One terajoule (TJ) of energy is equivalent to the energy held in 700 40-litre petrol tanks.
Key assumptions used to calculate energy use include:
Christchurch is defined as the area under the jurisdiction of the Christchurch City Council, including Banks Peninsula. Where specific separation of energy data by local authority area is not possible, best estimates are applied based on available information.
For consistency, the energy measures are reported in units of terajoules/day (TJ/day) rather than terajoules/month to remove the impact of differing days per month. The electricity data is also shown in gigawatt-hours per day (GWh/day) as GWh is a common measure of electricity use.
The raw energy data has been provided by energy suppliers or existing collectors of energy information. Where this has not been provided, best estimates have been developed based on available information. In some instances, the raw energy data has been provided under confidentiality agreement due to the commercially sensitive nature of the data. In such cases, this has required the aggregation of the raw energy supply data into broader classifications of energy type.
For simplicity, energy supply to Christchurch is assumed to equate to the energy usage.
Christchurch’s energy supply is presented in terms of:
- the primary energy source (fossil fuels, hydro energy, geothermal energy, wind energy, biofuels, solar energy)
- key energy components (electricity, petrol, diesel, other fossil fuels, biofuels etc)
- the proportion of non-renewable and renewable energy
Christchurch’s electricity supply from the national grid plus an accurate basis for determining distributed generation in Christchurch is provided by Orion.
Christchurch’s electricity composition is determined by accessing monthly data from the Electricity Authority and assumes separate South Island and North Island electricity networks connected by the HVDC link. Aviation and marine fuels are specifically excluded as these fuels sold in Christchurch are almost all used outside of Christchurch. Diesel sold in Christchurch for rail is currently included despite some of it being used outside of Christchurch, but the impact is not considered significant.
In respect of petroleum liquids, the usage of petrol and diesel in Christchurch is assumed to equate to the amount of those fuels sold in the same period in Christchurch. This approximation is considered valid, as sales in Christchurch not used in Christchurch will be offset to some degree by sales in other regions that are used in Christchurch.
The Heating Degree Day approach (see www.degreedays.net) is used to convert sales data for heating fuels into usage data. For example, firewood sales data does not accurately reflect usage data as many residents purchase a winter's supply of firewood ahead of winter when it is used.
Notes from Neo Leaf Global Ltd.