I got solar about four years ago. Straightforward decision. The payback was under five years, and the panels would keep producing for another twenty after that. No-brainer.
But then I made the mistake of asking: "What should I do next?"
Should I add a battery? Switch my gas hot water to a heat pump? Rip out the gas heater and go full electric? What about an EV? Is the premium actually worth it, or am I just buying an expensive toy?
I went down the rabbit hole. Forums. Government rebate pages. Installer websites. YouTube channels run by guys who happen to sell the thing they're recommending. Everyone had a different answer, and almost everyone was trying to sell me something.
Worse, nobody could tell me how the upgrades interacted with each other. If I install a heat pump hot water system, my electricity goes up, which changes how much solar I need. If I insulate first, my heating costs drop, which changes whether a reverse cycle system is worth the money. The order matters, and nobody was modelling that.
I just wanted a tool that would line everything up side by side and tell me, in cold hard numbers, what was actually worth doing. I couldn't find one. So I built one.
What it does
Ohm Equity is a free calculator that ranks every major home energy upgrade by net present value (NPV). You punch in your postcode, home size, and a few details about your setup, and it tells you exactly which upgrades make financial sense, and in what order.
NPV is the same metric investors use to evaluate any investment. It accounts for the time value of money: a dollar saved next year is worth less than a dollar saved today. I use a 10% discount rate, which is roughly what you'd expect from an index fund. If an upgrade still comes out positive at that hurdle rate, it's worth doing. You'd be better off spending the money on solar panels than putting it in the stock market.
That's a high bar. And most of the upgrades clear it.
The order matters more than you'd think
This is the bit that most calculators get wrong (or just ignore entirely). They evaluate each upgrade in isolation, as if you'd only ever do one thing. But in reality, each upgrade changes your energy profile, which changes the value of every other upgrade.
Here's a simple example: if you install ceiling insulation first, your heating and cooling costs drop by 25%. Great. But that also means you need a smaller solar system to cover your usage, which changes the economics of solar. And if you switch from gas to a heat pump hot water system, your electricity usage goes up, which changes how much of your solar you self-consume (the most valuable kind of solar output).
The calculator evaluates upgrades in sequence. It finds the order that maximises total value across your whole upgrade roadmap, not just for each upgrade in isolation. The full logic behind this is explained on the methodology page. Sometimes that means a battery that looks marginal on its own becomes a solid investment when paired with a properly sized solar system. Sometimes it means insulation should come before solar, not after.
What it covers
Pretty much every major residential energy upgrade available in Australia right now:
- Solar panels, sized to your actual usage, with STCs and state rebates baked in.
- Battery storage, including the new Cheaper Home Batteries program, VPP revenue, and degradation over time.
- Heat pump hot water, the single best upgrade for most homes with gas. Payback is often under two years.
- Reverse cycle heating, for homes still running gas ducted heating. The COP advantage over gas is significant, especially in milder climates.
- Induction cooktop, cheap to switch, and often the first domino in ditching gas entirely.
- Ceiling insulation. Older homes can save 20 to 40% on heating and cooling. The rebates in VIC are particularly generous.
- Draught sealing. Costs almost nothing, saves more than you'd expect. Usually the highest-return upgrade available.
- Electric vehicle. Models the price premium over an equivalent petrol car, fuel savings, reduced maintenance, and charging costs.
- Home automation: smart thermostats, solar diverters, and standby power reduction.
Where the data comes from
Every assumption in the calculator is sourced from public data: electricity and gas rates from the Australian Energy Regulator and Canstar Blue, equipment costs from SolarChoice installer surveys, rebates from the Clean Energy Regulator and state government programs.
And here's the important part: every single assumption is visible and adjustable. Click "Under the Hood" on the calculator and you can see (and change) the electricity rate, gas rate, discount rate, escalation rates, equipment costs, everything. If your actual tariff is different from the default, plug it in and the numbers update instantly. No black boxes.
The estimates are designed to give you a reliable ballpark for comparing options. Your actual costs will depend on installer quotes and your specific usage patterns. Always get 2 to 3 quotes before committing to anything.
What's next
I'm working on expanding to more countries, better time-of-use tariff modelling, and writing more posts like this one, digging into specific upgrades with real numbers. If you'd rather skip straight to the numbers, check out the pre-computed examples for each Australian state. The next post is a deep dive into what solar actually costs and saves in 2026, state by state.
If you spot a data error, have feedback, or just want to tell me my numbers are wrong, I want to hear it. You can contact me on the contact page.