Biofuels: the US could switch to electric cars and solar power on just a fraction of the land
Biofuels have possibly made climate change worse, not better. There's a way to put this land to better use.
Putting food into cars is a poor use of land. And solar needs less land than many people expect. That’s the two conclusions I reach when I look at biofuel numbers in the US.
The US is the world’s second-largest cereal producer. But only a fraction of that goes into human mouths. 44% goes to animal feed. And 44% to biofuels.
Take a look at the chart below. It shows where the USA’s domestic corn goes. You can see the massive growth in biofuels over the last few decades. It makes up basically all of the country’s growth in cereal demand.1 In fact, without it, US domestic corn use would be lower than it was in 2000.
If this biofuel is replacing gasoline, then what’s the problem? Surely that’s a good thing for the environment?
The assumption is that biofuels have ‘net-zero’ emissions: the CO2 produced when they’re burned is offset by the CO2 sequestered when the crop is growing. A range of studies have challenged this, suggesting that the carbon sequestered by croplands is not enough to offset the emissions from growing the crops and land use changes.2 They estimate that biofuels have increased emissions, not decreased them. While these emissions are difficult to measure, the fact that there is even a credible debate as to whether they have made things worse or better suggests they’re not a great climate solution.
There is also a ‘carbon opportunity cost’ to using that land for farming. If we were to stop farming, natural vegetation could return and carbon would accumulate in the vegetation and soils.3 These ‘carbon costs’ are not considered in the USA’s emissions accounts. On the surface, we just see the displaced gasoline (and emissions reductions that result). It looks like a climate win.
When researchers take the full climate costs into account, cereal and vegetable oil biofuels tend to come out worse.
Putting cereals into cars is not only bad for climate change, it’s a terrible use of land.
With some simple back-of-the-envelope calculations (if you spot any errors, please let me know), we can see just how much potential this land has.
Using the USA’s biofuel land for solar PV could power the US three times over
The US uses a UK-sized amount of land to grow biofuels.4 In return, it accounts for around 10% of the country’s motor gasoline supply. It accounts for a lower share of total transport fuels (including jet fuels etc.).
Let’s put that land into context. Solar PV needs about 20 m2 to generate one MWh of electricity per year. If you were to use the 25 million hectares that is currently used for biofuels, for solar instead, you’d produce 12,500 TWh.5
In 2022, the US generated 4,300 TWh of electricity.
Putting solar panels on biofuel land would therefore power the US three times over.
Of course, I’m not advocating this as an actual strategy, for several reasons. The US would need huge amounts of storage if it were to rely on solar power alone. And solar should be prioritised on roofs, car parks etc. before being put on other land.
But it shows just how much potential this biofuel land has, and at least some of it could be used for renewable energy.
Its cars could go fully electric, powered by solar, on just a fraction of biofuel land
Rather than looking at electricity production as a whole, let’s focus on transport. After all, that’s what biofuels are used for.
What would happen to land use if, instead of growing biofuels, we used solar to power electric cars?
You can drive about 150 times as far from a solar-powered electric car compared to using corn bioethanol.6
You can see this in the chart below. From one hectare of land, you could travel over 3 million kilometres in an EV. You can travel just 22,000 kilometres on corn.
My back-of-the-envelope ratio of 150 is in line with other published estimates. These range from around 75 to 200 for corn – the ratio will be lower in regions with higher corn yields than the national average.7
Let’s scale this up to the entire US car fleet.
Every year, vehicles drive around 5 trillion kilometres in the US.8 How much land would it need to go fully electric and power it from solar?
If we get around 3.4 million kilometres per hectare, then we need around 1.5 million hectares to drive 5 trillion kilometres. If our EV efficiency is a little lower, it might be up to 2 million hectares.
That sounds like a lot, but remember that the US currently uses 25 million hectares to get just 10% of its road fuels from bioethanol.
These calculations also put the electricity demand of EVs in perspective. If the country’s cars all went electric, the US would need around 800 TWh of additional electricity. My calculations are similar to other quoted ones albeit on the lower end (they tend to be around 800 to 1100 TWh).
It currently generates 4,300 TWh – so this would increase its electricity demand by one-fifth.
