Each definition fixes the five things that usually stay vague: numerator, denominator, which hours count, what is excluded, and where the expected value comes from. Every number shows those next to it.
Available means operational, not performing. Curtailed is available and not dispatched: it never reduces 01 or 02, it shows up in 05, 06 and 07.
Could the equipment run?
Hours a unit was operational ÷ daylight hours in the period, per inverter, weighted by rated capacity. Operational means producing, in standby without a fault, or held down by a command: available is operational, not performing, so curtailment never lowers it. Nothing is excluded. A data gap is “unknown”: removed from numerator and denominator and reported beside the number as an unknown share, never counted as available.
Did the O&M contractor deliver what was signed?
Same calculation, but the intervals on the contract's exclusion list are removed from numerator and denominator: grid outage, grid-operator curtailment, market curtailment, owner shutdown, force majeure, scheduled maintenance within the agreed quota. The number carries the contract reference.
What did downtime cost in energy?
1 − energy lost during unavailable intervals ÷ expected energy of the period. Expected energy per interval comes from measured irradiance and the plant's own reference performance, or from peer inverters when the sensor is out. Exclusions as in 02 when the contract ties damages to energy, otherwise none; the number says which.
What did downtime cost in money?
As 03, but every lost kWh is valued at that interval's price, day-ahead or the price the owner actually receives. A lost kWh at a negative price is worth nothing. An hour lost at noon in June can cost nothing; an evening hour in January costs a lot. This is the number to tie liquidated damages to.
Did the plant capture what was there?
Actual energy ÷ expected energy, with expected from irradiance, module temperature and dated master data. Everything counts: outages, curtailment, soiling, clipping, degradation, strings out. Not an availability, never called one.
Where did the gap go?
Expected minus actual, split into grid outage, grid-ordered curtailment, market curtailment, export limit, clipping, unavailability, and underperformance as the remainder. The parts sum to the gap exactly.
Did we earn what the market offered?
Actual revenue ÷ (expected energy × interval price). For storage, against a named benchmark dispatch, and the benchmark is part of the definition.
| Choice | Source A | Source B | Source C |
|---|---|---|---|
| Hours counted | 24 h | daylight | daylight |
| Weighting | per inverter | by capacity | by capacity |
| Data gaps | available | down | left out |
| Exclusions | grid outage | none | contract list |
| Unavailable means | fault code | no power in daylight | fault code |
Each choice is defensible. Together they move the number by two percentage points. Two points is the whole argument.
Synthetic example. The numbers are made up, the mechanics are not.
Or the names stay vague.
Plus what “unavailable” is based on: a fault code, or inferred from power, setpoints and irradiance.
| What you see | Look at |
|---|---|
| Hidden performance limitations | 05, 06 |
| Production losses | 03, 05 |
| Curtailment | 06 (grid or market), 07 |
| Grid constraints | 06 (export limit) |
| Gradual underperformance | 05 as a trend |
| Missed valuable market periods, storage | 04, 07 |
Seven KPIs, one question each, and the five things each one has to fix. A PDF to keep next to your contracts.
Technical availability asks whether the equipment could run, with nothing excluded. Contractual availability asks whether the contractor delivered what was signed, so the intervals on the contract’s exclusion list are removed. Same data, two right numbers.
No. Curtailed is available and not dispatched. It never reduces technical or contractual availability. It shows up in the energy performance index, lost energy by cause and revenue capture.
One minus the energy lost during unavailable intervals, divided by the expected energy of the period. The number says whether contract exclusions were applied.
A gap is “unknown”. It is removed from numerator and denominator and reported beside the number as an unknown share. It never counts as available.
You get performance ratio and availability as a base row with the rules written down, the difference against each reported number with what explains it and what stays open, a method card next to every number and a 30-minute walkthrough. Nothing changes in your monitoring.
Send one plant, one month