A Chinese agronomist has helped Canadian greenhouse technology move forward, curiously by moving backward.
Dong Jianyi uses only materials and the laws of thermodynamics to grow cucumbers, peppers, lettuce, tomatoes, and more—even in the frigid Alberta winter—all without using a single watt.
A geologist who abandoned the oil industry due to crashing oil prices, Dong Jianyi’s Fresh Pal Farms is believed to be the largest “passive greenhouse” in Canada.
Growing vegetables in China’s cold north necessitates innovation, and passive greenhouses which don’t use electricity are common in that part of the country.
“In north China, it also gets really cold and pretty dark in winter, but people can grow year-round,” Dong told CBC. “Where I lived in China, there were so many passive solar greenhouses. But in Canada, I didn’t see any on the commercial scale,” he said.
The 300-foot long, 30-foot wide greenhouse is constructed out of a steel frame with two polyolefin plastic roofs. An electric motor allows operators to extend and retract an insulating blanket to trap heat absorbed during the day. This keeps the 10,000-square foot interior space at 82°F compared to outside December temperatures of 20°F.
On the north side lies a 24-inch thick clay wall, which captures light more easily from a south-lying sun. At night the clay radiates heat into the space, further ensuring the plants can survive winter temperature that in Olds, Alberta can fall to -31°F.
Last year Dong grew 29,000 pounds of tomatoes alone last year while saving $30,000 in energy and heating costs.
The passive solar greenhouses have a high upfront cost, Dong admits, but they pay back the investment in subsequent years through energy savings, as greenhouses tend to be powered by natural gas.