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HOMER Pro 3.11

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Generator Lifetime

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Input Variable





Unlike the lifetime inputs for most other components, the generator lifetime is specified in hours of operation instead of years. This is because the lifetime of a generator depends largely on the hours of operation rather than its age.

It is not always easy to obtain lifetime data for a particular generator, as it can depend on operating conditions, maintenance frequency, fuel quality, and other factors. But it is possible to estimate longevity based on the engine type. Reciprocating internal combustion engines are the most common engine type. Of these, compression-ignition (diesel) engines tend to last several times longer than spark-ignition (gasoline, propane, or natural gas) engines. For longevity, low speed (1800 RPM) is superior to high speed (3600 RPM), liquid cooling is superior to air cooling, and pressurized oil lubrication is superior to splash lubrication. The following table serves as a rough guideline for estimating the lifetime of certain types of generators.

Generator Type

Size Range (kW)

Estimated Lifetime (hrs)

High-speed (3600 RPM), air-cooled gasoline, natural gas, or propane generator


250 - 1,000

High-speed (3600 RPM), air-cooled diesel

4 - 20

6,000 - 10,000

Low-speed (1800 RPM), liquid-cooled natural gas or propane generator

15 - 50

6,000 - 10,000

Prime-power, liquid-cooled diesel

7 - 10,000

20,000 - 80,000

Natural gas microturbine

25 - 500

50,000 - 80,000

Because its lifetime is specified in operating hours, the more frequently the generator operates, the shorter its lifetime is in years. This affects the economics of the system because more frequent replacements leads to higher annualized cost. HOMER takes this into consideration when deciding whether to operate a generator or to use an alternative dispatchable source, such as a battery, the grid, or another generator.

After it has simulated a system, HOMER calculates the generator's expected lifetime in years and reports it as the generator operational life in the Simulation Results window.