The Virginia DEQ Air Division divides electric generators into two categories: emergency generators and non-emergency generators. Since air permit applicability is based on the generator’s potential to emit air pollutants, it is important to understand the difference in the generators and their potential to emit.
To qualify as an “emergency generator” the unit can only operate when there is an interruption of power from the utility (or during brief maintenance and testing exercises) and for no more than 500 hours per year including testing and maintenance. An emergency generator’s potential to emit is assumed to be 500 hours per year under the worst case conditions.
In order for an emergency generator to be exempt from permitting it must meet the following criteria:
- It operates only when there is an interruption of power from the utility, or for routine scheduled testing and maintenance.
- It operates no more than 500 hours per year including testing and maintenance.
- Diesel engines have an aggregate brake horsepower of less than 1,675 horsepower (1125 kilowatts).
- Gasoline engines have an aggregate brake horsepower of less than 910 horsepower (611 kilowatts).
- Owners must maintain records of the hours of operation for each emergency generator to demonstrate that it complies with the air permitting regulations.
Exception to the Emergency Generator Exemption
Emergency Generators located in the Northern Virginia counties may require permitting because the Northern Virginia Region is a Nonattainment Area. Emergency generators located in the Northern Virginia Region are evaluated based on the potential to emit of 8760 hours per year operation – not 500 hours per year as described above. If the potential to emit is greater than 25 tons per year of NOx a permit is required and a Reasonable Available Control Technology evaluation is conducted.
Non-Emergency Generators
“Non-emergency generators” are those units used for peak shaving, distributed generation, or for generating electricity for any reason other than emergency use previously explained. A non-emergency generator has a potential to emit based on a maximum 8,760 operating hours per year (24 hours per day X 7 days per week X 52 weeks per year). Because the potential to emit is based on 8,760 hours per year, non-emergency generators will likely require a permit regardless of size. This includes generators located at residences that are used for non-emergency reasons.
Any generator used for demand side distribution, or when a utility asks for help producing extra capacity, is NOT emergency generation
For a permit applicability determination, please submit a completed Form 7 application to the appropriate regional office.