I'm not naive enough and I hope I never was to think that technology on its own can solve the world's problems, but what it can do is move the goalposts, and improve the feasibility of solving them.

Tom Smith

Tom has a Ph.D. in Engineering from the University of Cambridge, a first-class degree in Physics from Imperial College London and has won several awards for his work including the Royal Institution Science Graduate of the year award, 2004 and the Sunday Times One minute pitch for £100,000 in 2005. He is driven by a lifelong passion to make sustainable energy and water services available to all.

We caught up with Tom to find out more about his world.

How did you become the inventor of energy and water related technologies?

I've always been fascinated by the use of novel physics, particularly lesser-known fluid mechanical and thermodynamic phenomena to avoid mechanical complexity in solutions to real world problems. But it wasn’t until I became a research student in the Department of Engineering at Cambridge that this became a practical reality.

I grew up in the Cambridgeshire fens, and Cambridge is my hometown, really. I raised my first pot of funding from the California Energy Commission in the middle of the California energy crisis in 1999, off the back of an undergraduate project at Imperial College. I suddenly found myself with money but nowhere to work, and no experience at all. I asked David Newland, then Head of the Department and my neighbour, what he thought I should do. He introduced me to John Young and Nick Collings in Division A. Initially I asked if I could rent some lab space, but that wasn't bureaucratically possible, even then when the rules were much more relaxed than they are now. So, Nick agreed to act as my supervisor and I became a research student. So long as he was willing to officiate and sign off the paperwork, I had one of the greatest pool of resources the world could offer at my fingertips. This arrangement lasted from 2001 to 2005 – around the same time that a group of undergrads including Tom Newby and Mo Ali were setting up the first Engineers Without Borders (EWB) group in the UK.

I owe a lifelong debt of gratitude to Nick. He took me under his wing, provided some lab space and an EPSRC bursary as well. So, I was well funded, but completely out of my depth. It was a very steep learning curve, but it was an amazing place to land. There was always somebody on tap to help me solve any problem. I could just knock on the doors of world renowned experts in just about any field - and ask questions. I remember knocking on the doors of Mike Ashby with materials problems, Malcolm Smith with control questions and Ann Dowling who helped me to get my head around the way that engineers approach fluid mechanics. I’ll never forget Allan McRobie’s 10^th scale Millenium bridge, or his reconditioned Phillips model of the economy – an early analogue computer based on pumps, valves and tanks of fluid. John Young gave me a huge amount of time, and helped me to become more structured and rigorous in my approach to Thermo-fluids. That sort of environment is incredibly precious. And it's not really until you leave it that you realise how unique it is.

There are many examples where phenomena such as thermoacoustic oscillations or the Joukowski (water hammer) effect can solve problems in a way that's significantly more efficient, robust, cheaper, or easier to implement than established approaches to everyday problems.

Applying this ethos to different challenges has taken me in many different directions over the years. When I was a research student, I was exploring ideas at the interface between thermo-fluids and control theory - using analogies between analogue electronic components (resistors, capacitors, inductors, transistors), and thermo-fluid components (capillaries, gas springs, tubes of dense fluid, heat exchangers). I was particularly interested in how analogue oscillator circuits built from these components could be used to create and optimise heat engines - and heat pumps - with no, or very few mechanical parts. These have become known as Thermofluidic oscillators – hence the name of our first company, Thermofluidics. Over time, I’ve worked on projects in different physical realms, moving through optics, electronics, thermochemistry and most recently, power electronics. The technical disciplines I've worked in have changed over the years, but the unifying objective has always been the same: to exploit well-known but under-exploited phenomena to solve real world problems in the simplest possible way. To some extent, that's involved re-visiting ancient technologies and attempting to revive them with modern materials and know how, whilst in other areas, it's involved starting from scratch.

Tom checking the drive pressure on a recently-installed Joukowski-effect pump prototype in the Savar slum in the textile district of Dhaka, Bangladesh, Jan 2018. With Badrul Alam, of IDE Bangladesh, the pioneer of the Treadle Pump in Southern Asia during the 1980s.

