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Solar True Payback — No Installer Spin

Every solar quote gives you an optimistic 5–7 year payback. This calculator adds what they leave out: inverter replacement, panel degradation, declining feed-in tariffs, removal of old panels, and the opportunity cost of your capital sitting in silicon instead of an index fund.

Region defaults
System details
💡 Average generation: A 6.6kW system in a good location (facing north/south) produces ~24–28kWh/day. Installers often quote peak days. Annual average including cloudy days and seasonal variation is typically 15–20% lower than the headline number.
Energy tariffs
⚠️ Feed-in tariff reality: Australia's FiT has fallen from 44–66¢ (2010) to 4–8¢ (2025). The EU average is 6–8¢. UK SEG is 15¢ but dropping. Model conservatively — assume it continues to fall, not rise.
⚡ The hidden variables
What installers don't volunteer
Panel degradation (% per year) 0.5%
Most manufacturers quote 0.5%/yr. Independent studies (NREL, 2022) put real-world degradation at 0.5–0.8%/yr. After 25 years your panels may only perform at 80–87% of original capacity.
Inverter replacement at year 8
Inverters typically last 8–12 years. Your panels are warranted for 25 years. You will almost certainly replace the inverter at least once, possibly twice.
Inverter replacement cost $2,500
A quality single-phase inverter (Fronius, SMA, Enphase) runs $1,500–4,000 installed. Microinverters are more expensive but individual panel replacement is cheaper.
FiT annual decline (¢ per year) 0.5¢
Australian FiT has declined ~1.5¢/yr on average since 2010. Many analysts expect it to reach near-zero as grid saturation increases during daylight hours.
Annual maintenance / cleaning $150
Panels need cleaning 1–2 times/year especially in dusty areas. Dirty panels lose 5–15% efficiency. Also factor in monitoring system costs and occasional panel replacement.
Panel removal cost (if replacing old system) $0
Removing old panels costs $500–2,500 depending on system size and roof type. This is rarely included in upgrade quotes. Old panels cannot be left in place.
True Payback Period
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Enter your system details
Cumulative cashflow — solar vs index fund
Negative = still in the hole. Green line crossing zero = true payback.
Year-by-year breakdown
Research basis & sources: Panel degradation: Jordan & Kurtz, NREL (2012) — median degradation rate 0.5%/yr; real-world studies show 0.5–0.8%/yr. Inverter lifespan: EnergySage Solar Inverter Guide — string inverters 10–15 years, microinverters 20–25 years. Feed-in tariff decline: Clean Energy Regulator (Australia) — FiT history 2010–2025. Soiling losses: SolarEdge soiling study — 5–15% production loss on dirty panels. Opportunity cost comparison uses compound growth at specified rate — consistent with long-run equity market returns in S&P SPIVA data. Disclaimer: Results are estimates. Actual payback depends on household usage patterns, local tariffs, roof orientation, shading, and future energy prices. Get multiple quotes. This is not financial advice.
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📖 Why installer quotes are always optimistic Tap to expand

Solar installers calculate payback by dividing the system cost by the annual savings — assuming zero degradation, no maintenance, stable feed-in tariffs, and an inverter that lasts 25 years. None of these assumptions are accurate.

The hidden variables this calculator adds:

  • Panel degradation — panels lose about 0.5–0.8% of output per year. After 25 years they may only work at 80–87% capacity
  • Inverter replacement — inverters last 8–12 years. You will almost certainly replace yours at least once during the panel warranty period
  • FiT decline — Australia's feed-in tariff fell from 44¢ in 2010 to ~6¢ today. It may fall further as grid saturation increases
  • Maintenance and cleaning — dirty panels lose 5–15% efficiency

True payback is when the cumulative savings (including all running costs and the inverter replacement) equal the total system cost. This is almost always 3–7 years longer than the installer's estimate.

Self-consumption is critical. Energy you use directly from your panels is worth the full grid rate (~32¢). Energy you export earns only the FiT (~6¢). Shifting appliances to daytime use dramatically improves ROI.

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