r/solar • u/[deleted] • Feb 01 '23

News / Blog An acre of solar PV generates 197X more propulsion-miles vs an acre of corn ethanol + internal combustion | Clean Wisconsin

https://www.cleanwisconsin.org/wp-content/uploads/2023/01/Corn-Ethanol-Vs.-Solar-Analysis-V3-9-compressed.pdf
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23

u/Cuttlefish88 Feb 01 '23 edited Feb 01 '23

“Looking at land-use efficiency, corn-derived ethanol used to power internal combustion engines requires about 85x (range: 63-197x) as much land to power the same number of transportation miles as solar PV powering electric vehicles.”

For fuck’s sake, when they give you an average and a range, don’t turn around and give only the maximum (outlier) end of that range!

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u/[deleted] Feb 02 '23 edited Feb 02 '23

If you follow the source of that data point, it explains that 197x was arrived at using less than maximum values. From the reference:

Recent research from the Lawrence Berkeley National Laboratory suggests that utility scale solar power in the United States generates between 394 and 447 MWh per acre per year. (For this document we’ll assume a more conservative 350 MWh/acre)*

So this is a fun exercise to me - finding the maximum efficiency difference between ethanol and electrons: Let's use that 447MWh/acre as an example. That's enough to send a Tesla Model Y 1.66 million miles (as opposed to the article's more conservative 1.3 million mile estimate).

So, one acre of corn = 7,110 lbs of corn = 328 gallons of ethanol.

The source argues that an ethanol vehicle would travel 6600 miles on 'an acre of ethanol' (328 gallons). But these numbers suggest that a model Y sized ethanol-powered vehicle gets an average of 20mpg. As I have recently owned a new vehicle that could run on E85, I can attest that 20mpg for an SUV on E85 is optimistic. In real mixed driving, an electric vehicle will have much more efficient city miles, while the ethanol vehicle's efficiency easily drops below 15mpg. For example, the Ford Explorer goes only 11 miles on a gallon of E85 in the city.

If we rerun these numbers using those more efficient modern panels making 447MWh/acre: 197x turns into 251x. Now let's account for the relative disadvantage of internal combustion in cities: 328 gallons of ethanol * 15mpg = 4920 miles per acre. Now we're at 337x.

Now it's time to take into account the 140 gallons of diesel it took to produce 328 gallons of ethanol.

There are 137,381 Btu in a gallon of diesel. There are 83,950 to 95,450 Btu in a gallon of ethanol. I'll use the maximum Btu/gallon of ethanol going forward to give the ethanol lobbyists the best chance.. 😂

Let's pretend that a modern ethanol combustion engine is operating at 40% efficiency. (Possible but not likely) Diesel engines really do hit 40% efficiency once they're warmed up. So, we can assume equal efficiencies and avoid the need to convert between combustion efficiencies of the fuels. This gives ethanol another little boost, and boy howdy, it's going to need it.

137,381 Btu * 140 gallons = 19,233,340 Btu

95,450 Btu * 328 gallons = 31,307,600 Btu

So it looks like we just traded ~19 million Btu of fossil fuels to create ~31 million Btu of ethanol. That net gain in liquid fuel is actually worth:

31,307,600 Btu - 19,233,340 Btu = 12,074,260 Btu

12,074,260 Btu / 95,450 = 126.5 gallons of ethanol per acre per year

Yikes. So a productive acre of solar panels can propel a mid-sized SUV 1.6 million miles, while a 'productive' acre of corn ethanol is netting only 126.5 gallons of ethanol (equivalent net btu) per acre per year.

