Solar ROI Calculator — Return on Investment Explained
Return on investment, or ROI, is one way to measure whether solar is a good use of your money. It compares total lifetime savings to the upfront cost. But for most homeowners, payback period and annual cash savings are more relevant day-to-day figures. ROI is useful for comparing solar against other investments like shares or home renovations.
Solar ROI tells you how your money performs over the long term. But payback and cash-flow numbers are usually the ones that answer, "Is this worth it for me right now?"
How Solar ROI Is Calculated
Solar ROI is typically calculated over the expected system lifetime, usually 25 years. The formula:
ROI % = (Total lifetime savings - Total system cost) / Total system cost × 100
System costs $8,000 and generates $30,000 in savings over 25 years? That's 275% ROI. Simplified example — real calculations factor in degradation, inverter replacements, electricity price changes, and other variables that affect the net result.
Factors That Affect Solar ROI
System cost
Lower upfront cost means higher ROI, assuming similar savings. Australian system prices have become more competitive over time, which has improved ROI for new installations.
Self-consumption rate
This is the big one. The more solar you use directly, the higher your effective savings rate. A household at 50% self-consumption will see a meaningfully different ROI than one at 30%, even with the same system.
Electricity prices
Higher retail prices increase the value of every kWh you self-consume. If prices keep rising — which has been the historical trend — your actual ROI may beat the estimate. If they stay flat, the reverse.
System degradation
Panels produce less as they age. Most degrade at 0.3% to 0.7% per year. Over 25 years, that's a 10–15% reduction in output, which cuts into lifetime savings and ROI.
Inverter replacement
Inverters typically need replacing every 10 to 15 years. That's a significant cost that should be in any lifetime ROI calculation. Plenty of estimates skip this — worth checking what assumptions were used.
Typical Solar ROI in Australia
A well-sized system on a good roof can show a 25-year ROI somewhere around 200% to 400%. That sounds impressive, but it is not the number most homeowners feel month to month. The practical question is still simpler: how much cash does it save each year, and how quickly does it pay back?
A number based on your bill is more useful. Put your usage and tariff into a solar savings calculatorthat models the lifetime figures.
Estimate your solar ROI
Upload a bill and see estimated lifetime savings and return based on your household data.
Frequently Asked Questions
Common questions about solar ROI
What is a good ROI for solar panels?
Somewhere between 10% and 20% per year over the system life, for most well-sited installations. Self-consumption and local electricity prices are the biggest levers.
How is solar ROI different from payback period?
Payback tells you how long until you break even. ROI tells you the total return over the system lifetime as a percentage. A system with 5-year payback and 25-year life has a different ROI than one with 7-year payback and the same lifespan.
Does solar ROI account for degradation?
A thorough calculation should account for gradual panel degradation (typically 0.3% to 0.7% per year) and inverter replacement costs every 10 to 15 years.
How does electricity price inflation affect solar ROI?
Rising electricity prices increase the value of self-consumed solar, which improves ROI. Most estimates assume an annual price increase, but actual movements are uncertain.
What is the ROI of solar plus battery compared to solar only?
Solar-only systems typically show higher ROI due to the significant extra cost of a battery. The gap narrows if you're on a time-of-use tariff with high peak rates.
Related guides
This guide is for informational purposes only and does not constitute investment advice. ROI estimates vary by household and are based on assumptions that may not hold over time.