Buy the megawatts your load can use—not just the number stamped on the generator.
Contents
| Step | MW remaining |
|---|---|
| Generator nameplate | 6.00 |
| Illustrative site derating: −0.30 MW | 5.70 |
| Illustrative auxiliaries: −0.15 MW | 5.55 |
| Illustrative electrical losses: −0.05 MW | 5.50 |
| Redundancy / unavailable-unit reserve | Apply separately to the complete plant. |
Put the measurement boundary in the headline
Six megawatts at generator terminals and six megawatts at the customer meter are different commitments. Fans, pumps, gas compressors and cooling equipment use power. Transformers and conductors add losses. An offer should state where its guaranteed output is measured.
The numbers above illustrate the arithmetic; they are not a derating curve for any listed engine. The practical request is for a site-specific net-output calculation with each deduction visible.
Four labels prevent most rating confusion
Nameplate: the original equipment rating and stated conditions. Site output: output after ambient, altitude, fuel and cooling effects. Net export: site output less auxiliaries and electrical losses. Firm capacity: the amount the plant can support under the agreed outage or redundancy case.
Do not substitute a standby rating for continuous or prime duty. A model may carry several valid ratings with different operating limits. Fuel quality, methane number and gas pressure can be just as important as temperature for a gas engine.
Packages are sums, not redundancy guarantees
Three 2 MW units sum to 6 MW nameplate. If one unit must be unavailable while maintaining service, the surviving nameplate total is 4 MW before site deductions. A 5 MW load is therefore not supported on an N+1 basis by that arrangement.
Likewise, a proposed rehabilitation rating belongs in a separate configuration. It must not replace the existing tag rating in the equipment record. Our Wärtsilä listings retain both the historical nameplate basis and the conditional rehabilitation concept so buyers can compare them without counting extra engines.
Use a common bid sheet
Require every vendor to fill in the same fuel, ambient, altitude, duty, frequency, voltage, auxiliary-load boundary and outage case. Then compare dollars per usable kW. A cheaper price per nameplate kW can be a more expensive price per dependable site kW.