The average size of a residential solar PV system installed in Australia has grown significantly over the years, which raises an interesting question: Should owners of larger systems even worry about energy efficiency in their homes?
Energy efficiency in the home has always gone hand-in-hand with installing solar panels. After all, a dollar saved is a dollar earned, right? But making your home more energy efficient costs money, and as the price of PV drops, it’s tempting to just bang on some more solar panels to make up for that extra consumption rather than addressing the consumption itself.
And that seems to be happening if we look how the average system size sold in Australia continues to grow:
Average rooftop solar system size in Australia by month 2012 to 2023. Image: Australian Energy Council
Let’s pause to consider the ramifications of piling on the PV without a plan.
Some say that, as our solar PV systems grow even larger, we may be unwittingly succumbing to a phenomenon called ‘solar rebound’.
Solar Rebound: The Enemy Of Energy Efficiency
The rebound effect occurs when efforts to reduce energy use lead to an unexpected increase in consumption. It can happen because people, feeling the benefit of more efficiency, end up using more of the energy than before the efficiency improvements. It’s a well-understood human trait that’s been studied for over a hundred years.
Solar owners have their own special sub-category called “solar rebound.” This happens when, after switching to solar, they feel less guilty about their environmental impact, or can afford to consume more with lower energy bills, and so end up with an increase in gross energy consumption.
Free Energy From The Sun
Yeah, but it’s free energy from the sun! I should be able to use as much as I like!
Of course. It’s your call. Just be aware your actions may have unintended outcomes. For example, diverting excess solar energy into a hot water system is a practical idea. But if this action leads to piping hot water 24/7 that you didn’t previously use, it can easily escalate to more, longer, and hotter showers.
If your reason for installing solar is to increase your comfort level, and you’re aware of the additional resource use and willing to pay for it, that’s fine. On the other hand, if reducing your carbon footprint is your end goal, you’ve become a victim of solar rebound and perhaps gone backwards trying to achieve your goal.
Even though solar power is cleaner than fossil fuels, it still requires resources for production. No energy source is entirely without environmental impact.
Here’s another one: A proud new owner of a 15 kW solar system is grinning from ear to ear because he can now run his air conditioner from morning to night at a reduced cost. Yet he hasn’t once thought to draught-proof his house or upgrade his window treatments and roof insulation to reduce the air conditioner usage.
Exceptions To The Rule
Of course, there are exceptions to the rule. If your solar inverter is export-limited, you could argue that it’s more beneficial to self-consume curtailed electricity that would otherwise go to waste as long as it doesn’t affect your overall consumption habits.
Another exception: You’ve installed a whopping 20 kW solar array that’s way too big for your current needs, but you’ve put a deposit on a brand new EV that will soon be living in your garage. Your overall energy use will soon be less because you won’t be burning petrol.
A residential 20kW solar system.
So here’s a question – As we pile on the PV, left unchecked, is there a compounding effect of people succumbing to solar rebound, or is it all a load of hot air? .
What Do The Experts Say?
Anecdotal Observations
Tim Forcey is one of Melbourne’s top home energy experts. He has advised energy companies, governments, and thousands of everyday individuals. He is a regular contributor to publications such as the Conversation and Renew Magazine. He administers the “My Efficient Electric Home” Facebook group, which has over 50,000 members, and is the author of the “My Efficient Electric Home Handbook.”
I asked him if the solar rebound effect was something he’d noticed anecdotally.
“I’m not seeing much in the way of rebound with solar in Victoria.
You don’t get solar because you aspire to a big footprint. Or I’ve not seen that anyway. In fact, having solar has made lots of households far more aware and less wasteful of their electricity use. And in Victoria and some other places, having solar drives people to reduce or eliminate their gas use. And petrol eventually.
Also, there are lots of folks building big homes with large footprints. They’re going to do that whether or not solar is a thing, so they might as well whack on a big system. There’s no solar rebound there!”
Tim doesn’t mind getting his hands dirty checking for air gaps with his thermal imaging camera. Image: Tim Forcey
Research Articles
In October 2021, researchers comprising experts in USA energy and environmental policy published a paper in the online journal “Economic Enquiry” entitled “Electricity consumption changes following solar adoption: Testing for a solar rebound.”
They concluded that instead of reducing overall electricity use, solar adoption actually increases total electricity consumption compared to households without solar panels. This increase amounts to a rebound effect of about 28.5%.
As I journeyed down this rabbit hole myself, I found many more academic articles in environmental economics or energy policy research that concluded similar outcomes. I didn’t read them all because they’re boring as bat shit, but there was a general consensus that the rebound effect is alive and well, although difficult to quantify due to indirect effects.
Bugger.
Key Takeaways
I’m with Tim, but… I’m not disregarding what the majority of researchers say. I’m sure most solar owners have the best of intentions. However, we’re all human, and solar rebound probably affects more of us than we’d like to think.
So, back to the original question: Do You Need An Efficient Home If You Own A Massive Solar System?
Given the susceptibility to the effects of solar rebound, it’s fair to say you should be equally mindful of home energy efficiency as owners of smaller systems or anyone who uses electricity, whether from a renewable source or not.
And now, with escalating grid electricity prices, especially after sunset coupled with the cost-of-living crisis, even if you have surplus solar to spare, energy efficiency matters.
But what if you also own a massive solar battery?
Let’s leave that discussion for another time.
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