126.5 gallons * 15mpg = 1897.5 miles per acre

1.6 million / 1897.5 = 843x more miles per acre

We're now at 843x

Variables that were ignored:

  1. Cost & logistics of drilling, transporting, and refining the diesel fuel used for farming.

  2. Cost & logistics of installing and maintaining solar panels

  3. Average & record panel efficiencies improving

  4. Region & orientation of solar panels strongly affects output

  5. Region, soil quality, irrigation/drainage strongly affect corn production

  6. Fuel values & costs: diesel ~$5.00, ethanol ~$3.25

  7. Two benefits of ethanol:

-A byproduct of ethanol is high quality animal feed

-Burned ethanol is still harmful to breathe, but most agree it is better than breathing leaded fumes

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u/qhp55 Feb 02 '23

Starting with the caveat that I wholeheartedly agree with your premise and think we need to generate a much larger % of our electricity via solar or other renewable means.

But corn and ethanol yield numbers from 2001 are nowhere near good estimates for 2022. Both farming and processing technology advance quicker than that. I think the original Clean Wisconsin link uses better numbers. The average corn yield in the US is now somewhere near 175 bushels/acre or 9,800 lbs of corn. Efficient (read: even remotely close to economically viable) ethanol plants are making between 2.8-3.0 gallons of EtOH per bushel of corn which bumps the numbers up to ~490-525 gallons/acre.

The article linked in your comment also states that it takes 131,000 btu/gal to convert corn into ethanol. The corn-to-ethanol process now takes around 25,000-30,000 btu/gal as plants become more and more efficient and heat integrated.

I know there are several USDA studies and articles that analyze life cycle emissions that are more recent.

IMHO and what I think most people overlook is that there are a lot of emission sources where it isn't a choice between either electricity or petroleum/ethanol. It makes complete sense to convert all light-duty vehicles to electric. But some things will never be electrified with current battery technology (commercial airplanes), or that will be difficult to electrify (heavy equipment, long-range trucking) The oil from corn and other crops can be converted into biodiesel or renewable diesel to offset standard petroleum diesel. The ethanol itself can be converted into sustainable aviation fuel (SAF). It seems like there are announcements every couple of weeks from companies pursuing SAF or Renewable Diesel as final products from their current ethanol production.

I believe the end goal needs to be a blend of a whole variety of energy sources. Electrifying what we can, and finding the optimum source of liquid fuel for what we can't. Or - innovation and alternative energy sources like nuclear.

We use hydrocarbons for a LOT. If there is something that can provide us hydrocarbons while somewhat scrubbing the air of CO2 (i.e. corn) instead of just bringing hydrocarbons to the surface of the planet, seems like a benefit to me.

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u/[deleted] Feb 02 '23 edited Feb 02 '23

You're right to point out the difference in crop yields between 2001 and today. I didn't notice my source was from 2001 until I had finished my math, and I didn't feel like starting over.

Let's use your 525 gallon/acre figure. Subtract 140 gallons of diesel for farming, so:

137,381 Btu * 140 gallons = 19,233,340 Btu (diesel input)

95,450 Btu * 525 gallons = 50,111,250 Btu (ethanol output)

50,111,250 - 19,233,340 = 30,877,910 Btu net energy gained, (equivalent to 323 gallons of ethanol)

323 * 15mpg = 4845 miles

1.6M EV miles per acre from solar vs 4845 mi on ethanol... solar is still 330x more efficient than ethanol

And even though we won't be electrifying aircraft too soon, the electrification of ocean-crossing container ships saves money vs burning even the cheapest, dirtiest bunker fuel.

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u/qhp55 Feb 02 '23

Yeah still pretty mind-blowing how much more efficient PV is.

Thanks for the link on the container ships! I hadn't heard that before - cool stuff.

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u/showMeTheSnow Feb 01 '23

Doesn't need any water or pesticides either.

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u/goathill Feb 02 '23

Very true, but if we get that granular we should take into account the manufacturing needs to produce/ship panels. I wholeheartedly think solar is better, but it's important to account for many factors and not just one single metric.

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u/showMeTheSnow Feb 02 '23

Fair, we are talking way different lifetimes here as well.

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u/samtrois Feb 02 '23

And works on my roof.