I've always been interested in tackling the world’s big problems. Via a random path, I ended up working at the interface between off-grid energy and water access; particularly in low income countries. My primary focus has been on solar-powered water pumping for irrigation and drinking water supply, originally powered by novel thermofluidic oscillators – and my first inventions and patents were in that field. But these are fundamentally surface-level devices: it isn’t practical to transfer heat to the bottom of a well in order to pump water up, and most farmers don’t have access to near-surface water (fewer than 10% in sub-Saharan Africa). So I needed to find a way to couple surface-level fluid oscillations to deep groundwater without negating the advantages of thermofluidic oscillators by adding sliding seals and fault-prone moving parts. This led to our first product to reach market-readiness – a “double-acting hydraulic ram” (DAHR) pump, which uses the Joukowski (water hammer) effect to enable essentially any surface pump to access deep groundwater using shockwaves instead of pistons and seals or impellers below ground. There were several inventive steps involved in the DAHR development leading to two separate patent families. The first was my own work by the latter was very much a collaborative effort across the team.

We took the first DAHR pump, now called a “Suction Lift Extender (SLX)” into production in Birmingham and Shanghai during the 2020 lockdowns (another story) and launched a product under the brand “Impact Pumps” shortly afterwards. The world’s only deep-well Joukowski effect pump is now sold via an expanding network of distributors across the globe.

What inspired you into your field?

It's always hard to identify a single source of inspiration. I think if engineering is in your blood, you may not know it, but it's probably there fairly early on. Like many engineers, I spent much of my childhood taking things apart – rarely putting them back together again, at least in their original form. There's a sort of compulsion which combines scientific curiosity with a creative urge, that I am sure many readers will recognise in themselves.

It’s a bit easier to identify what inspired me to focus on off-grid power and water, than my choice to do so as an engineer. I went off and did some voluntary work in South America after my A levels. I was working on a smallholding for several months in the Andes. It seemed obvious that some of the everyday problems that people were facing could be greatly alleviated by simple technological solutions.

I'm not naive enough and I hope I never was to think that technology on its own can solve the world's problems, but what it can do is move the goalposts, and improve the feasibility of solving them.

I saw opportunities everywhere to move water around more efficiently, or provide basic services powered by moving water; opportunities that weren’t being exploited because of disinterested or dysfunctional governments and because they were beyond the reach of markets at the time. I'd already signed up to study physics at Imperial College, which later gave me the tools to broach technical problems across the spectrum, but it opened a dichotomy. How was I ever going to do anything practically useful with relativity and quantum mechanics? On the one hand I wanted to be completely rooted in the real world, and on the other hand there was all this fascinating stuff over here. And I couldn’t really square these two facts. The answer was engineering: it became apparent that a combined physics/engineering education is extremely powerful: I attribute that – alongside an excellent and very capable team of colleagues - to more or less every success we have shared since.

Tom visiting a self-built solar surface pump installation on a mango farm in the Ayeyarwady Delta. Lower Burma/Myanmar, January 2012.

How did your career develop?

It’s been a bit of a random walk, to be honest. I've never really thought about the word “career” (at least, not as a noun), and that's possibly not wise. But it's worked out well so far. I've always easily become fascinated by problems and have become completely obsessive over some of them, generally finding a way to continue working on them by hook or by crook, sometimes very well-funded with plenty of resources, and at other times, barely scraping by. It's been a bit like that all the way along. Over time, though, it's grown, and the revenue has come back from solutions to earlier problems that have enabled us to snowball the operation if you like. But there's never really been a long-term goal or plan. It's just been a continuous process of satisfying curiosity or rising to a challenge.

Have you had a career defining moment?

There are several significant moments and not all of them positive, some quite challenging. I recently did a TEDx talk, and whilst preparing it I had to think about this question to be able to tell a relatable story. The defining time that I always come back to is when a technology that I had co-created first went into the ground in the real world and visibly changed somebody's life. It was an emotionally very powerful experience, on a farm in Western Kenya in 2018; so not that long ago in the grand scheme of things. We put our first DAHR prototype into the ground. The farmer who was hosting the trial just fell to his knees. He told us about how he had been lifting heavy buckets of water every day since he was a child. It was then that we felt that we could actually impact people's lives in a tangible way. It was right in my face for the first time, as opposed to a hypothetical point to aim for. There was a sudden transition in my perspective; a feeling of a long-held yearning for purpose - suddenly becoming fulfilled.

