The gas generated in landfills can be tapped after the completion of the landfill, and when burnt as fuel has a calorific value about half that of natural gas. This is due to the fact that there is only about 60% combustible methane in the gas created and this has a calorific value of 37 GJ/t compared to 50 GJ/t for natural gas.

Trying to estimate countrywide landfill gas emissions is not straightforward. The two complimentary forms of landfill gas emission prediction are modelling and measurement. Modelling is a useful predictive tool but it needs validation by actual measurements. Research in this field has been carried out by AEA Technology Environment under contract to the Department of Environment Transport and the Regions (DETR). In order to make an estimate, waste arisings and disposal, together with composition data over recent years and predictions for the future have to be studied. Also, studies into data on methane generation, oxidation and collection, together with a look at UK landfill design and management have to be looked at. Coupling all this data with the first order exponential decay model as outlined by the IPCC has produced results which say that emissions of methane from landfills for the year 2000 are likely to be in the order of 660,000 t/y (K A Brown et. al.).

Although the system is in equilibrium one year to the next, it shall be assumed that only 75% of this can usefully be captured because of that which will escapes before a landfill can be capped. The energy available through generation would then be 0.75´660,000´(calorific value of methane)´(efficiency)´(load factor). Typical efficiency of this process is 75%, there is a load factor of 0.9 (all load factors from www.bwea.com/old/fs4cap.htm), and the calorific value of methane is 37GJ/t. This gives a potential to generate 392 MW of power. Add this to the 232 MW already existing from capped and trapped landfill gas in the UK (from www.biogas.org.uk) gives the total potential of just over 0.6GW. Putting this into perspective, the total installed capacity of the UK as a whole is about 73GW (figure from Electricity Association, year ending 1998) so ideally landfill gas alone could satisfy about 0.9% of the UK's energy requirements. This kind of analysis shall also be conducted upon waste incineration, gasification and anaerobic digestion (in Sections 2, 3 and 5 respectively) to draw comparisons between the processes.

Generating electricity from landfill gas is clearly a better sustainable solution than merely trapping and not using it in any productive manner. It is a resource that should be employed. There is the added bonus for the site operators of an extra generated financial revenue from the electricity sales. However, all of the environmental burdens still apply. The only offset is where electricity generation by non-renewable sources can be reduced.