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u/todd_ted Feb 01 '23

Too bad the Wis GOP gerrymandered the districts and are against renewables, legal cannabis, public lands, etc.

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u/AviatorBJP Feb 02 '23

Math checks out. It might even be a little conservative. Solar panels are about 100x as efficient at collecting solar energy than corn (~20% vs ~0.2%) and EVs are more than double as efficient at using power than ICE vehicles (~80%+ vs ~30%).

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u/[deleted] Feb 02 '23

I did a little math showing that solar panels are 843x as efficient as corn ethanol per acre.

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u/AviatorBJP Feb 02 '23

Yeah, your math checks out too. (For bystanders who don't read his link, he considered things like the energy it took to cultivate and harvest the corn in the first place.)

That being said, making ethanol from corn is a fool's errand. If we need to be making liquid fuels from photosynthesis, algae biofuels would be much better than corn. Firstly, the algae is at least 10x better at capturing sunlight than corn (but still 10x worse than solar panels). Secondly, algae cultivation can be done with stationary equipment that is much easier to electrify than traditional farm equipment.

But for every transportation mode that can easily be electrified, solar PV + batteries is a clear winner every time.

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u/goneskiing_42 Feb 01 '23

So why not cover all the parking lots with solar? Using empty land when parking lots are an even larger waste of space, and that solar can help feed into electric vehicle charging seems like the way to go.

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u/Findit_Filmit Feb 01 '23

France just passed a law that all parking lots will have to have this done by 2028.

The solutions are there it is the will that isn't. I feel like if people could see the ecological disaster the future holds they would have a pep in their step.

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u/Cuttlefish88 Feb 01 '23

Because it costs literally twice as much if not more…

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u/[deleted] Feb 01 '23

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u/Cuttlefish88 Feb 01 '23

Obviously new construction should include solar, but calling it a blight is just rank NIMBYism that drives up energy costs.

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u/Roland_Bodel_the_2nd Feb 02 '23

Roofs is cheaper than lots because you don’t need to build the structure to hold the panels…

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u/bob_in_the_west Feb 02 '23

There are so many reasons from upfront costs, needing to clean what the rain used to clean, needing lighting below the solar roof or simply losing customers if there are problems with the structure.

Business owners likely know a lot more reasons.

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u/xmmdrive Feb 01 '23

I don't know much about corn farming, but are there other non-fuel advantages to growing it?

Does part of the corn used for ethanol also go to livestock feed or is that not really a thing?

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u/Findit_Filmit Feb 01 '23

Yes corn is used for other sources. But one of the bigger problems is corn out of any other crops needs to the most nitrogen inputs. And this causes much of that nitrogen to run off into streams etc and then you have massive algae blooms in the ocean causing eutrophication killing hundreds of thousands of marine life and devastating fishing economies. One of the big reasons why corn as fuel is just not worth it.

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u/[deleted] Feb 02 '23

Yes, and don't forget that the production of nitrogen fertilizer consumes fossil fuels.

Not that it needs to. Solar can fix that too.

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u/Findit_Filmit Feb 02 '23

PV magazine is the shit. Thanks for sharing.

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u/xmmdrive Feb 01 '23

Thanks for the answer. And I'm guessing there's better crops to use for feeding livestock once the incentive to produce ethanol is gone?

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u/StewieGriffin26 Feb 02 '23

Soybeans are also livestock feed for their protein, but they're not really a replacement for corn or silage.

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u/Findit_Filmit Feb 01 '23

A lot of cows usually eat a mixture of hay and the remnants of cotton plants. I'm sure it changes with goals in mind. But I'm one of those environmental loons who think that we should stop breeding cattle due to the vast agricultural land they need to just be fed on top of their water intensity and the burping out methane doesn't help either.

