Last week I told you about the tragedy of US “renewable fuels” policy and how at least in terms of climate impact, our modern corn ethanol industry was at best no better than gasoline, and more likely worse. This outcome was driven by the tragedy of carbon lost by plowing up grasslands to grow corn. This week, I want to pick up where I left off, and share with you a little math that I frankly found both surprising and relevant to why we’re here at Blue Nest Beef.
Before going into numbers, it’s probably helpful to understand a few concepts.
Plants only convert about 1-2% of the energy in sunlight into stored chemical energy. That’s in the whole plant, of which grains like corn are just the seeds. So when we convert corn into fuel, we end up with just a small fraction of the energy of the sun converted into the chemical energy in fuel. And because of how combustion engines work, only a fraction of that fuel energy gets converted into what we call “useful work.” In end, very little of the sun’s energy shows up as miles travelled when you go through corn first.
In contrast, a modern solar panel converts about 20% of incoming solar energy into electrons. And electric motors used in cars are about 90% efficient with few further losses in between. So an acre of solar panels will inevitably lead to much more energy that ends up as “useful work” than an acre of corn. That means more miles per acre, but how many more?
By my estimates, it turns out that the answer is roughly 60 times more! You read that right – not 2x, not 10x, not even 20x, but a whopping 60x more! Using the best estimates I could find, I calculated that an acre of corn planted for ethanol would allow an average gasoline-powered car to travel 7,704 miles. That sounded like a lot until I calculated that the same acre covered in solar panels could move an average electric vehicle of today 455,227 miles. That’s more than 18 laps around the entire planet.
Here’s the math:
Corn > Ethanol – 1.5 billion bushels of Iowa corn go into ethanol production. Iowa’s average corn yield is 178 bushels per acre. This implies 8,426,966 acres of Iowa land produce corn for ethanol. Corn yields 2.8 gallons of ethanol per bushel, thus we get 498.4 gallons of corn ethanol per acre. Each gallon of ethanol contains 76,000 BTU’s of energy, and with a few units conversions, we can calculate that the total yield of energy from ethanol is 2.74 kWh/m2/y, or a meager 0.17% of the total energy in sunshine that falls on Iowa in an average year (1607 kWh/m2).
But all of that energy does not make it to the wheels. Average passenger vehicle fuel economy is 25 MPG, but the energy density of ethanol (27 MJ/kg) is only 61.8% that of gasoline (46 MJ/kg), so the implied fuel economy of pure ethanol for an average car would be 15.5 MPG. Thus, a pure ethanol car could drive 7,704 miles on the ethanol produced from corn on one acre of Iowa farm land in one year (15.5 x 498.4).
Given all the land in Iowa currently growing corn for ethanol, that means Iowa farmers are fueling an impressive 64.9 billion miles of America’s transport needs.
Solar PV > Electric Car – Rather than using an ideal efficiency for solar panels, I derived from this report that the average of annual energy actually produced energy on US solar farms was 0.000103 GWh/ac/y per kWh/m2/y of solar insolation. This allows me to account for the non-panel equipment and empty space between panels in actual solar installations and all practical elements of uptime and power output. Then using an average insolation for Ames, IA of 1,607 kWh/m2/y, this means we would expect it to take 6.03 acres to produce 1 GWh of total energy during a full year, which is the equivalent of 165,798 kWh/ac. For an important apples-to-apples comparison with ethanol, that converts to 40.97 kWh/m2/y which means we capture 2.5% of the total insolation on a unit area of land in Iowa (~15x more than with ethanol).
But because of the high efficiency of electric motors, more of that energy makes it to the wheels. Currently, an average electric vehicle in the US has a fuel efficiency of 0.346 kWh/mile (2.75 miles per kWh). Accounting for 5% transportation grid losses, this means we need to produce 0.364 kWh of electricity at the source to produce 1 mile of travel on the road. This implies an average EV can travel 455,227 miles on the electrical energy produced on one acre of land in Iowa in one year (165,798 / 0.364).
That’s pretty impressive! It goes to show that when an electron, not food, is what you want, it’s a more efficient path to convert a drop of sunshine into motion through a solar panel than through a kernel of corn. What could that mean in practice?
Iowa covers 35.7 million acres, of which 30.6 million acres is pasture and crop land. The 8.4 million acres of land currently used to produce ethanol is 23.6% of Iowa’s total land area of 27.5% of all pasture and crop land. So let’s go back and see how much land area it would take to produce the same 64.9 billion miles driven as currently provided by Iowa’s corn ethanol system.
Because we can produce 455,227 EV miles per acre, we could produce enough energy to power all of those miles on only 142,614 acres (64,921,779,764 / 455,227). And if we don’t want to put up wall-to-wall solar panels, and we cut their density by 50%, we would still only need 285,228 acres to produce the same number of miles. That’s a meager 0.8% of Iowa’s total land area and 0.9% of Iowa’s pasture and crop land. And if we wanted to meet the entire electricity needs of the state, that would require only 610,861 acres or only 7% of that former ethanol land (at the same 50% coverage).
Let’s call this vision for a synthetic savanna in Iowa “SavannaLand.” It would be like a tallgrass prairie again, but with synthetic silicon “trees” scattered in pockets here and there, just not too many. The synthetic part of the footprint would power our synthetic economy needs, but it’s much, much smaller. So now we can live as part of the ecosystem instead of crushing it.
Notice that we have put up solar panels on only 3.4% of the former ethanol land, so now Iowa has 8.1 million more acres of land that can now grow more food for people. That’s almost twice the land I noted last week (4.4 million acres) that was converted from grassland to corn for ethanol. So now we can return at least that much land to its rightful state, drive the same miles, grow more food, and restore broken ecosystems all at the same time.
Using the range of carbon sequestration rates I mentioned last week of 0.4 to 4 tCO2/ac/y, that means just this 8.1 million acres of land formerly growing corn for ethanol, could sequester 3.2 to 32 million tons of CO2 per year and the farmers could be paid for that, too! This would be the equivalent of taking 0.7 to 7 million passenger cars off the road, offsetting the entire CO2 footprint of 0.4 to 4 million homes, or changing out 120 million to 1.2 billion incandescent light bulbs for LEDs in addition to the emissions benefits of the PV systems themselves.
And what else belongs on a savanna? You guessed it – grazing animals. “You may call me a dreamer,” but I don’t think it’s too much to ask to convert that 8.1 million acres back into tallgrass prairie using cattle as a tool to produce food while restoring grassland bird habitat and pumping carbon back into the Earth where it belongs.
In my opinion, this synthetic savanna model is something that would do some serious good for both people and planet not only in Iowa, but in many former grasslands around the world.
Blue Nest Beef Co-Founder & CEO
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