Thought about growing a biomass crop for combustion fuel on your farm? This article offers three questions farmers can ask to evaluate growing energy producing combustion crops. It examines wood, woody crops and grasses in more detail.
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|Switchgrass briquettes a combustion fuel. Photo: Daniel Ciolkosz, Extension Associate, Penn State.|
Technically speaking, just about any recently living material can be combusted. However, that does not mean that all fuels are equally suitable. Farmers who are considering growing biomass for combustion should ask the following three broad questions when selecting a crop to grow:
Although these questions offer a good method to compare the value of different feedstocks, the answers are not always obvious. The information in these pages will help farmers as they evaluate which feedstock is the right option.
While wood is the most commonly used biomass fuel, many other feedstocks can be used as well. Depending on a farmer's circumstances and resources, it may make sense to consider any of a wide variety of feedstock options. Some of the more common feedstocks include forest wood, woody crops such as fast-growing trees, annual and perennial grasses, crop residue and animal manure. Most of these biomass products have one-half to two-thirds the heating value, on a dry basis, of coal. Manures have the lowest heating value, while woody products have the highest.
Wood fuel is widely available in woodlots on farms in most areas of the United States and throughout the world. Typically, saw timber has a much higher value than fuel wood. Therefore, firewood collection can often be used as a management tool to remove undesirable species and improve the long term value of a woodlot.
Fast growing tree species such as poplar or willow can be grown as short-rotation field crops, with trees harvested every few years for fuel.
Grasses show great potential for providing biomass combustion fuel, with high yields and easy compatibility with existing farming equipment. Switchgrass and Miscanthus are popular perennial grasses for biomass production, while fast-growing annual grasses such as sorghum and sudan grass can provide high productivity without the long establishment period needed for perennials.
Research has suggested that a portion of the stalks and leaves from current field crops (i.e. corn, wheat) can be harvested and used as a fuel without damaging the field's long-term productivity. These crop residues could provide a valuable additional product for farmers to sell for fuel.
Manure is not a common combustion fuel in the United States, but is an important source of fuel in many developing economies. For information about a prototype system for dairies, see Eco-Combustion Energy System.
The scale at which the crop is grown can vary widely. At the small end, some farmers may choose to grow biomass fuel only for their own use (~3 tons or less per year for home heating in the northeast United States). At the other extreme, farmers can grow biomass for sale to large scale power plants that use 1,000 tons per day or more. These wide differences in scale can have a large impact on suitability and profitability of different feedstocks and cropping systems.
Because of economy of scale, larger operations are often more economically attractive, because costs such as equipment, certifications and regulatory permits end up as a smaller portion of the total operating costs. Also, larger operations match better to the size of industrial buyers. For example, a single power plant that co-fires biomass could easily need biomass feedstock from more than 50,000 acres of farmland! These large buyers would rather deal with a few large producers than with many small producers.
However, smaller operations often tend to be more ecologically friendly, since they are more likely to be part of a diverse landscape with many different crops and land uses rather than a massive monoculture. Smaller operations also tend to be more resilient to unexpected problems. For example, if a bioenergy plant shuts down, smaller suppliers will probably be able to adjust and find alternate markets more quickly.
Other articles in this Combustion Series: