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Great points

Some (very rough) numbers to give scale here:

Corn in the US covered ~90 million acres in 2024. Something like 40% of that gets turned into ethanol IIRC.

Based on solar capacity figures around ~200GW, the surface area of the PV panels themselves (not the installation) are about 250-300k acres.

Both solar and bio-ethanol render an energy output on the order of 250-350TWh/year. Broadly similar levels of energy, but using a tiny fraction of the land area and chemicals and industrial pollution for the former.

https://afdc.energy.gov/data/10339

I think this implementation and purpose is slightly different. The climate they are testing in is East Africa. One harvesting is the photovoltaics for energy. But the second harvesting is for food crops. The partial shade provided by the PV panels allows the plants to lose less water from evaporation and protect against overexposure to sun so that food crops like beans and corn can provide higher yield in a normally difficult climate zone. I agree harvesting the sun as PV + biofuels is a step down, but PV + food crops in a difficult climate zone is a step up.

Don't throw biofuels out, there are plenty of fuels you can make from the parts of plants that we do not eat. Corn stover, walnut shells, bigasse, olive pits, etc. are all unused components that can be converted into fuel sources through gasification, anaerobic digestion, fermentation, etc. into usable fuel. Many times it's better than letting these leftovers rot in the fields and release methane into the atmosphere.

Honestly, I'd like to see some of the excess solar energy put into up converting such waste streams into storable fuels that can be used as denser alternatives to batteries when needed (winter heating, air travel, etc.).

Also, biofuels have >10x the energy per unit of mass compared compared to even the best batteries in the lab (and some sources put that at closer to 100x). There are a lot of use cases for biofuels (as a replacement to petroleum) that batteries can't come close to handling.

Converting the waste stream from agrivoltaics into biofuels appears to be the best option: reduced land for "energy" crops, increased output for food crops, and biofuel to replace petroleum.

I feel like hydrogen is the answer to fossil fuels, not biofuels. Battery electric vehicles (BEV) are great for personal vehicles. But for heavy transport, batteries just don’t work. They are too heavy and can’t be “refueled” quickly for continuous operations. We are already having issues with having too much solar power and not enough demand. We could be load shedding that by using it to create hydrogen.

We have gas stations everywhere because individuals need that kind of convenience to operate comfortably. BEVs have the same infrastructure in that every outlet is a charging station. While the barrier to entry for hydrogen is too high for personal vehicles, the logistic hub nature of heavy transport would be much easier to convert, using hydrogen storage/filling stations at strategic location to support hydrogen powered semi-trucks, local delivery trucks, busses, etc.

The most effective way to store hydrogen as a fuel is in hydrocarbons. Hydrogen gas, as itself, seems at first blush, to be great because it combusts into water, but it doesn't store as efficiently or safely as hydrocarbons. The wax candles on your table don't spontaneously combust when you touch them with a static charged finger.

The fact that plants already will produce hydrocarbons for us without much over sight only makes things easier.

Now that being said, our current natural gas infrastructure can accommodate something like 10% hydrogen gas, so it would be great if we could store extra solar electricity within our own pipelines by generating hydrogen gas, back feeding it into the lines, and then deplete it later, with a molecular sieve to pull out hydrogen gas alone, or burn it with the methane.

And the best way to get from hydrogen to hydrocarbons might very well be processes that merge H2 (from electrolysis) with low value biofuels (usually hydrocarbons with a low amount of hydrogen I think?) into higher density synthetic fuels. That way you can use the waste parts of food plants, not so much for their (low) energy content but for their convenient access to carbon for "repackaging" H2.

Yes, like hydrolyzing vegetable oil, you can pack more hydrogen onto a carbon chain. You can also use the Fischer–Tropsch process to make longer chains out of smaller molecules like carbon monoxide and hydrogen.

I understand what you are saying but I disagree. Yes, hydrogen is not as energy dense and has different safety issues, but I think it is overall still the better long term option. Biofuel is not scalable in the same way as green hydrogen. The more biofuel we produce, the more agricultural land it competes for that could be used for food, timber or even carbon capture vegetation. The more solar and wind we add to the gird, the more load shedding issues we will have and the more opportunity we have to convert that to hydrogen.

ICE engines running on biofuel are about as efficient as they are going to get, whereas hydrogen power is a fairly immature technology and has a lot of potential efficiency gains as the technology matures.

I think biofuel from waste products will still be useful for certain applications, for instance in medium and long haul aviation, where the energy density of hydrogen would pose a significant challenge. But biofuels are just not scalable to the levels required for global demand vs land requirements. Using biofuels just for aviation would require cultivating land the size of Texas, California, and Florida. [0][1][2] It is just not feasible to scale as a primary fuel in a fossil fueless future. Hydrogen can scale with electrical capacity, which can come from nuclear, solar, wind, geothermal, hydro, etc.

[0] back of the napkin math/conversions based on 2 and 3

[1] https://its.ucdavis.edu/blog-post/making-policy-in-the-absen...

[2] https://www.theglobaleconomy.com/USA/jet_fuel_consumption/

I'm not talking about growing plants directly for the production of biofuels, that is a silly proposition when there are mountains of unused organic waste being produced annually by nature and by agriculture. Utilizing the organic "waste streams" that already exist to produce fuel is quite sufficient for our storage needs. Agricultural waste, poop, dead trees and branches, dry grass or other "wildfire fuels" to produce methane, hydrogen and oil through gasification , fermentation and anaerobic digestion is simply low hanging fruit that is available to us right now. I've worked in this field, doing gasification, so I'm quite aware of what is possible.

Would you rather we burn grass and dead standing wood in natural environments to curtail wildfires, or would you rather it was used to make clean energy that is carbon negative? Yes carbon negative. You put carbon back into the ground through the use of biochar, where it is stable for thousands of years, and actually improves the soil.

Anaerobic digestion of all of your household waste (including feces) is also possible for production of all of your stove and heating gas.

Internal combustion engines aren't at their end of technology cycle. You should probably look into supercritical CO2 closed loop turbines if you think that we aren't still innovating. Regardless, by using an internal combustion engines, or an external combustion engine (Stirling engine, or modern steam engine) instead of a furnace, one can produce heat and power all in one unit from within your house or district (depending on how you want to scale things).

I love solar, I really do, as well as batteries. But you need to use everything at your disposal if you want to get away from petroleum.

Converting waste to fuel is great.

Meanwhile, I’m pretty excited about this project to make it cheap and easy to convert solar power to liquid fuel. Starting with carbon-neutral natural gas.

https://youtu.be/cRg1ZVwttNU?si=JWK5ZUdlNWooNYtt

Correct arguments all around re: utility scale solar, but the incentives for an individual farmer to immediately adopt are huge: local generation makes power cheap, shading makes water use more efficient, etc. Obviously there is a capital cost for the system and costs for maintenance, etc., but given the trend of increasing global energy costs and the resulting burden on households (https://www.nature.com/articles/s41560-023-01209-8), it seems like a very nice idea.

The article's arguments don't revolve around landuse, and in fact the article doesn't discuss landuse at all.

In rural parts of Colorado, I have seen large signs on farm building protesting the use of agriculture land for solar.

The main advantage that I see in agrivoltaics is for the purpose of density. If you can get both power and food production in a more dense footprint, located closer to a population center, then that will be much more efficient for purposes of transportation. Both electricity transmission and food transportation get worse across larger distances.

Power transmission is really efficient, HVDC is around 3% per 1000km, AC is around 6%. It is more efficient to put solar panels in sunny areas and transmit across country than have less efficient local ones. Oregon where I live is bad for solar with lots of rain, it is better to put panels in California desert and bring up here.

Food is similar where transportation doesn't matter much. Staple foods can be shipped by train, barge, and ship which reduces the cost. Some places are better at growing food. The canonical example is that New Zealand is so much better in growing sheep that more efficient to ship lamb by air. Growing local only makes sense for vegetables that need to be fresh or don't transport well.

Who complains about the land use of solar?

Obviously not a bottleneck? There's millions of desert acres.