Nice article; perhaps it would have been even more compelling if SI units were used.

Corn yield is about 1kg/m2; 1kg corn contains about 15MJ. This energy spread over one year (1 harvest per year) results in 15,000,000J / 365/24/60/60 s = 0.476W average power per square metre from the grain. Conversion to alcohol incurs certainly some losses. Overall, easy to beat with solar power.