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How can we decarbonise heat in large buildings?
The next time you’re in a large public building like a library or leisure centre, pause to consider all the energy it takes to keep you at a comfortable temperature with access to hot water when you go to the bathroom. It may not be something you’ve thought about, but it’s a huge undertaking – one that is normally met by burning fossil fuels.
Add up all the large buildings in the world and you have a huge amount of greenhouse gas emissions. According to the International Energy Agency, space and water heating accounts for almost half of global energy use in buildings, while the operation of buildings as a whole, accounts for 26 per cent of global energy-related carbon emissions.
A lot of the talk when it comes to decarbonising heat focuses on heat pumps, particularly in the residential sector. But there are other complementary technologies that have an important role to play. Solar energy, for example, is typically associated with electricity generation, but the power of the sun can also be used to provide heat directly.
UK-based startup Naked Energy has developed unique on-site solar technology that can supplement heat pumps and provide buildings with both heat and power. As the company has just completed the UK’s largest ever solar heat installation on the British Library, we felt there was no-one better to talk to about this exciting technology than its founder and CEO Christophe Williams.
What is the elevator pitch for Naked Energy?
Top level, I’d say we’re in the gas replacement market. We want to get people off gas, and the key way we’re doing that is through developing distributed renewable heat assets – our solar collectors. These are more efficient than all other market leading products, and by being more efficient, we generate more energy and, by default, more carbon savings for a given area than other leading technologies. By generating more energy, we enable end-customers to save more money and carbon and become more energy independent, which protects them from volatile fossil fuel prices.
We’ve developed independently proven technology from the drawing board to the market, and we own 100 per cent of our own IP. As a business, we own the technology and outsource manufacturing to the giants so we can scale and supply customers around the world.
Tell me about your product range
We have two products under the brand name Virtu. With VirtuHOT, the clue is in the name – it gets hot and generates pure heat up to 120 degrees Celsius. Each tube has a peak output of 400 watts in an area of just 0.6 square metres, and that’s very efficient. Critically, a kilowatt-hour (kWh) of energy at, say, 30 degrees Celsius is not as valuable as a kWh of heat at 100 degrees Celsius. There’s a value to heat, and VirtuHOT can produce energy at those higher temperatures, which is really important for customers who need a lot of heat all year round.
The second product is called VirtuPVT, and that’s a photovoltaic thermal product. We’ve combined very high efficiency photovoltaic (PV) cells with our unique heat transfer absorber. The sun’s energy comes through the absorber, and we run a fluid through it to capture the heat, which we use in the building. VirtuPVT is therefore simultaneously producing very efficient PV electricity and very efficient thermal energy from the same bit of roof space – from one source of energy, the sun, you’re getting two forms of output. The heat can go up to around 60 to 75 degrees Celsius, so it’s not process heat, but it’s in the sweet spot for sanitary hot water for hotels, hospitals, care homes, and the manufacturing industry as well.
Both products take advantage of their form factor (their size and shape) and are very efficient and unique technologies. What’s more, with their tubular design, there’s a modularity to them, and they are very quick to install and very low profile – they rise only 26 centimetres off the roof line when installed on a flat roof. This means planning is much easier and the wind shear and visual impact is much lower. We were the only technology that was allowed to be installed on the British Library, which is a grade one listed building, and that’s predominantly down to the form factor, which is really important.
How does your solar thermal technology compare to standard PV panels?
A PV panel ultimately just produces electricity. It’s a great technology, billions of dollars of investment have gone into making it a commodity, and it’s quite ubiquitous in the market now.
PV panels convert the sun’s energy at around 20 per cent efficiency, and you get electricity for that, which is very useful. However, with solar thermal you can convert between 60 to 80 per cent of the sun’s energy into thermal energy. So, it’s three to four times more efficient in terms of converting the sun’s energy into usable clean energy.
I would say that PV has a high value energy output but low efficiency at conversion, whereas solar thermal is highly efficient at conversion but has a lower value output. When you net the two together, you get more useful energy and that’s why we combined the technologies.
Importantly, heat is less easy to transport than electricity, which you can run through cables. You can transport heat in district heating, but solar heat is important because we generate clean heat where it’s needed: on the buildings.
Why is the tubular shape of your collectors beneficial?
As you go to higher latitudes, the sun is lower. At this time of year in the UK, for example, it doesn’t get very high in the sky. What you tend to have to do for PV is tilt the panels towards the sun and then space them out.
When you shade a PV panel, because all the PV cells are in series, the output of the whole panel is limited to the output of the shaded cells – so it brings the whole panel down rather than just part of the panel. To avoid shading, developers therefore put in corridors to space out the panels, which are angled at 20, 35, even 45 degrees to the sun, meaning they stick up a little bit. As a result, they could be a metre off the roof line and catch the wind. Aesthetically, seeing them stand up like that is also less attractive.
With our collectors, the absorbers are tilted at the optimum angle to the sun within the tube. In between each of those tubes we have a reflector, which is nice because the empty latent bit of roof space that would not normally capture the sunlight is used to bounce more solar energy into the tube. We capture about 15 per cent more energy in total throughout the year by having that reflector in there, and that’s another quite unique aspect of our design.
Your website mentions that you offer four times the carbon savings of solar PV, please could you unpack this figure.
To compare apples with apples, we take a unit of energy – or the kilowatt-hours generated in a given area – and then we look at what’s being displaced. That’s the key denominator.
