Solar vs Stock Market
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It is a genuine and increasingly popular comparison — especially among FIRE (Financial Independence, Retire Early) communities who evaluate every large purchase as an investment. The key nuance is that solar provides a guaranteed, tax-free, inflation-linked return, while stock markets offer higher potential returns with significant volatility. A cash-purchased solar system is most comparable to a fixed-return bond or gilts, but with an IRR typically between 8–13% — well above current bond yields.

Internal Rate of Return (IRR) is the discount rate that makes the Net Present Value of all cash flows equal to zero. For solar, the cash flows are: Year 0 = −installation cost; Years 1–25 = annual savings from self-consumption (at Ofgem Q2 2026 rate of 24.67p/kWh) plus SEG export earnings (12p/kWh Octopus Outgoing), with 3.5% electricity inflation, 0.5% annual panel degradation, and a £1,000 inverter replacement at Year 12.

The chart plots net profit relative to your initial investment. Because you pay the full installation cost upfront, you start in negative territory. As annual savings accumulate each year, the solar line rises towards zero (break-even) and then into profit. This is structurally identical to any capital investment — including buying shares — where you first pay capital before receiving returns.

At historical S&P 500 average returns of 10.7%, a cash-invested portfolio often generates higher nominal returns over 25 years due to the power of compounding. However, solar returns are: (1) guaranteed — not subject to market crashes or volatility; (2) tax-free — no Capital Gains Tax or Income Tax; (3) inflation-linked — each 3.5% electricity price rise increases your solar income; and (4) immediate — you begin saving from Month 1 without waiting for a sale event. Most financial advisers recommend solar as a complementary asset to a portfolio, not a replacement.

The S&P 500 figure uses the widely cited 10.7% average annual total return since 1957 (including dividends, before CGT). The FTSE 100 figure uses 7.2% average annual total return, consistent with long-term historical data from the London Stock Exchange. Both figures are nominal, not inflation-adjusted. Neither accounts for dealing fees, platform charges, or the capital gains tax due on disposal.

Most solar panels carry a 25-year performance warranty but continue generating electricity well beyond that. Studies show panels still operating at 80–90% capacity after 30 years. Beyond Year 25, you have a fully paid-off energy asset delivering near-pure profit. The stock market comparison has no equivalent "free energy" dividend — your shares only have value when sold.