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Regional air emissions 2015: slight year-over-year increase in CO2 levels; long-term reductions remain significant 

Since 2001, SO2 down 95%, NOx down 68%, CO2 down 24%

The retirement of Vermont Yankee Nuclear Power Station and the continuing trend of increased oil-fired generation in New England were factors in a slight increase in carbon dioxide (CO2) emissions in 2015 compared to 2014, as well as slowing year-on-year declines, as reported in the 2015 ISO New England Electric Generator Air Emissions Report, issued January 2017. However, significant retirements of coal-fired generation contributed to the region’s continuing long-term reductions in the emissions generated by the region’s power plants.

Year-over-year changes: 2015 vs. 2014

Table 1-1 from the emissions report summarizes the year-over-year changes for total system emissions (the amount of system emissions) and emission rates (the pounds of emissions given off, on average, with every megawatt-hour [MWh] of electricity produced). This is akin to comparing how many gallons of gasoline a car used versus its miles per gallon (MPG). For both emission amounts and rates, SO2 was down significantly, NOx dropped, and CO2 was up slightly.

Several key factors contributed to the changes between 2014 and 2015:

  • A 15% decrease in production from non-emitting generators—With the loss of 604 megawatts (MW) of zero-emission generation from Vermont Yankee Nuclear Power Station in late 2014, emitting generators—largely those fueled by natural gas—filled the resulting energy gap. Natural gas-fired generation increased by about 5,750 gigawatt-hours (GWh), or about 12%, in 2015.
  • Ongoing retirements of coal-fired resources—Coal-fired generation fell by about 23% in 2015. This decrease is consistent with the approximately 270 MW of coal-fired-generation that retired in 2014. Additional retirements are expected in the coming years.
  • A 10% increase in oil-fired generation—Continuing a trend over recent years, oil-fired generation increased by 174 GWh in 2015. The increase came largely in January, February, and March—the same months that natural-gas-fired generation made its lowest contributions for the year. This phenomenon largely reflects winter-time constraints on the interstate pipelines bringing natural gas into the region. These pipelines are operating at or near full capacity to serve heating demand during most of the winter. When the cleaner-burning natural gas units are not able to obtain the fuel they need—or spikes in the price of natural gas make these units less economical—oil- and coal-fired units often take their place, with a resulting increase in emissions. Gas-fired generators with dual-fuel capability may switch to burning oil at these times, as well. Oil prices in 2015 were also approximately half of what they were the previous winter, making oil-fired power resources competitively priced more often.

Charts and graphs from the emissions report below show each fuel type’s contribution by month, as well as changes in fuel types and emission rates over recent years.

Long-term trends: 2001–2015

Total emissions for sulfur dioxide (SO2) and nitrogen oxides (NOx) declined from 2001 to 2015 by 95% and 68%, respectively, while CO2 emissions decreased by 24%. This table and graph from the emissions report show the total amount of air emissions on an annual basis in kilotons (kTons).

A shifting fuel mix

The type and magnitude of a generator’s emissions are directly linked to the type of fuel that powers it, and the fuel mix used to produce New England’s electricity has changed significantly over the past decade.

Natural gas-fired resources account for the vast majority of new generators built in New England since 1997. This ongoing trend to meet electricity needs with higher-efficiency, lower-emitting gas-fired generators instead of oil- and coal-fired generators has been the biggest contributor to the long-term decline in regional emissions. Transmission system upgrades have further reduced the need to run older, less efficient oil and coal units.

The region’s increasing development of wind, solar, and other zero-emission resources will further contribute to reducing greenhouse gases. As of January 2017, about 44% of all proposed projects in the generation interconnection queue are wind-power resources.

Tighter emissions controls

Implementation of emission controls, as required by federal regulations and stringent, leading-edge requirements set by the New England states, have helped reduce emission levels from coal-fired resources when they do run, contributing to the striking long-term decrease in SO2, in particular.

More imported electricity

Since 2004, lower-priced electricity from outside New England has increasingly flowed in to serve regional demand. This external generation, which served 17% of New England’s energy needs in 2016, doesn’t count toward regional air emissions.

Less demand for electricity from the regional power system

Since about 2005, annual regional demand for wholesale electricity has been declining, and with it, so has electricity generation. The economic downturn and slow recovery helped dampen electricity consumption. Several long-term factors have also been at work to reduce the amount of power consumers pull from the grid:

  • Energy-efficiency (EE) investment—The New England states are national leaders in implementing EE measures, such as the use of more efficient lighting, appliances, cooling, and building operation. These EE programs are having a noticeable effect. The ISO’s EE forecast projects the $1.1 billion that the states invest annually from 2020 to 2025 will save an average of 1,608 GWh each year for the region and slightly decrease the growth of gross regional energy usage from 1.0% to -0.1%. Growth in peak demand, the periods of highest electricity usage, will slow from 1.1% to 0.4%.
  • Demand resources—Like power plants and other supply resources, demand resources are competitive assets that help meet New England’s electricity needs. But instead of generating power, they reduce the amount of power they’d normally pull from the grid. EE measures are an example of passive demand resources, while active demand resources include practices like powering down machines or switching to an on-site generator. (Learn more.)
  • Distributed generation—The growing numbers of small-scale solar power systems are one example of how more and more New Englanders are supplying some or all of their own power. The ISO’s forecast of regional solar photovoltaic (PV) power predicts that PV installations in the region will more than double by 2025.

For more information

To learn more about the ongoing evolution of the grid and challenges associated with a changing fuel mix, read ISO New England’s Regional Electricity Outlook.

For information on winter power system performance, see “Winter 2015/2016 recap: New England power system performed well and prices remained low” and “2016/2017 winter outlook: sufficient electricity supplies expected.”