Waste not, warm lots: five remarkable ways we’re repurposing waste heat

When you think of renewable energy, you probably imagine wind turbines on the horizon or solar farms soaking up the sun. But what if we told you that some of the most exciting sources of sustainable energy are hiding in far less glamorous places – like under your feet, behind your screen, or even… in your toilet?

This World Environment Day, we’re spotlighting the unexpected, the overlooked, and the unusual ways we’re harnessing waste heat to create a greener future.

Here are five innovative (and surprising) we’re using the heat we usually throw away – to keep homes (and sometimes whole communities) warm, at the same time cooling carbon emissions.

1. Server heat – from screen time to city heat

Every search you make, every video you stream, every email you send; it’s all managed by data centres. And those humming hubs of the internet give off a lot of heat. Traditionally, that heat’s just vented into the air.

But not in East London’s Silvertown.

Here, we’re developing ectogrid™, our revolutionary low-carbon energy network that will serve more than 6,000 homes and businesses in the historic Royal Docks. As part of our plans for this major development, we’ll be capturing and reusing heat from data centres to warm up the entire neighbourhood. This unused – and often unwanted – heat will be redirected to buildings with heating needs, giving waste energy a second life.

So next time you binge-watch a series or dive deeper into YouTube, know that the content coming through your screen could soon also be helping someone stay toasty on a chilly London evening.

2. Deep Earth energy – boreholes beneath the buzz

You’ve heard of ground source heat pumps, but imagine scaling that up – way up.

Beneath the streets of London, our Citigen energy centre is doing just that. A trio of industrial-sized heat pumps, powered by boreholes plunging 200 metres underground, taps into the Earth’s natural warmth for a renewable and sustainable source of heating – this is where geothermal energy meets city-scale ambition.

Drilling through centuries of London soil hasn’t been without drama: ancient pipes, plague pits, and a logistical ballet through the Square Mile. But the result is a 4MW system – more than 1,000 times more powerful than a standard home heat pump – cutting carbon emissions from the site by 30%.

A similar transformation is now under way in Nottingham at the Queen’s Medical Centre (QMC),  one of the UK’s largest teaching hospitals. As part of our 15-year energy partnership with the health trust, we’ve installed 64 boreholes driving 150 metres under the car park, accompanied by four state-of-the-art, high-efficiency heat pumps (each the size of a double-decker bus). Together with other innovations such as double glazing throughout, we’re aiming to cut the QMC’s heating and cooling emissions by over 40%, all while creating a more comfortable and cost-effective hospital for Nottinghamshire patients and NHS staff.

It's a powerful example of how renewable technology can make even the busiest urban spaces cleaner, greener, and more comfortable.

3. Sewage-powered heating – yes, really.

Brace yourself, we’re getting into the mucky stuff. But stick with us – it’s surprisingly clever.

We’re working with Severn Trent Water and HORIBA MIRA on a project designed to capture waste heat from sewers near Coventry. Yep, sewage as a source of clean energy.

How does it work? Waste water, which stays a consistent 20°C year-round, flows through a stainless-steel heat exchanger within the sewage pipe. A heat pump then transforms that warmth into usable energy for nearby homes and businesses. And just to reassure you, all this is done within a closed-loop system, so your shower water never meets the, ahem, original source.

The potential’s huge: the UK processes 11 billion litres of waste water each day – enough to heat 33 million homes in the future.

4. EVs that give back – your car, your power bank

What if your car could do more than just sit on drive when it’s not being used?

Through the V4Grid project, we’re testing V2X technology – allowing electric vehicles to not only draw power from the grid, but also return it when needed. It’s like your EV becoming a mini power station.

From Vehicle-to-Home (V2H), keeping your house warm during peak hours, to Vehicle-to-Building (V2B) and Vehicle-to-Grid (V2G), helping to balance national supply and demand, this tech gives a whole new meaning to ‘charging ahead’.

It means more efficient renewables, reduced pressure on the grid, and a more resilient energy system, powered by parked cars.

5. AI that forecasts your heating needs

Okay, this one’s not technically about waste heat – but it is about wasting less of it. And that’s just as important.

Optiheat is our AI-powered forecasting tool that predicts heating demand up to five days in advance, with up to 95% accuracy. It’s like having a smart weather wizard for your radiator.

From entire cities to individual buildings, this clever tech ensures just the right amount of energy is used – no more, no less. That means lower bills, lower emissions, and no more surprise chills. Just cosy, climate-friendly comfort.

From sewers to servers, boreholes to batteries, we’re finding heat in the unlikeliest of places – and turning it into something powerful. Because when it comes to building a greener world, no source of energy should go to waste.