Investing in rooftop solar is often framed as a way to cut electricity bills, but it is also a financial decision. The payback period — the time it takes for cumulative savings to equal the upfront cost — is the key metric. How does solar stack up against other common investments like shares, bonds, term deposits, or real estate? This article uses real Australian data, including typical system costs, feed-in tariffs, and electricity rates, to compare returns.

Understanding Solar Payback Periods

The solar payback period is calculated by dividing the net system cost by annual savings. For a typical 6.6 kW system in Sydney, installed cost averages $4,500–$6,500 after the federal Small-scale Technology Certificate (STC) discount. With an average feed-in tariff of 5–8 c/kWh and self-consumption of 40–60%, annual savings range from $800 to $1,200. That gives a payback of 4–7 years. Over a 25-year panel lifespan, the return on investment (ROI) can exceed 300%, equivalent to an internal rate of return (IRR) of 10–15%.

Comparing Returns: Solar vs. Other Investments

1. Savings Accounts and Term Deposits

As of March 2025, the best high-interest savings accounts in Australia offer around 5.5% per annum, and 1-year term deposits pay 4.8–5.2%. These are effectively risk-free but taxable. Solar, by contrast, generates tax-free savings (you are not earning income, you are reducing expenses). A 5.5% savings account yields roughly 3.85% after 30% tax, whereas solar’s 10–15% pre-tax equivalent is entirely tax-free. On a risk-adjusted basis, solar handily beats cash.

2. Australian Shares (ASX 200)

The ASX 200 has returned about 9.5% per annum over the last 20 years including dividends (pre-tax). But shares are volatile — in 2020 the market dropped 30%. Solar returns are stable and inflation-linked (electricity prices rise). A 6.6 kW system’s IRR of 10–15% is comparable to long-term equity returns but with much lower volatility. However, solar is illiquid: you cannot sell a panel for cash quickly.

3. Bonds and Fixed Interest

Australian government bonds yield around 4.2% for 10-year maturities. Corporate bonds offer 5–6%. Solar’s 10–15% IRR is far higher, but bonds are liquid and have defined maturity. Solar panels degrade slowly (0.5% per year), but their cash flows (savings) rise with inflation, while bond coupons are fixed. For income-seeking investors, solar provides an inflation-hedged, tax-free yield.

4. Real Estate (Residential Property)

Australian residential property has delivered average capital growth of 7–8% per year over the long term, plus gross rental yields of 3–4%. After costs (stamp duty, maintenance, management fees, interest), net returns are often 5–7%. Solar’s 10–15% IRR is higher, but property offers leverage (mortgage) and capital gains. For a householder, solar is a smaller, more accessible investment with no transaction costs like stamp duty.

Risk and Liquidity Considerations

All investments involve trade-offs. Solar panels have a 25-year performance warranty but require little maintenance. The main risk is that electricity prices fall or feed-in tariffs drop. However, Australian electricity prices have risen 5–10% annually over the past decade. Even if prices stabilise, the savings are real. Solar is illiquid — you cannot sell a panel quickly — but for a homeowner planning to stay put for 5+ years, that is not a problem.

Case Study: Sydney Homeowner

Consider a Sydney household with a $5,000 (after STCs) 6.6 kW system. They consume 60% of generated solar and export the rest at 7 c/kWh. Annual savings: $1,100. Payback: 4.5 years. Over 25 years, total savings (assuming 3% annual electricity price rise) exceed $30,000. The IRR is 13.6%. If they had invested $5,000 in the ASX 200 instead, with 9.5% pre-tax return and 30% tax, after 25 years they would have about $27,000 after tax — less than solar. And solar savings are tax-free.

How to Maximise Solar Returns

  • Increase self-consumption: Use appliances during the day, add a battery (though battery payback is longer, typically 8–12 years).
  • Choose the right installer: Get quotes from at least three CEC-accredited installers. Prices vary by $1,000–$2,000.
  • Optimise orientation: North-facing panels in Australia produce 15–20% more than east-west.
  • Monitor feed-in tariffs: Some retailers offer higher rates (e.g., 12 c/kWh from AGL on some plans) but may have higher daily charges.

For a deep dive into the economics, read The Complete Guide to Distributed Energy Economics.

Tax Treatment of Solar vs. Other Investments

Solar savings are not taxable; you are simply spending less on electricity. In contrast, interest, dividends, and rental income are taxed at your marginal rate. Capital gains on shares and property are taxed (with a 50% discount if held >12 months). Solar panels also add value to your home — the CSIRO estimates a 3–5% increase in resale value, which is capital gains tax-free for a primary residence.

Conclusion: Solar as an Investment

For most Australian homeowners, solar offers a superior risk-adjusted return compared to cash, bonds, and even shares. The payback period of 4–7 years is competitive, and the tax-free nature of savings amplifies the advantage. While solar is not a liquid investment, its low volatility and inflation protection make it an excellent addition to a diversified portfolio. As electricity prices continue to rise, the case for solar only strengthens.

Related articles

  • The Complete Guide to Distributed Energy Economics
  • How to Calculate Solar Payback Period
  • Solar vs. Battery: Which Pays Back Faster?
  • Understanding Feed-in Tariffs and Time-of-Use Rates
  • The Impact of Electricity Price Rises on Solar Payback