Keeping up a supply of carbon dioxide in summer typically means burning more natural gas than would otherwise be necessary, he said.
The Renewable Heat Incentive (RHI), now delayed (see p28), will have a big impact and makes biomass boilers an interesting proposition, he said. "You get twice the carbon dioxide per MWh of heat from biomass compared with natural gas but the flue gases aren't clean enough."
To avoid the problem of too high levels of nitrogen oxides, sulphur oxides and ethylene - all harmful to tomato plants - carbon dioxide can theoretically be cleaned out of flue gases or absorbed in solvents for later use, he said.
Modern combined heat and power systems are worth serious consideration but anaerobic digestion (biogas) formats are not going to be a big winner for the industry, he advised. Nor is deriving carbon dioxide from compost likely to be viable.
However, extracting carbon dioxide from fresh air sounds fanciful but is something that ought to be considered, he concluded. "We would feel as sick as a dog if we ignored it and found out in five years' time that it worked after all."