The Generator Runtime Calculator calculates how many days a generator can support its critical loads during a power outage. This information is an input for characterizing supply redundancies in the TRN Lite risk assessment methodology. This tool provides two different options for calculating runtime:
If daily consumption (kWh) is known or a reliable estimate is available
If daily fuel consumption is unknown, but generator size (kW) is known
Using either of these options, you will obtain an output establishing the number of days that current redundant generator systems will be able to meet critical loads. This analysis provides a high-level estimate. For users who have done or are planning to do more refined assessments of the runtime capabilities for their supply redundancies, those estimates may be more appropriate to use as inputs for the TRN Lite analysis. This tool provides estimates for runtime only for generators using fossil fuels. For other types of electric supply redundancies, the user should use other resources to characterize their runtime capabilities.
To see the calculations behind the results, click the “Show Calculations” checkbox. Click “Example” to see an example analysis including entered data and results.
Calculator related questions, suggests, and issues can be submitted here:
Select the fuel type used by your generator. Note that natural gas is not included as a fuel type for generators in this tool. Natural gas generators are connected directly to a natural gas line. Unless a natural gas disruption has also occurred, a natural gas generator will have an "infinite" runtime. However, natural gas generator manufacturers recommend running for no longer than 500 hours at a time so the generator can cool down and any required oil changes or filter replacements can be conducted.
Fuel Type
BTU content of fuel per gallon
BTU per Gallon
Select Method
Daily Consumption
kWh
Include consumption from all loads (whether critical or not) supported by the generator
Calculation assumes that generator has sufficient capacity to meet required kW demand
ERROR: Daily consumption must be greater than 0 kWh.
Generator
Enter the data below to characterize your generator. Refer to the tool tips next to each question for more information.
Generator Size
kW
Include capacity dedicated to all loads (whether critical or not) supported by the generator
ERROR: Generator size must be greater than 0 kW.
Daily Load Factor
%
% of total generator output used to serve load over the course of the day (e.g., 100kW generator could produce 2400kWh in a day, but in practice may only produce 600kWh)
ERROR: Load factor must be a value between 0 and 100.
Generator Efficiency
%
For a diesel generator, 30% is a typical efficiency; older and part-loaded equipment will be 20-25%, and new or larger generators can be up to 40% efficiency. For other fuel types, the efficiency may be similar, but check the generator manufacturer website for a closer estimate.
ERROR: Generator efficiency must be a value between 0 and 100%.
WARNING: The generator efficiency you have entered is higher than is typical, please confirm before proceeding.
Daily fuel consumed by generator (BTUs)
BTU per Day
Gallons per day consumed
Gallons per Day
Onsite fuel storage capacity
gallons
Only include fuel that would be allocated to this generator
ERROR: Fuel storage capacity must be greater than 0 gallons.
Days critical load can be met
Days
Is fuel delivery available from offsite and can it arrive before onsite fuel runs out ( days)?
Additional fuel may be obtained via contracted delivery, mutual aid agreement, etc.
Refueling
Enter the data below to describe any refueling processes in place to provide additional fuel for your generator during an outage. Refer to the tool tips next to each question for more information.
If refueling is available, will the fuel storage dedicated to the generator be completely refueled?
These calculations assume that refueling occurs with 20% fuel remaining
How many gallons will be supplied?
gallons
Only include fuel that would be allocated to this generator
ERROR: Number of gallons supplied must be greater than 0 gallons.
Additional days provided by a single refueling
Days
Does the refueling recur every days or is it one-time event?
If recurring, must arrive again within the specified number of days since the last delivery.
Results
The results below show the calculated runtime for the supply redundancy described by the inputs to this calculator. The runtime is shown in days and in hours. Use the runtime in hours as an input to characterize your electric supply redundancy in the TRN Lite Detailed Information – Supply Redundancies subsection.
Complete the form and address any errors above to view calculated generator runtime.
Longest duration this supply redundancy could support:
The expected runtime is longer than the greatest outage modeled in the TRN. Days