Unravelling home energy use across Australia
If asked what’s the biggest energy user in Australia, many people would likely say ‘air conditioning in summer’. But they’d be wrong. Paul Ryan and Alan Pears dig deeper into energy use averages and trends.
There are many ways of looking at home energy use. Each one provides useful insights, but can also distort our understanding. In this article, we try to begin unravelling this very big ball of string. We start with an overview, then look more closely.
State-by-state energy use by activity
Figure 1 shows the average metered energy use per household in each state, excluding ‘behind the meter’ solar PV consumption.
The average is the total energy use estimated for each activity, divided by the number of households in that state (see box for more on how this is calculated). This means that the average household in Victoria, for instance, would have 0.46 of a ducted gas heater, 0.70 of a gas water heater and 0.07 of a gas-boosted solar water heater! Even households with the same appliances may consume very different amounts of energy for many reasons.
So, care must be taken in understanding that the average house would not exist in practice, but averages do help illuminate the major contributors to household energy consumption.
Why is average energy use different in each state?
Broad factors are significant, such as climate, performance of buildings and the percentages of homes with various appliances. Which appliances are popular in a state may be dictated by climate—more heating in Victoria compared to Queensland—or historical network configurations—more gas heating in Victoria than Tasmania, for example.
And then the appliances themselves can vary in efficiency. Gas and electric appliances can have very different efficiencies. Gas-fuelled appliances have lower efficiencies, ranging from 60% to 90% due to combustion losses. Electric appliances also vary in efficiency; for example, an electric fan heater converts electricity into heat at 100% efficiency, but a reverse-cycle air conditioner (heat pump) can be 300% to 600% efficient as it extracts and shifts heat from the outside air rather than creating heat directly.
In the colder states, space conditioning, dominated by heating, is the largest energy user. Even though Tasmania is colder than Victoria, its lower heating energy use reflects high use of electric heating with higher efficiency than the gas heating used in most Victorian homes.
Water heating is a big energy user, but it varies across states. NT has quite warm ‘cold’ water and solar heating is widely used. Victorian water heating is dominated by gas, which is less efficient than the electric heating used widely in most other states.
Lighting, cooking and other appliance (whitegoods, IT, TVs etc) energy use per household is fairly similar across the states.
Digging deeper into energy use for specific activities
Figure 2 shows estimates of average space conditioning energy per home within each state in relation to the types of heating and cooling equipment installed.
Cooling is provided by evaporative coolers and fans as well as reverse-cycle equipment capable of both heating and cooling. The latter is used for heating some of the time and cooling for some, but it was not possible to separate those two activities for this graph. However, Table 1 shows the overall cooling and heating energy use by state. The surprising insight is that much less energy is used for cooling than for heating.
A few factors are at play here. First, reverse-cycle air conditioners are 300% to 600% efficient, providing 3 to 6 units of cooling energy per unit of electricity, while gas heaters are only 60% to 90% efficient, providing 0.6 to 0.9 units of heat per unit of gas burnt. Second, most Australians use cooling equipment fairly carefully, and the length of hot seasons is much shorter than cold seasons in many areas, so heating runs for much longer periods within a year. Third, ducted heating systems use much more energy because they heat a much larger area and they are generally very lossy due to duct leaks and thermal losses.
And finally, the relative numbers of homes with each type of heater will affect its overall contribution. In the ACT and Victoria, some 46% of households use gas ducted central heating—almost half!—while another 20% use gas room heaters. In Tassie 31% of households use wood heaters, while other states do not have as large heating loads due to climate.
Of course, newer homes need much less heating if they have been properly built to regulations. Each extra Star rating gives a percentage improvement in heating energy use as shown for Melbourne’s climate in Figure 3. While 8 Stars is the legal minimum in many countries, in Australia we’ve been at 6 Stars for the past 12 years, with any change not on the cards until 2022. [Ed note: Getting an effective change in standards and compliance is something that Renew is working on at the moment, see p. 9 for more.]
Figure 4 shows the water heating differences by state. In general, these are due to the higher energy consumption of gas water heaters, which have combustion losses and higher standby losses than electric units. Gas water heaters may use 15,000 to 30,000 MJ annually, while an electric resistive unit might use 12,000 to 16,000 MJ. Of course, heat pump electric units would use much less again (2000 to 6000 MJ—a wider range as efficiency varies depending on model), but they are only used in 2% of households.
