The expected CO2 savings associated with each scheme were estimated by calculating the potential reductions in the community’s consumption of both natural gas and electricity from the national grid. These savings could be made either through reducing energy consumption or by replacing energy from the national grid with renewable, clean energy. The carbon intensity of natural gas is taken as 0.204kg/kWh and 0.543kg/kWh for electricity as outlined by the Energy Saving Trust . Using these figures, one tonne of CO2 could be saved by, for example, reducing the electricity consumption of the area by 1.84MWh per year.
The implementation of any new systems will have a defined embodied energy. This energy consumption is from the production, transportation and construction of the materials involved. This will in turn have a defined amount of CO2 emissions which can be calculated from the use of the equivalent amount of grid energy required in the processes.
The embodied carbon of any changes or installations, for example the CO2 emissions associated with the construction and installation of a wind turbine, are included in the calculations. Once a carbon neutral system is generating energy it is emission free, so the energy used in its construction (and associated emissions) can be cancelled out by the energy generated. This ‘payback’ of emissions will happen over a defined period, for example it is estimated to be around one year for a modern wind turbine.