In short. Retrofit makes sense when the engine and alternator are sound and the duty suits the option. Replace when the set is worn, undersized, unreliable or cannot meet rules economically. Compare total lifetime cost and risk, not purchase price.
Inputs
| Input | Question |
|---|---|
| Condition | Hours, oil use, repairs, spares availability |
| Capacity | Does it still match the load and growth? See generator sizing |
| Rules | What is required for this location |
| Duty | Standby or prime, hours per year |
| Fuel options | Gas, HVO, diesel |
| Downtime | Can the site tolerate it, or is temporary supply needed? |
Cost view
Lifetime cost = capital + installation + fuel + maintenance + downtime risk − residual value
Compare over the same period for each option. Include the cost of failure for critical loads.
Decision steps
- Establish compliance requirement.
- Assess condition by inspection and load test.
- List feasible options. See RECD, dual fuel, replacement.
- Estimate lifetime cost and risk.
- Choose, with a staged plan and temporary power. See rental power.
Also see upgrade and replacement planning.
Illustrative example
A 20-year-old set with rising repair costs and obsolete parts fails a load test. A retrofit would add cost to an unreliable base, so replacement wins. A well-kept 8-year-old set with low hours is retrofitted instead.
A condition assessment checklist
| Check | Observation |
|---|---|
| Engine hours and age | Compare with typical overhaul interval |
| Oil consumption | High consumption signals wear |
| Compression or blow-by | Test as per maker |
| Smoke at load | Black, blue or white points to different faults |
| Cooling system | Overheating history |
| Alternator insulation | Insulation resistance and polarisation index |
| Controls and switchgear | Obsolete parts, spares availability |
| Load test | Carry rated load with stable voltage and frequency |
Cost comparison skeleton
- List the remaining useful life for the retained set.
- Estimate overhaul and retrofit cost for that life.
- Estimate fuel and maintenance for the retained set.
- Estimate purchase, install, fuel and maintenance for a new set over the same period.
- Subtract the residual value.
- Add the cost of failure risk for each option.
Capacity and growth
If the load has grown or will, a set that is too small gets replaced anyway. Combine the condition assessment with a fresh sizing study so you do not retrofit the wrong size. See generator sizing.
Staging the change
- Order the new set early; lead times can be long.
- Prepare the foundation, cables and exhaust while the old set runs.
- Arrange temporary power for the changeover.
- Commission with tests. See commissioning.
Disposal of old equipment
Dispose of oil, coolant, batteries and the old set responsibly through authorised handlers. Keep disposal records.
Decision summary table
Record the final choice, key numbers, risks accepted and review date. Keep it with the set file.
The master engineering question
Are we investing in a base that will still be reliable for the life we are paying for?
What to send us
Send set data and records. Send your application details.
Questions engineers ask
What age forces replacement?
No fixed age; condition and rules decide.
Can the alternator be reused?
Sometimes, after testing.
Is rental needed during the work?
For critical sites, yes.
What about resale?
Include residual value, if any.
General guidance only. Values illustrative.