Can I add every wind-energy loss percentage to obtain total losses?

The short answer

Loss percentages cannot always be added directly. Some apply sequentially to the energy remaining after earlier reductions; others are defined against a shared gross baseline. A valid total depends on those definitions and on avoiding overlapping loss categories. Start with an energy ledger rather than summing an unexplained percentage list.

Identify the denominator of each loss

For each category, record the physical mechanism, applicable period and energy boundary. Ask whether the value represents a fraction of gross aerodynamic opportunity, turbine electrical energy or another quantity. Keep availability, curtailment and electrical losses distinct where the model requires it.

Check for overlap. A supplier's net curve or forecast may already include a loss that a consultant proposes to deduct again. A detailed table is not necessarily more complete if it counts the same mechanism twice.

Use arithmetic consistent with the definitions

For an illustrative sequential case, 100 units reduced first by 10% leave 90 units. A further 10% reduction of the remainder leaves 81 units, giving a 19% combined reduction. Adding the percentages would give 20%, a different convention.

This example does not prescribe a loss model for every project. If both losses are explicitly measured against the same baseline, the calculation needs to reflect that basis instead. Document the chosen method and the reason it matches the evidence.

Reconcile the final energy boundary

Show a clear path from resource and curve calculation to net energy at the comparison point. Time-dependent losses should be treated at suitable resolution when coincidence matters. A single annual percentage may hide whether losses occur during high-value generation.

The report should retain individual definitions, sources, overlap checks and the combined result. This allows the buyer to compare quotations without mistaking an arithmetic convention for a real performance advantage or an independently verified project loss budget.