State by state variations in hot water usage may also play a role, as households in warmer climates use less hot water and have higher temperatures of ‘cold’ inlet water.
The main differences are due to the shares of households with different hot water system types and fuels. In Victoria, the ACT and WA there is a higher share of gas water heaters; Victoria has 70% gas water heaters and 7% gas-boosted solar, the highest share of solar-gas in Australia, while the ACT has 46% gas hot water and WA 63%. NSW and Queensland have more electric water heaters: NSW 58%, Queensland 67%. Tasmania is almost all electric for water heating at 87%.
For most equipment in the category ‘Appliances’, average energy use hardly varies around Australia. But that’s not the case for pool pumps (Figure 5), for the obvious reason that pools are much more common in warmer climates, varying from 5% or so in Tasmania and the ACT, to 8% in Victoria, 10% in SA, 16% in NSW, 19% in WA and 36% in the NT.
Many pool pumps use from 1000 to 3500 kilowatt-hours a year: that’s $300 to over $1000 a year in energy costs. If 36% in the NT have a pool, then an average pool-owning home was using about 1660 kWh/year in 2014 just to run the pool pump (or an average of 4.5 kWh/day)—more than some efficient homes would use in total. And that’s not including pool-related energy use from pool heating and lighting.
There are better pool pumps out there: a voluntary energy labelling scheme is in place and this will become mandatory in 2020 along with minimum energy performance standards (MEPS). The best pool pumps currently available use just 250 to 400 kWh/year—or 15% to 25% of that used by the average in the NT. Let’s hope the next baseline study can show a big change here. Optimising running time can also make a big difference, particularly when combined with off-peak rates or demand-response incentives.
Renew last did a buyers guide in 2012; a bit old for product listings, but useful to consider more ways to improve pump efficiency.
Trends over time
Figure 6 shows the trends in energy use over time. Up until end 2014 is estimated data, post-2014 is projected. While there’s clearly not much happening in the ‘cooking’ space, it’s a good news story for space conditioning, lighting and water heating, with big drops over time and projected beyond 2014. Lighting energy use dropped with the introduction of LEDs. Space conditioning trended down with better housing standards and a shift from gas to reverse-cycle air conditioners, which saw rapid MEPS improvements up to 2011. Water heating saw lower hot water usage and shifts to solar and heat pump water heaters and from gas storage to instantaneous units.
The story for the ‘Appliance’ category is a bit more mixed, with what’s actually happening hidden in that graph as it combines whitegoods, IT, home entertainment and other equipment in one line. Breaking these down (Figure 7) shows both the good and the bad.
The big bump in IT + home entertainment energy use in the early 2000s happened when plasma TVs burst onto the scene and people started buying bigger units. That’s since been pleasingly reversed with home entertainment energy use trending down due both to the shift to LED-backlit LCD TVs (even though they’ve still been getting bigger) and fewer TVs—as people have started using tablets and phones for entertainment.
The decline in whitegoods energy use is due to MEPS and labelling for these appliances—a great success! Note that it doesn’t include any changes to MEPS post-2014, which is why the line only declines slightly.
Finally, Figure 8 shows the whitegoods story in more detail. The improvements are almost entirely in refrigeration efficiencies. In fact, dishwasher and washing machine energy use is trending up slightly, due to these appliances now almost universally heating their own water; it’s not that much though, and it’s even not as bad as it looks, because this increase will have been offset by a decrease in energy used for water heating in the household’s hot water service. Even so, there are manufacturers addressing this, with some new European dishwashers using a heat pump to heat the water, cutting their energy use to as low as half the average.
From 2015 on, these graphs show projections only, so things could have changed quite a lot since then. For example, a user of the Facebook group My Efficient Electric Home reported recently that there are now more heat pump clothes dyers appearing in the shops, which could lead to a big drop in energy use for this class of product. And there has been a shift, at least among Renew readers, away from gas for heating, hot water and cooking. Plus solar PV (and storage) are moving fast and will make a big difference to net metered consumption over time. Let’s hope there’s a new study soon to show just where we are at now and where we’re heading.