The system was switched on on the 20th of February 2025. A 13 kilowatt Sungrow SH10RS hybrid inverter, an SBR160 battery with 16 kilowatt-hours of usable storage, fitted to a single household on a residential property near Launceston, Tasmania. Installed cost: $25,000. The promised payback was somewhere between five and seven years depending on which assumption you believed about generation, self-consumption, electricity prices, and how much you'd actually use the battery.
It's now early April 2026. Fourteen months in. I have just over a year of high-resolution telemetry, a corrected payback estimate, and a small list of things I genuinely could not have known on day one — and which the salesperson, the installer, and the inverter dashboard each told me different versions of.
This is that list.
1. The inverter isn't honest about small loads
I wrote about this in detail in another piece, but the short version
is: Sungrow's battery_discharge_power reading is accurate at the kilowatt
scale and reads zero for sub-1 kilowatt loads. The dishwasher draws 0.7 kWh
per cycle and the inverter never registers it as a discharge. The state of
charge clearly drops; the discharge metric clearly says nothing happened.
Over a typical week the discrepancy is about 30 kilowatt-hours. About $5.64 to $8 a week of battery savings the official telemetry was missing. Annualised: ~$416 a year of value the dashboard wasn't crediting to the system.
I would not have noticed this for years had I not deliberately compared two different signals from the same data feed. Most owners of most home batteries will live their entire ownership without anyone telling them the official number is short.
The fix changed my estimated payback from 5.7 years to 5.3 years on exactly the same hardware and usage. Five months recovered from arithmetic.
2. The EV is the single biggest accelerator of payback — and the calculator was ignoring it
Day 1 me would have been told that the system pays for itself in 5-7 years on the back of solar self-consumption, battery arbitrage, and grid export. The salesperson's spreadsheet doesn't mention petrol.
But we have an EV — a Kia EV3 GT 2WD — and it gets charged predominantly from this same system. Its charging profile is the second-biggest energy event in the household after the battery itself: 134 kilowatt-hours charged in the most recent week, 657 kilometres driven. At current Tasmanian petrol prices (~$2.20/L) for an equivalent ICE doing the same kilometres, that's about $138 of fuel a week the system has displaced.
The kicker: the inverter dashboard's payback estimate doesn't count any of it. Petrol displacement isn't on Sungrow's menu of metrics. It's not on iSolarCloud's headline tile. The whole calculation is happening as if the EV doesn't exist.
When you actually fold petrol displacement into the payback maths — and you should, because not buying petrol is exactly as much of a saving as not paying the grid bill — the numbers change dramatically:
| Solar-only | With EV petrol displacement | |
|---|---|---|
| Daily savings | $12.75 | ~$32.50 |
| Annual run-rate | $4,654 | ~$11,850 |
| Payback timeline | 5.3 years | ~2 years from now |
The remaining payback gap from today (about $19,700 of the original $25,000) closes in about 20 months at the EV-inclusive run-rate, instead of about three years at the solar-only rate.
A caveat: the high-resolution EV telemetry is only two weeks old. The calculation above assumes this week's charging volume holds — and one of the eight days included a 262 km road trip, so the average is inflated. A more conservative annual estimate is closer to ~22,000 km/year of driving, not 30,000. Even the conservative version still roughly halves the payback timeline compared to the solar-only number.
A necessary caveat: the EV has its own purchase cost and its own ROI calculation. We didn't buy the EV to improve the solar payback — we bought it for a dozen reasons that have nothing to do with panels on the roof. The petrol displacement is a real saving, but it's not a free lunch; it's a saving that sits inside a separate capital decision. The point here isn't "buy an EV to fix your solar ROI" — it's that most solar payback calculators ignore the interaction entirely, and if you happen to have both, your real payback is shorter than the dashboard tells you.
A related observation: solar-share charging works — up to a point
Pulse — the software layer I built around the Sungrow telemetry — has a "solar-share charger" mode that prefers to charge the EV during peak solar hours. The mode works: roughly 60-67% of the EV's charging volume now happens between 11am and 4pm, exactly the window the algorithm targets.
But "60% of the volume happens in the solar window" is not the same as "60% of the volume comes from solar". The actual solar share of EV charging is closer to 61%, even with all that midday weighting. The remaining ~39% comes from grid because:
- Big charging days outsize what the array can produce. A 40 kWh charge on a Tasmanian autumn day exceeds the array's daylight surplus once the household and battery have taken their share.
- The household competes with the EV for the same solar. During peak generation, the inverter is also charging the battery and powering the house. The EV gets the leftovers.
You don't see this in the marketing. You don't see it in the simulator tools. You see it in the data after several months, and only then if you deliberately compare grid pull during charging windows against EV consumption in those same windows.
