40% of US corn goes to biofuel (ethanol), contributing less than 4% of US fuel supply. With soybean oil it's even worse, 40% contributes 1%. Converting all farmland currently used for biofuel production globally to solar would produce 23x as much energy, enough to electrify the entire global (automotive) vehicle fleet.

I'm not familiar with how much feedstock is required to produce bioplastics, but it looks like plastics production globally is, I believe, around 500 million (metric) tons -- ie 500 billion kilograms, vs roughly 120 billion liters of biofuel. Napkin math at 1 kg/L (the density of ethanol is about 0.8 kg/l, so that's close), and that's about 4x more required, assuming no wastage by mass.

In other words, you're right to be skeptical; I don't think the math works.

Methanol and methane produced via DAC has been proposed as an alternative, but will only be feasible economically with extremely low energy costs. Possible with high solar penetration (see Australia), but far from a settled political question.

https://www.wri.org/insights/increased-biofuel-production-im...

https://ourworldindata.org/biofuel-land-solar-electric-vehic...

Then it's a way to subsidize agriculture?

If your heart too loves the sight of vast fields, (my clanker computed) converting all of it to solar meets 4–5× total U.S. electricity generation, agrivoltaics look nicer and can generate 3× U.S. electricity.

https://agrivoltaics.rutgers.edu/image-gallery-of-agrivoltai...

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