Tom re-wiring PV modules prior to setting up a trial delivering water to a vegetable garden beside a mosque in Hemayetpur, nr. Dhaka, Bangladesh, February 2018, with colleague Cai Williams and technical team members from IDE (International Development Enterprises), Bangladesh.

Please can you tell us more about Thermofluidics and its subsidiaries Impact Pumps and Blue Tap?

The structure of the group is evolving as we speak. Thermofluidics initially focused on a thermofluidic oscillator class known as “Non-Inertive Feedback Thermofluidic Engines” or NIFTEs – which we developed to commercialise as a thermally powered water pump with entirely liquid moving parts. But “Thermofluidics” has become something of a misnomer. Following the precipitous decline in the price of photovoltaics, thermofluidic oscillators are no longer competitive in solar-powered applications, despite the numerous advantages offered by their lack of moving parts. This drove us away from solar thermal as an energy source, forcing us to abandon NIFTE and “re-skill” in power electronics. We never got NIFTE to market and are sadly no longer pursuing it actively, though it's a great bit of technology waiting for an application, and we got it working very well.

Thermofluidics just wasn't the right brand to be taking novel water pumps to market in Sub-Saharan Africa. So, we created Impact Pumps in 2019 and spun it out as a subsidiary in 2020. That was mainly for branding and marketing reasons. But it was also so we could raise separate investment into different projects.

Photovoltaic-electric surface pumps are generally still cheaper, more efficient and more reliable than their submersible counterparts, which must be located at the bottom of a well under the waterline. Nonetheless, they can’t draw water from beyond suction depth on their own (theoretically 10m at sea level, but in practice about 7m with cavitations and air ingression issues). The DAHR (or SLX) is now widely used to extend the reach of PV-powered surface pumps beyond suction depth.

Hydraulic ram pumps have the peculiar characteristic that they de-couple their pumped load from their hydraulic power source. A consequence of this is that they can enable a centrifugal surface pump to operate close to its “Best Efficiency Point (BEP)” for a broad range of varying power inputs and water levels. This makes the centrifugal–SLX combination very well suited to solar-powered groundwater pumping applications, in which power availability and water levels both vary considerably with time. Their lack of sliding seals or submerged motors allows DAHR pumps to run completely dry - and even pump air - without allowing it into the surface drive pump. They are also largely impervious to silt and suspended solids, whereas conventional submersibles are generally intolerant of turbid or corrosive environments, and seize after only a few seconds of dry running.

At the beginning of 2023, Impact Pumps introduced a range of solar surface centrifugal pumps called SolarPlex, with miniaturised power electronics integrated into the motor heat-sink, improving efficiency and reducing costs.

In May 2023, we installed 20 community drinking water access sites with the SolarPlex/SLX combination at their core with French partner UDUMA in southern Mali; to address the domestic water needs of approximately 10,000 people. So far, this has been a great success, with no service events recorded at all at the time of writing, more than a year on. This is statistically significant. Until recently, our claims were more anecdotal: we had evidence, but not statistically significant evidence.

Tom with colleague Tom Law (former CUED research student of Ann Dowling on the Silent Aircraft Initiative); monitoring an early DCC PV-solar electro-chlorinator prototype in a cattle watering borehole in a rainy field in Devon. The aim was to test the ability of the equipment to treat water at the limit of its capabilities – low sunlight and soft water. October 2022.

During COVID, the situation in rural water supply was diabolical in East Africa. Several NGOs pulled-out or suspended operations, whilst governments were cutting their aid budgets to focus on domestic priorities. We were working with our partner FundiFix to set up field trials in Kitui County, in Kenya, struggling to get Impact Pumps’ equipment out through the Nairobi curfews. Eventually the trials went ahead. They were eye-opening in many ways. One of these was the high chloride levels (salinity or hardness) that we found to be present in most drinking water wells. We hypothesised that it might be possible to chlorinate the water at these sites using photovoltaics alone, by electrolysing it directly as it comes up out of the ground. This would eliminate the need to source and transport costly and short-lived chemical feedstocks in such cases. If it worked, this method could extend remote off-grid water chlorination (the only method to kill viruses and provide residual protection against post-source contamination), to a much greater number of people.

