It is by now well established that to mitigate the worst effects of climate change, we need to reach net-zero carbon emissions as fast as possible. That means getting more of our energy from renewable sources and finding ways to store it for long periods to overcome the intermittency of wind and solar.

Huge battery installations and green hydrogen – where excess renewable energy is used to split water – are often touted as the most promising storage solutions, and clever new ways to hoard excess power are popping up all the time (see “Giant dome filled with CO2 could store excess power from renewables”). However, the possibilities for storing renewable energy as heat are often overlooked.

When we think about renewables, we tend to think about electricity. But heat itself is also a valuable commodity. About half of the world’s total energy demand is for heat, whether for warming homes or to power the industrial production of food, medicines, materials and more. Besides, stored heat can also be used to generate electricity when the sun stops shining and the wind dies down.

The good news, as we discover in our feature “How incredibly simple tech can supercharge the race to net zero”, is that a whole range of heat storage technologies are emerging. Known collectively as Thermal Energy Storage (TES), many of these innovations are disarmingly simple – from toasted bricks to molten salt. Crucially, they should also be affordable. Early estimates suggest that these technologies could be as little as a fifth of the cost, per kilowatt-hour, of energy storage using green hydrogen. In a recent report, the International Renewable Energy Agency said TES offers “unique benefits”.

The problem is that there is relatively little awareness of TES, and even less investment. Private backers are beginning to put serious money into pilot projects in the US and Europe. But governments everywhere need to step up if we are to make good on TES’s promise as a relatively easy way to make a hefty dint in renewable energy’s intermittency problem. If the prices are as good as they look, we can’t afford not to.

With funding from Innovate UK, the Welsh government and the UK Space Agency, UK non-profit xRI has built two of these BESS cars. Over the course of three months in 2024, the vehicles have scanned more than 1.5 million homes.

The aim is to combine the data gathered by the BESS cars with other information, including drone and satellite imagery, to build a comprehensive database on the state of the UK’s buildings. Collating this information into an AI-powered database will help councils, housing associations and other property owners more quickly design and finance big retrofit projects, the team hopes.

New Scientist took an exclusive ride in a BESS car to find out more about this technology and how it can help the UK speed up the decarbonisation of its building stock.

UK city-dwellers may have spotted a strangely shaped car cruising around their neighbourhood earlier this year. It looks just like a Google Street View vehicle, with a camera rig emerging from the back end to scan its environment – and like the Google cars, it, too, is scanning and photographing city streets.

But these modified Teslas aren’t just taking photos. They are kitted out with state-of-the-art sensors and scanners that enable them to report back on the exact dimensions, heat loss, materials, age and state of dilapidation of every building they drive past.

Armed with this so-called built environment scanning system (BESS), the cars have been on the hunt to find out how leaky and run-down the UK’s building stock really is. Between March and May, they scanned thousands of streets and millions of buildings across London, Liverpool, Cardiff, Glasgow, Manchester, Leeds and South Yorkshire.

The data from the BESS vehicles is being combined with thermal imagery captured by drones and planes in a £4 million government-funded project to build a huge digital database detailing the state of buildings across the UK. The aim is to help housing associations, councils and other property owners quickly plan retrofit projects across hundreds of properties at once, says Ahsan Khan at xRI, the UK not-for-profit organisation behind the project.

Decarbonising the UK’s building stock is one of the trickiest challenges for the journey to net-zero emissions. The country’s 30 million buildings contribute around one third of the UK’s total greenhouse gas emissions, with most of the pollution down to the use of gas to heat space and water.

Another issue is that many UK homes are old and draughty. Retrofitting these properties to become more energy efficient will be crucial, but with such huge variety in the age and condition of buildings, knowing where to start is a major challenge. “We’re hamstrung as a nation, because we don’t quite know what we’ve got, where it is and what we can do to it, in terms of the built environment,” says Khan.

The only mechanism right now for judging a building’s sustainability is energy performance certificates (EPCs). These are mandatory documents that grade every building on a scale of A to G and offer owners advice on how to improve their rating. But EPCs, which rely on judgement calls made by in-person assessors, are “expensive, slow and inaccurate”, says at Innovate UK, a government agency part-funding the project. The UK Space Agency and the Welsh government are also funders.

For organisations looking to retrofit hundreds of properties in one go – housing associations or councils, for example – EPCs are of little use. Instead, they often have to send their own assessors to properties to plan a schedule of works, an expensive and time-consuming exercise.

Speeding up retrofits

The hope is the new database will digitise much of this process. If it works as planned, it will use machine learning to tell councils how many of their properties already have double-glazed windows fitted, for example, or which houses need a top-up of cavity wall insulation. In an instant, it will be able to locate exactly which homes have the space and sunshine for rooftop solar panels. Crucially, it should be able to calculate predicted savings on energy bills, providing return-on-investment information for organisations to unlock access to green finance.

“The xRI project represents a leap forward in our understanding of the existing stock,” says Mat Colmer at Innovate UK. “Verified data sets will improve and automate the process of renovation, speeding up the whole retrofit process.”

With around 7.5 per cent of homes in England, Scotland and Wales scanned already, Khan says the framework is in place to build a beta version of the database, due to be released later this year. For now, xRI is focused on decarbonising buildings. But the BESS vehicles collect data on everything they see, from tree cover to potholes, which could be put to use in the future. “The volume of data is just mind-boggling,” says Pitts.

at Leeds Beckett University, UK, says the project is “exciting”, but warns that in-home surveys will still be crucial before starting any retrofit work. “Homes have been messed around with so many times. So identical homes could be completely different,” he says. “While this fast, rapid stuff is great to accelerate progress and momentum, it cannot and should not replace really good-quality surveys in advance of doing the work.”

at Nottingham Trent University, UK, says the neighbourhood data gathered by the BESS vehicles could prove useful when planning local power grid upgrades or climate resilience projects. But data should be captured mindfully, she says. “What is the minimum amount of data we need to make a good decision?” she says. “Because that minimises the environmental impact of storing that data.”