3. The dishwasher has a perfect daily pattern
We run the dishwasher once or twice a day. Not "roughly". Exactly. In a 16-day window, we ran 22 cycles — alternating between 1-cycle days at 0.7 kWh and 2-cycle days at 1.3 kWh. The pattern is so regular it forms a perfect saw-tooth on the energy chart.
This was a small revelation. I thought our dishwasher use was variable because we are variable. It turns out the appliance is the constant — it's full once a day and we run it. Once full again, we run it again. The randomness was in our perception, not in the data.
Once you can see the pattern, you can act on it. The dishwasher cycle is about 25 minutes of high-power draw. We used to run it after dinner — which meant it drew from the battery during the evening, reducing what was available for the overnight load. Moving the wash to the morning was the real win: at 7:30am the battery has surplus from the prior day's solar, the overnight load has passed, and the dishwasher runs on stored solar rather than competing with the overnight essentials.
Could you push it further to 12:30pm and run it on direct solar instead of battery? Yes — and it would move the appliance from 89% solar/battery sourced to 100% direct solar. But the marginal gain is small. The meaningful shift was evening → morning, not morning → noon. The battery is just a delay line for solar. Once you accept that, "battery sourced" and "solar sourced" are the same thing on different time scales — and the real question is which loads compete for the overnight reserve, not which ones happen to coincide with peak generation.
4. EV efficiency is real, not marketing
The Kia EV3 GT 2WD is rated for around 4.9 kilometres per kilowatt-hour real-world. After several thousand kilometres of mixed driving in Tasmania (highway, mountain, urban, the occasional 250+ km road trip), my measured efficiency is 4.94 km/kWh.
That's the energy at the wall outlet, not the battery. So it includes the ~10% loss between the AC plug and the cells. The real efficiency at the wheel is even better than the spec says.
I list this because most EV reviews extrapolate from a single test drive under favourable conditions and wave a number around. Mine comes from the odometer (1,051 km in 17 days, verified against Kia Connect's API) divided by the EV charger's energy meter (252 kWh, verified against the inverter's flow data). The arithmetic isn't optimistic. The car is doing what it said it would do. That's news.
5. The payback timeline gets shorter once you measure properly
I've already touched on this but it deserves its own bullet because it's one of the most important things I've learned in 14 months: the more accurately you measure, the shorter the payback gets, because every methodology error in a payback calculator is biased toward undercounting savings.
The errors I've found and corrected so far:
- Battery discharge under-counted by 30% (Sungrow's small-load blind spot, point 1 above).
- EV petrol displacement excluded from the payback calc entirely (point 2 above — the biggest single correction).
- Self-consumption value computed against a low-end weighted rate that understated peak hours.
Each of these moved the payback estimate in the same direction: earlier. There's no error I've found that moved it the other way. That's not a coincidence — the human bias when designing payback calculators is to be conservative because no-one wants to over-promise. Conservative assumptions get baked in. The owner notices nothing.
If you're 14 months into a solar system and your dashboard says payback is "on track" — measure properly, derive the numbers from raw telemetry, and your real timeline is almost certainly shorter than you think. In our case, the corrected solar-only figure is 6 months better than the inverter's headline. Add the EV to the picture and it's about 3 years better. The system has been quietly outperforming for months.
What I'd tell day-1 me
Three things.
One: don't trust the inverter dashboard for financial decisions. It's built to monitor the asset, not to advocate for the owner. Pull the raw data into your own database from week one. Build cross-checks. Compute the numbers that matter to you, not the ones the manufacturer chose to surface.
Two: optimisation has diminishing returns past a certain point. The big wins came from the hardware decision (battery sized to actually cover the overnight load), the EV decision (matching it to solar generation timing), and the basic charger logic (prefer solar windows). Squeezing the last 5% of efficiency out of when the dishwasher runs is fun and educational but doesn't move the bill much.
Three: the system is a living thing, not a static asset. Tariffs change. The car changes how you use electricity. The seasons change what the array produces. Your household routines change. The numbers you projected on day 1 are stale by month 6, and stale numbers compound. Build the muscle of going back to the data every quarter and re-deriving the real picture.
The headline metric, after 14 months, with the corrections from points 1-5 baked in: 21.1% paid back on a solar-only basis, ~5.3 years to break-even on solar alone, $5,277 in solar savings against the $25,000 install cost. Once the EV petrol displacement is folded in, the forward-looking payback is closer to two years. Either way: on track. Quietly working. And teaching me, every few months, something I thought I already knew but didn't.
The numbers in this piece are derived from continuous 5-minute interval telemetry on a single home solar system on a residential property near Launceston, Tasmania, since February 2025. EV charging and odometer data is from Kia Connect, captured continuously since March 2026. The payback estimate uses the corrected SOC-derived battery discharge methodology described in the companion piece "Your inverter is undercounting your battery savings".