Image credit Lufa Farms
Lufa Farms founder Mohamed Hage was complaining about how hard it was to get decent fresh food in Montreal in winter, that it is "handled, packaged, shipped, stored, refrigerated and reshipped perhaps dozens of times before it could appear on our dinner plates." Especially in a Montreal winter. Now, after four years of work, he has built a 31,000 square foot farm under glass on a rooftop and is supplying fresh food within 24 hours of harvesting.
I have been dismissive of vertical farms, but rooftop farms like this just might make sense.
One could make a case that growing under glass in winter is a problem. Greenhouses consume a lot of energy; that's why I have written in Stop Eating Fossil Fuels, Start Eating Food
The fact of the matter is, you can't separate a local diet from a seasonal diet. You shouldn't be buying hothouse lettuce and tomatoes, you should be eating them when they are in season.
But Hage makes an interesting case for burning natural gas to grow out-of-season vegetables, noting that being downtown on top of an existing building makes a big difference.
The simple answer:
We use a lot less natural gas than equivalent facilities operating in the winter. And we offset the gas we do use by not requiring our produce to be refrigerated and transported around the world to reach our consumer.
The not-so-simple answer.
First, the heating demands of a greenhouse occur almost exclusively during the night. Night time temperatures in cities tend to be much higher than in the country due to the thermal mass of city buildings and roads and the heating of city homes and offices.
Second, we employ energy "curtains". These semi-transparent curtains, deployed in cold evenings help plants retain their heat resulting in a significant reduction in the energy needed to heat the greenhouse.
Third, by selling directly to the city consumer and delivering to group drop-off points in the city, we drastically reduce the energy needed to conventionally package, ship, refrigerate and store produce that is distributed to your local grocery store.
Last, the combined respiration of the plants in the greenhouse - collectively an enormous evaporative surface - cools the air and helps to reduce the "heat island effect" created by the typical black tar roof. This contributes to lowering the cooling requirement for the building underneath the greenhouse.
They have plans for using biomass in the future; I would have thought that they might be able to tap into all that waste heat that is exhausted by office buildings all day, even in winter. There must be some way to capture it and store it for night time.
According to an article in the Canadian Press, the biggest selling point is improved taste.
"The primary reason it tastes better is because we're harvesting everything fresh, when it's ripe," says Lauren Rathmell, a McGill University biochemistry grad who oversees the cultivation of seeds on one side of the greenhouse. "We can pick something in the morning and it's on their plate by evening."
It is clear not too many people are willing to live a Canadian 19th century diet of seasonal food; they get tired of turnip. Perhaps building rooftop greenhouses is the next best thing.