Development of dual purpose greenhouse coupled with north wall utilization for higher economic gains

A dual purpose greenhouse was designed, developed and tested for simultaneously producing full crop on the greenhouse floor and nursery plants on the existing north wall (in optimized stacks) for higher economic gains. Using solar geometry, it was computed that the optimum ratio between the height of two consecutive stacks (H) and width of the tray (W) is 1.07 at 31°N. The optimally designed nursery trays were mounted in two stacks on the north wall in such a way that at solar noon no fraction of solar radiation leaves through it and also does not cast any shadow of the upper stack onto the lower stack and on the plants grown on the floor. Nursery plants of tomato crop were raised on these two stacks having three trays of length (L) as 160 cm and width (W) as 67 cm size each with H as 72 cm. During the four winter months, the small greenhouse of 600 cm × 400 cm size can be used commercially to produce about 45,000 nursery plants by completing five cycles. This can be done in addition to the normal crop raised on the greenhouse floor and significant extra revenue can be generated. These returns can further be increased at higher latitudes because at constant H, width of the tray (W) increases with increase in latitude. Economic analysis showed that for tomato crop, currently the cost of greenhouse construction (without north wall stacks) can be recovered after five years time but with simultaneous nursery raising on the north wall, the whole investment cost (greenhouse and stacks) can be recovered in less than two year's time and thereafter it becomes a profitable venture. Optimum number of stacks and other stack parameters for realistic north wall heights of 210 cm, 260 cm and 310 cm have been computed and discussed at 30°N, 35°N, 40°N, 45°N and 50°N latitudes.