I file this one under – an interesting technology that will probably never have any significant application. I could be wrong, but see what you think. Researchers have created a “Self-Enclosed Bio-Photoelectrochemical Cell in Succulent Plants.” Essentially they made a plant into a solar cell that can generate a small amount of electricity, with the source of electrons being photosynthesis. From the press release:

The researchers created a living solar cell using the succulent Corpuscularia lehmannii, also called the “ice plant.” They inserted an iron anode and platinum cathode into one of the plant’s leaves and found that its voltage was 0.28V. When connected into a circuit, it produced up to 20 µA/cm2 of photocurrent density, when exposed to light and could continue producing current for over a day. Though these numbers are less than that of a traditional alkaline battery, they are representative of just a single leaf.

That is certainly a tiny amount of current, but the idea, obviously, is to wire in thousands of leaves, and have a field with thousands of plants. The potential advantage of this approach is that you can essentially grow your solar cell. Most of the work is done by the plant itself. This could potentially reduce manufacturing costs in both money and carbon. In addition the researchers were able to harvest a small amount of free hydrogen from the process. That is potentially more useful – if this could be optimized to produce green hydrogen, there are many possible advantages for a green economy.

But there are some significant down sides as well. First, the use of platinum cathodes is a non-starter. Whenever the word “platinum” appears in reporting about a new battery or solar technology, I know that is not going anywhere. NASA may be interested in use in satellites and probes, but they are not going to be mass produced for general use, and will not contribute significantly to changing our economy over to near-zero carbon.

There are also many practical issues. Wiring all those leaves cannot be an easy task. Also, they report that the setup worked for a day. Does that mean they stopped the experiment after a day or it stopped working after a day? Either way, we need to know what the longevity of the system is, and what effect this all has on the health and life of the plant.

In the end this is similar to attempts at developing an “artificial leaf” that will generate hydrogen from solar energy. What we have is a proof of concept – you can actually harvest electricity from plants. But that’s not the hard part. The hard part is developing a practical, cost and carbon effective, system that can scale. We also need to consider land and water use. Perhaps the best thing about current solar panels is that you can put them on the roofs of buildings. If every building in the US had solar panels the most recent estimate is that this would produce 40% of our current electricity use. Where are we going to put all these plants without using up precious arable land?

Let’s, however, consider the future. Is there any potential for this type of technology? I think ultimately it is unlikely, because the numbers simply don’t add up. But if there were to be any role for such technology I think it would have to involve genetically engineered plants. We know that plants can generate a lot of excess energy beyond their basic function – to produce fruit, for example. That energy could instead be diverted to direct electricity and hydrogen production. We would want plants that are fast growing, capture a lot of sunlight, can grow in areas that are not well suited for crops, and invest minimal energy in their own structure. Ideally they would be “pre-wired”, meaning that their leaf structure would be maximally amenable to hooking up to a system to harvest the electricity (no platinum needed).

I don’t know if such a plant is plausible, but I think that is what it would take. Perhaps in the far future, when we have the technology to essentially design organisms to our specifications, it will be more feasible. Future  societies may be able to just grow their power source and plug in.

Of course, we always have to think about what competing technologies will be available by that same timeframe. In a hundred years or so, when extreme genetic engineering is possible, what will regular solar panels be like? We may have cheap efficient organic solar panels we can just 3D print at will, and put on every surface. That seems more likely than an electricity tree.

I then like to consider – will there be any niche applications? Perhaps this tech will not be practical for large scale use, but there may be some applications where its advantages are greater than its disadvantages. It’s a good rule of thumb to consider that many competing technologies exist side-by-side in different uses and contexts. Perhaps when settling Mars it will be more weight-efficient to carry seeds than solar panels, or the machinery to build them. At least this may be a back-up technology if needed. Even some remote locations on Earth may find a use for such technology.

But I suspect, if a practical electricity-generating plant is created, it will be a novelty, used in the same way a potato clock is used, as a curiosity rather than a practical application. As an aesthetic it may be fun to have plants producing electricity rather than “hard” technology. But if I had to bet I would say this is not going to be any significant solution to our energy needs.