If you look at PV, it’s displacing grid electricity. The grid in the UK is getting cleaner whereas we are displacing predominantly on-site gas emissions, and gas is dirtier than the grid. When we look at the carbon factor of the primary energy source that we’re displacing and compare it to PV, it can be up to four times better in terms of the carbon offset.
By now, everyone is used to hearing about heat pumps – how does solar heating compare?
I think the general policy and direction is to try and electrify everything. We’re already electrifying transport and now we want to try and electrify heat. Overall, that’s a phenomenal amount of energy.
Absolutely, heat pumps are a great technology, whether they’re air source, ground source, or water source. But even though they’re great technology and they’re very efficient, they add load to the grid, particularly for big commercial and industrial applications and you also need to connect them to the grid, which can be challenging. What we say is that every kilowatt-hour of solar thermal we generate on or adjacent to a building, the less energy we need to import from the grid and the less we need to invest in terms of building the grid capacity to electrify heat. So, it’s complementary – it’s not a heat pump or solar thermal, I would say they work together.
In fact, solar thermal can actually help to improve the economics of heat pumps. Today, when you put a heat pump in a business, your operating costs actually don’t reduce. In fact, they might increase because you’re subjected to power costs rather than gas costs, and those are quite variable. So, aside from all the costs and complexity of putting the heat pump in, you’re then probably not going to save any money. If you put solar thermal with a heat pump, however, the system actually pays back, and you’re going to improve the operating costs of your site.
Nearly every single project we’ve done is with a heat pump and if you put enough solar thermal and auxiliary energy on your roof, then you need a smaller heat pump and it’s going to run more efficiently. What’s really important is that not a lot of customers are ready to 100% electrify because of the up-front cost. For these customers our partners can put a solar thermal system on, which throughout the year will save up to half of their entire bill. The equipment that we install is also heat pump ready, so when they do electrify, they’ve already invested in a balance of plant, the storage, and all those other components.
What applications is your technology suitable for?
The key requirement is that the customer needs to have a year-round demand for hot water, even in the summer. Typically, that’s the hospitality sector, so it could be leisure centres or hotels. Hospitals and medical clinics also need a lot of hot water, and in the residential sector, you’ve got multifamily apartment buildings, as well as care homes and university campuses. It doesn’t have to be just VirtuHOTor VirtuPVT because they can work together. On the British Library, we have 710 VirtuHOT units alongside 240 VirtuPVT. Manufacturing is really crucial too. The food and beverage, textiles, and chemicals industries all need a lot of hot water, and we can deliver that.
What about energy storage?
Solar thermal is intrinsically a storage technology. Every single solar thermal system, whether it’s for a small family home or the British Library, which has a 15,000-litre water tank, has storage. So not only are we generating renewable heat on the building, which is supporting electrification, but you can also use hot water from up to three days ago, and that gives you flexibility. In Europe, there’s 185 gigawatt-hours per annum of solar thermal storage. That’s a lot of energy that’s built into every single system.
What were the main challenges for delivering the British Library project?
I think the biggest challenge for us as a technology company was size. We own the technology, and we work with our trusted partners. We have an installation partner called Convert Energy that did the actual installation for us, and then we worked very closely with CBRE, the principal contractor that represented the client who is the British Library. Because it’s the biggest solar heat project ever in the UK, the scale was exciting but really a challenge. Then the second point I would say is that it’s the British Library, so reputation-wise, it’s like, wow, this has got to go well.
The third challenge was that it’s a grade one listed building that’s highly protected, so getting any solar technology on the roof was a massive challenge. English Heritage did a detailed study with Camden Council to actually look at getting planning permission, and only our product was allowed to go on. We also had to do a glint and glare study. Because of the way we’ve designed our technology, with cylindrical collectors and reflectors, all the energy goes into the absorbers, whereas if you install all flat panels, you can get a lot of light reflected and bounced off into buildings.
Then, the fourth point would be sheer complexity. The actual roof area, where we collect the energy, is 300 metres away from the plant room, where we deliver it. The British Library has 14 floors in total – 5 below ground and 9 above ground. It’s an extraordinary building, and if you go to the plant room, it’s the size of a football field. So the hot water cylinder is 300 metres away, and getting all that heat there, with all the pipework, all the design, all the planning of the plant room, and the logistics of getting all the energy integrated was just extraordinary.
How is your technology being used in the British Library?
We generate heat predominately and power. All the thermal energy is going into hot water for the taps, to heating the building, and it’s also being diverted to a dehumidification process. This last application is really novel, particularly for the British Library because they have some extraordinarily important manuscripts, such as Shakespeare’s portfolio and Magna Carta. These have to be kept at a perfect humidity rating and it’s a silica gel process where these gels either release or absorb moisture depending on the temperature. The heat that we generate helps to moderate that temperature.
What are your next steps building on The British Library project?
We’ve got a partnership with E.ON, the big energy company, and we’re expanding into a few more markets. We’re expanding into the Netherlands – we have partners there –, Iberia, and the US. Meanwhile, E.ON operates EU-wide, so we’ve got some really exciting projects in Germany that we’re going to be commissioning, which are starting construction now.
We’re going bigger on scale. These projects are more complex, they take more time, but that’s the impact that we want to have at Naked Energy. Project by project, and building by building, we want to help customers save money and reduce their carbon.
Interview by Matt Hempstead
The text has been edited for length and clarity.
