Exploring the economic and environmental impacts of biofuel.
Biofuels have garnered significant attention as an alternative energy source designed to meet various environmental and economic goals. Understanding biofuels—what they are, how they work, and their impacts—is crucial for designing sustainable energy systems.
What is Biofuel?
Biofuel is a type of energy derived from organic material (biomass), which includes plants, algae, and agricultural waste. Biofuels are renewable because they are made from biomass that grows using sunlight and can be regrown through natural processes. Biomass can be converted to more usable forms through different processing methods.
Crops Used for Biofuel Production
Various crops are cultivated specifically for biofuel production, each chosen for its yield efficiency, growth cycle, and climatic suitability. Some of the most common include:
Corn:Â Predominantly used in the production of ethanol, especially in the United States.
Sugarcane:Â More efficient than corn in terms of energy output and predominantly used in countries like Brazil.
Soybeans and canola:Â Used for biodiesel production, these crops are processed to extract oils which are then converted into diesel-like fuel.
Miscanthus and switchgrass:Â These are examples of cellulosic biomass used for biofuel production, offering benefits like high yields and low fertilizer requirements.
Production and Usage
Some biofuels are processed and converted into liquid forms—primarily ethanol and biodiesel—which can be used directly in engines or power plants. The process typically involves fermentation for ethanol and transesterification for biodiesel. These biofuels are often blended with fossil fuels to power vehicles or supply power grids.
Another form of biofuel is wood. Wood is cut down from forests or tree plantations and then chipped into little pieces before it's burned in a power plant to drive a steam turbine to make electricity. The idea here is to replace coal or natural gas burning with wood burning to produce electricity. Similarly, when a person burns wood or wood pellets in his or her fireplace or wood stove for heat, that's using biofuel.
Comparison with Fossil Fuels
Proponents argue that biofuels, being derived from renewable sources, could significantly reduce dependency on diminishing fossil fuels. Burning biofuels and fossil fuels both necessarily emit carbon dioxide (since they're both made of hydrocarbons), which biofuel advocates claim will be absorbed by the next generation of biomass growth.
The argument is that the carbon released from biofuels is "green" since it's already part of the above-ground carbon cycle. This is in contrast to fossil fuels, whose carbon has been sequestered underground for hundreds of millions of years, so burning it keeps adding additional carbon dioxide to the atmosphere.
Energy Conversion Analysis
We can't evaluate biofuels properly unless we do at least a brief analysis of the thermodynamic energy conversion efficiencies involved in both biomass and alternatives. EROI (Energy Return On Investment) is the ratio of usable energy delivered (technically exergy) to energy required to deliver that energy. The higher the EROI of an energy source, the more usable energy can be delivered with a given energy input. It's generally accepted that an energy source must have an EROI of at least 3.0 in order to be economically and environmentally viable. An EROI of 1.0 means no net gain in usable energy and no benefit is achieved.
It's important to note that EROIs of energy sources change over time based on relative abundance and the processes used to capture it. For example, the EROI of fossil fuels is declining since they are becoming more scarce and harder to extract.
Crude oil extraction involves building infrastructure such as drills, pipelines, refineries, tanker trucks, and ships to extract it from the ground, refine it, and transport it to its point of use. Some of this equipment requires fossil fuels to operate, which gives crude oil and its products—such as gasoline, diesel, jet fuel, and propane—an EROI of around 10-20.
The EROI of natural gas is somewhat higher at around 20-30.
While the EROIs of biofuels vary based on harvesting and processing methods, the consensus is that the EROI for corn-based biofuel is around 1.0. For sugarcane-based biofuel, the EROI is around 1.8. For wood, it's around 0.8. For palm oil, it's around 3.0. None of these EROIs make biofuel sustainable. In the US, corn can only be grown for ethanol due to very heavy government subsidies. Without these subsidies, ethanol production would cease since it isn't economically sustainable—nor environmentally sustainable.
