Can a Wattwatchers device help to lower your home-loan interest rate?

People ask how data helps to cut your power bills? It does, providing insights for reducing your cost of living without sacrificing your lifestyle. But the value-add doesn’t end with cutting electricity bills and avoiding ‘bill shock’. Data, especially very granular and real-time data, helps you to buy better, run your home more efficiently, optimise your solar, and choose your most cost-effective battery or electric vehicle. As my family discovered, it also can help you to get a better deal with a bank!

When our then growing young family first moved into our own home – this was at the start of 1993, with the house located on Sydney’s northern beaches – my memory is our bank mortgage rate was 13.5 percent. This seemed good given home borrowing interest rates had been as high as 18 percent in the second half of the 1980s, when we’d regarded home ownership in Sydney as an impossible dream. 

Nearly three decades and a total of four children later my partner and I are still in the same home, minus the grown-up offspring but with two dogs. With many minor and some major renovations along the way, we still have a mortgage. Remarkably, however, we’ve just seen our mortgage rate fall to 1.79 percent, an unimaginable number for our entire adult lives up until now, and a Wattwatchers device helped to make it happen.

You’re going to want an explanation for this claim.

Some months ago we learned that the ethically-minded Bank Australia has a Clean Energy Loan offer, with backing from the Australian Government’s ‘green bank’, the Clean Energy Finance Corporation (CEFC). If you qualify, and depending on the version you target (and qualify for), it can take 0.4 or 0.5 percent off your headline interest for up to five years. With historically low mortgage rates already, and especially low fixed-rate packages, that offered an amazing opportunity to crack 2 percent and go lower still (we were coming off 3.15 percent, which was very low in historical terms, but still on the high side in today’s terms).

So what did we need? There’s an extended list of energy-saving and carbon emission reducing upgrades and activities that can help you qualify, and you need to be able to tick the box for at least three of them. In our case it was having a smart energy monitoring device (for us a Wattwatchers of course) installed in the past 12 months; getting rooftop solar PV installed, and we opted for a premium-quality 6.6kW system (Q Cells panels, SolarEdge inverter, designed and installed by boutique Bondi-based Sydney firm Lokic Energy Solutions); and finally a house-wide LED lighting upgrade, completely replacing several dozens of fittings, delivered by our go-to electrician Glenn Beames, from Beames Electrical based in Engadine, in southern Sydney’s Sutherland Shire.

Data first, then add rooftop solar and LEDs

We needed to provide Bank Australia with evidence for each qualifying item.

I’m part of the Wattwatchers team, so I got the device itself installed for free. But the solar system and the LED upgrade were significant financial investments, with the good news being that both pay for themselves over reasonable time, while also helping to improve our family’s quality of life and enjoyment of our home, while delivering on our personal environmental commitments. For example, we don’t have air-conditioning, but replacing heat-generating halogen down-lights with cool-running LEDs is a big plus (the Wattwatchers device readily shows how power-hungry those pesky little halogen down-lights can be, and how energy-lite the new LEDs are).

We have a cleaner pool, because we run the filter pump for longer in solar hours without pushing up our power bill. Based on the data I get from the Wattwatchers device, I move the automatic timer that controls when the pool pump runs to match the availability of solar – longer hours in the summer months, coinciding with when the pool gets most use, and fewer hours in the winter when less filtering and cleaning time is required. On cloudy days, when solar generation is poor, I sometimes pop out from my home office and turn the pool pump off manually just to keep electricity imports from the grid as low as possible.

The pandemic means extra home time

Covid-19 has proven to be a bonus for our smart home energy management, if not for our social lives.

On the mobility front, my partner Nat Isaacs recently took the wheel of an all-electric, zero-emission Nissan Leaf. We haven’t worried about investing in a special EV charger for our home. We’re on site most days (thanks heaps Covid-19) and run an everyday extension lead to the car, charging it whenever the solar generation is running strong. The Wattwatchers device allows us to know when it’s the right time to charge the Leaf, and allows us to track how its going in real-time, in the wider context of the whole home, with comprehensive historical references. (On a good solar day, we can run the pool pump, the EV charging and the dishwasher all at the same time without needing to import a single electron from the grid. Happy days!)

It’s true that by using our home solar to charge the EV we are increasing overall electricity consumption for our home, but we can still do that while importing minimal electrons from the grid. By charging with home-generated solar, mainly if not always, we’re also eliminating another fossil fuel-driven energy bill, which is the one most people get regularly for filling up a typical internal combustion engine (ICE) vehicle with petrol or diesel.


The game we play is maximise the green (solar self-consumption), and minimise the blue (grid imports) and also the yellow (solar exported to the grid). October 21, 2020 was a good solar day. The pool pump went on slightly early for it to fit totally in the solar curve. The EV was being used in the morning, but went on the charger before midday. Turning the dishwasher on briefly pushed consumption fractionally beyond solar capacity for a few minutes, but all in all a good day.

What does the future hold?

Based on our Wattwatchers-assisted calculations, we can still accomodate at least one more significant electrical load in the house to optimise our return on the investment in solar. Currently our hot water system is gas-powered, but it’s nearing the end of its expected working life and the logical replacement is electric, whether an old-style heating element system or a more contemporary heat pump model, that we can time to recharge in the middle of the day when solar is likely to be most abundant (we may have to wear higher charges on rainy days and during extended periods of cloud cover, when solar output inevitably is poor, but on balance we expect to come out ahead financially with significant reductions in our negative environmental footprint).

We’re keeping open minds on the potential to add a home energy storage system (battery) in the future, but right now it doesn’t make compelling financial sense for us, based on the data. Ideally, we’re hoping that a two-way charging electric vehicle would remove the need for a stationary battery, because vehicle-to-grid is looking like the future we want. 


Murray Hogarth is Director of Communications and Community Networks with Wattwatchers Digital Energy. My Energy Marketplace (MEM) is an Australia-wide project – led by Wattwatchers, and supported by a $2.7M grant from the Australian Renewable Energy Agency (ARENA)* – to roll-out partly-subsidised smart energy management solutions to 5000-plus homes, small businesses and schools. is Wattwatchers’ new mobile app (see below). Email for more information.























The My Energy Marketplace project is receiving funding from ARENA as part of ARENA’s Advancing Renewables Program. The views expressed herein are not necessarily the views of the Australian Government, and the Australian Government does not accept responsibility for any information or advice contained herein.