Solar-powered castles and heat pumps in Roman ruins as heritage bodies veer into net zero ‘obsession’

Heat pumps have been installed in ancient Roman drains and solar panels placed on a crumbling castle in a net zero push which risks “damaging” Britain’s most precious historic buildings. 

Conservation charities including the National Trust and Historic England are adapting ancient buildings to make them more eco-friendly and meet ambitious net zero targets, despite resistance from members. 

A heat pump system has been installed in the ancient Roman drains which lie beneath Bath Abbey, while Historic Environment Scotland has installed solar panels on Crichton Castle, near Edinburgh. 

The heritage charity, in charge of 300 of Scotland’s nationally important buildings, carried out the work in 2005 and upgraded the panels in 2019 in a bid to “limit the impact of climate change on Scotland’s wonderful old buildings”.

The solar energy system replaced a petrol generator, which is now only used as a back-up and allows the castle to access energy off the grid to power lighting, a computer and heating.

The National Trust has pledged to reach net zero carbon emissions by 2030, 20 years in advance of the Government’s target. 

Neil Record, who sits on the board of the National Trust members’ forum, Restore Trust, said the net zero “obsession” was a “disaster” for Britain’s heritage.

“The National Trust’s principal objective is the preservation of its historic treasures. It’s taken an inappropriate turn to take upon itself the net zero project.

“The National Trust isn’t a major source of emissions. They want to publicise the fact they are, in their own mind, reducing their carbon footprint. They are spending members’ money on virtue-signalling.

“I am very worried that the net zero obsession will lead us to damaging and irreversible changes to our precious historic buildings.

“If we start to destroy the fabric of historic buildings through this fashion – and it is a fashion – it would be a disaster for our heritage.”

The charity, which owns over 500 historic houses, castles, parks and gardens, has installed heat pumps at sites including Wimpole in Cambridgeshire, Powis Castle in Wales and Croome in Worcestershire.

Some critics have questioned whether its net zero target – as well as opposition to recent government moves to water down pollution targets for housebuilders, and the publication of a controversial report that linked Winston Churchill to slavery – reflects the views of members and its conservation mission.  

Some of the Trust’s over five million members have described feeling “betrayed” at the apparent change of direction.

Restore Trust, founded in 2021, describes itself as a “forum where members, supporters and friends of the National Trust can discuss their concerns about the future of the charity”.

Its website states: “The National Trust carries out a vital and complex task in looking after historic buildings, collections, gardens and countryside. 

“It needs to maintain high standards and cannot afford the distraction of ephemeral trends and political activism.”

A document compiled by Historic England informs conservationists how net zero upgrades can be installed so as to minimise their visual impact, such as by painting heat pump vents in the rooms of listed buildings so they appear to blend in with the room’s décor. 

In one example, it shows the garden of a Grade-II listed farmhouse being dug up to accommodate a ground source heat pump.

Edward Levien, commercial director of Isoenergy, a firm which specialises in installing heat pumps in historic and listed properties, including for the National Trust, said that the charity was investing “a lot of money over the years in renewables and they’ve got a long pipeline of a lot of heat pump projects and some solar” planned for the future.

The firm has led projects installing heat pumps for the National Trust at Kingston Lacy in Dorset, Buscot Park in Oxfordshire and Cambridgeshire’s Wimpole Hall, and worked on fitting heat pumps in Bath Abbey’s ancient Roman drains.

He said: “In the work we do with the National Trust the main considerations are archaeology and trees. We have watching teams to do inspections in and around the building to make sure we’re not unearthing anything that should be conserved.

“We did find a priest tunnel once that no one knew was there.”

He said his firm also discovered “a skeleton in a field” at a non-National Trust property in Wiltshire when installing a ground source heat pump.

“The police were called and [they] cordoned off the area,” he explained, adding that the remains were removed and later proven to be “very old”.

He was unable to comment on the skeleton’s precise location or say what happened to it after its discovery.

He said that “the main challenge with old leaky buildings is the design of the system itself [and] calculating the heat loss of an old building” due to poor insulation.

While ground source heat pumps could be hidden, he said, air source pumps are more visible and installers needed to “look at taking that away from the building to not impact visuals”.

He said that when submitting proposals to local authority planners for installing carbon-neutral heating and energy sources “most of them get waved through”.

He added: “A lot of councils have declared climate emergencies and need to be seen to be doing the right thing.”

While heat pumps do not require planning permission, installing them in listed buildings or conservation areas still requires approval from a local council.

Chris Yates, senior manager at the Federation of Environmental Trade Associations, a green energy industry body, questioned whether some of the green upgrades to historic buildings would work properly. He said if a property is not insulated a heat pump will be “working harder” and is “not going to be as efficient.”

He added: “If proper heat loss calculations are done on the property and then it’s [decided] what needs to be done to insulate it fully, it may be that the heat pump can be used.

“There are people that have done it and there tends to be a return on investment but that depends on good heat loss calculation from a qualified installer.”

However, in large old properties, like cathedrals, castles or palaces, fitting adequate insulation “would probably be more tricky”, he added. 

Shrewsbury Flaxmill Maltings, a Grade I listed five-storey 18th century flaxmill operated by Historic England, incorporated a bivalent heating system which kept gas boilers to top up ground source heat pumps during the winter when it installed the carbon-neutral tech in 2021.

The heritage charity said that the budget for the project would not stretch to cover the cost of installing enough boreholes to fully heat the site with heat pumps, which now provide 69pc of its energy needs.

A Historic England spokesman said the project demonstrated how heat pump insulation can make a “real difference” on a larger scale and that introducing energy efficiency measures helped make buildings sustainable for the future.

A spokesman for Historic Environment Scotland said: “As part of our commitment to become net-zero by 2045, HES has a responsibility to reduce our carbon emissions and explore innovative approaches to sustainable and renewable energy.” 

A spokesman for Restore Trust said the group supported efforts by the National Trust to make its properties more energy-efficient, but said: “The National Trust’s first duty is to look after the properties in its care for future generations, and nothing must be done which would be detrimental to landscapes or the historic fabric of buildings.”

A National Trust spokesman said: “The Government’s own research shows there is no property type or architectural era that is unsuitable for a heat pump.

“The use of renewable heating in many of our houses has enabled us to improve the conservation conditions for our fragile collections alongside the fabric of our historic buildings.”