Vertical farming is expected to grow to $9.7 billion worldwide by 2026, but it faces challenges, including high energy costs, technological limitations and the ability to scale. Agriculture in a controlled environment has been around since the 1970s, but according to University of Arizona professor of biosystems engineering Gene A. Giacomelli, what made moving indoors possible was a drop in price in LED lights, which plunged as much as 94% in 2015 from 2008.