In spring 2014, when my wife and I had our new home built, we were also looking at putting solar panels on the roof, but the financial numbers didn't quite add up. We also didn't want to have just panels without a residential battery that could store excess solar energy, but back then batteries were still very expensive and didn't provide a lot of capacity.

That situation improved rapidly over the next two and a half years, and when our nest egg term deposit matured in early 2017, we looked at available solutions again and did the math. With solar panel manufacturers now providing 25-year warranties and battery technology having progressed rapidly, a small installation of 16 solar panels with a peak production of 3.6 kW and a residential storage battery with 8 kWh capacity was just within reach.

We were still driving a petrol-hybrid car at that time but already knew that our next car was going to be a fully electric one, so we calculated the electricity bill savings plus all the money we would later save by not having to buy petrol anymore, and compared it with the interest we would earn if we left the money in the bank and put it in another term deposit.

The numbers were within just a few dollars difference, which was quite a surprise, because we had asked a professional and experienced solar installer and requested high-quality components with long-term warranties in the quote, instead of going for the cheapest offer we could find. Our home is fairly new and therefore well-insulated, with a ducted heat pump system, energy-efficient appliances and LED lights, and our household energy consumption per year was only around 2,100 kWh back then, so the potential savings weren't actually that high.

Now, some of you will probably say that my math is wrong, because I'd have to calculate the full return of investment, meaning when the money spent on the solution would be paid back in full by the savings. But we didn't look at it that way, because the system also increased the value of our house, and we had always wanted to reinvest the funds in a way that would provide a regular income to us, just like living in your own home allows you to save the rent you'd have to pay otherwise if you invested your money in shares or deposits instead.

Our solar panel and residential battery system has now been up and running for seven years and nine months, and we haven’t had to pay a power bill since September 2017, thanks to solar feed-in credits from our carbon-positive certified electricity retailer Ecotricity and generous distribution charge discounts from our local lines company Northpower. Our 16 solar panels are still performing well, with no significant degradation, and we’ve had only one issue with our battery, when its inverter failed in the middle of winter 2024 (the worst possible time for that to happen, of course).

Because of the 10-year warranty it was replaced by the manufacturer at no cost to us, and it has even improved the battery’s performance a wee bit.

In October 2017 we got our electric car we'd been saving for separately, as it had always been the plan to get one, once they became affordable and provided us with enough battery capacity and range for our travels. We've driven more than 41,000 km since then, and we’ve paid a bit more than $114 in total for "fuel electricity” at ChargeNet rapid charger stations when on longer road trips, while the rest of the time we've been charging at home for free. That's less than 28 cents per 100 km.

Initially we thought that we wouldn’t be better off financially, because what we’d save on electricity and petrol expenses would be offset by the interest we weren’t getting anymore, by not reinvesting our nest egg. However, over the years rising electricity and petrol prices and falling deposit interest rates have proven it to be one of the best investments we ever made, because we locked in the lower prices from 2017, and because the sheer efficiency of both our solar system and our electric car has blown us away and exceeded all expectations. Also, since time-of-use electricity pricing was introduced, our battery has become even more useful, because during cloudy weather periods in winter we can charge it up overnight when electricity is cheaper and let it discharge during the daytime peak and shoulder periods, which saves us money and helps reducing and smoothening the demand on the electricity grid.

In addition to the financial side of things, the feel-good factor by doing the right thing, producing energy in situ from a renewable resource, reducing emissions, making a contribution to fighting climate change, keeping profits from going overseas and supporting our country’s energy independence is nothing to be scoffed at. Also, home-made bread just tastes so much better when baked with power from 100% Aotearoa New Zealand sunshine.

Our home still uses bottled LPG for cooking and hot water for the shower, although we’ve already managed to bring down our usage to about one 45 kg bottle every two years. We’re looking to switch to a battery-backed induction cooktop (to avoid costly and invasive wiring upgrades) and a hot water heat pump in the medium-term future, when an opportunity presents itself, and probably install another 1.5 to 2 kW of solar panels to support these. To be perfectly honest, we appreciate having a second energy source in the house, during power outages due to cyclones or toppled pylons, so we’re currently keeping an open mind, in case domestic hydrogen electrolyser appliances ever became a thing.

Since 2017, technology has continued to progress rapidly, and prices have come down even more. We’d be able to get a solar system twice the size and capacity and an electric car with twice the range for the same amount we invested back then, so there will never be a better time for all of us to make the switch to electric than now.

‍