Achieving high CO2 levels to promote growth "isn't a problem in winter, when the vents are closed and the plants aren't very active - you want it more in summer", he explained. "If you can get from 500 parts per million to 850ppm that would give you a yield increase of 20 per cent. You can buy CO2 in liquid form for £100-£125 a tonne, or use exhaust gas from the boiler. But running it is expensive when you don't need the heat in summer, in which case it's as expensive as buying CO2."
A CHP system "gives you electricity too - CO2 and lighting is a very good combination", he said. "But National Grid connections are a bit of an issue in the UK." CO2 can also be harnessed from biomass burning, he added. "It's not new but we have made it more efficient. An amine scrubber dissolves the CO2 at low temperatures, which can be stored and introduced later into the glasshouse. We are also developing systems to get CO2 from anaerobic digestion."
Energy4Growth is a collaboration between UK glasshouse specialist Cambridge HOK and two Dutch-based consultancies.