IRR Calculator: Internal Rate of Return for Energy Projects
IRR — the internal rate of return — is the annualized return an investment earns across its whole life, accounting for the timing of every cash flow. Unlike simple payback, which stops at break-even and ignores everything after, IRR captures the full economic value of a project: early versus late cash flows, declining savings from degradation, and any residual value at end of life. It's the rate that makes the net present value (NPV) of all cash flows equal to zero — the actual annualized yield of the investment. Investors and developers compare IRR against a hurdle rate — the minimum return they require to commit capital. If IRR exceeds the hurdle rate, the project creates economic value; if it falls below, the project destroys it relative to the alternatives. For residential solar and storage, a hurdle rate of 6–10% is typical. For institutional infrastructure funds, 8–12%. For corporate efficiency programs, 15–20%. IRR puts every project — solar, batteries, heat pumps, EV fleet — on a single comparable scale, making it the right tool when the decision is not just "does this pay back?" but "does this beat my alternatives?"
Total installed cost after tax credits, rebates, and incentives.
Year-1 electricity savings, export revenue, or avoided cost minus O&M.
Equipment resale or scrap value at end of life. Usually 0 for solar/batteries.
annualized return over 25-year life
positive — project adds value
sum of all cash flows (not discounted)
IRR vs. 7.0% hurdle rate
Results update live as you type. For planning and field-check estimates — always verify against applicable standards and equipment ratings.
How we calculate this →How IRR and NPV are calculated for an energy project
IRR is the discount rate that makes the net present value of all project cash flows equal to zero. The calculation starts by building the full cash flow series: Year 0 is the negative upfront investment (cash out); Years 1 through the project lifetime are positive cash inflows — the annual net savings or revenue, grown each year by the escalation rate; the final year also includes any salvage value.
NPV at the hurdle rate is straightforward: divide each year's cash flow by (1 + discount rate)^year to find its present value, then sum all of them including Year 0. A positive NPV means the project returns more than the hurdle rate; a negative NPV means it doesn't clear the bar.
IRR requires solving numerically. We use bisection: test the NPV at a very negative return (−50%) and a very high one (+1,000%), then progressively narrow the bracket until we find the rate where NPV = 0, accurate to eight decimal places. This handles nearly any realistic cash flow profile for an energy project, including escalating savings and non-zero salvage values.
The verdict is simple: if IRR > hurdle rate, the project creates value relative to the alternative represented by the hurdle rate. If IRR < hurdle rate, the project destroys value on a risk-adjusted basis — even if it has a reasonable payback, the returns don't justify the capital relative to alternatives.
Note: IRR assumes cash flows are reinvested at the IRR itself, which can overstate returns for very high-IRR projects. Modified IRR (MIRR) addresses this but requires an explicit reinvestment rate. For most energy projects with IRR in the 8–20% range, standard IRR is a reliable metric.