There is no perfect energy source. Each and every one has its own advantages and compromises. This series will explore the pros and cons of various energy sources. Learn about other forms of energy generation here.
Biomass energy has been around since long before anyone spoke of renewables or alternative energy sources. There was a time when wood was the primary fuel for heating and cooking around the world. It is still used that way today, though in many fewer locations in countries like ours.
When we speak of biomass today, we are basically talking about several different applications:
- Direct burning for domestic heat: This is the traditional method of burning wood, peat, dung, etc., for cooking and heat. It is still widely used, especially in developing countries where it is responsible for many respiratory illnesses and deaths.
- Electric generation: Biomass is used to feed a boiler which then provides steam to a turbine which is connected to a generator. Feedstocks are mainly forest wood residues, and urban/industrial waste wood. EIA predicts that by 2020, biomass will produce 0.3 percent of the projected 5,476 billion kilowatt hours of total generation. Roughly 19,786,000 Mw hrs of electricity was created from biomass last year.
- Co-generation: Essentially the same as item #2 above, with the addition that useful heat is withdrawn from the process, improving its efficiency in a combined heat and power (CHP) arrangement.
- Gasification: The biomass is heated in an environment where it breaks down into a flammable gas. After the gas is cleaned and filtered, it can then be used as natural gas, usually in a combined cycle turbine. Feedstocks used primarily include forest and agricultural residues.
- Anaerobic Digestion: The biomaterials go through a fermentation process that converts the organic materials into biogas, which is mostly methane (60%) and carbon dioxide (40%) biogas. Converting methane into CO2 and water by burning it is a net positive from a greenhouse gas (GHG) perspective, since methane is a much more potent GHG than CO2. Enzymatic digestion and other catalysts are used to enhance conversion. Suitable fuels are organic materials with high moisture content such as animal manure or food processing waste. Landfill gas which is siphoned off of active landfills can also be considered part of this category, though, in this case, there are concerns about toxins released, though some technologies claim to eliminate many of them.
- Biofuels: This category includes any kind of biomass that is converted into liquid fuel, primarily for transportation. Most common are ethanol and biodiesel. Ethanol can be produced from food crops such as corn in this country, sugar cane in Brazil and sugar beets in Europe. “Cellulosic” ethanol can also be made from wood or paper waste as well as specially grown grasses such as switchgrass or from agriculture residues. Biodiesel is generally made from animal fats or vegetable oils. Much “homegrown” biodiesel is made from recycled restaurant grease. Commercially, soybean oil is used in the US, rapeseed and sunflower oil in Europe, and palm oil in Malaysia. Algae-based biofuel is a special case, which we covered in a separate posting. While convenient for transportation, biofuels require considerably more energy to produce than biomass.
Biomass is often advertised as carbon neutral or nearly carbon neutral, but this can be misleading. It is true that the carbon released upon burning it was only recently (in relative terms) pulled out of the atmosphere, so it can be viewed as returning what was already there before the plant came up. But any additional carbon emitted in cultivating, harvesting and transporting the fuel, which can be considerable, is incremental to that. The less carbon emitted in these stages of production, the closer the resulting fuel is to carbon neutrality. There is also the question of fertilizers, pesticides and herbicides, if used, and the energy and resources used and carbon emitted in producing them.
Biomass Energy Pros and Cons:
- Truly a renewable fuel
- Widely available and naturally distributed
- Generally low cost inputs
- Abundant supply
- Can be domestically produced for energy independence
- Low carbon, cleaner than fossil fuels
- Can convert waste into energy, helping to deal with waste
- Energy intensive to produce. In some cases, with little or no net gain.
- Land utilization can be considerable. Can lead to deforestation.
- Requires water to grow
- Not totally clean when burned (NOx, soot, ash, CO, CO2)
- May compete directly with food production (e.g. corn, soy)
- Some fuels are seasonal
- Heavy feedstocks require energy to transport.
- Overall process can be expensive
- Some methane and CO2 are emitted during production
- Not easily scalable
While biomass seems compelling at first blush, given that it is renewable and can be domestically produced, there are a number of drawbacks that make it far from a perfect solution. Primarily, as our population continues to grow, the competition for arable land and water needed for food production is going to make a number of these options unsuitable. That doesn’t mean that biomass cannot and should not play a role in our overall energy picture for some time to come. The most attractive and efficient options are those that utilize existing waste materials as inputs, which is, after all, the way nature operates. There are a number of these options that utilize forestry, agricultural, and even industrial waste (e.g. paper) as well, as trash found in landfills and recycled nutrients from waste water treatment facilities. Not only are these more efficient input sources, but in many cases using them will also help to address waste disposal issue. It could be argued, though, that in the future, many of these same materials might be needed for compost, particularly as the production of phosphorus, a key ingredient in fertilizer, begins to decline.
[Image credit: OakRidgeLabNews:Flickr Creative Commons]
RP Siegel, PE, is the President of Rain Mountain LLC. He is also the co-author of the eco-thriller Vapor Trails, the first in a series covering the human side of various sustainability issues including energy, food, and water in an exciting and entertaining format. Now available on Kindle.
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Article source: http://www.triplepundit.com/2012/05/biomass-energy-pros-cons/