Solar Conversion
The journey from sunlight to electricity using biofuels is a chain of conversion processes, each with its own efficiency. First, energy from the sun is captured by plants that convert sunlight, carbon dioxide, and water into hydrocarbon biomass. Photosynthesis is, on average, about 1% efficient at converting sunlight to biomass. Then energy is required to harvest and transport the biomass. Furthermore, energy is required to convert that biomass into a usable form, whether it's through fermentation, transesterification, pyrolysis, or gasification. For instance, converting corn into ethanol has an average efficiency of about 45%.
If we look at it a different way, the energy from the original sunlight that ends up in biofuel is less than 0.5% at best. If that biofuel is converted to electricity in a power plant, another half of that energy is lost to heat, leaving that biofuel-based electricity with less than 0.25% of the original energy that was in the sunlight used to make it.
Compare that to the 20% conversion efficiency from sunlight to electricity of a solar photovoltaic system. Solar panels are 80 times more efficient at converting sunlight to electricity than biofuel. That means 80 times less land and much less water can be used using solar panels compared to biofuel. Furthermore, both solar and wind energy systems currently have EROIs above 20.
And that brings us to the biggest tragedy of biofuel production.
Environmental Impacts
Not only does the thermodynamic and economic case for biofuels not work out, but the environmental cost of producing biofuels is massive. The cheapest way to harvest biomass for biofuel production is to cut down old-growth forests, and this is being done. The wood is already there. These old-growth forests take several hundred to thousands of years to grow and for the ecosystems to establish—much longer than it takes for a tree plantation to grow.
In order for other biofuels to be "renewable," the land must be made available for crop growth. Tragically, old-growth forests are leveled in order to make room for plantations of corn, sugarcane, oil palms, and spruce. Not only does this lead to biodiversity loss (of plants, animals, fungi, and microorganisms) and soil erosion, but huge quantities of carbon are released from the soil and converted into carbon dioxide. There goes the "closed carbon loop" argument.
We can think of old-growth forests as giant carbon reservoirs, similar to fossil fuel deposits under the ground. It's often argued that the carbon from fossil fuels is sequestered under the ground, and the carbon in forests is part of the active carbon cycle, so no net changes occur when forest trees grow, then die and decay. But as long as there is no major forest disturbance, such as clear-cutting for biofuel plantations, the carbon embodied in the plants, trees, animals, and soil in forests doesn't get released into the atmosphere. In fact, that undisturbed forest will continue to pull more and more carbon out of the air—something that fossil fuels can't do. And the older the forest, the higher the rate of carbon absorption from the air.
Monoculture plantations for biofuel production are highly susceptible to pests and disease, requiring the use of synthetic pesticides that further harm ecosystems. Additionally, synthetic fertilizers derived from fossil hydrocarbons must be used to grow these plantations. Much of this fertilizer runs off along with the topsoil into waterways, leading to eutrophication and damaging algal blooms.
Clearing forests for biofuel production is an environmental tragedy.
Can Biofuel Make Sense?
Economically and environmentally, biofuels are best used where they can be integrated seamlessly with existing agricultural practices, utilizing waste products without requiring additional land or resources. If a biomass waste product has no other use than to be converted to fuel, then a net positive benefit can be achieved.
An interesting concept being explored is creating biofuels from algae. Since algae can be grown in bioreactors of various forms, their growth has the potential to be more controlled and use less land and water. Not only do they have a higher photosynthetic efficiency, but they can be grown in brackish or saltwater, reducing the requirement for fresh water. The Department of Energy reports that algae have the potential to yield at least 30 times more energy than land-based crops currently used to produce biofuels.
The Verdict
Due to biofuel's low EROI, it's unlikely that it will be economically viable to produce in the long term without subsidies. And that's a good thing since producing biofuel wreaks havoc on established ecosystems vital to Earth's and humanity's health. It seems that biofuels are even more damaging than fossil fuels, and there is no need to use them with other energy sources available that are more economically and environmentally sustainable.
Questions for you:
Do you see any way biofuel can be sustainable?
Are there any benefits to biofuel not discussed above?
Should we continue to subsidize biofuel production?
Please comment and let's start a conversation.