Biofuel Energy: Energy from Living Creatures

Among renewable energy sources, biofuels are the most controversial.

The concerns over biofuels are several–fold. They are not very efficient and require a lot of land, water and other resources to grow the crops and convert them to energy. And they are often made from plants that would otherwise be used for food, putting two human needs—energy and food—in competition.

But, in a civilization dependent on transportation, liquid fuels will play a critical role in our energy economy for some time to come.

The Promise

In theory, biofuels can be created from any biological source. Plants are by far the most common and there are many different kinds of plants that can be converted into biofuels.

The two most common ways to convert biomass into biofuels are:

1. Grow sugar crops or starch and use yeast fermentation to produce ethanol.
2. Grow plants that naturally produce oils, such as oil palm, soybean or algae, and convert the oils into biodiesel.

Sugar is the simplest biomass to turn into fuel. It can be fermented directly into ethanol or into new, improved liquid fuels.

In Brazil, which became energy independent in 2006 in part by replacing 40 percent of its gas with biofuels, sugar is converted to ethanol at a cost of 60 cents a gallon, getting 8 BTUs out of every 1 BTU put in.

The second easiest plant material to convert to fuel is starch. A few cents' worth of enzymes turns the stuff inside a kernel of corn to sugar, and from there to ethanol, but with a far worse energy balance: just 1.3 BTUs for every BTU put in.

Cellulosic ethanol can be created by converting the tough, fibrous material that makes up grasses, stalks, husks, cobs, tree trunks, branches, leaves, etc. Cellulose is the single most prevalent form of carbon in nature and it is well suited for biofuels. When it is turned into fuel, its energy balance is up to 36 BTUs for each BTU put in.

But, cellulosic ethanol is also the most difficult to use. The crystalline structure of cellulose—very long chains of six–carbon glucose molecules—makes it hard to dismantle and breaking those strands requires special enzymes. In 2007, these enzymes cost more than 50 cents a gallon, about twenty times the price of the enzymes needed to convert corn.

No one has built a commercial–scale plant in the United States capable of converting cellulose to ethanol, though companies are developing plants in Georgia, Florida, California, Iowa and Idaho.

The Challenge

Biofuels may play a smaller role than other renewable energy technologies in reducing global carbon emissions, for one simple reason: plants are far less efficient at converting an acre of solar radiation to usable energy.

Even switchgrass, a cutting–edge energy crop, is less than one–hundredth as efficient as the best solar cell.

Plants also have ongoing needs for nutrients and require all the work of growing, harvesting, and processing. The amount of water demanded by biofuels production is immense, with most crops requiring about a thousand tons of water for each ton of biomass.

Several European countries were heavily subsidizing palm oil diesel to meet their greenhouse gas targets until they discovered that rainforests were being felled across southern Asia to meet that demand, producing a net increase in atmospheric carbon.

The amount of land required to grow enough biomass to displace significant amounts of petroleum with biofuels is daunting. The United States uses 140 billion gallons of gasoline and 40 billion gallons of diesel fuel each year. Converting the nation's entire soy crop to biodiesel would meet just 6 percent of diesel demand.

The Future

The Organisation for Economic Cooperation and Development (OECD) has called for the end of all biofuels subsidies, arguing that a switch to these fuels would cut energy–related emissions by just 3 percent while exacting huge costs.

The OECD recommended that rather than rigging the market in favor of a particular technology, a "technology–neutral" price be put on carbon to allow the market to find the most efficient ways to reduce global warming pollution.

Biofuels innovators will have to navigate all of these tensions, and the start–ups are well aware of the challenge. By working within a carbon cap, these innovators will focus their research on more efficient sources of biofuels.

For example, Amyris Biotechnologies, based out of California, is innovating new ways to reengineer the metabolism of yeast to ferment sugar into a pure hydrocarbon fuel. Unlike the ethanol usually made from sugar, this fuel is as energy dense as gasoline, and can be shipped through existing pipelines and pumped into any car now on the road.

Amyris fuels promise to relieve some of the ecosystem pressures because sugarcane is much better than corn at "fixing" carbon—that is using photosynthesis to turn atmospheric carbon dioxide into carbohydrates. And growing and harvesting sugarcane requires less input of fossil fuel, meaning the net reductions in carbon emissions from Amyris fuels exceed 85 percent, around seven times those of ethanol.

By putting a cap on America's global warming pollution, inventors and investors will have new incentives to pursue new, low carbon biofuels like those being produced by Amyris.

Sources:

• Earth: The Sequel—The Race to Reinvent Energy and Stop Global Warming
• http://en.wikipedia.org/wiki/Biofuel
• http://www.experiencefestival.com/a/Biodiesel_-_History/id/1296562
• http://www.answers.com/topic/biofuel?cat=technology

Posted: 01-Jan-1900; Updated: 20-Jun-2008