A few years ago there was much talk in agricultural circles of growing alternative crops, such as willow, to supply energy from the land in addition to its role of providing food.
However, there were only a handful of farmers who put the ideas into practice as it all seemed a little too radical for many, and a diversion from the serious business of producing for a known and established market.
Investing in willow
One farm that took the plunge back in 2010 was that belonging to Gurteen College in Co. Offaly which planted 80ac of willow in total, with the first harvest occurring four years later.
The college had a ready use for the willow and that was to provide heating and hot water to the farm, student accommodation and all the other consumers of hot water in the establishment.
The investment, around €750,000 at the time, is now paying off handsomely with the all-in costs of producing and drying the willow, and buying in extra wood for chipping, being around €40,000 per annum, as compared to the estimated cost of €200,000 of continuing with oil.
Willow is a low input crop, it is cut every three years and receives a dose of slurry after each cut, otherwise it is left to its own devices although, come harvest time, there is a special header required for the front of the harvester.
Dedicated harvesting header
Harvesting is a job for a contractor and this year Farrelly Brothers from Kells, Co. Meath took the job on with a John Deere 8400, which is rated at 540hp when leaving the factory.
The harvester itself is kept as standard, but the header is a special unit bought in from the UK which is the third, and so far the most successful, model used by the firm.
The willow plants are set in rows of two with space between each line for the harvester wheels. The head is therefore dealing with a twin row of saplings on each pass.
Cutting height is set at around 9″ and two serrated circular blades draw in the saplings, cut them from their stumps and then feed them into the cylinder intake.
The cutting action is created by having the blades set at slightly different heights, enabling them to overlap and so produce a shearing action.
Once free from the stumps, the sticks are fed into the chopper lower end first, where they are cut and blown into the trailer in the normal manner.
Oil cooling essential
The harvester is run with the usual 40 blades on the cylinder and it is only a matter of minutes to revert back from the willow harvester to the standard forager header and be ready for silage.
The two harvesting blades are driven by hydraulic motors which are, in turn, driven by a pump attached to the input PTO shaft.
The major way in which this particular header scores is that the oil circuit is plumbed into the harvester’s own oil cooling circuit, keeping its temperature down and so avoiding the overheating problems associated with the previous units.
Harvesting speed will obviously depend on crop conditions; in a thick standing it can be as low as 3km/h, but it was a lot quicker at Gurteen due to the thinner crops produced on the drier soils of the site.
Wet ground vs energy yield
Kenneth Flynn is the farm manager and he explained to Agriland that although willow will yield more on wet ground, the problem then becomes one of harvesting it at the right time.
Ideally, it should be cut in late winter rather than early spring as that is the time when the plant is preparing to bud and contains the most energy.
When leaves first start to appear, the energy content drops and the leaves themselves can form a dust during drying which reduces the efficiency of the boilers.
This season, the harvest was later than optimum for various unforeseen reasons, but once started, it could keeping going without the delays associated with working on waterlogged soils.
Around 25ac are harvested each year and the operation normally takes one or two days.
Once harvested the chips are taken to a store with underfloor drying. 20% is the target moisture content with it usually coming in at around 50% or more.
Drying is in two stages – first cool air is blown through to remove any natural heating and then warm air is introduced to bring the moisture content down to the desired level.
Having several hundred tonnes of wet willow chips to dry takes a good deal of heat, and would be expensive if relying on bought in fuels.
To overcome this, hot water is drawn off from the hot tank and is used to heat the drying air, in effect, the willow is used to dry itself.
Once dry, the chips are loaded into one of two hoppers and are then automatically fed into the boilers at a rate determined by the temperature of the water in the main reserve tank.
This hot water is then distributed throughout the college buildings according to need.
Wood chip supplement
Altogether this sounds the ideal solution, yet there is not enough willow grown to supply all the college’s needs, so it needs to be supplemented by wood chips, the split being 60/40% in favour of the willow, although it does vary from year to year.
The wood is brought as fresh logs which are then left to dry naturally before being chipped by a forestry contractor.
The boilers will work equally well off either material and there is no need for any adjustment when switching between the two.
Given the cost saving, the college is delighted with how the system is working in its favour. There will though, be a need to replant the willow at some point, but not for at least a decade.
There is little management involved in the crop; brambles are the biggest weed problem and disease is kept in check by there being seven different varieties of willow in the field.
It is, overall, a system which works well and with the college being a registered charity rather than state-funded establishment, it needs to take particular care of its budget, and the willow crop is a big part of that.