Case Study: Nowra Couple Goes Completely Off-Peak With 13kW + Battery

The Patel family in North Nowra wanted to do something most South Coast homeowners only talk about: get completely off-peak. Not off-grid — they kept their connection — but no daytime grid imports, no peak-rate evening usage, and a power bill under $50 a quarter. With a 13kW solar system paired with a 13.5kWh Tesla Powerwall 3, they pulled it off. Here's how the numbers actually worked.

The starting point: a $1,420 quarterly bill and rising rates

Anjali and Ravi Patel moved into their 5-bedroom North Nowra home in 2019. With three teenage kids, two home offices, ducted air conditioning and an EV charger added in 2024, their power consumption had grown to roughly 38kWh per day on average — well above the NSW residential average of 18kWh.

By early 2026, their Origin Energy bill had crept to $1,420 per quarter (around $5,680 annually). Peak-rate electricity in their Essential Energy network area sat at 38¢/kWh between 2pm and 8pm, with shoulder rates of 28¢ and off-peak of 24¢. Their old 5kW solar system from 2017 was producing about 6,500kWh a year but exporting most of it for just 6¢/kWh.

"We were exporting energy at 6 cents and buying it back four hours later for 38 cents," Ravi told us. "It felt like we were subsidising the grid."

The plan: oversize solar, add battery, eliminate evening imports

Our system designer recommended a complete replacement rather than a battery retrofit. The 2017 panels were already at 84% of original output, the inverter was due for replacement in 2–3 years, and adding battery to legacy infrastructure would have meant compromised system architecture.

The new system specs:

• Solar: 26 × Trina Vertex S+ 500W panels (13kW total) — 14 panels north-facing, 12 panels east-facing for morning generation
• Inverter: Fronius Symo GEN24 10.0 Plus hybrid inverter
• Battery: Tesla Powerwall 3 (13.5kWh usable, 11.5kW continuous output)
• Monitoring: Fronius Solar.web + Tesla app for combined visibility
• EV charger integration: Smart load control to charge the family Tesla Model 3 only from solar surplus

The east-facing array was a deliberate choice. North-only arrays peak generation at midday, but the Patels' biggest battery-charging opportunity was 8am–11am when the family was finishing breakfast and the battery was nearly empty. Splitting the array meant generation started 90 minutes earlier on summer mornings.

The investment: $24,800 after rebates

Total system price before rebates was $32,600. After incentives:

• STC rebate (federal): –$4,800 (143 STCs at $33 each, applied as point-of-sale discount)
• Cheaper Home Batteries Program: –$2,000 (NSW federal battery rebate, applied at install)
• Old system removal credit: –$1,000 (panels and inverter resold for parts)

Net out-of-pocket: $24,800. The Patels paid this in full from savings rather than financing — but at our standard 6.49% green loan rate, the same system would have cost $267/month over 10 years, less than half their old quarterly bill divided across the months.

Six months in: the actual numbers

The system was switched on in October 2025. By April 2026, we had two complete quarters of real performance data to report.

Generation

13kW system produced 16,200kWh across the first six months — tracking to roughly 19,500kWh annually. That's slightly above our pre-install estimate of 18,800kWh, helped by an unusually sunny December.

Self-consumption

The Patels self-consumed 78% of solar generation (vs the typical 30–40% for a non-battery home). The remaining 22% was exported to the grid at 7¢/kWh feed-in tariff with Origin Energy.

Grid imports

Grid imports dropped from 38kWh/day average to 1.4kWh/day average — a 96% reduction. Most of the remaining grid import happens on consecutive cloudy winter days when the battery doesn't fully recharge.

Bills

Quarter 1 (Oct-Dec 2025): $32 bill, after $112 in feed-in credits offset $144 in supply charges and minimal grid usage.

Quarter 2 (Jan-Mar 2026): $64 bill — slightly higher because of cloudier February weather and increased EV charging during a Newcastle road trip.

Average across both quarters: $48. Annualised saving: $5,488.

The payback maths

$24,800 invested, $5,488 saved annually = 4.5-year simple payback. Factor in projected 6% annual electricity price increases (consistent with AEMC forecasts), and the actual payback is closer to 4.1 years.

The Powerwall 3 is warrantied for 10 years and expected to deliver useful life of 12–15. The Trina panels are warrantied for 25 years at 87% performance. The Fronius inverter is warrantied for 10 years (extendable to 15).

Over a 20-year horizon, with 5% annual electricity price growth, the Patels will save approximately $182,000 against their counterfactual bill.

Use our free Solar Savings Calculator to model your own off-peak scenario based on your usage and roof.

What the Patels would do differently

"In hindsight, we should have done this in 2022," Anjali said when we visited for the six-month review. "The maths only got better as electricity prices kept rising, and the battery rebate didn't exist back then. But the regret is real — that's $20,000 in bills we paid that we didn't need to."

Three lessons from their install we'd pass on to other Nowra and Shoalhaven homeowners:

1. Don't undersize the battery. The Patels considered a 10kWh battery to save $3,000. We modeled both options, and the 13.5kWh battery delivered 18% more annual savings — paying back the difference in under three years.

2. East-facing panels are underrated. Pure north-facing maximises annual generation, but for battery homes, morning generation matters because it tops up the battery before peak afternoon loads.

3. Smart EV charging is essential for high-usage homes. Without solar-only EV charging logic, the Tesla would have been pulling from the grid every night at peak rates, ruining the off-peak goal.

Could you replicate this in your home?

The Patels' result is achievable for any Shoalhaven or Illawarra household with: a roof that can fit 13kW (typically 70–80m² of unobstructed pitched roof), a daily usage above 25kWh (so the battery actually fills and drains daily), and willingness to invest $20,000–$28,000 net. Smaller homes get smaller versions of the same outcome — a 6.6kW + 10kWh setup at $14,000–$16,000 will eliminate 70–85% of most three-person household bills.

Frequently Asked Questions

Why didn't the Patels go fully off-grid?

Two reasons. First, Essential Energy's network supply charge of $1.20/day is small compared to the cost of an off-grid backup generator and oversized battery bank that would handle a 7-day cloud event. Second, staying grid-connected means they earn export credits (about $400/year) that wouldn't exist off-grid. Pure off-grid would have cost an additional $18,000–$22,000.

Did they need Essential Energy approval for a 13kW system?

Yes. Anything above 5kW per phase in Essential Energy's network requires a connection application before installation. The Patels' install was on a 3-phase connection so the 13kW was approved without export limiting. On single-phase connections in Nowra, systems above 5kW often need export limiting to 5kW.

Will the system survive a coastal storm?

The panels are rated to 5400Pa front load and 2400Pa rear load — comfortably above the AS/NZS 1170 wind loading requirements for the South Coast. We use stainless steel mounting hardware on all coastal installs to handle salt exposure. The Patels' system survived the March 2026 east coast low without issue.

What happens if the Powerwall fails out of warranty?

Replacement Powerwall 3 in 2035 (estimated) is likely $7,000–$9,000 installed, based on current battery price decline curves. By that point, the original investment will have paid back twice over, and battery prices are expected to have fallen substantially.

How much did the install disrupt their household?

One full day to remove the old system, two days to install the new system, plus a 4-hour Essential Energy inspection and meter reconfiguration scheduled two weeks later. The household had power for all but about 90 minutes across the entire process — we use a generator backup during the meter swap.

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