Producing biofuel starts with growing feedstock and choosing the right feedstock is paramount. The difference between a good and a mediocre feedstock can be the difference between a yield of 400 gallons per acre and double or even ten times that amount. What properties make for a good biofuel feedstock?
There are three categories of properties that are looked at when assessing a biofuel feedstock: Nutrient requirements, yield, and growth conditions.
Under this category are food and water, the basic necessities for all life. For plants, food comes down to sunlight, a carbon source, and other essential nutrients (nitrogen, phosphorus, etc.). A desirable feedstock should do well in a wide array of light conditions, would ideally use CO2 as its only carbon source and be able to handle large quantities of it, and would need very little in the way of fertilizer. Fertilizer is a major limiting resource and also contributes to global warming. The less fertilizer a feedstock uses, the more environmentally friendly it will be.
Beyond food is water and less is more in this category. Water is a scarce and valued resource, so the less a particular feedstock requires the better. Right now, the best water to fuel yield comes from algae, which produces a liter of fuel for every 3.15 liters of water (under ideal conditions). This is good, but not great. For biofuel to be really sustainable, water use will need to be on the order of 0.2 liters of water for every liter of fuel produced.
Yield is often measured in gallons per acre and is an important metric for assessing feedstock. There is only so much land available to plant crops and some of that will have to be used for food. Thus, the less land a particular biofuel feedstock requires, the better. Soybean is probably the lowest yield feedstock considered for biofuel production, with an average output of 40 gallons of fuel for every acre planted. That is a low number compared to corn, which provide 400 gallons/acre and sugarcane, which can produce 800 gallons/acre. Of course, all of this pales in comparison to algae, which has been shown to produce as much as 6,000 gallons/acre. Most estimates suggest that yields need to reach 15,000 to 20,000 gallons per acre before biofuel can be considered sustainable in terms of land use.
This simply refers to climate. Some feedstock does okay in the cold and others do better in tropical locations. For countries looking to use biofuel to gain energy independence, this is very important. For instance, the tropical plant Jatropha is not going to be of much use in the temperate climate of Europe. Feedstock is very much specific to regions of the planet; there is no “one-size-fits-all” feedstock.
Below is a list of feedstock currently under consideration or research for potential use in biofuels. Many of these will be explored in greater detail in subsequent articles.
- Sugar beet
- Palm oil
- Certain fungi
- Animal fat