more: That way, "we would save 70 percent on the cost of fresh produce because right now 70 percent of the price is transport and storage costs," he said.

Fresh and healthy produce would thereby also become more readily available to those with slim budgets, he added.

No vertical greenhouse exists yet, but "several cities in Scandinavia and in China have expressed an interest," Hassle said.

Each installation would cost around 30 million dollars (21 million euros), much more than a regular greenhouse. But the investment would rapidly turn a profit, he insisted.