|WILLOW FARMING & BIOMASS
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Biomass is any plant material, vegetation, or agricultural
waste used as a fuel or energy source. Willow as a biomass is an
excellent source of renewable energy (unlike our ever-decreasing supply of
fossil fuels) and, when burning, releases much lower sulphur emissions, which
contribute to acid rain. Fewer greenhouse gases are emitted, slowing down the
effect of global warming.
SOURCE OF SUSTAINABLE DEVELOPMENT
Producing willow as an energy crop contributes to sustainable development,
as it results in the land and the farmers' skills and equipment to be put
to good use; protects jobs in rural areas; helping rural communities to remain
rural areas are growing and experiencing increasing energy demand. However,
building large power plants is not as desirable as the smaller facilities that
have fewer environmental impacts and can operate with locally produced biomass
Many types of biomass can be used as a source of fuel. However willow is almost
certainly the easiest to produce:
- It is one of the fastest growing woody fuels in Northern Europe
- Can be grown with low inputs of agro- chemicals
- Is easily established from
- Re-sprouts vigorously after each harvest;
- Offers large potential for genetic
- Has an energy balance in the region of 20:1 (e.g. the
energy obtained can be 20 times as much as the energy used to grow the
- Can be
used as a vegetation filter during "bio- remediation" of
waste water or contaminated land.
WILLOW FARMING PROCESSES
- Land to be prepared as for a
cereal seed bed, but cultivated more deeply.
- Willow planted in spring using
cuttings from one year old plants, usually around 20cm long.
- New plants are cut back to ground
level at the end of their first year to encourage the plant to produce
- Harvesting occurs before February,
prior to leaves developing, as they cause mould. Willow usually harvested
on a three-year cycle.
- Chipped willow is the most common
form, however after harvesting it contains around 50% moisture, which
needs to be reduced to 8% before it can be used to produce energy.
- Wet chips quickly heat up and
start to decompose. Much of the energy value may be lost, and mould spores
are a health hazard, so good drying measures are important.
- Ventilated floor driers are
the most effective drying method. Drying takes up to four weeks using
the ventilated floor method.
- Rabbits can be a problem in particular areas and suitable fences
may need to be erected
- Willow needs a moist site, but not too wet as this can
make harvesting difficult
- ‘Leatherjackets' are a common pest and insecticide
is needed, however, moderate numbers of other insects have little effect
- Willow occasionally gets a disease called ‘rust'.
A strategy of planting several different varieties of willow per site helps
to overcome this.
CONVERSION TO ENERGY
The chipped willow can be supplied to a power station or biomass fuel trader
or it can be processed for the farmer to produce power for himself or to sell
as a value-added product, such as heat. This conversion to energy can be achieved
through the methods of combustion or gasification .
Combustion is a well established and most economical way of producing energy
out of biomass. Heat emitted can be used directly, i.e. to produce hot water
in a central heating system. Equipment ranges from small wood stoves used for
domestic heating to large burners that can power whole communities such as
hospitals, industrial estates and prisons.
Gasification (heating with restricted air supply) converts solid organic material
into a combustible gas that is generally used in a diesel engine or gas turbine.
It is not economically viable to transport or store the gas, because it has
a low calorific value in relation to its volume. The gas is normally used immediately,
to generate electricity. This electricity can then be consumed by the farmer
and any excess can be transported to the grid, where the electricity provider
will pay per unit provided .