With a few months of work and an excellent chemical engineering intern (Sophia Motteu from Imperial College), we were able to prove the concept in the lab. We successfully raised a grant to re-purpose one of our solar pump motor controllers as a current regulator and integrated it with a salt-swimming pool chlorinator and a photovoltaic array to treat water directly to WHO standards as it’s raised from the ground.

At its heart this ended up being a control problem, to achieve a fine balance between water safety and taste, with varying power and water flow rates requiring novel algorithms to overcome the limitations of affordable electrical current and water chemistry sensors.

By last year, we had prototypes deployed above a Victorian well near Oxford and a water borehole at a livestock farm in Devon – at the extreme opposite ends of the hardness range. These worked sufficiently reliably for us to make the first tentative steps towards water treatment for human consumption.

Earlier this year we signed an agreement with Blue Tap another Cambridge spin-out, founded by Department of Engineering alumna Francesca O’Hanlon, Tom Stakes and Rebecca Donaldson in 2017. Now a subsidiary of Thermofluidics, Blue Tap is taking this project forward. The first unit has recently been installed at a community water site managed by FundiFix.

As we bring more technologies to market (and we're getting better and quicker at doing that), we expect to grow our portfolio of subsidiaries further. We form partnerships with NGOs, charities, governments and other companies, but there’s a general trend in water service provision, towards private sector service models; small enterprises that deploy technology and charge communities or individual users a small fee to provide a maintained water service. Most of our partners fit into this category. Until recently, price wars have led to a flood of low-quality solar equipment on the market, as users prioritise up-front costs over product lifetime. Despite the manufacturing cost reductions we’ve been able to achieve through innovation, it has been difficult to respond to this without compromising quality.

Tom installing a hydraulic ram pump in a gorge in the high Ardèche, South Eastern France, August 2022.

Nonetheless, the total cost of ownership of a solar pump spread across its lifetime tends to be significantly lower for high-quality products than cheap ones – and much lower than for fuel-powered alternatives. This is driving a surge in “Pay-As-You-Go” models, which can “unlock” microfinance for small farmers and water utilities by linking the cost of capital equipment to service delivery (e.g. improved harvests, or volume of water delivered). This takes much of the financial risk associated with purchasing equipment off the borrower, thereby significantly increasing technology adoption rates.

Pay-As-You-Go is usually associated with remotely “switching off” a product in the event of non-payment for its delivered service. It has been shown that provided the technology is difficult to hack, the risk and administrative cost of microfinance lending can thus be dramatically reduced, reflected in substantially lower loan interest rates for Pay-As-You-Go enabled technology. However, switching off products that underpin people’s livelihoods is extremely contentious, opening up an ethical conundrum that is coming to define the field; even in situations where lack of funding from government agencies makes it the only viable way to fund service improvements at scale.

Pay-As-You-Go was pioneered with solar lighting by companies including MKOPA, Bbox and others that are now quite well known. Many of them were UK university spinouts, and are now substantial and well-known companies. We’ve recently integrated the SolarPlex with remote monitoring and Pay-As-You-Go capabilities using PGP encryption – and because the power electronics is integrated into the pump motor, this is very difficult to hack – which is essential to ensuring its success.

We do work with charities, but most of the organisations we've worked with are registered as companies associated with charities. When we work with charities it tends to be because impact funders and philanthropic donors receive tax incentives to work through them, so they end up playing a role. Some of the companies we work with have a foundation arm. It's very complicated and quite hard to explain exactly how it works. But I would say mostly, we're working with SMEs in the field in Africa.

In water supply for drinking and sanitation, there's still a big charity legacy, but it's moving towards the small private sector. That's also very complicated. It has pros and cons associated with it. Charity involvement in water is fine while it lasts. But charities are not a long term solution. They are dependent on the whims of philanthropists or donors to keep going. There's a long history of failure in charitable water projects with charities installing equipment and pulling out, leaving a legacy of rusting equipment that no longer works. On the other hand, the private sector tends to favour users with the greatest ability to pay. People on the lowest rung of the economic ladder are the last to be served, and often get left behind entirely.

