Investing in a residential home battery and solar system is generally considered feasible only if the payback falls within the battery warranty period typically 10 years. According to this bloke, thats easily doable.
Josh Mylne is, among other things, a dad, a scientist, and an energy nerd. He has an unhealthy addiction to Excel spreadsheets, only perhaps surpassed by SQs Ronald Brakels.
Hes extracted an obscene amount of data from his various apps and home energy bills and reckons his solar power, battery, heat-pump and induction cooking set-up is on its way to paying for itself in less than 10 years. Way less.
Josh lives in my home state of WA, so I thought Id go around and have a chat or as his wife calls it, nerd out together.
Unhealthy Addiction
The Excel addiction and energy nerdism started around 2005 when Josh and his family moved from the UK back to Australia. They were skint, so due to budgetary constraints, out came the Excel spreadsheet to guide their finances.
They continued being a one-car family and used bicycles as much as practical. Fast forward to the COVID-19 pandemic and the decarbonisation journey began in earnest.
On Go The Solar Panels
In November 2020, they had rooftop solar power installed. The system consisted of 19 x Q.MAXX-G2 Qcells 350W solar panels (6.65kW total), and a Huawei SUN2000 single phase 5kw hybrid inverter.
Josh says: I knew nothing about solar at the time. This video on YouTube from the Solar 101 webpage is 25 minutes and it explains everything. After watching it, I used the SolarQuotes website to arrange three quotes and the guide at Solar 101 to work out what was quality gear.1
After the solar panels were installed, the electricity bills dropped by about $950 p.a. But that wasnt enough for Josh. Hes not a big fan of supply charges or the miserly feed-in tariff offered by Synergy in WA. He became a net exporter of electricity, but that didnt reflect in power bills due to the difference in import tariff (30c per kWh) and feed-in tariff (2.5c to 10c per kWh), and the aforementioned supply charge ($1.07/day). Grrr. More work to do.
Getting Off The Gas
The goal was to decarbonise their lives as much as possible, so getting off the gas was a priority. At the same time as the solar panels went on, the gas hot water system was replaced with an iStore 270L heat pump.
Gas usage immediately plummeted by 95%. The bill, however, dropped by only about 80% still an impressive saving of $750 p.a. This was once again because of the despised supply charge. A kitchen renovation in July 2022 provided an excuse to ditch gas altogether when they installed an induction cooktop, providing further savings.
Having no gas bill now saves them $900 p.a. The only gas at their place now comes out of a bottle when they fire up the BBQ.
Home Battery + More Solar Power
Not content with the savings already achieved, the family decided (or maybe Josh decided) to purchase a home battery in November 2021. At the same time the Huawei Luna 10 kWh battery2 was installed, they threw another 7 x 350W solar panels on the roof, bringing it to a total of 9.1kW of solar capacity.
Josh must have been bouncing off the walls in excitement at the thought of expanding his Excel spreadsheet to include the battery. Hes now worked out theyve become 93% self-sufficient for energy. To put it another way, only 7% of the electricity they use comes from the grid, averaged over the whole year.
He says that the battery gets them all the way through the night 310 days per year (84.9%), although its almost impossible to have a day thats 100% self-sufficient as any spike of use that goes above 5kW has to be covered by the grid.
After one full year with the battery, I analyzed how often the battery gets you all through the night to the next day (see the graph below). Out of the whole year, 341 days (93.4%) made it past 9 pm, 334 days (91.5%) made it past midnight, 320 days (87.7%) it got past 4 am, and 310 days (84.9%) it made at all the way through all night to the next day with no grid draw at all.
I must admit at first glance I struggled to get the graph below, which shows the ability of Joshs battery to see them through the night without grid power, over a period of 12 months. The green is not actually a Christmas tree, but the data. The white bars (which look like the data) are, in fact, showing where the battery didnt make the distance, and the grid kicks in. If you stare at it long enough itll make sense.
The Bottom Line
So pretty pictures and graphs aside, after extracting data from Joshs spreadsheets, he reckons the combined solar power plus battery investment will pay back in 6.4 years. This is a conservative estimate because the cost of the heat pump and induction cooktop could arguably be left out of the equation as the gas appliances were at the end of their life. That would bring the payback down to 4.9 years.
Article Courtesy of: Kim Wainwright | www.solarquotes.com.au