Which assumptions should I stress-test before trusting a wind payback estimate?

The short answer

Start with the assumptions that affect useful energy, its value and project cost. Change one input at a time to see what drives the result, then combine plausible adverse conditions. Sensitivity analysis does not assign probabilities unless a justified probability model is supplied. A spreadsheet that produces one precise payback year may still depend on uncertain wind, tariff and operating assumptions.

Establish a traceable base case

Use an explicit installed cost, annual generation at a defined boundary, useful-energy share, export treatment and operating-cost allowance. Record the source of each input and whether it is confirmed, modeled or assumed. Avoid treating a supplier’s rated power as evidence for annual production.

Keep the same scope when changing assumptions. For example, a lower energy case should not quietly receive a better tariff or a reduced service allowance unless those changes form a separate, explained scenario.

Compare one-at-a-time sensitivities

Illustrative simple-payback screen: initial cost is 20,000 currency units, annual electricity value is 4,000 and annual operating cost is 1,000. The base net benefit is 3,000, so payback is 6.7 years.

Changed assumption	Annual net benefit	Simple payback
Electricity value 20% lower	2,200	9.1 years
Operating cost 50% higher	2,500	8.0 years
Installed cost 20% higher	3,000	8.0 years

These are hypothetical cases, not forecasts, prices or typical uncertainty ranges.

Investigate the assumptions that matter most

The table points to where better evidence may be useful. If useful-energy value controls the decision, improve wind and load matching before spending effort on immaterial formatting details. If a site-cost item is uncertain, obtain a scope-specific local estimate.

Then test combined adverse cases and a discounted project model. Document which variables are linked before combining sensitivity cases. The final decision should state which conditions must hold for the investment to meet its objective, rather than presenting the base-case payback as a guaranteed outcome.