CO2 Best practice guide: Costs

The cost of generation and distribution, as well as the cost of the fuel, are the key factors that must be considered.

It is usual in tomato production, for example, to employ CO₂ enrichment using flue gas from natural-gas boilers and, because this is essentially a ‘by-product’, it is widely considered to be ‘free’. However, there would be little enrichment in the summer months if reliance were placed solely on greenhouse heating to supply the CO₂ and, in practice, the boiler is frequently run with the sole aim of generating CO₂. This generates surplus heating energy and the surplus heat should be stored for later use as hot water in heat-storage tanks.

Modern nursery installations can burn gas at rates in the region of 200 m³/hr/ha, and a heat-storage capacity of around 150–200 m³/ha is typically recommended. The heat store should be suitably insulated to ensure that heat is not wasted. This clearly has a major impact on energy consumption, and simulations have shown, for example, that maintaining a minimum daytime CO₂ concentration of 600 ppm could almost double energy use. Practical information on managing boiler set points for CO₂ dosing can be found on the GrowSave web pages. Results from PE 003 (2011) ‘CO₂ enrichment in the future: a technical and economic analysis of alternative CO₂ sources’ provides some more information on the options. Table 1 gives an idea of CO₂ costs from fossil-fuel burning.

Table 1. The cost of CO₂ derived from the combustion of fossil fuels 

* typical costs at the time of writing (March 2016)