Energy utilisation in the glasshouse industry

Abstract

The total annual energy consumption in Britain is about 9505 x lo9 MJ of which agriculture directly uses less than 1.4 % to produce over 50 % of the country's food. Of the agricultural consumption, glasshouse heating uses 35 %, or 900 000 tonnes, of fossil fuel annually. Heating costs account for about 30% of production costs of glasshouse crops. Boilers used on glasshouse holdings can operate at thermal efficiencies of 80-85 % with an overall system efficiency of at least 70%.Ways of increasing efficiency are discussed.Heat losses from glasshouses are high compared with other buildings due to the light-transmitting envelope but can be reduced by good maintenance, provision of windbreaks and the use of insulating covers drawn over the crop at night. Double skinning by lining with clear plastic film offers attractive fuel savings but the consequential light loss and crop reduction is likely to result in a net monetary loss. Research on crop response to temperature has established optimum temperature regimes for most crops. Reduction of temperature to save fuel usually results in a loss of crop and income which greatly exceeds the fuel saving. The use of light modulated temperature controllers offers promise of increasing the output from a given fuel input. The use of waste heat from electricity generation and industrial processes is unlikely to give any benefit in the near future.