In the absence of governments’ involvement in the water problem, dependence on water charities continues, and with it, reliance on funding which may or may not be there tomorrow. Alternatively, some sort of simple private sector model where people typically pay a small fee, two or three cents per 20L bucket for water, is increasingly common in sub-Saharan Africa. That money is used to maintain a water service. At the moment, it doesn't break even, so the companies, the small SMEs, doing this are generally still supported by water foundations and philanthropists, albeit to greater effect than before.

What we're trying to do is reduce the costs of providing a water service to an extent that doing so no longer depends on handouts. We’ve done that now at a few 10s of sites. However, if we can demonstrate this over a longer time period and on a large enough scale, it could tip the balance of feasibility for government agencies and development banks, enabling us to reach many more people.

Tom and colleague Cai Williams on the roof of Davis and Shirtliff’s headquarters in Nairobi, setting up a demonstration lifting water up a 5-storey fire escape with a variety of surface pumps in their catalogue. Cai now lives in Kenya and leads their East Africa operations. Davis and Shirtliff are Impact Pumps’ main distributor in East Africa. January 2019.

Do you have a market here in the UK?

We're trying to develop a market here. We've done a lot of fieldwork in the UK, because you can simulate many of the physical conditions encountered in the tropics but it’s much easier to mitigate problems that arise. We've got brick-lined Victorian wells in back gardens, we've got equipment in boreholes on farms, that sort of thing. You can't simulate the socio-political context or the climate though. Ironically, we’ve had a lot of problems here (e.g. with ice), that we don't get in Africa!

But you can get a very good alias for water chemistry that you might encounter in some parts of Africa. You get cattle wandering over your equipment and other real-world problems you can simulate. We've never really wanted to be wedded to one region of the world or one problem. The idea was that we would develop technology and deploy it in different markets all over the world.

That's more challenging than I originally imagined. Our technology is designed very much for an African context – and that ended up being more different to a European or American context than I originally anticipated. Particularly regulation, but also installation.

For example, a common design requirement for the UK installer base is “one person installation”, because the cost of labour is high – one installer, one van, lots of tools. In most African markets, one person installation” becomes “one tool installation”, because most plumbers in Africa will have only one or two tools, that they will probably have made themselves. So we try to design everything to be serviceable with one tool, or with homemade tools that are ground out of scrap metal. They'll do almost everything with those tools. You can’t assume there will be electrical power – for example to heat up and join pipes. But you can assume that every plumber is comfortable making a small fire from dry leaves to soften and form plastic with their homemade multitool; or cut a serviceable pipe thread with a broken hacksaw blade. You have to design for that context, and that requires a different mindset from the way we do things in the UK. But on the upside, it doesn't matter so much if you need three or four people to lower the thing into the ground; there are always lots of curious onlookers willing to lend a hand.

Recent regulation is forcing British livestock farmers to prevent their animals from entering water courses, and that’s opening up new opportunities for us here. Nonetheless, when trying to put a product developed for Africa into a Western market, you have to modify it, rewrite instruction manuals, or whatever it may be to make that transition. We're undergoing that process at the moment.

How do you decide what the next project will be?

People are starting to come to us with problems to solve. I guess the off-grid water world is pretty small once you get to know it. There are well known SMEs and NGOs associated with each region. They hear about us and we hear about them and so projects come to the door. But we still have to go out and actively promote our technology.

It’s not just water problems that come to our door either. We'll happily put our heads to solving any problem that looks interesting: we’re not wedded to a single challenge, discipline or philosophy. We were funded very well by the Wellcome Trust for a number of years to develop our first products because of the positive impacts they could have on human health. It was initially about irrigation and nutrition in Sub-Saharan Africa. We later moved into water supply for drinking and sanitation. That set the context, and we've emerged from that experience with a set of very robust, highly efficient and cost reduced technologies that have many applications in less challenging environments.

