The National Trust has a target of producing 50% of its energy from renewable sources on its land by 2020. It’s a challenging target. The new biomass boiler which was installed at Ickworth Park near Bury St Edmunds in Suffolk and which was switched on in July 2015, is one of five pilot renewable energy projects that will address that goal. This is the story of how trees on the 1,800 acres estate are being turned into fuel.
Completed in 1829, the Rotunda was later described by architectural historian Nikolaus Pevsner as ‘a crazy idea … it makes for a lumpy appearance outside and creates very unsatisfactory shapes for rooms inside’. More recently architectural commentator Gervase Jackson-Stops said the Rotunda was like a ‘huge bulk, newly arrived from another planet’ and an ‘overgrown folly’.
The 199kw boiler is fuelled by wood chip produced from timber taken from the 600 acres of woodland on the estate and it will supply 100% of the fuel for heating the Rotunda and the West Wing. These are the main buildings in the centre of the park, and were the idea of the 4th Earl of Bristol, Frederick Augustus Hervey, who intended to use them as a place to display the treasures he gathered during his 30 years of travel in Europe. The Earl was seen more in Italy than in Suffolk.
Incidentally the Hervey family became more eccentric and more notorious right up to the 20th century; read more here. But ever since Ickworth was passed to the Trust in lieu of death duties following the death in 1951 of the 4th Marquess (and 8th Earl) , the buildings have been a nightmare to heat and the bills for the heating oil have been enormous.
Around 156 tonnes of wood chip fuel would be needed each year in addition to the 40 tonnes that was currently being supplied to the boiler at the Regional Office of the Trust at Westley Bottom a mile away. An independent assessment concluded that extracting this amount from the estate on rotation would be sustainable.
Removal of timber from the estate first started in autumn 2014 when ‘harvesting’ machines extracted non-native softwood trees like Western Red Cedar, Norway Spruce and Larch, from a small area of Lownde Wood in the south of the estate. The logs had to be stacked nearby as the wood chip store still had to be built. This was to be located next to the existing wood store in the north of the estate. In September last year, harvesting of softwood resumed in Lady Katherine’s Wood on the east side of the estate (photos 1 & 2). The harvester cuts the tree at its base, and as the trunk is lifted up, it is fed through rollers. Knives strip the branches off the trunk, and a chain saw cuts the trunk into 12′ lengths. This all seems to happen in just a few seconds and it is fascinating to watch.
These plantations of softwood were likely planted forty or fifty years ago but they had not been managed for a long time. Not all of the softwood is cleared, no more than 30% of the canopy in fact (photo 3). This is to keep some cover for wildlife until the wood is replanted with native broadleaf species that will improve biodiversity. It also serves to protect the wood from strong winds which could blow down thinly spread trees. Standing and fallen deadwood is left, again for the benefit of wildlife.
The land for the wood chip store had by this time been cleared so all the timber, including that from Lownde Wood, was taken up to wood store in the north of the estate (photos 4) where it was piled into five long stacks (photo 5), enough timber to last Ickworth’s needs for an estimated three and a half years. Ideally the timber needs to be stacked for 18 months to 2 years to dry out before it is chipped.
Over the winter, the building of the wood chip store was completed (photos 6, 7 & 8), and in early February a wood chipper was brought on site to chew the timber up into wood chips and shoot the chips into the store (photos 9 & 10). With the store filled, there are enough chips to last about six months. So the chipper will need to visit a couple of times a year.
Not any old chip will do. Certainly not the chips laid down in the children’s play area or used in the gardens of the house. The chip is G30 grade, which means it averages 30mm length. You can get a G100 grade chip but the biomass boiler can only burn up to a G50 chip. In order for Ickworth to claim payments under the Renewable Heat Incentive (RHI) scheme, a probe is used to check the moisture content of each batch of wood chips before it is delivered to the boiler. If the moisture content is too high, the amount of fuel that has to be burnt increases, and the efficiency of burning decreases. At present the chips are averaging a moisture content of about 25%.
Until the store was built, wood chips were bought in from an outside supplier. But in March, with the help of a newly acquired telehandler, the three outdoor rangers at Ickworth, who are responsible for managing the process, mucked in with the first delivery to the biomass boiler of home-grown chips. Loading up the telehandler (photo 11), tipping chips into an adapted trailer (photo 12), and pouring the chips into a trough outside the boiler house (photo 13). It’s a mile from the chip store to the boiler in old garages next to the West Wing. From the trough, a screw conveyor takes the chips into a large hopper inside. Every so often you can hear a whirring noise from the hopper as the chips are sent into the boiler.
38,000 litres of oil (34 tonnes) was being consumed each year at Ickworth, but now the 156 tonnes of wood chip is expected to save about £13,000 a year in fuel costs. And although wood emits carbon dioxide when burned, it is close to carbon neutral as almost the same amount of carbon dioxide would have been absorbed from the atmosphere during the growth of the trees. As a result, Ickworth Park is reducing its reliance on fossil fuels, and reducing their carbon emissions by about 100 tonnes each year.