New technologies are increasingly being installed alongside the old ones as the National Trust introduces renewable energy to key heritage sites to meet ambitious carbon-friendly targets.
On my way into Scotney Castle, a magnificent National Trust property in Kent in south-east England, I was rather horrified to see that a large number of what looked like healthy mature trees at the side of the drive had recently been felled. However, when I met Ross Wingfield, the estate warden, he explained that they were sweet chestnut coppices that were normally cut down every few years but these had been left at the request of the castle's previous owner. They were now being brought back into use again, with a large part of the wood produced being used in the form of woodchip as a renewable energy source to fuel a recently installed biomass boiler.
He said: "Within a few years we intend to be totally self-sufficient in the supply of woodchip for the boiler. The whole of the Scotney Estate is 708 acres, of which about 250 is sweet chestnut coppice. On 12- to 15-year rotation the trees are cut down and allowed to regrow." For years the woodlands had been properly maintained, the timber used for fencing and as poles for growing hops, to supply the huge beer brewing industry of that time. But as hop growing was reduced, on some estates in Kent the practice of coppicing almost ceased with a resulting decline in the woodlands, though it continued at Scotney and the wood was used for fencing or other timber products.
The increase in the rate of coppicing of all estate woodlands will not only produce a renewable source of fuel for biomass boilers but will also improve the habitats. Wingfield explains: "You coppice on a rotational basis in random plots as this gives the wildlife a chance to move around. Wild flowers move into the open coppiced areas for the first couple of years after the trees have been felled, so you get an increase in insect species – butterflies, bees, dragonflies etc. Then they lead to an increase in the number of animals that feed on the insects. We also leave around piles of wood – habitat piles – as shelter for the animals.
"At the moment we are running a bit behind in coppicing and so in wood chip production and are having to buy some in. When we get going again, the really good stuff will, as before, be sold off for post and rail fencing. Everything else will be stacked and seasoned until the wood moisture content is 20-25 per cent, which takes about two years. Then it will be chipped and delivered to the boiler."
It is obvious as Wingfield shows me the boiler and explains how it works that he is a great enthusiast for what is happening and is pleased that, as he says, "the wood is working for the estate". Over 20 years the woodchip will work out cheaper than oil or gas and they will be gradually reducing their carbon footprint.
He said: "We cut the coppice down, we season it, we chip it, we put it in the boiler. It goes through here and the carbon dioxide comes back out of the flue. By the time that has happened, the coppice we have cut down is regrowing and that is absorbing the carbon dioxide that you have produced. In fact, the growing coppice absorbs more carbon dioxide than the fully mature trees.
"You cannot at the moment make this carbon neutral because you need electricity to start the boiler and run the computer and also fossil fuel to run the chain saws to cut the trees down and the tractors to move them. But I have been told that we will be 85 per cent to 90 per cent carbon neutral".
The installation of the biomass boiler at Scotney Castle is part of a policy of the National Trust to reduce electricity and oil consumption by 20 per cent and gas consumption by 15 per cent by 2020. "By cutting our energy use we are not only saving carbon, but also cutting our bills and reducing our contribution to climate change, a major threat to the historic houses and countryside in our care," says Kirsty Rice, energy manager with the National Trust.
The National Trust is seeking energy reduction in numerous ways, many of these being evident at Gibson Mill in the heart of Hardcastle Crags near Hebden Bridge, Yorkshire. The mill had employed 21 workers producing cotton cloth up until 1890. Thereafter it became a cafe, dance hall and skating rink with boating on the mill pond until its final closure in 1945.
In 1956 the last surviving member of the mill-owning family left the property to the National Trust. With the installation of mains electricity prohibitively expensive since the property is one and a half miles from the nearest road, Andrew Yeats and Eric Parks, who were responsible for the eco-renovation of the mill, say: "The National Trust decided to turn the problem into an opportunity. To make a virtue out of necessity, they developed an adventurous carbon neutral sustainable brief to deliver a demonstration visitor/community centre that would use only the natural resources available on the site."
In the repair and reconstruction of the mill, locally resourced materials were used wherever possible with building materials such as gypsum plaster board and concrete, which involve high energy and large CO2 emissions in production, being rejected in favour of natural clay board and clay blocks. Recycled or natural materials such as newspaper and sheep's wool were used for insulation. In all the renovations, care was taken to preserve the original look of the building.
Energy is generated by a combination of water-powered turbines, photovoltaic panels, solar hot water panels and biomass from the woodlands. The original 1926 Gilkes Francis turbine was reconditioned and has been producing well over the expected 9kW. To ensure electricity at lower river flow rates a smaller cross flow type turbine was installed to provide 1.5kW. In the cafe a 60kW biomass boiler provides hot water, while a 14kW Swedish 'Kakkelovn' thermal mass log-burning space heater stove keeps the room warm.
Two further biomass appliances were installed in the warden's cottage, both fuelled by wood harvested from the surrounding countryside. To provide electricity when there is slow river flow and low photovoltaic output, 24 batteries have a capacity of 48kWh.
As well as no mains electricity, the site also lacked mains drainage and water. Incidentally, a nearby spring was able to supply water by gravity. A concealed and landscaped header tank was installed as backup and the water was delivered to the mill by an underground pipe. Dry compost toilets were provided for the staff and disabled, while those for the rest of the public were based around the Swedish Aquatron separator, the products of both being used as a fertiliser in the woodlands.
Finally a solution had to be found to allow disabled people to access the first and second floors of the mill. As with other problems in the project, necessity led to invention and George Johnson Lifts came up with the country's first human-powered passenger lift. Using a system of pulleys, pull'ropes and weights, it can be operated by one person.
In summing up the Gibson Mill project in an article by Yeats and Parks, Rob Jarman, head of sustainability at the National Trust, says: "This is a flagship project for the National Trust. With a low environmental footprint, Gibson Mill provides a vision of how to marry the needs of heritage conservation with strict environmental standards. A mixture of traditional and 21st Century technologies are being used to light heat and power the mill."