Understanding EPA Generator Emission Standards
Emission levels for generators vary based on how a generator engine is used: Engines can be either nonroad or stationary engines.
Nonroad engines are any portable engines, other than in cars and motor vehicles. Stationary or standby engines are engines that will remain at one location for 12 months or more. Generators that fall into this category are then broken into subcategories for new or existing and emergency or non-emergency engines.
Manufacturers classify different stationary engines with ratings based on how they will be used, their total power load, and their operation time. These three ratings are:
- Standby rating: primarily used in stationary emergency applications and applies to variable loads with an average load as a factor of the standby rating, with 100% of the rating available for the duration of a power outage
- Prime rating: primarily used in non-emergency applications and applies to varying loads and unlimited operating hours
- Continuous rating: used for non-emergency applications where the generator set is used to supply constant or non-varying load for unlimited hours, and the continuous rating is equal to the generator’s average power
Lastly, engines are further segmented based on their method of ignition. Engine ignition types are compression ignition, which use diesel fuel, and spark ignition, which can use gas including natural gas, landfill gas, gasoline, propane and others. Both compression and spark ignition engines are required to meet the U.S. EPA New Source Performance Standards (NSPS), which regulate emissions based on the manufacturing date of the engine and its maximum horsepower rating.
The EPA has developed a series of summary tables to help determine if generator emissions are compliant with the regulations for stationary engines, with additional requirements for maintenance and reporting.