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u/cabb36 Feb 01 '23

Large grazing herbivores are vital to a healthy grassland and grassland is vital to a healthy aquifer. You may find this TED Talk educational.

https://youtu.be/vpTHi7O66pI

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u/Findit_Filmit Feb 02 '23

For sure that's why I really like the reintroduction of buffalo to areas. The entire west has been destroyed based on ranching practices meant for an animal that was never meant to be there. I know its a bit woo woo hippie but cows are just awful and if less than half the land was dedicated to solar projects. We could have the grasslands back with a fair amount of buffalo. Weve just spent so long working against the land I worry what that will mean for us in the end.

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u/cabb36 Feb 02 '23

Buffalo restoration would be great, but they are difficult animals to work with. Cattle are much easier and fill the ecological role. Dairy cattle operations could use some change, and many farmers are implementing methane recapture practices to reduce their impact.

Covering half of pastureland with solar panels would be unequivocally destructive. By blocking the sunlight from the ground the plants would die leaving bare dirt. When it rains that leads to massive runoff and flash flooding with minimal amounts soaking into the ground. This washes away soil nutrients as well as prevents aquifer recharging.

Solar projects are best left to areas that have already eliminated their agricultural or environmental use, like on buildings and over parking lots.

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u/Findit_Filmit Feb 02 '23

The way cattle grazes destroys the land the hay that is farmed for that cattle very often is just left barren and fallow and has lots of run-off issue, I wish there were more gov incentives for cover crops but it isn't many. This is why 5% of farms use cover crops.

They make a type of solar panels for agriculture but regular solar panels let enough light to allow for grasses to grow cause grasses don't need tons of light. But I do hear your point, parking lots and buildings first. Source: https://modernfarmer.com/2021/05/researchers-find-pasture-land-is-great-for-solar-panels/

I hear you on buffalo they aren't easily domesticated but it has been done there are even buffalo farms my friends uncle owns one up in Wisconsin.

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u/cabb36 Feb 02 '23

I really recommend watching the full video I linked to. It discusses proper grazing techniques to mimic predator-prey behavior that limits the overgrazing you’re talking about. Any herbivore kept on a small amount of land will inevitably eat everything down to bare ground. Which is why they need so much land to begin with…

I will look into these solar panels you linked to, but you’d be surprised just how much sunlight grass needs to be the dominant plant in an area. I saw something recently about “transparent” panels that may be promising though.

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u/Findit_Filmit Feb 02 '23

Theres transparent panels and there are others ones that are better and essentially are just more spaced out panels.

https://www.youtube.com/watch?v=lgZBlD-TCFE

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u/[deleted] Feb 01 '23

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u/StewieGriffin26 Feb 02 '23

Absolutely no way you're growing corn and have solar PV on the same field.

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u/DazzlingLeg Feb 02 '23

I mean, you’d yield 10x less corn and 99% less solar energy, but you could do it…

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u/[deleted] Feb 01 '23

not corn

But you can grow something someone might eat instead.

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u/[deleted] Feb 02 '23

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u/[deleted] Feb 02 '23

Go ahead. Tell me what happens, mr. sassy pants.

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u/[deleted] Feb 01 '23

[deleted]

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u/bascule Feb 01 '23

If you can capture it in real time.

If only there were some sort of technology that could convert solar radiation into electricity 🤔🤔🤔

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u/[deleted] Feb 01 '23

[deleted]

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u/bascule Feb 01 '23

If people charge during the day there's no second battery required.

It's needed if people charge at night, but the flipside is in a Ford Lightning-style configuration your EV can provide backup power to your home rather than having a separate dedicated battery for that.

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u/[deleted] Feb 01 '23

Hey, nice try.

The numbers in the title compare the average SUCCESSFUL crop of corn.

I’m a farmer, and I’m here to tell you that sometimes our fields deal with flood and drought. Go ahead and factor that in; don’t forget to account for climate change.

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u/Troutrageously Feb 02 '23

Oil and gas drilling has entered the chat.