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Solar greenhouses, Chinese-style

April 5, 2010
Chinese Greenhouse

Dr. Sanjun Gu in a Chinese-style solar greenhouse with a cucumber crop planted in September and harvested between December and April. Shandong, China, April 1998.

In Europe and North America, eating fresh perishable produce out of season usually means hauling it in refrigerated containers from regions where it’s in season, or growing it locally in heated greenhouses. Our large greenhouses tend to use technology developed in Holland: Huge boilers burn through prodigious amounts of natural gas, coal, wood, or other fuel to fill a network of pipes with hot water, radiating heat into vast leaky structures clad in a single pane of glass. Although these greenhouses boast extremely high yields, the amount of fuel needed to heat them generally far exceeds the amount that would be needed to haul an equivalent amount of produce from a region where it’s in season.

There are alternatives. One is the high tunnel, a simple unheated hoop structure clad in clear plastic. Small farmers in North America are increasingly building high tunnels to extend their growing season without spending a lot of money on energy-intensive technology.

Another alternative is a greenhouse design developed in northern China in the mid-1980s that relies primarily or entirely on solar energy for heat. By 2000 these greenhouses already covered about 260 thousand hectares (650 thousand acres) in northern China, and by 2004 they were supplying residents of northern China with 90% of their fresh produce in winter. That’s when Manitoba vegetable farmer Wenkai Liu first brought the technology to North America. Other Manitoba growers have adopted the design since then, but, to my knowledge, it has yet to be tried in other regions of Canada or the United States.

I learned about the Chinese-style greenhouse from horticulturist Sanjun Gu, who worked down the hall from me between 2004 and 2007, before being hired as a state horticulture specialist at Lincoln University in Missouri. In the late 90s, when I was working as a pest management consultant in gigantic Dutch-style houses in southern British Columbia, Dr. Gu was working in the newly-developed Chinese-style houses at the Shandong Academy of Agricultural Sciences Vegetable Research Institute in  northern China. He showed me the picture above, taken in April, 1998, when we worked together in 2005. Those are ripe cucumbers on the vine in April, nearing the end of a growing season that started in September and stretched through Shandong’s winter, with peak harvests targeting the New Year and Chinese New Year (early February) holidays. Shandong is about the same latitude as Frankfort, KY, where we have to wait until late May to get our first cucumbers from the high tunnel, and late June to start our field harvest. That caught my attention.

Greenhouse specs

Cross-sectional view of a solar greenhouse with dimensions in meters (from Tong et al., 2009)

The Chinese greenhouse design is simple. A thick wall and partial roof on the north side act as heat sinks to absorb solar energy during the day and radiate it back into the house at night. Arched struts extend from the peak of the roof to the soil surface, up to 12 m (39 feet) south of the north wall. These are clad in a single layer of plastic. An insulating blanket rolls down over the plastic at night to retain heat.

Researchers in China and Manitoba have documented remarkable effects of these passive-solar greenhouses on indoor temperatures. A team led by G. Tong, at Shenyang Agricultural University, recently published a complex set of models that successfully predict temperature variation within a Chinese-style greenhouse from incoming solar radiation, windspeed, air exchange rates, and temperatures of sky, air, and soil.

On a chilly mid-February night, the temperature inside their greenhouse remained 10-15 °C (18-27 °F) warmer than outside. The effect was even more pronounced in Manitoba, where indoor temperature on a cold February night remained 30 °C (54 °F) warmer than outdoors. In Shanyang (northern China) and southern Manitoba the greenhouses kept conditions favorable for cool-season vegetable production through the depth of a very cold winter without burning fuel for heat. In Shandong, a little further south, they grew warm season crops — including cucumber, zucchini, tomato, pepper, eggplant, yard-long beans, and bitter melon — through the winter using only passive solar heat.

Temperature inside and outside a greenhouse in Shenyang

Temperature inside and outside a Chinese-style solar-heated greenhouse in Shenyang, China, February 18 & 19, 2004 (Data from Tong et al., 2009).

Manitoba greenhouse

Temperature inside and outside a Chinese-style solar-heated greenhouse in Elie, Manitoba, February 19, 2005 (Data from Zhang, 2006).

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Click images in the gallery below to expand.

References

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5 Comments leave one →
  1. Bob Martin permalink
    October 30, 2011 12:23 am

    After reading the articles, and the white paper, I couldn’t find a reference to ventilation. Was ventilation provided, at what rates, and how did this affect the presence of insect pests, fungi, and/or bacterial problems during winter months?

    • November 1, 2011 9:10 am

      Chinese solar greenhouses are passively ventilated by rolling up the plastic during daytime. This, of course, is not practical on many cold winter days. I am not aware of studies determining the impact of Chinese greenhouses on pest and disease pressure, but I’m sure that a wide variety of insect pests, fungi, and bacterial pathogens are well adapted to the environments found in these greenhouses.

  2. John King permalink
    May 23, 2011 5:22 pm

    The price of veg in the winter is higher and the cost of the Chinese construction is much lower than the technology Richard above describes. The roofs are retractable for heat ventilation in the summer and being dug into the ground also helps keep it cool in hot weather. These were poor farmers who are now becoming wealthy ones. They can now eat water melon year round, which has got to be a good thing.

  3. February 15, 2011 12:09 pm

    This approach was studied in Canada – in fact I was a consultant to a project in Montreal that was built approximately like the cross-section drawing. This project and other greenhouse waste heat energy utilization studies were then underway (1980). The greenhouse project that I worked at was established at the PetroFina Refinery (it was later shut down) and was intended to use the low temperature cooling water output of the refinery. Anther example in Canada is the Ark, a Demonstration Project (John Todd) built for the UN Habitat Conference 1976 in Prince Edward Island and operated by the Institute of Man and Resources – the result was determined that year aroud crops will not grow well in this style of insulated north roof/wall – summer production is greatly reduced – thus it was never commercialized in Canada nor can it compete with the advanced Dutch greenhouse. I appreciate the article for drawing attention to the concept and no doubt the Chinese have adapted this approach to their needs (for short cycle, seasonal winter crop harvest). However with SolaRoof we have the true breakthrough that the greenhouse industry is seeking: a north insulated roof/wall during cold nights and transparent as needed during summer days, using Dynamic Liquid Insulation/Shading. Using Liquid Bubble Insulation in the winter daytime in a north wall/roof (of a tunnel with its length running east/west) we have also demonstrated amplified light level during winter days entering from the south (with reflections), while concurrently greatly reducing heat loss through the north side of the greenhouse. SolaRoof is an OpenSource global collaboration for sustainable living and livelihoods with the purpose of cooperation to BUILD a sustainable future for all. Please join and participate!

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  1. Solar greenhouses, Chinese-style — Climate Today

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