Tuesday, May 21, 2019

Artificial Photosynthetic Energy System Using CO2 As Fuel Sounds Promising - Maybe 50 Years Down The Line

There was no denying Janice's excitement after watching the third installment of the excellent HBO miniseries 'Chernobyl', recounting the horrific events when that town's nuclear reactor's core melted down.  Janice knows I am full throttle into nuclear energy as the only way to reduce fossil fuel consumption for an energy gluttonous society.  And she already knows how I criticized the practicality of the "Green New Deal", e.g.


 But, give Janice her due, as she quoted for me an article appearing in  the current issue of the Proceedings of the National Academy of Sciences, reporting the work of French researchers. Basically, their experiments show a practical (?) way to convert the greenhouse gas CO2 into two energy rich fuels: ethane and ethylene. The trick to accomplishing this entails matching a photto-voltaic solar cell to a mineral called perovskite, creating  a “photo-voltaic minimodule” 

When I asked about the efficiency in this experimental context, Janice noted it's now 2.3 %, and we can compare this to the 20 percent peculiar to consumer-grade photo-electric solar cells.  Now, if the latter can barely provide 3 EJ (exajoules) of energy at full use and in every place, sunny location they may be used, how will these new photovoltaic minimodules make the cut? Well, they can't.

A separate (Daily Kos) article about the finding assures us that these experimental systems are "not the end of the story".  Also:

"The system built by the French team uses only “inexpensive all–earth-abundant” materials. There are no rare elements, or items restricted to just one part of the globe. Perovskites are a class of minerals that are based around crystals of calcium and titanium oxide. They are not only found in many areas, including Russia, Europe, and the United States, and they can also be manufactured in the lab. The photo-cell used was one that doesn’t require rare elements or high end components. And the metal used for the anode and cathode of the microcells was plain old copper rather than the much more expensive alternatives used in some systems. All of that means that the microcells should be able to be built cheaply, and not depend on materials that are hard to obtain, no matter where they are being made."

Fair enough, so let's say all those current technical limits are eliminated and the efficiency can be ramped up to 10-11 percent or about 5 times what the French experiment disclosed. Then what?  A huge positive aspect, as noted in the same piece,  is that the solar energy storage problem is addressed. (I.e. turning sunlight into an energy form that is easily stored).  Thus, we learn that "While the full cycle may be carbon neutral, the storage part of the cycle is carbon negative.." 

In other words, we aren't adding to the carbon burden by storing the energy.  Because of this we're also informed: "It could potentially create fuels that could drive most vehicles already on the world’s roads."

Now the downside requires we look at the current energy consumption context of just the U.S. For reference, current yearly U.S. energy consumption is 94 EJ.. To put the numbers in a harsher perspective, any serious major effort to "decarbonize" the planet will require an amount of clean energy on the order of 100 trillion kilowatt-hours per year  or 360 EJ. To reach this target even within 3 decades the world's nations would need to add 3.3 trillion more kwh of clean energy every year. Solar and wind simply cannot scale up to that level in that time, so the only remaining form of energy - apart from fossil fuels - is nuclear and at least one climate scientist (James Hansen)  has recommended such incorporation . See e.g.

Ok then, even if a perfected photovoltaic system of this type were to come onstream by next year it is doubtful we'd be looking at a capacity of even 1.0  trillion kwh of clean energy per year just for the U.S.   But assume we can make that cut.  With an increased U.S. energy consumption to about 100 EJ by 2020, that means an integrated energy system would need to deliver 27.7 trillion kwh at peak.  Alas, the "clean energy" fraction - even with the photovoltaic find in place (and properly working!) would deliver barely 3.6 percent of the total. 

That still means we need nuclear energy, nuclear reactors to help make up the energy deficit - unless we stick with fossil fuels (Or radically cut the population by proportion to the energy or cut the energy consumption).  Climate scientist James Hansen was blunt  about clean energy limits even before this latest revelation:

"Look at the data. The developing nations of the world are never going to stop using oil and coal as long as they're the cheapest forms of power. Also, the hope of the environmentalists that wind and solar will solve everything is just happy talk."


"If we are to avert catastrophic climate change we have to build nuclear power plants on a massive scale and crank them out fast enough to stop all fossil fuel emissions by 2050."

In the meantime, quoting Janice's article:

"This system of “artificial photosynthesis” converts  CO2 to hydrocarbons at a rate that doesn’t seem astounding … except that it appears to be possible to make at low cost and large scale. They leave room for that efficiency to be greatly increased by looking at all stages of the process for ways in which catalysts and electrolyzers could be tweaked."

Which is why it's likely to be a powerful component in the clean energy mix - in maybe fifty years.

But our energy needs are not diminishing while we wait for the maturity of artificial photosynthesis conversion systems.  That's why we need to get underway with construction of those nuclear reactors - or face a very dire future indeed.  That will be facing the Hobson's choice of consuming ever more fossil fuels adding to the greenhouse warming or  clean energy sources that lack the punch' to drive our energy -intense civilization.

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