Tell the world to stop blaming your home air conditioner for peak power spikes

Guest post by TonyfromOz (Anton Lang)

The Peak Power story is that spikes in electricity occur 6 to 10 days a year and we need to cut back on the power we use at home to ease spikes. In Australia, the spikes are on the hottest days of summer, and commentators tut-tut and blame the profusion of air conditioning in our homes. Their story goes that there is no point in building more power stations because the spikes are short lived. [See Western Power, Reneweconomy, The Queensland government, and Urban Ecology for examples of people making out residential air conditioners are to blame. That last link has this hysterical quote "The big mistake was putting air-conditioning in cars." If people were not used to being cool in their vehicles, they would not demand it in their homes. (Tony O'Dwyer, National Economics)". Never let the riff raff use the industrial magic tools eh? Keep the air conditioners for the elite academics, pollies and white collar office workers! -- Jo]

But here’s the kicker. There’s one day of the year when more people are at home than any other day, so if home air-conditioners were the problem, then Christmas Day should be a peak electrical headache. Instead, it’s the lowest electrical consumption day of the year. It’s not just the lowest, but far and away the lowest, and not just this year, but every year that power records have been kept.





A half a dozen days a year the Summer Power generation in Australia does indeed spike, and demand is sometimes as high as 32,000 to 35,000MW. But the load curves of power use tell us that homes are not the problem. The load curves are always lower over the weekend, and especially on Sundays. Peak power spikes just don’t seem to happen on the weekend. While some workplaces are open on a Sunday, there is only one day a year when almost every workplace is shut–Christmas. Nearly everyone in the country is at home, possibly with the air-con on all day. Arguably there is more cooking than usual, and the fridges get worked pretty hard as well.

The graph above shows two Load Curves. The top line is a normal working day, Wednesday 18th December 2013. The red line below that is the power consumption for Christmas Day 2013 — which looks closer to a typical Winter load curve with a small peak in the morning, then a slight dip and a further small rise again in the late afternoon. On a normal work/school day residential power consumption has a two peaks a day, one in the AM and one in the PM when everyone gets back home.



Compare the two points where both curves dip to their least power consumption. The lowest electricity use on a normal work day minimum is still at least 17,500MW, while on Christmas Day it’s down to 15,500MW.



The peak electricity use on the work day shown is 27,500MW, and the peak for Christmas Day is 19,500MW. The average for the work day is around 22,000 MW, and for Christmas Day around 17,000. Usually, a normal working/school weekday the peak is closer to 30,000MW with the average around 25,000MW. Schools are closed in Australia from mid December to the end of January (many schools have closed before the 18th December).



This Christmas Day load curve can be used as a good indicator of residential power consumption. See how the gap between the dip point around 4AM and the peak for that day is barely 4000MW. On one of the record Peak Power days, the gap between the dip point and the peak is sometimes as high as 14,000MW–with most people at work.

That maximum extra residential consumption for the day of 4,000MW tells us that residential consumption is not the largest contributor on Peak Power days, and that home air conditioning should not shoulder the blame for spikes.

Solar is not the answer

Perhaps rooftop solar power might contribute to lower power consumption? There is currently around 1.8GW in Nameplate Capacity for rooftop solar power. Across this one Christmas Day, those panels will generate around 500MW only during the daylight hours for that Christmas Day. Because all of those homes are actually consuming power during the day, then virtually all of that solar generated power is being consumed by the residence on that day, with very little being fed back to the grids. Even adding that 500MW from rooftop solar generation to the peak power consumption, Christmas Day consumption is still considerably lower than for any other day of the year.

[Sure solar power is blunting the peak slightly, but is the cost worth it? We could have generated all that peak electricity (and more) by building another gas fired plant and then spent the money we saved on a beach holidays for everyone instead... Shall we vote on that? - Jo]

Residential power consumption here in Australia is only 20% of all power usage, and the Christmas Day load curve shows that residential power cannot be the cause of huge power consumption on days when those peaks rise considerably.

Reading this probably raises more questions. Rather than answer them all here, I’ll answer in the comments. I just know what that first question will be.

[Jo notes that the evil destroyer of the "climate" (if CO2 mattered) appears to be nothing less than industrial production. In other words, to produce less CO2 we have to stop the factories, offices, shops, schools and hospitals, and the trains and trucks. It really is about quality of life. Shall we switch it "off"? - Jo]

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