Fuel options for biomass boilers:
Heating with wood or straw can be very cost effective, especially when compared to oil and gas prices which are ever increasing. Biomass boilers will take a range of fuels including logs, wood chips, wood pellets and straw bales.
Wood fuel in its most raw form and can easily be purchased by the tonne and cut to a specified length to suit the boiler. To burn effectively the logs need to have been dried or seasoned for at least six months, and space for storing logs to keep them dry is required.
Virgin wood consists of wood and other products such as bark and sawdust which have had no chemical treatments or finishes applied. Wood may be obtained from a number of sources.
Burning more efficiently than logs, these are made by chipping dry core wood lengths to different specifications. Wood chips need a covered storage area and may require the use of a telehandler or front end loader to fill the feed hopper for large capacity boilers.
Formed from timber by-products, are delivered in bags or in bulk, where they are known as blown pellets. There are a number of different specifications and it is important to purchase the size suitable for your boiler. They require little in the way of outside storage space and can be housed in bags in a small outside covered area.
Energy crops are grown specifically for use as fuel and offer high output per hectare with low inputs. Based on your location it is worth checking which strains perform best under UK conditions, and typical outputs expected.
Herbaceous energy crops:
These include the woody, perennial, rhizomatous grasses such as miscanthus and offer the advantage of an annual harvest. The establishment costs may be high.
This fuel is sometimes readily available through a farm business or can be grown specifically to use as fuel.
Managing your own biomass energy crops:
Short Rotation energy crops:
- Biomass energy crops can be divided into short rotation energy crops that are harvested on a cycle of anything from 2 to 20 years, depending on the crop and the system, and herbaceous energy crops that are harvested annually.
- Short rotation coppicing (SRC) of willow most commonly, or poplar, typically yields a crop every three years that can be directly chipped during harvesting, or chipped subsequently after a period of drying.
- Short rotation forestry (SRF) is closer to conventional forestry, but on a shorter time scale, typically 8-20 years.
Longer rotation energy crops:
- Trees have been used as a biomass fuel for millennia and it is therefore natural to consider trees as potential energy crops. Conventional forestry, however, operates on a relatively long time scale. This involves committing an area of land to forestry for many decades, with the bulk of the income from the investment not realisable for many years, which provides poor cash flow.
- If the primary purpose is not the production of timber for sawlogs, but for energy, then there is not the requirement to operate on such a long time scale.
- In addition, the annual rate of increase in biomass per hectare tends to be greater when trees are only a few years old than later in their lifetime, although this varies from species to species.
- Consequently, there is considerable interest in short rotation operations that harvest fast growing trees for biomass when they are just a few years old. As the stems are harvested young, the biomass produced tends to have a relatively high proportion of bark.