“Without artificial lighting the result will be an uneven crop, as plants closest to the windows are exposed to more sunlight and grow more quickly.”
WHEN you run
out of land in a crowded city, the solution is obvious: build upwards. This
simple trick makes it possible to pack huge numbers of homes and offices into a
limited space such as Hong Kong, Manhattan or the City of London. Mankind now
faces a similar problem on a global scale. The world's population is expected
to increase to 9.1 billion by 2050, according to the UN. Feeding all those
people will mean increasing food production by 70%, according to the UN's Food
and Agriculture Organisation, through a combination of higher crop yields and
an expansion of the area under cultivation. But the additional land available
for cultivation is unevenly distributed, and much of it is suitable for growing
only a few crops. So why not create more agricultural land by building upwards?
Such is the
thinking behind vertical farming. The idea is that skyscrapers filled with
floor upon floor of orchards and fields, producing crops all year round, will
sprout in cities across the world. As well as creating more farmable land out
of thin air, this would slash the transport costs and carbon-dioxide emissions
associated with moving food over long distances. It would also reduce the
spoilage that inevitably occurs along the way, says Dickson Despommier, a
professor of public and environmental health at Columbia University in New York
who is widely regarded as the progenitor of vertical farming, and whose
recently published book, “The Vertical Farm”, is a manifesto for the idea.
According to the UN's Population Division, by 2050 around 70% of the world's
population will be living in urban areas. So it just makes sense, he says, to
move farms closer to where everyone will be living.
Better
still, says Dr Despommier, the use of pesticides, herbicides and fungicides can
be kept to a bare minimum by growing plants indoors in a controlled
environment. Soil erosion will not be a problem because the food will be grown
hydroponically—in other words, in a solution of minerals dissolved in water.
Clever recycling techniques will ensure that only a fraction of the amount of
water and nutrients will be needed compared with conventional farming, and
there will no problem with agricultural run-off.
A wide
variety of designs for vertical farms have been created by architectural firms.
(The idea can arguably be traced back as far as the Hanging Gardens of Babylon,
built around 600BC.) So far, however, the idea remains firmly on the drawing
board. Would it really work? The necessary technology already exists. The
glasshouse industry has more than a century's experience of growing crops
indoors in large quantities, says Gene Giacomelli, director of the Controlled
Environment Agriculture Centre at the University of Arizona in Tucson. It is
now possible to tailor the temperature, humidity, lighting, airflow and
nutrient conditions to get the best productivity out of plants year round,
anywhere in the world, he says. The technology of hydroponics allows almost any
kind of plant to be grown in nutrient-rich water, from root crops like radishes
and potatoes to fruit such as melons and even cereals like maize.
There are a
number of ways to do it, but essentially hydroponics involves suspending plants
in a medium—such as gravel, wool or a form of volcanic glass known as perlite—while
the roots are immersed in a solution of nutrient-rich water. A constant flow of
air keeps the plants bathed in carbon dioxide. Any nutrients and water that are
not taken up by the roots can be recycled, rather than being lost into the
soil. “You can grow anything with hydroponics,” says Dr Giacomelli.
He and his
colleagues have created the South Pole Food Growth Chamber, which has been in
operation since 2004. This semi-automated hydroponic facility in Antarctica is
used to provide each of the 65 staff of the Amundsen-Scott South Pole Station
with at least one fresh salad a day during the winter months, when supply
flights to the station are extremely limited. The chamber has a floor area of
22 square metres and produces a wide range of fruit and vegetables with little
more than the occasional topping up of water and nutrients. It does, however,
require artificial lighting because the station is without natural daylight for
most of the winter.
And that
highlights a big potential stumbling-block for vertical farming. In the
Antarctic the need to provide artificial light is a small price to pay for
fresh food, given the cost of importing it. But elsewhere the cost of powering
artificial lights will make indoor farming prohibitively expensive. Even though
crops growing in a glass skyscraper will get some natural sunlight during the
day, it won't be enough. Without artificial lighting the result will be an
uneven crop, as the plants closest to the windows are exposed to more sunlight
and grow more quickly, says Peter Head, global leader of planning and
sustainable development at Arup, a British engineering firm. “Light has to be
very tightly controlled to get uniform production of very high-quality food,”
he says.
