Growing Vegetables in Permanent Ice
The crew of the Chinese Great Wall Station can now exist without some of the supply flights from the mainland. Thanks to their own greenhouse, the first in the Antarctic, they have their own supplies of fresh tomatoes, cucumbers, bell peppers, lettuce, and various herbs.
King George Island at the edge of the Antarctic is a surreal sort of place. The island has an area of 1,150 square kilometers, more than 90 percent of which is covered by ice. The rest is coarse gravel. The island is dotted with occasional patches of lichen and grass which defy the icy temperatures and harsh winds. Penguins and seals swim in the water around the coast. But in spite of this, people actually live on the 62nd parallel south, as countries such as Chile, Russia, and China have established research stations on King George Island. At times, the icy island is home to several hundred men and women. About 300 remain even in the Antarctic winter when many scientists leave the White Continent. The Antarctic dwellers receive their supplies from ships and planes from Chile.
At least, they did, until now. The crew of the Chinese Great Wall Station can now exist without some of the supply flights from the mainland. Thanks to their greenhouse, the first in the Antarctic, they have their own supplies of fresh tomatoes, cucumbers, bell peppers, lettuce, and various herbs. Among other things, this was made possible by the material PLEXIGLAS® Alltop from Evonik.
The Polar Research Institute of China and Shanghai Dushi Green Engineering Co., Ltd. worked on the design of the Antarctic‘s first greenhouse for two years. “Among all the materials we researched, PLEXIGLAS® Alltop has proven to be most suitable as covering materials for greenhouses on extremely cold Antarctica,” says Le Lu, an engineer at Shanghai Dushi who was involved in developing the greenhouse at the Great Wall Station.
Use of material under extreme weather conditions
The problem with the design was that in the southern summer the sun shines almost all day on King George Island; at the South Pole itself, the sun shines 24 hours a day at this time of year. But even in the Antarctic summer the radiation energy is very low. This is due to what is known as the obliquity of the ecliptic, in other words, the 23.5 tilt of the earth‘s axis to the plane of its orbit around the sun. Near the pole, this causes the incidence of the sun‘s rays to be very flat and, as a result, they have little power.
Consequently, to ensure that tomatoes, cucumbers and so on thrive, the construction of the first greenhouse in the Antarctic required a material that lets through the sun‘s rays, which are vital for plant growth. After all, a rule of thumb in vegetable growing is: one percent more light results in one percent more plant growth.
Besides, it‘s not only extremely cold in the Antarctic; it‘s also very, very windy. The continent is regarded as the windiest on the planet. Wind force 10, in other words, severe storm, is a daily occurrence on the permanent ice. “We‘ve built many greenhouses around the world. But the project in the Antarctic was especially exciting for us,” says Weimin Wang from Evonik, who was responsible for the construction of the greenhouse in the Antarctic. “Our material can demonstrate its strength especially well under these adverse conditions.”
Because of its 91% light transmission, PLEXIGLAS® Alltop guarantees that the plants get sufficient natural sunlight. Six hundred square meters of 16 millimeter thick multi-skin sheets provide good insulation and UV transparency so that the plants can grow under conditions that are as close to nature as possible. In addition: the material also exhibits no visible yellowing even after 30 years. As a result it, retains its maximum light transmission and is especially durable.
Second greenhouse already being planned
PLEXIGLAS® Alltop is also very stable in high winds. But on its own, that‘s not enough to withstand the bleak conditions on King George Island. In collaboration with Evonik, Shanghai Dushi developed a special aluminum profile to reinforce the construction, which is coordinated precisely to the geometry of PLEXIGLAS® Alltop. After extensive trials, the Chinese research icebreaker Xue Long delivered the material to the Antarctic.
“Now we want to build a second greenhouse in the Antarctic together with our partner. It‘s already in the planning phase,” says Weimin Wang from Evonik. The second greenhouse will supply scientists at another Chinese research station in the interior of the enormous ice-covered continent with fresh vegetables. A place where temperatures drop even lower and the winds are even more bleak.
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