(This is Part 8 of a series. Go back to Part 7.)
Energy from biofuels is now getting a lot of buzz everywhere: Ethanol from corn, sugar, cellulosic grasses, even trees. Biodiesel from natural crop oils and even used cooking oil. Instead of importing oil we grow it instead. And on average it produces fewer greenhouse gases than petroleum. What's not to like?
Though the various biofuel schemes may appear attractive on the surface, I believe there are several long-term problems with them. For these reasons, considered below, it seems to me that biofuels will likely be only a first-generation alternative fuel, perhaps supplanted in time by more viable and sustainable energy resources.
First, a problem with some biofuels is a low energy return on energy invested (EROI). The most optimistic assessments of the EROI of corn-based ethanol, for example, are 1.3-to-1. That is, to get 1.3 units of ethanol out you have to invest 1 unit of energy in. That’s a poor deal, a minuscule return on energy invested. Compare it to the 18-to-1 current EROI of petroleum.
First corn has to be planted, fertilized, harvested—all of which requires lots of energy. Then the corn is transported to an ethanol plant, where the fermentation and distillation processes require more energy. Finally, the finished ethanol has to be transported to wherever it will be used. When you add up all the energy invested to get the ethanol you're only getting a little more energy out of it than you put in.
The second problem is that ethanol from corn also competes with corn for food. More generally, ethanol from food crops has strong potential for a negative effect on the price and supply of food. There is only so much suitable agricultural land on the planet and almost all of it is already being used for food crops. Thus ethanol from food crops can place further pressure on an already-strained world food supply.
The promotion of corn-based ethanol in the U.S., for instance, has already doubled the price of corn in the last year. Riots have occurred in Mexico over the steeply rising price of corn tortillas, and some experts are predicting food riots in other corn-importing countries.
What about ethanol from sugar then? Sugar-based ethanol, as made in Brazil, has a relatively decent EROI of around 4.7 to 1, vastly better than corn ethanol.
Yet ethanol from sugar also has the problem that it is competing directly with land and water for food crops. Sugarcane is a very water-intensive crop, a problem that we’ll examine a little further on. Moreover, the clearing of land in Brazil to grow sugar for ethanol has been a major driver in the deforestation of the Amazon. It would be ironic indeed if some “solution” to humanity's energy challenge served to worsen another of our great challenges—the deforestation of the planet.
The real promise of ethanol, it seems to me, will come from cellulosic ethanol. This is ethanol that, instead of being made from the sugar or starch grain of a plant, is made from the cellulose that holds the plant together.
The first advantage of cellulosic ethanol is that it is capable of relatively high energy returns. Initial studies have yielded an EROI of roughly 3-to-1, but researchers believe that this can be greatly increased over time.
An interesting fact about cellulose is that it is often considered the
waste product of the plant. If we could perfect cellulosic ethanol we could grow corn, for example, first for food—20% of the plant—and use the other 80% of the plant to produce ethanol. After the process to produce cellulosic ethanol, what’s left is called lignin and can be burned to provide the energy for the process. Notice that the whole operation can be self-energizing now and that we’re using the whole plant for the first time.
The big challenge with cellulosic ethanol is that the cellulose must be broken down into simple sugars so that the fermentation process into ethanol can begin. Right now there are two main processes for doing this, acidic hydrolysis and enzymatic hydrolysis, and neither one has been proven on a commercial scale.
The breakdown of cellulose by enzymes is probably the more promising of the two processes, since it holds the promise of being combined with fermentation to produce a one-stage process in which bacteria convert cellulose to ethanol in a single step. Lee Lynd and his colleagues at Dartmouth are showing progress in making this technology, called
consolidated bioprocessing, a reality. Yet it is still quite a way from being viable.
Successful commercialization of ethanol produced from cellulose would bring big benefits, since everything from corn stalks to grass clippings to sawdust to paper sludge could be turned into ethanol. Yes, even trees could become a source of liquid energy—though we need to be cautious there, because the issue of deforestation could again become involved.
