallon whiskey run uses almost nine pounds of corn, plus some barley.  It yields one to two gallons of shine. So, to make our numbers simple, we can say ten pounds of corn for two gallons of ethanol, or five pounds per gallon. We’re just trying to get in the right ball-park here.

One pound of corn has almost 400 calories and 15 grams of protein, so we can say that each gallon of fuel could have been one person’s daily food ration instead. So we’re looking at a one-to-one ratio here. I don’t mean that making fuel necessarily would take food out of people’s mouths–there might already be enough food. But the cost of a gallon of corn ethanol will always be above whatever it costs to eat corn all day (because you have to pay for processing also).


Biodiesel is basically oil, usually vegetable oil, that has been processed so it can run in a Diesel engine. Ordinary oil works as a fuel also, but requires a converted engine. Many different kinds of oil will work, though soybean oil is the most popular in the US at present and Canola is most popular in Europe. Yields for Canola are significantly higher than for soy, and happens to be the crop I found information on–it averages around 160 gallons of oil per acre, depending on where it grows.

So, what is the cost? Canola oil is edible, but it’s not something you could live on alone for a day (yech!). Instead, choose some food crop that likes the same climate as Canola (corn does not) and compare the per-acre yield.

The same source lists a 48 gallon-per-acre yield for soybeans. Now, estimating the food value of that many soybeans if they aren’t pressed for oil is difficult for several reasons, not least of which being that humans generally process soy before eating it. I don’t feel like trying to figure out how many servings of tofu per acre a soybean field yields….but soy does grow in the same climate as corn and farmers often alternate the two crops in the same field (I live in a rural area that mostly produces corn and soybeans and chickens, so I see this rotation up close). So we can express the cost of fuel oil derived from soy in corn–corn yields roughly 6,200 pounds per acre, or 1,240 human-days of food. That’s almost 26 human-days per gallon–expensive, especially as compared to ethanol on a gallon by gallon basis (although oil is a more efficient fuel).

Of course, biodiesel can be made from waste fry oil, in which case it has no cost at all, apart from the expense of processing and transportation.

Liquified Biogas?

I listed this one without actually knowing if it exists. Liquified natural gas (LNG) is a popular (though debatable) alternative fuel. Natural gas is methane from fossil sources. Since biogas is methane from non-fossil sources, liquified biogas (LBG?) should be a possibility. And it is! They make it in Sweden!

Calculating the cost in land of (LBG) is somewhere between very simple and very hard. Hard because it can be made of almost anything, easy because biogas is already being produced by anything rotting anaerobically. Methane is a more powerful greenhouse gas than carbon dioxide is, so it is better for the planet to burn the stuff than to release it–which is why you can actually get a negative carbon footprint by using waste methane (from landfills or from livestock waste pools) to generate power.

In my post-petroleum society, the problem with biogas is therefor not how do you produce it but how do you gather up and use the gas being produced anyway. Its cost in land is therefore essentially zero. But to use it as a transportation fuel you have to liquify it (why? I’m not sure, but I’m guessing its volume is way too large in gaseous form) and that means chilling it to -259° F. How? That’s some serious refrigeration. Does the chilling have a cost?

Liquifying methane involves a 10% energy loss. That is, however much methane you want to liquify, you need 10% as much again to power your freezers. Once chilled, however, the methane will stay liquid indefinitely at no extra cost, provided it is properly insulated (I assume you’d need to use some kind of refrigerant chemical for this, but while commercial refrigerants are all currently greenhouse gasses themselves, climate-sane refrigerants are possible and we can assume our futuristic society has one).

Of course, 10% of nothing is nothing, but if our futuristic society is depending on waste methane its total supply is limited–and if liquified, is 10% smaller than it might otherwise be.  And if you’re transporting it by truck, you’ll lose even more fuel powering the truck. That might become a factor in the final cost of the product.

Bringing it all together

For full disclosure I ought to say I’m terrible at basic math. Curiously, calculators don’t help because the problem is that I sometimes change numbers without knowing it. So my calculations here are not guaranteed to be free of error–my objective is not to provide finished numbers but to suggest a way of thinking about energy costs in a post-petroleum world.

And as I’ve said, at-the-pump prices in such a world would depend on so many factors that I’m not even going to try to make a guess–except in my capacity as a novelist.

In my book, the US no longer uses the dollar as its currency but the share. “A share,” in this context, is theoretically equal to survival rations for one person for one day–food, water, and everything necessary to maintain adequate shelter, all at a very basic level. In practice, one share pays for basic room and board at a hostel. Having stayed at many hostels and seen their variation in price, I’d say a share is equal to about $20.

Now, the concept of a “human-day in food” is very similar to a share, except a share also includes water and a roof. Put all this together, and I can actually get rough prices for how much the raw materials for each of these fuels would be in my fictional societies:

  • Corn ethanol: .6 share, or $12 per gallon
  • Waste biomas ethanol: free but not unlimited
  • Canola biodeisel: 3 shares, or $60 per gallon
  • Soy biodeisel: 12 shares, or $240 per gallon
  • Waste oil biodeisel: free but not unlimited
  • Liquified biogas: free but not unlimited

Remember, these are raw material prices. Pump prices would be higher and would vary a lot from place to place depending on how much free raw material was available in your area–transporting fuel long distances might be prohibitively expensive. Ball park, I’d say we’re looking at pump prices at $20 or more a gallon, though, so you’re not going to have a private automobile.

(Unless it’s electric. Would there be enough electric capacity for electric cars? My novel assumes not, but that’s another discussion).

But if your house is on fire or if you need an ambulance, help will be on its way quickly. If you live near the water you can travel or ship goods by solar sailboat. You’ll shop locally and so will your neighbors, so your local economy will be strong. You’ll like it.