The Weird Science Behind Living Solar Panels

Algae. It’s gross green goo that collects in still water…and can possibly make our future greener, too. Researchers are finding weird and unique ways to turn living algae into solar panels and hydrogen farms. So how exactly can algae do all this? And will they end up on our plate of choices for renewables anytime soon? Let’s take a look at the weird science behind living solar panels.

As renewables continue to grow, more and more developments appear to sprout out of nowhere. Well, not exactly nowhere. This time it’s algae, and it’s coming from a pond near you. It’s been a while since we checked in on the scummy stuff, and new research is revealing some surprising ways we may one day be able to use it to our advantage.

Greener Solar PVs in More Ways Than One

Algae are pretty good at taking in sunlight and producing energy. That energy, as your middle school science teacher will remind you, comes in a chemical form, usually glucose — not the electricity we usually mean when we say “energy” on this channel. And yet, a team from Amrita Vishwa Vidyapeetham University in India (or Amrita University for short) has developed a way of using common algae from a pond in their neighborhood to generate electricity from the sun.¹

How does this actually work? Hold on tight, because to explain that we’re going to have to do some organic chemistry, a notoriously difficult discipline. Put as simply as I can, photosynthesis is a chemical process where plants turn water and carbon dioxide into chemical energy. You almost certainly remember this, but did you know electron manipulation plays a key role?

Part of the photosynthesis process involves atomically flaying electrons away from water molecules. This produces oxygen, which personally I am a big fan of.² But what happens to the electrons? Well, the photosynthesis process helps transfer them along a photosynthetic electron chain and produces nicotinamide adenine dinucleotide phosphate (or, mercifully, NADPH).³ This chemical is critical to managing anabolic reactions, and these reactions keep living things alive (again, big fan).⁴

Some electrons don’t make it to the NADPH stage, and instead exit the cell in a phenomenon called exoelectrogenesis.³⁵ Now, we have free floating charge carriers with nothing to do and nowhere to go. If you’re aware of the mechanics behind a solar panel, the light bulb above your head might be turning on right now. Just like an ordinary inorganic solar panel, if we apply some electrodes to this setup we can collect those charged particles and turn them into usable electricity. And that’s what the Amrita team did. They sandwiched their local algae between activated carbon-coated copper foil and a titanium dioxide-coated (TiO2), fluorine-doped tin oxide electrode.

This isn’t the first bio photovoltaic device (BPV), though it might be the first one where living macroalgae are generating electricity.¹ While the field is still VERY new, Amrita’s version does seem to be the best performing one so far.

The previous high-scoring algae, Chlorella vulgaris came from a 2018 experiment. It had a photocurrent density of 0.0654 milliampere per square centimeter (mA/cm2) and an open circuit voltage of 0.127V.³⁶ Amrita U’s Pithophora roettleri achieved a photocurrent density of 1.25 mA/cm2 and open circuit voltage of about 0.58V.¹³ In both cases this is a huge step forward, but how does it compare with inorganic solar tech? Well, current-gen commercial cells have an open circuit voltage of around 0.5-0.6V, so the algae is really pulling its weight here.⁷ On the other hand, modern PVs boast a photocurrent density of around 20 to 40 mA/cm2. So, the algae still has a long way to go.⁸

I should also note the C. vulgaris device and the P. roettleri devices had different set ups, and were composed of different materials, so this isn’t an apples to apples comparison. It’s not like the species of algae was the sole source of the improved voltage and density.³ They didn’t just pluck the algal version of Pikachu from a pond or something. Though the fact that the Amrita researchers just fished some algae out of the nearest pond instead of seeking out or cultivating the best species for the job and still got amazing results is actually one of my favorite parts about this study. If any old clump of algae can do this, there’s most likely room for optimization and advancement.

Remaining Challenges and Possible Applications

As cool as the tech is, the green goo doesn’t have the green light just yet. Heck, it’s not even really lab-viable at the moment. It’s just one set of experiments, after all, so I’m looking forward to seeing other researchers replicate and improve on it. Even so, there are already some hurdles that will need to be cleared. The efficiency is of course low, and at least for now, algae’s lifespan can’t compare to the 20 years sported by an average commercial solar panel. This is one of those “cross that bridge when we get there” kind of issues, but scalability is also going to be an issue. Each cell is going to need its own attention and upkeep if the algae is to survive for a meaningful amount of time.

As one of the researchers and authors of the paper explained to pv magazine, the scalability and efficiency hurdles are made all the harder by the necessity of a liquid reservoir in these cells. Gotta have a place for the algae to chill and photosynthesize without the water parameters or temperature getting out of hand. As that researcher put it, this is something that “needs to be overcome before it can be widely adopted as a viable energy source.”¹

Even considering these potential issues, what if we can work out these kinks? It opens the door to some truly green and very sustainable solar panels. If we allow ourselves a really optimistic outlook for a moment, then larger scale solar panels using algae instead of precious metals would mean less destructive mining to get those materials. For now though, this remains just a potential/theoretical application.

Farming Hydrogen

Of course, solar power isn’t the only kind of green energy, and there’s more than one way to skin an… alga? I’ve never had to refer to algae in the singular tense before, it feels weird. Anyway, researchers from the University of Córdoba in Spain are working on another neat use for algae: farming hydrogen.

