How do you calculate emissions?
We calculate emissions using the emissions factors from a number of sources, as no single source exists for all generation types.
- The 2015 emissions factor for geothermal, coal and gas is published by MBIE.
- The factor for diesel is unpublished but is based on average diesel emissions over the past 10 years, also supplied by MBIE.
- The emissions factor for co-gen comes from EnergyLink, and excludes Kinleith’s wood fired station.
- Hydro and wind are rated at zero.
The classification of each generation station and unit as to generation type is undertaken by Transpower, based on the information available from generators. More information is available here. (PDF)
To get your personalised carbon emissions, we calculate the portion of your usage attributed to each energy source for each half hour period, and we multiply these by relevant emissions factors. These are added together to give the total emissions for each half-hour period, and each half hour is added up to give a daily total.
So, you'll work out my individual carbon emissions from NZ-wide information?
That's right. The electricity market operates nationally - not locally or individually - so we believe that calculating your individual carbon emissions using the average emissions at a national level is most appropriate. Plus, we're all responsible for how much power we use as a country. That's because our electricity supply is influenced by national demand, or how much we're all using at any given time. If demand exceeds the supply of cleaner, renewable electricity, our non-renewable energy sources (like coal and gas) are fired up to meet it, and they produce lots more carbon emissions.
Are there things that might be different for each person, though?
You betcha! Once it's in the national grid, electricity discharges at the first available grid exit point, so if you live close to a renewable generation station, you're more likely to use electricity from that source than any other. Here are a few factors that can have an impact on the generation mix, and might mean your carbon emission profile is different to the national profile:
- Where you live - most of our hydrogeneration is in the South Island so if you're a Benmore local it's likely that more of the electricity you use comes from hydrogeneration. When there are constraints in the market, like power outages and maintenance on the HVDC cable (which transports electricity from the South Island to the North Island) it can mean that the power generated down south can't be moved north and will stay, and be used, down south.
- Whether you're near any embedded generation - NZ has generation stations which are embedded within local networks rather than connected to the National Grid. If there is embedded generation near your property then the electricity you use is more likely to be generated there.
- How much power is lost in the lines on its way to your place - we calculate your emissions using the volume of electricity recorded at your meter. To supply you that electricity, the generators have to generate slightly more electricity than what's needed, because some is lost in the process of getting power from sites of generation, through the National Grid and into the local distribution network. It's usually around 7% that's lost, though this can vary depending on where you live.