Solar ROI vs IRR: Understanding Your Investment Returns

ROI measures the total percentage return over the system's lifetime. A R2 million solar system generating R15 million in cumulative savings over 25 years has a 650% ROI. This metric is intuitive and easy to communicate.\n\nHowever, ROI does not account for the time value of money. A 650% return over 25 years is different from the same return over 10 years. For comparing solar to other investments, IRR is more appropriate.

IRR expresses the annualised return accounting for the timing of cash flows. Commercial solar systems in South Africa typically achieve IRRs of 20-35% after Section 12B, depending on tariff and yield.\n\nAn IRR above 20% significantly exceeds most alternative business investments. For context, prime lending rate in South Africa is around 11-12%, meaning solar returns are roughly double the cost of capital.

Section 12B improves both ROI and IRR by reducing the effective investment cost. The 125% deduction in year one creates a large positive cash flow from tax savings, dramatically improving IRR because the benefit is front-loaded.\n\nWithout Section 12B, a typical commercial solar system might achieve a 15-20% IRR. With the 125% deduction, IRR jumps to 25-35%, making it one of the highest-returning capital investments available.

Use IRR when comparing solar to other investment opportunities or when presenting to financially sophisticated decision-makers. IRR allows direct comparison with bank deposit rates, property returns, or other capital projects.\n\nUse ROI when communicating total value to non-financial stakeholders. Our calculator provides both metrics for your convenience.