Generator Power Ratings Explained
A reliable generator is one of the most crucial pieces of equipment a commercial business or organization, such as health-care facilities or educational institutions, can purchase. However, before you invest in a generator, you need to understand some essential specifications and ratings.
Manufacturers classify each generator with industry-standard operational or power ratings such as stand-by generators and prime power generators. The Environmental Protection Agency has mandated specific ratings to reduce the 76 million tons of emissions in the atmosphere in the United States. The EPA’s tier ratings for gensets are discussed below.
Although these values help consumers identify the appropriate generator for their energy needs, they can be confusing for an end-user. To help clarify what each of the diesel generator standard ratings represents, we’ll look at each one, starting with the power ratings. Read on to find generator ratings explained.
What do a generator’s power ratings mean?
There are four different operational ratings based on the maximum allowable power output in relation to the usual load profile and running time.
Emergency Standby (ESP)
The emergency standby power generator is a common mobile source of energy during power outages or other emergencies. Although it is required to provide power “for the duration of the outage,” according to the industry standard ISO-8528-1, this generator type is designed to handle up to 200 hours of use per year, which is the lowest of the four ranking categories.
Prime (PRP)
Prime power gensets are ideal as a primary source of energy, not just temporary backup power. The PRP rating indicates that this category of generators can operate with varying load for an unlimited number of hours per year. There are various applications for this type of generator, including:
- Hospitals or critical-care facilities
- Mining
- Off-the-grid areas
- Microgrids
Limited-Time Running Prime (LTP)
A limited prime power generator is intended to supply electric power to a utility as a requirement of a financial agreement.
Continuous (COP)
Continuous power rated generators can supply power nonstop for unlimited hours per year, similar to prime power. However, the load must be constant.
As with all generators, maintenance must be carried out as set by the manufacturer to safeguard your equipment’s working condition and years of use.
What are the EPA ratings for generators?
Although our nation’s air continues to improve as evidenced by a substantial drop of 73% in six common pollutants, including carbon monoxide, over the last almost 50 years, our energy use has increased. To further curb atmospheric pollutants, the United States government introduced new regulations in the 1950s that forced generator manufacturers to limit the pollutants released by engines. As a result, diesel engines must comply with EPA tier 1 ,2, 3 and 4 ratings that were introduced in phases beginning in 1990.
Tier 1
The first phase authorized the federal government to issue operating permits to stationary power sources such as generators. This stage set emission standards for all new non-road diesel engines, regardless of horsepower categories, except for engines used in marine vessels and locomotives.
Tier 2
The second phase, adopted in 1998, tightened pollution regulations. It concentrated on the emissions of carbon monoxide, unburned hydrocarbons, particulate matter (PM) and nitrogen oxide (NOx), which is the generic term for mono-nitrogen oxides NO and NO2. This phase covered all sizes of engines manufactured between 2001 and 2005.
Tier 3
This phase, implemented between 2006 and 2008, restricted exhaust emissions for engines with 50 to 720 hp.
Tier 4
The final ruling, signed in May 2004, set guidelines to phase Tier 4 across all engines and equipment using those engines starting in 2008 through 2015. The new standards are intended to reduce particulate matter and nitrogen oxide emissions by 90% nationwide.
What are the Tier 4 requirements?
Considered the strictest of standards, Tier 4 generator requirements include new generator components designed to meet the drastic emissions reduction set forth.
EGR
An exhaust gas recirculation circuit was added to engines as part of the Tier 3 regulations. The EGR takes a percentage of exhaust gas and recirculates it with fresh intake air, causing a reduction of oxygen in the combustion chamber, which in turn results in less NOX in the exhaust.
DPF
Most Tier 3 engines included a diesel particulate filter or DPF to reduce particulate matter. These perforated, ceramic filters use a coating of precious metals catalysts to remove PM from the exhaust stream.
DOC
Diesel oxidation catalysts are another technique to reduce exhaust pollutants. These filters are similar to a catalytic converter in a car as they have a catalytic coating that converts carbon monoxide, hydrocarbons, diesel particles and other matter to carbon dioxide and water.
SCR
The exhaust gas recirculation was not able to reduce NOx levels to meet Tier 4 regulations alone. Manufacturers therefore install an after-treatment system called selective catalytic reduction, or SCR. The addition of the selective catalytic reduction ensures that the engine can meet emissions standards and that the engine runs cooler than prior models.
ULSD
Ultra-low sulfur diesel was introduced in 2009-2010 and has since replaced all stock diesel in the United States and Canada. It is the only kind of diesel you can purchase. Because DOC and SCR catalysts were unable to handle the higher levels of sulfur in standard diesel fuel, sulfur levels were reduced.
TPEM
To help alleviate the initial cost of manufacturing the Tier 4 final engine, the EPA created the Transition Program for Equipment Manufacturers. This ‘flexibility program’ is a temporary exemption that permits diesel equipment manufacturers to delay the installation of Tier 4-compliant engines in their equipment for up to seven years.
Manufacturers can continue to build Tier 3 engines during this transition. Generators produced during this period are considered flex. The program will phase out when a manufacturer reaches a specific number of engines or sales within their company. Several flex generators are still available; however, they are in limited quantity for a limited time.
Let us help you select the right generator
These ratings, whether they be power or environmental, are set as such to protect you the end-user. Following all instructions and recommendations, including maintenance and testing, will ensure your diesel generator performs optimally for its specified application.
Contact our team to order the right generator for your needs now.