Choosing Diesel Generator Set



In this post, we will discuss about the step to choose engine diesel generator set for electricity supply on the plant or project, especially to supply electricity during the project execution. The main issue here is total cost during the operation of the engine. However, the diesel generator set price will be considered but this price won’t affect significantly to total cost at the end.

First, we need engine datasheet from manufacture or you can search online for this datasheet before doing the calculation. The datasheet shall include with: fuel consumption and lubrication oil consumption.

1.  Fuel Consumption

This data will help us to define how much the engine will consume it fuel during the operation. Fuel consumption normally in Liter/hour (L/h). If we got this data, it will be easier to continue the calculation. The others unit to define fuel consumption are g/kWh (gram/kilo watt hour) and lb/BHP-hr (pound/break horse power hours). For these last two units, we will need some conversion calculation to be L/h. Following are the conversion calculation:


kW = Full power output of generator

ρ     = Diesel Fuel Density



Lb        = Pound

BHP    = Break Horse Power

ρ           = Diesel Fuel Density (0.85 kg/l)

kW       = Full load output of generator

2. Lube Oil Consumption.

To calculate lubricating oil consumption, we should know the lube oil consumption from the engine manufacture. The unit of lube oil consumption similar with fuel oil consumption unit, some manufacture give in L/h, others kg/kWh and lb/BHP-hr.

The next step was to define the evaluation period. For example, if you use the diesel engine generator set for project purpose and the project duration 2 years, it mean the evaluation period for the diesel engine generator shall be 2 years, equal to 24 months, equal to, 720 days. Now, define the diesel engine generator set operation during the day, for example the diesel engine generator set purpose to supply the working equipment/tools (i.e. welding, cutting machine, etc.). So, we can assume that the diesel engine generator set will run for 8 hours for a day or 5760 hours for 720 days.

After define the running hour for the engine, now you can calculate how much fuel and lube oil will be used during the running hours and multiply with the fuel and lube oil price.


Fuel Consumption Rate  = L/h

Lube Oil Cons Rate         = L/h

Engine running hour      = 5760 h

Fuel price                         = USD xx


  1. On this calculation, engine assume working with full load during running hours
  2. Working day assume on this calculation is 360 days in a year
  3. Maintenance cost not considered


  1. Expensive diesel engine doesn’t mean the total cost will be high, the total price depend on fuel consumption of the engine
  2. Lower engine fuel consumption rate mean more economical for the total cost.
  3. Higher rated power of generator will increase the fuel consumption rate

Any discussion regarding this topic, please comment 🙂


– Experience and learning


11 thoughts on “Choosing Diesel Generator Set

  1. What you have typed all makes sense, but there are a couple of other factors you should also consider.

    1. You should only run the generator at 70 – 80% load to get the optimum fuel efficiency on most diesel engines.

    2. You haven’t factored in the servicing fee for the generator. The fuel and lube are big costs, but running a generator also requires servicing which includes the replacement of oil, fuel filters, air filter and oil filters. In addition to that you would normally require a representative from the generator company to do this servicing for warranty purposes.

    This will translate into a minimum of 20 services over the period of 2 years if the interval is set at roughly 300 hours. (Normally anything from 100 – 300 depending on the manufacturer)

    • You’re correct Nick, the generator should not run on full load for better engine life time, it’s not recommended by the factory, similar with transformer. I take a count for full load only to know the fuel consumption level and compared with other engine, so I know which ones is more economical. Those two factor have a significant impact to the total cost, that way I only consider it. Maintenance factor quite hard to predict. For new engine, normally manufacture will guarantee for 1 or two years (depend on manufacture), including services and spare part. Am I correct? I thought you’re the expert one 😀
      By the way, thank you very much for your comment 🙂

      • Hi Hurricane

        You’re correct, to do an apples to apples comparison you need a benchmark and most suppliers of generators and engines will give you the fuel consumption statistics at 100% load. My mistake your comparison methodology is correct!

        With regard to the maintenance figures, they are fairly easy to calculate if you know exactly how many hours your generator will run per day and what the service intervals should be. If you have this information speak to the company / person servicing the generator and try and setup a maintenance contract per anum, this will allow you to calculate the exact cost of the maintenance with a high degree of accuracy. Now the only anomaly will be the price of fuel! I’m not sure about Indonesia, but in South Africa this price changes every month 😦

  2. Hi Nick,
    Thank you very much for your suggestion 🙂
    Is that mean that fuel price in South Africa fluctuated related to global market condition?
    In Indonesia, our government has a regulation to control the fuel price, especially for domestic consumption and this price is not depend on the global market condition. For sure we have price increment for several times during the last ten years, but the fuel prices still lower than global prices. This regulation divide the domestic consumer into two level and regular consumer has lower prices than industrial consumer.
    I think this is normal, because we produce a lot of crude oil in Indonesia, although almost all block was old well.

    • Hi Hurricane

      Yes, our fuel price is adjusted monthly for any changes in the global market which makes it very difficult to determine the cost of ownership of a generator, car or engine requiring diesel or petrol.

      We have a very different energy market whereby the price of Petrol is regulated to an extent whilst the Diesel price is only a guide line price. In addition to this we have different prices for fuel on the coast vs the inland cities and towns.

      • Hi Nick,
        I see.
        It will be difficult to predict the future market condition.
        Like today, our currency falling down to lowest level for last ten years against US Dollar. This is absolutely worst for project and others business in our domestic.

  3. Pingback: Diesel Generator Working | diesel generator

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