Forestry and Short Rotation Coppice
When using biomass as a fuel source, most crops suitable for supplying a large scale industry can be placed in one of two main categories, either forestry or short rotation coppice (SRC). (Note that energy crops such as grasses, miscanthus and hemp were considered out of scope for large scale industry due to their relatively small use and low energy intensity).
While forestry has much more established supply chains and a higher energy intensity than SRC, there are a number of factors than make SRC a more compelling fuel source. SRC's may have the potential to supply large scale industries but at present are only available on a small scale. Their main benefit over forestry is that due to their short rotation period, much less land has to be dedicated to the growth of the crop. This overcomes some of the limitations in respect to supplying a large industry.
While there are some examples of poplar being grown, a large proportion of SRCs grown as a fuel supply have been willow.
For any biomass crop, forestry or SRC, there are a number of factors that must be considered. Some of these are outlined below:
Availability: How widely available is the crop? Are there enough sources to satisfy demand? For example, waste products from wood/paper industries would most likely not be able to satisfy a large scale demand. This is less of a consideration if the aim is to start a supply chain and is more important if a large volume is required.
Land Suitability: Different crops may only grow in certain soils or conditions.
Storage: Storage duration and methods may be affected by the moisture content, the state (chips/pellets/logs) and how bulky the fuel is. Careful consideration has to be made to ensure that the fuel will not start to decompose while stored as this will lower the energy intensity.
Energy Intensity: Different crops will have varying energy intensities. This is the amount of energy stored in the fuel and will influence how much of the fuel has to be burnt to obtain the desired input.
Carbon Footprint: The CO2 content of the crop. This can vary depending on the type of crop and length of time it has been growing for.
Environmental Factors: Some examples are: the biodiversity of wildlife the crop can support, how it degrades the soil, water use.
Crop Rotation: An extremely important factor. This is how long the crop is grown for before being harvested.
Crop Rotation and Land Use
As discussed previously, a short rotation can greatly reduce the area of land required to grow the crop.
In order to make a quantitative analysis of different biomass crops, a workbook was created to calculate the land requirement to supply an industrial plant with biomass. The way this workbook worked is outlined below:
Using data available in literature and from market (e.g. shops etc) it was possible to verify that this model worked correctly by comparing it to GlaxoSmithKline Irvine's estimation of how much biomass fuel would be needed for their planned plant.
The workbook can be downloaded here.