Indeed, even
in today's single-storey glasshouses, artificial lighting is needed to enable
year-round production. Thanet Earth, a 90-hectare facility which opened in Kent
in 2008 and is the largest such site in Britain—it provides 15% of the British
salad crop—requires its own mini power-station to provide its plants with light
for 15 hours a day during the winter months. This rather undermines the notion
that vertical farming will save energy and cut carbon emissions, notes Mr Head,
who has carried out several studies of the idea. Vertical farming will need
cheap, renewable energy if it is to work, he says.
Some
researchers, such as Ted Caplow, an environmental engineer and founder of New
York Sun Works, a non-profit group, argue that even using renewable energy the
numbers do not add up. Between 2006 and 2009 Dr Caplow and his colleagues
operated the Science Barge, a floating hydroponic greenhouse moored in
Manhattan (it has since moved to Yonkers). “It was to investigate what we could
do to grow food in the heart of the city with minimal resource-consumption and
maximum resource-efficiency,” says Dr Caplow.
The barge
used one-tenth as much water as a comparable field farm. There was no
agricultural run-off, and chemical pesticides were replaced with natural
predators such as ladybirds. Operating all year round, the barge could grow 20
times more than could have been produced by a field of the same size, says Dr
Caplow.
Solar panels
and wind turbines on the barge meant that it could produce food with near-zero
net carbon emissions. But the greenhouses on the barge were only one storey
high, so there was not much need for artificial lighting. As soon as you start
trying to stack greenhouses on top of each other you run into problems, says Dr
Caplow. Based on his experience with the Science Barge, he has devised a rule
of thumb: generating enough electricity using solar panels requires an area
about 20 times larger than the area being illuminated. For a skyscraper-sized
hydroponic farm, that is clearly impractical. Vertical farming will work only
if it makes use of natural light, Dr Caplow concludes.
One idea,
developed by Valcent, a vertical-farming firm based in Texas, Vancouver and
Cornwall, is to use vertically stacked hydroponic trays that move on rails, to
ensure that all plants get an even amount of sunlight. The company already has
a 100-square-metre working prototype at Paignton Zoo in Devon, producing
rapid-cycle leaf vegetable crops, such as lettuce, for the zoo's animals. The
VerticCrop system (pictured) ensures an even distribution of light and air
flow, says Dan Caiger-Smith of Valcent. Using energy equivalent to running a
desktop computer for ten hours a day it can produce 500,000 lettuces a year, he
says. Growing the same crop in fields would require seven times more energy and
up to 20 times more land and water.
But
VertiCrop uses multiple layers of stacked trays that operate within a
single-storey greenhouse, where natural light enters from above, as well as
from the sides. So although this boosts productivity, it doesn't help with
multi-storey vertical farms. Even if each floor rotates its crops past the
windows so that all plants receive an equal amount of natural light, overall
they would get less light, and so produce less biomass, says Dr Caplow. He
prefers the idea of the “vertically integrated greenhouse”. This idea involves
the integration of vertical farms into buildings and offices, with plants
growing around the edges of the building, sandwiched between two glass layers
and rotating on a conveyor. Shrouding buildings with plants solves the
natural-light problem for agriculture, acts as a passive form of climate
control for the buildings and makes for a nice view. But the area available is
much smaller.
The
immediate opportunity may simply be to take advantage of the space available on
urban rooftops, says Mr Head, and to pursue urban farming rather than vertical
farming. BrightFarms Systems, a commercial offshoot of NYSW, is working with
Gotham Greens, another company to emerge from the Science Barge, to create the
world's first commercial urban hydroponic farm in Brooklyn. When it opens in
2011, the 15,000 square-foot rooftop facility will produce 30 tonnes of
vegetables a year which will be sold in local stores under the Gotham Greens
brand name.
Although
this is urban hydroponics, not vertical farming, it is a step in the right
direction, says Mr Head. “I wouldn't be at all surprised if we saw large
retailers with greenhouses on their roofs growing produce for sale in the
shop,” he says. A few examples of this have already sprung up. BrightFarms, for
example, together with a firm called Better Food Solutions, began constructing
a large single-storey glasshouse on the roof of a big supermarket in October.
The supermarket agrees to buy the produce and owns the farm, while Better Food
Solutions builds it and runs it. The first fruit and vegetables are expected to
go on sale in early 2011.
It is
unclear how competitive this will be. Rooftop farming may not be able to
compete with other suppliers in a global market unless people are prepared to
pay a premium for fresh, local food, says Mr Head. And it is much less
glamorous than the grand vision of crops being produced in soaring green towers
of glass. But, for the time being, this more down-to-earth approach is much
more realistic than the sci-fi dream of fields in the sky.
Source of
Article: http://www.economist.com/
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