ENERGY USE IN GREENHOUSES - HOW LOW CAN WE GO?
In colder climates, the greenhouse industry is energy intensive and has therefore been heavily impacted by rapidly escalating fuel costs and in some cases, fuel availability. Greenhouses cannot survive the loss of energy in cold weather. Therefore, a greenhouse operation cannot depend exclusively on an interruptable energy source regardless of its relative cost. It is our feeling that the greenhouse industry has begun to take great strides in the reduction of energy use for heating purposes. Since energy represents a high fraction of the production costs, there is an incentive to conserve. Normally the first steps in energy conservation tend to be very effective in relation to the amount of energy saved per unit investment in conservation measures. It is generally true that each successive step in energy conservation provides a lower economic and energy savings return on the investment in capitol and effort.
Greenhouse operators are taking steps to conserve fuel in existing operations and investing in various greenhouse insulation practices. There is increasing interest in alternative heat sources such as solar energy and waste heat from industrial operations as well. However, the application of alternate energy sources lags far behind the adoption of energy conservation measures.
A very important question for the future of the greenhouse industry is the cost of production. Should crops be grown locally in a greenhouse or produced outdoors in a warmer climate and transported to the market? A number of studies have been conducted on the comparative energy requirements of these options and the figures developed by Roller in 1977 serve to illustrate the major points. The following Table shows some of his data and the energy inputs are normalized so that all of the energy required to produce fresh winter vegetables in the south and ship them north to market shows as 100 percent.