Although the market for lifting water out of wells and boreholes with solar energy is small in higher income countries like the UK, there is a growing interest in using some of our technology in heat pumps.  Many of the solutions that we have developed to problems that limit solar pump adoption in Africa - could also lower barriers to heat pump uptake in higher income countries. In many ways, the future of heat pumps is already familiar territory for solar water pump manufacturers.

Solar pumps often have to cope with turbid or silty water, highly corrosive (e.g. salty) environments and dry-running – when the water level drops below the pump inlet level. Open-loop heat pumps are held back by these issues, but so far this is a relatively niche market.

Solar pumps also have to be “supply responsive” with a highly variable power source (sunlight) – or hybrid solar/mains power. Furthermore, they have to be “demand responsive”, to buffer often extreme water-level variations and sunlight levels with variable end-user demand. There’s often a need for energy storage (raised tanks or batteries) and increasingly, solar pumps are expected to be able to export power – e.g. to batteries or micro-grids – when not in use. Similarly, as renewables and heat pumps have a greater and greater impact on power grids, heat pumps will need to be able to manage power inputs from multiple sources behind an electricity meter – such as rooftop PV, and batteries – possibly including electric vehicle batteries.

For both solar water pumps and heat pump compressors, this requires highly efficient variable speed motors that can simultaneously handle power inputs from multiple different sources. Furthermore, both applications require power to be conditioned and exported when it’s not needed. Achieving this all boils down to highly complex integration, inversion and control - in as few steps as possible, to minimise energy losses and production costs.

Increasingly, solar pumps are remotely monitored and controlled over the mobile phone/GSM network to enable “Pay-As-You-Go” or pump “As a Service” models. Similarly, there is growing interest in allowing a degree of centralised monitoring and control of heat pumps to provide dynamic demand/load shifting services to power network operators.

Thus, many of the challenges posed by an increase of intermittent renewable generation on the grid are the same challenges that solar-powered technologies have already met off-grid. A lot of the power electronics, control systems and networking capability we have developed for solar pumps is readily transferable to heat pumps – so perhaps Thermofluidics’ will come full-cycle and start working on thermal technologies again. We also see integration of off-grid productive assets like solar pumps with water and electricity grids very much as the future of our industry. In time, water and energy grids in Africa and the UK will look more and more similar, the first developed from the bottom up, the second from the top down.

Tom and Tom Law (former CUED research  student of Ann Dowling in the foreground), with friend and colleague Christoph Giger from Ennos, Switzerland. Setting up a pump test in a Victorian brick-lined test well in Beckley, Oxfordshire, June 2018.

How many people work alongside you on the technical side?

It's changed over time. I originally founded Thermofluidics with Christos Markides, a colleague from the Department's Hopkinson Lab. At the time I actually lived in Hopkinson’s house as well. A book titled "The House of Alice Roughton: Cambridge Doctor, Humanist, Patron and Activist"has been published about that house. It was an extraordinary place where Nobel prize winners sat around the same table as students, homeless people and refugees and I often think back to it. Alice was John Hopkinson's granddaughter and Bertram Hopkinson's daughter. John Hopkinson was a 19^th century philanthropist in the truest sense and his legacy continued right throughout the 20^th and into the 21^st century.

Then the 2008 crash came, we lost our first big contract with Honeywell. Times were tough. Christos took up a lectureship in Chemical Engineering at Imperial College, my old haunt, where he now runs the Clean Energy Processes lab. I followed my wife Suzanne Aigrain – then a post doc at Institute of Astronomy – down to Exeter, where she was appointed as a lecturer in Astrophysics. Tim Naylor, then head of Physics there helped me out, gave me an honorary position and an old photographic dark room to work in. But I struggled to raise funding or make significant advances with the technology.  Then in 2009, the Sunday Times ran a follow up article from the prizes I had won in 2004/05.

The original prize had generated all kinds of curiosity. Off the back of the follow up article, our current CEO came in as an Angel investor, bringing much needed commercial experience with him. At the same time my wife was offered a lectureship in Oxford, so we moved up here in 2010. My PhD external examiner is an academic in the Department of Engineering Science here. He and his group essentially took me in, gave me some lab space and were extremely helpful in helping us find our feet.

