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The Cornish village getting its heat from beneath the street

This is the year Vicki Spooner and her family finally got cosy at home in the Cornish village of Stithians.

The village is not on the gas grid, so for years Vicki, her husband and two boys relied on an oil boiler, which coughed clouds of noxious fumes on to their patio.

Then they decided to invest in an air-source heat pump, which acts like a fridge in reverse. It didn’t stink like the oil burner, but nor did it produce as much heat as they wanted.

Then the family was offered the chance to join a groundbreaking new project that might change the way many homes are heated — particularly in off-grid villages and on new estates.

The scheme involves drilling boreholes 100 metres underground, where liquid can absorb heat at a constant 10C-12C. This is then piped into people’s homes, where the warmth is extracted by a ground-source heat pump. Like an air-source pump, this relies on refrigerant technology running backwards — crucially, though, it’s 30-40 per cent more efficient than the air-source version because it doesn’t have to cope with really low temperatures in winter.

In this scheme, however, rather than each heat pump having its own piping — which can make the technology incredibly expensive — residents’ boreholes are connected to a communal network of horizontal pipes just below street level.

The Spooner family noticed the difference immediately. “There’s much more heat,” Vicki says. “When we come in after a dog walk, we can dry coats on the radiators, or if the boys have dunked their boots in the sea we can dry them too.”

Tristan Bowden, his wife Kirsty and their 18-month-old child are beneficiaries of the Heat the Streets project in Stithians, Cornwall © Photographed by Maisie Marshall for the FT

The project, which can warm radiators to 55C, is called Heat the Streets. It’s being pioneered by Cornish heat-pump manufacturer Kensa, which claims it’s a commercial first in the UK.

It’s hard to offer firm figures, bearing in mind the vagaries of energy markets, but Dr Richard Lowes, research fellow at Exeter University, says the heat pump should reduce emissions by 90 per cent compared with an oil boiler, and should prove cheaper to run than a gas boiler, too.

He told me: “There are around 4mn homes not on the gas grid, the majority of these in villages. For them, this looks like an ideal solution.”

Wouter Thijssen, managing director of Kensa Utilities, says: “We see Stithians as a blueprint for decarbonising millions of UK homes.

“Burton-upon-Trent was the first part of the UK to convert to natural gas in the late 1960s [rather than using gas that derived from coal] — we see Stithians as the first part of the UK to convert to the 21st-century version: networked heat pumps.”

Energy expert Jan Rosenow from the Regulatory Assistance Project described the street scheme as simple and elegant — especially for terraced homes which can’t get a drill rig into the back garden to provide ground source heat to individual homes.

So how far can this scheme spread? Sceptics say it will be too expensive to drill boreholes into the streets of Britain’s large cities, with their spaghetti of services already in place; and that the system is too expensive compared with air-source pumps.

“Just imagine you are putting in a heat network and you smash a gas main. It’ll bring chaos to whole streets,” says an expert working for an air-source heat pump firm, who preferred to remain anonymous.

But Andrew Sissons from the innovation agency Nesta says the drawbacks must be overcome. “I like the Heat the Streets scheme very much,” he says. “We have to get out of gas — and it will be very difficult to bring air-source heat pumps to some heavily populated city areas.

“We are likely to need shared ground-source heat systems in those areas — and innovation should bring down the price.”

The idea already looks attractive to some housebuilders who build new estates from scratch. It would be easy for them to lay a heat network alongside the water, power and telecoms as they lay the roads.

Persimmon, for instance — which has previously resisted government energy-efficiency schemes — is optimistic about the idea. Its energy director Gus Watt told me the firm was examining 12 potential sites around Britain. “We think this is scalable to developments with 100 or 1,000 units,” he says. “It has much lower maintenance costs than gas. It’s early days yet so we can’t know the eventual cost — but I’m very enthusiastic.”

A house and tree in Cornwall
Some 270 residents in Stithians hoped to join the village’s under-street grid but only 60 are able to benefit from this trial scheme

Another Stithians heat pump beneficiary is Tristan Bowden, who has lived in the village all his life. He and his wife Kirsty have an 18-month-old child, so they want the home comfortable.

He says the cost of heat from under his driveway is comparable to bottled gas but without the supply problems.

There’s also an aesthetic benefit. Air-source heat pumps can be noisy and ugly — and they can’t be installed at the front of homes in conservation zones. But with ground-source heat pumps, all the paraphernalia is hidden — though you need enough space inside the home for the pump, about as much as a tall fridge.

Since launching, the Stithians scheme has been hugely oversubscribed: some 270 residents wanted to join the village’s under-street grid but only 60 are able to benefit from this trial scheme, which is offering to hook people up to the network free of charge (a £3,500 fee for the heat pump and an extra few thousand for the installation would normally be payable). Residents must pay a monthly standing charge of £25, and the energy they use is payable on top — Kensa estimates an average monthly bill for Stithians’ residents to be £130, compared with £141 for an oil boiler.

Lowes says widespread adoption of the technology could help the UK’s net zero emissions targets, as well as people’s bills.

“The government and its energy regulator Ofgem need to get their heads around how local energy can be transformative,” he says.

Certainly, the efficiencies appear to be huge. A Grade-A gas boiler can be more than 90 per cent efficient. But thanks to the incredible alchemy of the heat pump, Kensa says its system can achieve efficiencies of 550 per cent — that means five times more energy is extracted than is put in.

The Heat the Streets project has been part-funded by the EU regional development fund (ERDF), which will provide around £3.6mn grant funding to the project including other sites across Cornwall.

The heat pumps will provide low-carbon heat and hot water 24/7, 365 days a year. As Britain’s temperature rises with climate change, heat pumps can also provide air conditioning by generating chilled water (typically at 6C-12C) to cool the building, operating in a similar manner to a chiller.

Under the Stithians model, Kensa Utilities will own the infrastructure under the street until it enters the property, after which the in-home pipework and heat pump will be owned by the homeowner — this, crucially, allows residents to choose their own heat pump and their own electricity supplier to run the pump.

Kensa says more than half a million households currently connected to traditional district heating systems, which pipe waste hot water from council incinerators, for example, can be at the mercy of unrestricted prices because they can’t switch suppliers. This has led to reports of communal boilers being switched off to save costs — or boilers being left on when they are not needed.

Kensa pioneered its heat from the street technology in projects involving council-owned tower blocks, where each individual property had its own ground-source heat pump connected to a shared ground pipe loop bringing ambient heat from the deep underground.

The system was welcomed by residents in sheltered housing at Higham near Rochester in Kent — an early pilot scheme.

One resident, Gill Chapple, told me that her pump, which is inside her flat, is about the size of a slimline dishwasher. “It takes a bit longer than gas heating to warm up — but it’s a lovely constant heat,” she says. “I can’t speak highly enough of it.”

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