The Big Sweetch
Abundant, Clean, Osmotic Energy... Just Add Water (& Salt!)
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The conversation around alternative, clean energy sources centers on wind, solar & nuclear, each of which you've no doubt heard of. Today I want to add one more to your shortlist. Not only does it have the potential to transform our energy supply but it's been hidden in plain sight for millennia. Recent breakthroughs have put osmotic energy on the map.
Only have 5 minutes? Check out the quote & the link below
Want to dig deeper? Read the full piece for a refresher on osmosis and how some companies plan to harness its power for clean energy
Extra Credit: Make an Osmosis Jones themed meme about osmotic power and Tweet @ me! (Check mine out for inspiration at the bottom of this piece)
“Blue energy's promise stems from its scale: Rivers dump some 37,000 cubic kilometers of freshwater into the oceans every year. This intersection between fresh and saltwater creates the potential to generate lots of electricity—2.6 terawatts, according to one recent estimate, roughly the amount that can be generated by 2000 nuclear power plants.”
— “Rivers could generate thousands of nuclear power plants worth of energy, thanks to a new ‘blue' membrane” (Article via Science.org)
Keeping Up with the (Osmosis) Jones’
Quick show of hands: how many of you saw the 2001 animated classic Osmosis Jones? It follows the story of a white blood cell/policeman (the namesake character voiced by Chris Rock) and a cold pill as they race around the insides of Frank (played by Bill Murray) who ingests a deadly virus. What I recall from the action-comedy is Bill Murray puking on someone and the hilarious (at least they were at the time, I was 10) renderings of what it might be like to travel through someones sinuses, lungs, bloodstream and gastrointestinal system. Now, I should mention, neither this movie, nor it's contents, have anything to do with today's piece. However it was the only pop-cultural reference I could find for osmosis, which happens to be our central theme!
Gin & Hypertonic
To start, let's think back to simpler times, before disciplines like chemistry and biology emerged on your academic schedule. A time when you had one hour blocked off for what was simply called science class. If you're like me, you probably learned about the term osmosis during this formative period. Let's revisit the dictionary definition to get our bearings:
Osmosis is the movement of a solvent across a semipermeable membrane toward a higher concentration of solute. In biological systems, the solvent is typically water, but osmosis can occur in other liquids, supercritical liquids, and even gases.
Generally speaking, systems, like our bodies, are always seeking equilibrium. And as such, physical and chemical actions take place to achieve said equilibrium. Eat too much sugar, your body pumps insulin. Leave a pot of boiling water off the stove, it eventually cools down to room temperature. The same goes for the cells in your body whose membrane is semi-permeable (it allows only certain substances to flow through). If you dip your cells in water, for example, the solution (water) flows into your cells that have a relatively lower concentration of H2O; if you dip them in salt-water, the reverse happens: water flows out of your cell into the salt-water, striving to get to concentration equilibrium.
If reading this triggered a flashback to your middle school science class, then I've done my job. Stay with me, we're almost at recess. Images 1(a) and 1(b) above show what happens when there is an imbalance, or a gradient, between solutions. In this case, water flows toward the hypertonic (higher concentration i.e. salt water) from the hypotonic side until equal forces in both directions reach an isotonic or stead-state scenario. The osmotic gradient creates a pressure differential, that up until recently, couldn't be exploited in any efficient or cost-effective way.
Pass the Salt!
Like many great technological innovations, this idea was dreamed up decades before it could be implemented. As early as 1954 it was suggested that the boundary between rivers and seas held huge amounts of untapped power. It wasn't until the '70s that American-Israeli chemical engineer, Sidney Loeb, invented a method to capture its power through a reverse dialysis heat engine. Nevertheless, the proof of concept was never fully commercialized and the majority of Loeb's contributions were in the field of desalination (also important, imho!).
The pursuit of osmotic power (also referred to as salinity gradient power or blue energy) hasn't stopped. There have proven to be two techniques:
The reverse dialysis heat engine aka RED (proposed above by Dr. Loeb)
Pressure-Retarded Osmosis
If you want to venture beyond our middle school science lesson, go ahead and do your own research on the two methodologies. But the common ingredient, the crucial piece for optimizing efficiency here is: membranes. Semi-permeable membranes to be exact. Loeb, for instance, in the RED process pictured above used a stack of cation & anion exchange membranes. The PRO method leverages a polymide membrane. Membrane materials aside, the whole goal here is to use the membrane to create an electric current. If you remember… Energy is not created, but harnessed (potential to chemical or kinetic to electric). The PRO method takes advantage of the pressure differential between two reservoirs to spin a turbine, thereby generating electricity. Alternatively, if you can make the “holes” in the membrane small enough for just ions to pass through, you can create an electric current that can be captured, transported and stored. If you can crank up the efficiency, this appears to be the ideal solution. Easier said than done, however.
Making Waves
Norway's state-owned electricity company, Statkraft, opened a prototype facility for osmotic power in 2009. The proof of concept was able to produce 4kW of power, roughly enough to support a single family home. Eventually, the plan was to build a large-scale 2mW facility (about 500x the prototype). As with many optimistic scientific endeavors, this experiment ended on a disappointing note. One would think that in a place like Norway, land of fjords, that this was the perfect setting to turn this osmotic dream into a reality.
The problem? You guessed it: membrane efficiency…
The technology at the time required tons of square footage of membrane to achieve even a paltry level of power. Imagine football fields worth of membranes floating in the fjords to collect enough electricity to power a hillside cottage. Scientifically, a cool feat of innovation. Politically and pragmatically, a nightmare. The plant was shut down just three years after launching, much to the chagrin of my fellow blue energy enthusiasts.
But just like Osmosis Jones, there's a hero in this story. In this case it involves French physicists and nanotubes. Research conducted by teams at Institut Lumière Matière in Lyon (CNRS / Université Claude Bernard Lyon 1), in collaboration with the Institut Néel (CNRS) found a way to optimize the semi-permeable membranes using boron nitride nanotubes (very small holes in non-scientific terminology). The result: they could extract the same amount of power from a 1mˆ2 membrane using nanotubes as the entire Statkraft prototype plant. This laid the groundwork for a next generation of blue energy companies to build an economically viable solution.
The BIG Sweetch
Enough science, let's talk startups. Sweetch, the highlight of this essay, is a French tech company based in Brittany (Bretagne) that is working to commercialize the technological breakthroughs discovered by that very team. They've raised a total of €10.4M in venture and grant money from the likes of Horizon 2020, Future Positive Capital, Demeter Partners & GO Capital. When evaluating a startup, as a rule of thumb, you look at team, product and market size. So far, we've looked at the product (well, the science behind it) and the total addressable market (planet earth) so I'd like to focus briefly on the team.
If you check out their “Who We Are” page you'll find an impressive list of the founding leadership. But if you scroll down a bit further, you'll find another co-founder, Lydéric Bocquet. If you zoom in on his bio, you'll notice something familiar: CNRS researcher! Hold on — didn't that team invent the nanotube solution that made the entire enterprise feasible in the first place!? Yes. They did. And their co-founder & scientific advisor is one of them.
Like any good deep-tech company they've patented their particular brand of the technology: INOD. Although they are pre-industrial, they have rollout plans for 2024 and I, personally, look forward to seeing the results.
If you enjoyed this piece, I also covered Sweetch in my Tour de French Tech series on YouTube & TikTok. Check it out below:
As promised, here is my Osmosis Jones-themed salinity gradient energy meme (+ a bonus). Show me what you got on Twitter!