There are a range of options which would improve the land use of fuels in the US
It doesn’t necessarily have to be a choice between using land for solar or growing crops. The prospects for agrivoltaics – where solar panels are placed on existing croplands and farming continues – are growing. It’s possible to do both at the same time.
So, the US could go for a combined approach.
Or, it could cover at least some of this biofuel land in solar and use the rest of the land for…well, nothing.
Humans don’t have to use the land because it’s there. It’s currently being used inefficiently to produce biofuels that we don’t need. We could just let it rewild: let natural grasslands and forests regrow. This would be good for wildlife, but would also be good for the climate.
I’ve sketched out some options for how this land could used (or not used) below.
While we fret over the amount of land needed for solar, we are often blind to how inefficiently we have used the world’s farmland.
Finally, let’s put electricity and transport aside completely. This land could be used for food, not fuel. The US might not need it, but other regions do.
The US allocated 144 million tonnes of corn to bioethanol each year. If this was a country, it’d be the world’s third-largest producer, behind the US and China. It’s about 1.5-times the production of the entire African continent. And equal to the output of Brazil and Argentina, combined.
In short, the US puts a lot of food into its cars.
The world’s croplands are still expanding. At a time when we should be using less land for farming, allocating high-quality farmland to grow food that we then put into cars is a mistake.
Note that some animal feed – called DDGS – is also produced as a by-product of ethanol production. Any replacement policy would have to take this – and the ‘feed’ deficit into account. However, it’s not the demand for animal feed that has driven the rise of bioethanol. It has been a mandated policy from the US’s ‘Renewable Fuel Standard’ to ensure that motor gasoline is blended with a certain percentage of biofuel.
DeCicco, J. M., Liu, D. Y., Heo, J., Krishnan, R., Kurthen, A., & Wang, L. (2016). Carbon balance effects of US biofuel production and use. Climatic Change, 138, 667-680.
Lark, T. J., Hendricks, N. P., Smith, A., Pates, N., Spawn-Lee, S. A., Bougie, M., ... & Gibbs, H. K. (2022). Environmental outcomes of the US renewable fuel standard. Proceedings of the National Academy of Sciences, 119(9), e2101084119.
Searchinger, T., Heimlich, R., Houghton, R. A., Dong, F., Elobeid, A., Fabiosa, J., ... & Yu, T. H. (2008). Use of US croplands for biofuels increases greenhouse gases through emissions from land-use change. Science, 319(5867), 1238-1240.
The US uses 60 million acres for biofuels (most of it for corn). That’s 25 million hectares. This is about the size of the United Kingdom.
Here's how we get to this number.
Solar uses around 20 m² per MWh.
This number is confirmed across a few sources. It's the figure from the UNECE's life-cycle assessment of electricity sources. So, actually, it considers the land use of the materials that go into the panel, and not just the land for the panel itself. However, the latter accounts for most of the land use.
The UK's Committee on Climate Change finds a similar figure.
20 m² is equal to 0.002 hectares.
Divide the 25 million hectares the US uses for biofuels by 0.002 and we get 12.5 billion MWh.
To convert to TWh we divide by one million. That's 12,500 TWh.
Let's run through the numbers.
Remember that solar PV needs around 0.002 hectares to generate one MWh of electricity.
That means it generates 500 MWh per hectare.
The Tesla Model 3 needs around 240 Wh per mile, which is 144 Wh per kilometre.
[500 / 144 * 1,000,000 = 3.5 million kilometres]
If you run the numbers on the Renault Zoe, which is a bit less efficient (270 Wh per mile), you get 2.9 million kilometres per hectare.
For corn bioethanol:
The US produces 16 billion gallons of biofuels (most of which is corn bioethanol).
That's 61 billion litres.
If it uses 25 million hectares of land, that's [61 billion / 25 million = 2,423 litres per hectare].
About 0.11 litres of biofuel is needed per kilometre driven.
That means you can drive 22,000 kilometres from one hectare [2,423 / 0.11 = 22,024 kilometres].
This comes from the US Bureau of Transportation Statistics: https://www.bts.gov/content/us-vehicle-kilometers-0