Thereafter, things moved quickly. We were awarded a small grant by the California Energy Commission, to investigate what would become the DAHR and later SLX.

Chez Hall and Rob Miller answered an appeal I put out for promising engineers to join our team. Thus Tom Law, who had recently finished his PhD in aeroacoustics with Ann Dowling - joined us. It was just the two of us and a couple of project students for a while.

A lot of the practical work took place on a farm in Devon, on the land of our friend and contractor Bart Stockman; an extremely talented practical engineer who runs our main workshop facilities and trial sites there. One thing led to another. Next, we were awarded some funding by the Carbon Trust, which enabled us to develop our NIFTE thermofluidic oscillator to a stage that we could install it at a field site in Southern France. Off the back of that, we were able to make a strong case to the Wellcome Trust, that the combination of NIFTE and DAHR could have widespread impact on malnutrition, by lifting water for irrigation. We were simultaneously approached by Cai Williams, a young engineer working in a cotton ginnery in Malawi. We took a gamble and recruited him to manage our transition to the field. It paid off. Cai did much of the practical management of our early trials in Kenya and Bangladesh, led our SolarPlex development, and now manages both our Chinese production and East African operations.

We benefited from over five million pounds from Wellcome over a number of years, enabling us to grow a small but highly capable and well-balanced technical team of about ten staff across R&D and production, with subcontracted field teams of similar sizes in Kenya and Bangladesh. This enabled us to get our first product into manufacture and pilot distribution via Impact Pumps, without further investment.

More recently, we’ve been honoured to appoint Professor Richard Carter (ex. Cranfield/WaterAid and Senior Visiting Associate at the Centre for Sustainable Development in Cambridge), to our Advisory Board. Richard is an important advocate of our work and has opened several doors for us. Our advisory board is complemented by Prof. Dan Rogers, who runs the Power Electronics group in Oxford University Department of Engineering Science.

What contribution to your field are you most proud of and why?

That's a tricky one. I think the “holy grail” for us would be to reduce the cost of providing water services to a level that they can be self-sustaining at a benchmark level of around $1US per cubic meter of safe water delivered – without dependence on charity or government intervention to survive.

We have growing evidence that we can get there. We haven’t recorded a single service event at any of the 20 community water access sites we set up in Mali. That's an outcome dependent on several factors and the contributions of many people, rather than a single achievement of one individual. But the fact is, we have never had a product fail in the field. And that is something I am proud of.

What do you see as being the next big thing in your field?

There are several “next big things”, and some of them probably won't be things at all. The area that I'm most excited about and interested in is, very broadly speaking, how we can use the ground as a store. I’ve already alluded to synergies between solar water pumps and heat pumps. Well, those synergies extend to water storage and energy storage as well.

There's a common misconception that rainfall is decreasing and groundwater is highly stressed across all of sub-Saharan Africa. Neither of those perceptions are entirely true. There are regions of extreme groundwater stress in existing desert areas like the Kalahari, and around the Horn of Africa. Namibia has acute water stress issues. But generally speaking, groundwater resources are not hugely stressed in most of sub-Saharan Africa; the critical water issues that do exist are more to do with lack of water management, a lack of governance, and a lack of infrastructure. Nonetheless, groundwater pumping is beginning to have an impact, and as pump technology and people’s quality of life improves and water use increases, this is going to become more of a problem.

According to Richard Taylor at University College London and others, the perception that rainfall is decreasing in sub-Saharan Africa, is largely based on one-or two-year datasets. If you're only taking data for a year or two, the chances are that you might be in the middle of an El Niño cycle. There might be a dry few years. Even droughts. But if you look at 10- or 11-year data sets, you see huge rainfall events in between: Rainfall is becoming less frequent, and much more extreme.

This certainly correlates with our own experience. For example, at the farm I mentioned earlier, where the farmer was overcome with emotion at having easy access to water for the first time in his life. Only a year later, his farm was completely flooded. I was stumped I hadn't imagined that this could be an issue at the time. When I'd been there, it'd been very dry. But these sorts of events are increasingly common in all the areas we're working. We’re seeing flood events and hearing reports of flood events, particularly at the moment, with 2023 and 2024 being El Niño years.

