ghg-inventory-1990-2013

‒ Eleven landfill facilities, totalling 29.4 megawatts (MW). These facilities are
electricity only (some landfill gas was used to heat a swimming pool in
Christchurch before the Christchurch earthquake of February 2011, but that
facility suffered major earthquake damage and has been removed).
‒ Four wastewater treatment facilities, totalling 11.3 MW. These are all
co-generation facilities, which provide heat and electricity for the processing of
sewage.
‒ Note: Accurate information is not available on the exact type of generation plant
used at these individual facilities, although it is known to be a combination of
gas turbines, internal combustion engines and some steam turbine facilities.
Generation data is collected for each year ending 31 March, with generation assumed
to be distributed equally across quarters to estimate December year-end generation.
‒ Generation data is usually collected from all 15 plants. However, in some years
estimates are made based on the previous year’s generation.
Fuel input information for generation is not collected for small generators (those less
than 10 MW), to minimise the burden on respondents, and ensure the Ministry of
Business, Innovation and Employment receives some information rather than
nothing. Estimates of fuel input are made on the assumption of 30 per cent efficiency
based on gross generation.
‒ All generation data collected is assumed to be net generation – that is, parasitic
load has already been taken off. It is then scaled up using default net to gross
generation factors sourced from the International Energy Agency. For all
thermal generation, the net to gross factor is assumed to be 1.07 (ie, an
additional 7 per cent of generation is generated but used by the plant to generate
more electricity). Fuel input estimates are then calculated based on the gross
generation using a default electrical efficiency factor of 30 per cent. This
estimated quantity of biogas is used as total biogas for energy purposes. Biogas
use estimates for landfill gas and sewage gas are calculated and reported in
petajoules (PJ).
‒ Energy quantities of biogas are then converted into greenhouse gas emissions
using default IPCC emissions factors. These factors are as follows:
CO 2 – 27.5 kt C/PJ or 100.98 kt CO 2 /PJ (before and after oxidation). This is
derived from the IPCC default net emission factor (it is assumed that the net
emission factor is 10 per cent less than the gross emission factor)
methane (CH 4 ) – 1.080 t/PJ
nitrous oxide (N 2 0) – 2.070 t/PJ.
Emissions from biogas are a very small part of New Zealand’s emissions Inventory.
Given this is the case, we believe the current process is sufficient for estimating
emissions from biogas. Efforts to improve emissions quality would be better focused
on other areas.
Residential biomass data is estimated based on information on the proportion of
households with wood burner heaters (Census of Population and Dwellings, see below)
and data from the Building Research Association of New Zealand (BRANZ) (2002), on
the average amount of energy used by households that use wood for heating. Finally,
industrial biomass data is based on the report Heat Plant in New Zealand (Bioenergy
Association of New Zealand, 2010).
The census is the official count of how many people and dwellings there are in
New Zealand. It takes a snapshot of the people in New Zealand and the places where
52 New Zealand’s Greenhouse Gas Inventory 1990–2013