In early 1994, the NEPOOL Environmental Planning Committee (EPC) conducted a study to analyze the impact that Demand Side Management (DSM) programs had on NEPOOL’s NOX air emissions in the calendar year 1992. The results were presented in a report entitled 1992 Marginal NOX Emission Rate Analysis. This was used to support applications for obtaining NOX emission reduction credits (ERCs) resulting from those DSM program impacts. Such applications were filed under the Massachusetts ERC banking and trading program, which became effective on January 1, 1994. The ERC program allows inventoried sources of NOX, VOCs, and CO2 in Massachusetts to earn bankable and tradable credits by reducing emissions below regulatory requirements. One of the activities is electric utility DSM programs installed since January 1, 1992. In 1994, the 1993 Marginal Emission Rate Analysis (MEA Report) was published, which provided expanded analysis on the impact of DSM programs on SO2, NOX, and CO2 air emissions for the calendar year 1993. The MEA Report was also published for the years 1994 through 2003 to provide similar environmental analysis for each of these years.
The 2004 New England Marginal Emission Rate Analysis provides calculated marginal emission rates that can be used to estimate of the impact of DSM programs on New England’s SO2, NOX, and CO2 air emissions during the calendar year 2004. The MEA Report is used by a variety of stakeholders including consulting firms, environmental advocacy groups, and state air regulators. For example, the MEA Report can be used to estimate the value (avoided emissions) of Renewable Energy Certificates (REC) by providing both REC suppliers and stakeholders with information that can be used to communicate the environmental benefits of RECs and works to enhance the overall REC marketplace.
3.1 CALCULATING MARGINAL EMISSIONS
In past MEA Reports, production simulation models were employed to first try and replicate, as closely as possible, actual system operations for the study year. Then an incremental load scenario was modeled where the entire system load was increased by 500 MW in each hour. The marginal air emission rates were then calculated based on the difference between these two scenarios. Although this methodology had produced sufficient results, some drawbacks existed. Since reference case scenario results were based on production simulation results, the reference case system never exactly matched the previous years energy production. This may expose prior results to minor errors, especially in the individual time period results shown.
For 2004, a new methodology has been developed to calculate the average emission rates of marginal units. This methodology uses the actual hourly generation as reported to ISO-NE and annual average air emission rates as found using available US Environmental Protection Agency (EPA) data and other default emissions data. For the time periods investigated, the average air emission rates of all dispatchable fossil units are calculated based on this information and applied as the marginal air emission rate. Specifically, the emission rates of those fossil units that are fueled with oil (including distillate, residual, diesel and jet fuel), and/or natural gas are calculated. For purposes of the 2004 MEA Report, this group of units is also referred to as the intermediate fossil units. Those fossil units fueled with coal, wood, biomass, or refuse/landfill gas are excluded from the calculation as they typically operate as baseload units and would not be dispatched to higher levels in the event that more load was on the system. All hydro and nuclear units are also excluded from the calculation. [emphasis added by IWA editor]