There are many synergies between providing off-grid energy and water services at the same time. These include simple measures like combining power and water microgrids by co-laying pipes and cables, as well as more challenging opportunities such as combining groundwater recharge with pumped-hydro or thermal energy storage in rocks. Groundwater wells and boreholes can turn both floods and droughts from being disasters to opportunities. Similarly, they can act both as a heat source - and as a heat sink.

How are we going to help? This is the question. There's a field broadly known as Managed Aquifer Recharge (MAR), which is growing in significance along with the level of support its receiving. MAR is essentially about getting as much water as possible into the ground when it rains instead of letting it run off to the sea. The challenge is to be able to store runoff quickly enough, at scale, without polluting aquifers.

There are several technologies that fall under the MAR umbrella, perhaps the simplest is known as sand dams, which are very interesting and very effective, but they only really apply in a certain type of hydrogeological context in seasonal rivers, which you get in Kenya, Tanzania, but not so much in West Africa or Southern Africa.

There are other technologies that involve directly injecting water into the ground: essentially running water wells in reverse. The water supply for the Namibian capital Windhoek, was essentially saved by a direct injection technology that was introduced between 2013 and 2016. There would certainly have been a water supply crisis, and possibly a humanitarian catastrophe if direct injection technology hadn't been introduced there at that time.

MAR is a really interesting area, and I think it's going to become a big thing in the future; not just in tropical deserts, but in water stressed areas in the UK too. Nonetheless, when I talk about using the ground as a store, I'm also thinking about energy storage.

Deep groundwater boreholes can be used in small pumped hydro-electricity storage schemes in areas without lakes and mountains, but with deep, high-yielding aquifers instead. Such schemes could be combined with MAR in confined aquifers that are not used for drinking, or if water quality issues could be addressed.  

Storing low-grade heat at near ambient temperatures in boreholes is already becoming established. Ground source heat pumps can store large amounts of very low-grade heat in a fairly effective way. This is being pioneered by UK-based companies such as Kensa, who are connecting small heat pumps to networked boreholes. Storing summer heat can improve the efficiency of heat pumps to a threshold level, at which they become cheaper to run than gas boilers; but it can also transform air-cooling in summer from being a highly energy intensive activity, into one that actually saves energy (and money), by storing summer heat for winter use. This is most economically achieved on utility scales.  

I think we're going to see more and more seasonal thermal energy and water storage in the ground. Certainly, in the UK, it's already happening. We need to start thinking of the ground more as a store, rather than as a source or a sink; in the same way we already do for the atmosphere when we talk about net zero. I think this is a theme that is going to grow in importance and significance as we move forwards.

What is the best career decision you've made?

Adaptability is the key to survival. If you're trying to do something that doesn't have an obvious, lucrative market for relatively small amounts of development – and such opportunities are rare, then being able to adapt quickly is essential. And certainly, if you're beholden to the whims of investors or grant funders, you have to be able to reposition the same ideas in many different ways to survive. But also, the global context is changing so fast in renewables and in water. At the rate that you can develop one piece of technology, that context can change completely. So I guess the best career decision I have made is to remain adaptable.

What is your advice to someone considering a career in engineering?

I’d say, “try not to over-complicate the already complicated”. This is advice I’ve been given many times, including by some of the people I’ve mentioned above. And I’m very bad at following it. Getting better I hope; but it’s really important advice. You can waste an awful lot of time and effort by not boiling a problem down to its bones and getting distracted too much by the bits that don’t really matter.

But I’d also say, “don’t wait to start”! Many engineers are already taking things to pieces when they're children. Even if you're not, but you're fascinated by the notion of doing so, have a go! What’s the worse that can happen? I think you need to be a little bit reckless and not think too much about the context of what you’re doing - to get to a point where you realise that by tinkering and assembling and putting different ideas together from different fields, you can achieve something new or better than where you started. There's a combination of curiosity, lateral thought, hard work – and dare I say, a little bit of arrogance, that underpin it all really. You don't need to wait until you start studying at school or university. Just get going!