According to scientists, probably the best candidate for cellulosic ethanol is a plant known as switchgrass. It is a grass that grows quickly, is not a food crop, and uses water efficiently. But even ethanol from switchgrass has two possible drawbacks, namely that it could potentially compete for land and water with food crops. This will be discussed further below.
Another interesting biofuel is biodiesel. Biodiesel is made from plant oils. Examples are soybean oil, canola oil, palm oil, etc. Biodiesel can also be made from waste vegetable oil (WVO). It can also be made from various animal fats such as lard, grease, chicken fat and so on.
Biodiesel can be used in any diesel engine, in any combination of percentages. Biodiesel also has the great advantage that it can be transported through the existing infrastructure. Ethanol can’t be transported by pipelines since it attracts water and contaminates itself. So it must be transported by truck. In contrast, biodiesel easily moves through pipelines.
Another advantage of biodiesel is that it has almost as much energy density as gasoline, whereas ethanol has only 66% of the energy density of gasoline. Thus, even after accounting for various factors, about 25% to 35% more ethanol must be burned to produce the same net amount of energy. In contrast, biodiesel matches gasoline gallon for gallon (within 2%) in producing energy.
Another factor is that diesel engines are about 20% more efficient than gasoline engines, which means that if we include energy density considerations that a gallon of biodiesel will power a car approximately 20% farther than a gallon of gasoline and almost 60% farther than a gallon of ethanol.
Diesel fuel has a reputation in the U.S. as a dirty fuel, but biodiesel is another story. According to the Proceedings of the National Academy of Sciences, biodiesel emits lower pollution emissions than either gasoline or ethanol.
But even biodiesel, seemingly desirable as it is, may only be a first-generation solution—because, like other biofuels, it has the potential to compete for fresh water and agricultural land with human needs. In the long term that need for water, in particular, will almost certainly collide with humanity's requirement—as the planet heats up and human population increases—for increasingly scarce fresh water.
The availability of water is not a mainstream topic as yet, but it will be. The authoritative IPCC report, reviewed by over 1,000 scientists from all over the world, says that by 2025 "hundreds of millions" of people won't have enough water, that by 2050 over one billion people will be so affected, and that by 2080 up to 3 billion people won't have enough water. Fresh water is destined to become a crucial issue on planet earth, and a challenge for biofuels is that they have the potential to compete for fresh water with food crops.
Another potential challenge of crop-based fuels is the argument that, even pushed to extremes, they could make only a relatively small dent in the thirst for energy. For example, the U.S. Dept of Energy estimates that even if an all-out effort were made, ethanol could only supply about 10-15% of the nation's need for gasoline.
The green analyst Lester Brown points out that raising U.S. fuel efficiency standards just 20% "would contribute as much as converting the entire U.S. grain harvest into ethanol." In a similar vein, even if we converted all the vegetable oil in the U.S. into biodiesel it would supply less than 10% of the U.S. need for diesel fuel.
Though they give higher energy returns, even cellulosic ethanol and/or biodiesel from high oil crops (such as palm oil) run into a similar problem: There just isn’t enough agricultural land in the U.S. or in the world for biofuels to make more than a relatively small dent.
Then I found out about biodiesel from algae. If we look at the gallons of fuel per acre of various crops, we find canola oil at 127 gallons per acre, the jatropha plant at 202 gallons per acre, the oil palm at 635 gallons per acre and cellulosic ethanol, if brought to its full potential, perhaps 1,000 gallons per acre.
But algae is capable of supplying anywhere from 5,000 gallons to 20,000 gallons of fuel per acre. It’s a whole other ball game. Even using the lesser figure, just 6% of the farm land in the U.S. could supply all its liquid fuel. And algae can grow almost anywhere: shallow ponds in the desert or even in human sewage. The ultimate may be algae in wastewater treatment plants, cleaning the water while yielding huge amounts of biodiesel. This has just been demonstrated for the first time in New Zealand.
(This is the end of Part 8. Go to Part 9.)
—jim sloman, 3.21.07
|
