Getting off the Grid: Solar Greenhouse Design and Rainwater Catchment Use

Passively heated solar greenhouses are quite common in East Asia, with “Chinese solar greenhouse” designs having been in use since the 1930s.  These designs are typically single-slope, and utilize a thermal mass typically comprised of earth or other natural materials to capture solar gain, and may experience temperatures 25-30^ΟC warmer than field conditions without the use of active heating elements.  Despite the significant promise of these low energy designs, solar greenhouses have been minimally adopted in North America.  However, with the dramatic increase in adoption of season-extension technologies in recent years, coupled with growing demand for locally produced food, solar greenhouses may be a viable season-extending alternative with greater solar gains than high tunnels, without the heating cost of traditional greenhouses. In 2013, a 6 m x 22 m “Chinese style” solar greenhouse was constructed at the University of Kentucky Horticulture Research Farm.  The greenhouse was divided into two sections with each containing a different media for thermal mass lining the north (south-facing) wall: 1) food-grade plastic barrels filled with water, and 2) a wall of corrugated metal and wood filled with sand approximately 30 cm thick.  Data loggers recording temperature and relative humidity at 15-minute intervals were placed at various locations in the greenhouse, including in the media, immediately adjacent to the media, in the center of the tunnel, and at soil level in the center of the tunnels.  Soil temperatures were also recorded at the center of the tunnel.  Summaries of two years of air and soil temperature data as compared to high tunnels and field conditions at the same site are presented. In 2014, the UK solar greenhouse was fitted with a rainwater catchment system utilizing an ultra-low pressure drip irrigation system.  The system was designed to create a replicable model for rainwater catchments for season-extension structures utilizing locally available materials, without the use of high pressure for irrigation created by elevating water tanks or using pumps.  This system has been found to cost under $500 for this design, and further develops the ability for solar greenhouse technologies to decrease the use of off-farm and energy-intensive inputs.