We’ve explored hydrogen many times before too, and for good reason. It can be a zero-emissions fuel, depending on how it’s produced. When used in a fuel cell the only waste product it leaves behind is water. Its scalability is one of the reasons many people are excited about pairing hydrogen with intermittent renewables for energy storage.⁹ Plus, hydrogen is everywhere. It puts the “H” in “H20.” It makes up most of the mass of all the billions of stars in the universe … and it’s present in all living things.¹⁰¹¹

Unfortunately, it’s difficult or energy-intensive to remove hydrogen from its hidey-holes. Even though it’s quite literally the most common element in the universe, it’s actually pretty hard to collect, and energy intensive to separate from other substances.¹² Also, hydrogen atoms are quite small, even for atoms, adding an additional challenge to collecting and storing them.¹¹ Plus, if you’ve ever seen a balloon, you know that hydrogen literally wants to get up and out of here at the earliest opportunity.

This is where you’re probably saying “Sure, Matt, I remember a couple paragraphs ago, there’s probably some weirdo species of algae that makes hydrogen” and you’re partly correct. The real answer is so much stranger.

Mircoalgae, in this case Chlamydomonas reinhardtii, does produce H2, but not a lot of it … unless it’s stressed out (like me trying to pronounce all these algae names). How do we stress algae? Not with mortgage payments or car problems, but by depriving it of nutrients like sulfur or nitrogen. As you can imagine, freaking the algae out doesn’t lead to long lasting colonies. Earlier experiments maxed out at just 10 to 15 days.¹³ To make things even trickier, algae produce oxygen, just like other photosynthesizers. However, too much oxygen in the algae’s environment can deactivate the hydrogen production process.¹⁴

Algae isn’t the only way to “grow” hydrogen. Some species of bacteria can do it too. Better yet, bacteria can eat the oxygen that the algae produces, making sure it stays in a low-oxygen, and highly productive state.¹⁵ This has led some researchers to mix algal and bacterial cultures together. Usually this results in the bacteria taking over, which doesn’t work out well. That’s why when researchers at the University of Córdoba in Spain found they had accidentally contaminated a Chlamydomonas algae culture with bacteria, their hopes weren’t high.¹⁵ They let it ride though and found that the contaminated cultures were actually producing more hydrogen than the monocultures. The end result was up to 13.5 times more hydrogen! ¹³

Naturally, this warranted further study. In addition to the expected Bacillus cereus bacteria, they also found two brand new species: microbacterium forte sp. nov. and Stenotrophomonas goyi sp. Nov.¹³ As it turns out, the algae and bacteria were actually helping each other grow. How? This is another oversimplification of some organic chemistry, so bear with me. The forte bacteria were helping the algae produce more hydrogen, while the other two bacteria were providing the acetic acid the algae needs to grow. They were also eating the oxygen, so the algae could keep producing hydrogen. Meanwhile, the algae was providing all the bacteria with vitamins they all needed to grow. With all the parameters in balance and everyone working together the culture wasn’t just producing more hydrogen than its rivals, it was also longer lasting too, pumping out hydrogen for 25 days instead of two or three! ¹³

It was a good balance: the algae was stressed enough to produce a lot of hydrogen, but not so stressed it stopped growing. Theoretically using algae to clean wastewater and/or cultivate biomass.¹⁶ A win-win win-win-win!

Where is this going?

There are a lot of possible paths forward. Unlike some other hydrogen producing setups, this culture was productive under all light intensities they tried. That bodes well for those future real world applications where the light isn’t always going to be lab-perfect. The combo-culture also handled a wide variety of temperatures, from 73 F (23 C) to 86 F(30 C).¹⁴ Before you laugh, that’s pretty tough for algae!

Neda Fakhimi, a co-author of the research, points out that these features mean we can couple a biohydrogen farm with other applications. Wastewater is particularly interesting as the algae can feed on the gunk in wastewater and clean it up.¹⁵ Combining hydrogen farming with these other kinds of facilities can, theoretically, help us achieve industrial scale hydrogen production.¹³¹⁴ Plus, the biomass that grows in this kind of setup can also be recovered and used for fertilizer, fuel, biomaterials and bioremediation. Normally hydrogen-producing algae are too stressed to produce much biomass, so this is interesting for the circular economy.¹⁷

The paper also suggests that there are many possible ways to further refine this tech. “Mutant strains” of algae cultivated or engineered for hydrogen production and longevity is one way forward.¹³ There’s also room for further optimization when it comes to the lighting. The fact that this particular cocktail of algae and bacteria yielded such a huge boost in both hydrogen generation and longevity begs the question: are there other, better bacteria and algae out there? Could there be even more effective symbiotic combos waiting to be discovered? Only time (and more research) will tell.

While this is all very promising, I have to rain on the parade a bit. Much like the algae solar panels from earlier, bio-hydrogen tech is still very immature. Though the Córdoba team made a huge leap in hydrogen production, we’re still talking about tiny amounts of hydrogen. Even a few hundred milliliters is a huge haul here.¹³ Scaling it up might be the solution, but we’d have to improve a lot of other components before we can even talk about how and if this scales. For instance, collecting biohydrogen is still inefficient. These facilities will likely require a lot of real estate, which is expensive¹⁸¹⁹ While the Córdoba team’s co-consortium was super long lasting, we’re still measuring algal longevity in terms of days. There’s a lot more research to be done before we know if this will be viable. And we’re years and years away from even speculating on possible commercial prospects.¹⁴¹⁸

Where does that leave us? Well, I want to stress again that algae tech, whether solar panels or hydrogen farms, is still far away from becoming a reality. These first steps are very exciting, but the technology is not ready to deploy quite yet. As was mentioned earlier, there’s a lot of possible paths forward. Perhaps we can genetically engineer algae that’s a super photosynthesizer, makes a ton of hydrogen, is tougher or lasts longer. Perhaps there’s another bacteria that will boost our algae’s performance, just waiting to be accidentally discovered. Maybe the perfect strain of algae is, at this very moment, collecting in a pond near you. Even though the wait will likely be a long one, and the future is unclear, I’m definitely interested to see how algae-tech grows from here.