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Behind The Bulb: Where Do My Electrons Come From?

In our first Behind The Bulb blog, we learnt that regardless of which power company we’re with, the electricity we use is at the mercy of the National Grid. But what are the actual generation sources that feed this beast?

We have over 200 power stations in New Zealand (impressive, huh?) with gentailers Meridian, Mercury, Contact, Genesis and Trustpower owning 98 power stations between them and operating another 81 on behalf of others, as well. For consumers, the key difference between our generation sources is their renewability and environmental impact - let’s take a look.

The renewables

On the global stage, New Zealand does a good job in producing renewable energy, with our resources, like water and wind, providing over 82% of our energy in 2019 according to MBIE (Aotearoa’s renewable electricity generation was the third highest in the OECD - not bad!). So, what are the renewables powering our homes and businesses?

  • Hydroelectricity uses the force of falling water to spin the blades of a large turbine, which is connected to a generator. We have over 60 hydropower stations, the majority found in the South Island, providing around 55% to 60% of our power with no greenhouse gas emissions. So, the more water we have stored in our hydro lakes, and the more secure our supply of hydro generation, the better it is for our carbon emission levels!

  • Wind energy is generated from the spinning blades of wind turbines. Wind farms generate around 6% of our electricity, but their ability to generate power is intermittent (if there’s no wind, there’s no power!). With 17 wind farms in operation right now, and more stages being planned, we could see this percentage rise in the coming years. Most of our wind farms are based in the North Island, and they, too, produce no greenhouse gas emissions.

  • Geothermal plants in the Taupo Volcanic Zone and Ngawha in Northland provide over 17% of our power, by piping high-pressure water and steam from wells under the ground to a generation plant. The energy from the steam spins a turbine, generating electricity. Geothermal generation produces some greenhouse gas emissions.

  • Solar electricity, usually installed on the rooftops of Kiwi homes, is steadily on the rise - according to MBIE’s latest Energy Report, our total solar generation in 2019 was enough to power every household in New Zealand for nearly 4 days. Solar PV (photovoltaic) systems provided just over 0.3% of total electricity generation in 2019, and it’s expected this will rise over the coming years with a number of plans in the pipeline, including a 300 MW solar farm in North Waikato to be built by Genesis Energy, and a 10MW solar farm at Hawke’s Bay Airport. Solar energy produces no carbon emissions, but like wind, it’s also intermittent.

The dirtier stuff

Here in New Zealand, electricity generation is responsible for approximately 4.2% of our total greenhouse gas emissions. So what forms of generation are the dirtiest?

  • Co-generation is the process of converting excess energy from industrial sites into steam, and then electricity. The electricity is usually used again on-site, and anything extra can be fed into the National Grid (it accounts for around 3% of our generation). Co-gen occurs mainly in the upper North Island and it produces moderately high greenhouse gas emissions.

  • Coal and gas, also known as fossil fuels, are non-renewable and come from plant and animal matter that’s millions of years old. When they’re burnt their heat is converted to steam, and the pressure of the steam is used to drive a steam turbine (known as thermal generation). Historically, coal-fired plants provide around 4% of NZ’s electricity, while gas provides around 15%. However, MBIE’s recent energy report showed a jump of 43% for coal use for electricity generation in 2019, largely due to low hydro lake levels and gas outages. Woah!

  • Diesel generation sits at the far end of the spectrum and is thankfully only used very occasionally as a form of backup generation. Needless to say, it’s super dirty, too.

When do they each get switched on?

That comes down to supply and demand. When our supply of clean and green generation keeps up with demand for electricity across Aotearoa, carbon emissions are low - wahoo!

Things aren’t quite so peachy when demand for power exceeds the available supply of renewables. Dirtier generation sources are fired up, producing lots of carbon emissions, and they also just happen to be more expensive to run (you might notice that jump in spot prices if you’re on our Freestyle plan and riding the wholesale market).

Demand for electricity has both daily and seasonal trends. The mad rush hours of breakfast and dinner are known as ‘peak’ times when demand for electricity is high, and it’s often during the peak hours that our infrastructure is stretched, and back-up generation is fired up to meet demand.

Likewise, the demand for electricity increases over the colder, darker months. However, winter tends to bring with it wind and rain, which usually means there’s more cheaper, renewable energy (there’s always a silver lining!). A high and steady supply of renewables generally does a lot to meet the increased demand for power over winter.

So what can I do?

It’s all about off-peak power, baby! By shifting the times that you use appliances like your washing machine, dryer, or heat pump to off-peak hours, you’re making the most of that nice, clean generation.

But how do you know when our generation is lookin’ good, or creating lots of nasties? Easy as - check out our epic tool, CHOICE, which lets you see the real-time carbon emission levels our generators are producing (thanks to some detailed data from Energy Market Services by Transpower). It’ll let you know when’s an environmentally better, or worse, time to use your electricity and help you to avoid those peak times of day when demand is high (usually first thing in the morning, and again in the early evening).

That means you’re already on your way to reducing your household’s electricity carbon emissions and making a difference - flick yeah!