Tomatoes: an investigation into apparent yield improvements associated with the installation of a micro-gas-turbine CHP facility

This project evaluated yield at a grower site through the first three growing seasons following the installation of a micro-gas-turbine CHP facility. Examination of production records for the site showed there to be an increase in average total yield of 12.58 kg/m2 (50.1 t/acre) or 25.4% between 2002 and 2003. This compared with a reduction of 0.65kg/m2 or 1.1% in these years for the average of three comparison sites. Comparison between sites was restricted to classic tomato types in these years. Production on the G&W site in 2002 was lower than in 2000 or 2001, whereas the reverse was the case for the other sites. The lower figure in 2002 may have been related to disruption caused by the installation of the turbine system in that year and problems this caused, in the interruption of CO2 supplies for instance. A comparison of the G&W yield in 2003 compared with the average of the more normal years, 2000 and 2001, showed an increase of 20.2% compared with a 5.3% increase for the other three sites over this period. Annual yields at G&W went from figures of 2.2%, 6.7% and 14.0% below average of the other sites in 2000, 2001 and 2002 respectively, to 9.1% and 9.5% above average in 2003 and 2004. There were no material differences in factors such as sowing dates, cultivar or plant populations over the comparison period. 

Solar radiation measurements for G&W in 2003 were 10.5% above 2002 but were 11.4% higher for the three-site average in these years. The disproportionate increase in yield at G&W cannot be ascribed to a disproportionate increase in radiation levels therefore, compared with other sites. Production at all four sites in 2004 was lower, by an average of 10.4%, than in 2003 and solar radiation levels by 6.7%. Production at Site B in 2004 was unexpectedly low, which was due to a severe Botrytis infection. Average yields for G&W are very similar to those of Site A, but this site has all modern blocks with larger glass and significantly higher gutters than has 47% of the glasshouse area at G&W, which is much older. Average yields for the two modern blocks at G&W in 2003 and 2004 were 10.5% and 10.7% higher respectively, than those of Site A. Solar radiation levels were, however, 3.5% and 4.7% lower than Site A in 2003 and 2004 respectively. Site A also has a significantly higher rated CO2 input from its CHP system than that at G&W.

Comparison of system CO2 output capacity for the four sites does not suggest this to be the primary reason for the differences in results achieved, although records of actual glasshouse CO2 levels recorded would be particularly useful in making more detailed analyses. Other potential benefits from the new system would be cleaner glass and improved light transmission from cessation of oil use (although this was already the case on two of the other three sites), and lower levels of pollutants in the combustion gases, possibly compared with the two gas-using sites and probably compared with the kerosene using one. More accurate monitoring and control of potential pollutants in glasshouses from the combustion gases from CO2 generation demands a higher priority than it appears to receive at present, not only from a crop perspective but also in relation to the health and safety of staff employed in glasshouses.  Records of average fruit size would be particularly useful in comparing the possible effects of varying CO2 enrichment levels and solar radiation receipt, but unfortunately these are not available

The primary conclusion is that production levels achieved by Guy & Wright following the installation of the micro-turbine system are greater than would be expected from these facilities, simply given their specification. This was established by comparison with three other sites, which were chosen to reflect similarities with G&W in glasshouse types or CO2 installations, both in relation to the replaced kerosene burning system and the new micro-turbine system

To investigate apparent yield improvements associated with the installation of a micro-gas-turbine CHP facility.