The capacity-weighted average age of the U.S. generation fleet was 29 years as of Dec. 21, 2018, unchanged for the fourth year in a row. Gas, solar and wind dominated new capacity added to the grid in 2018, while coal accounted for bulk of the capacity retired for the year.
An analysis of S&P Global Market Intelligence unit-level data shows that hydroelectric power plants were on average the oldest in service, with a capacity-weighted average age of 54 years, followed by gas-powered steam turbine facilities, with an average fleet age of 50 years. Wind and solar fleets remained the newest, with average ages of seven years and three years, respectively.
Average fleet age by region
At the power market region level, the New York ISO had the oldest overall average fleet age, at 37 years, unchanged from the end of 2017. The single-state region is home to the oldest nuclear-fired facilities, averaging 42 years, and gas-fired steam-turbine units that average 52 years.
With 30 years in overall average fleet age each, the Midcontinent ISO and the non-ISO category, comprising much of the southeastern U.S. and the western U.S. excluding most of California, both tied with the second-oldest fleets. MISO had the youngest gas-fired steam turbine units, aged 47 years on average, and the youngest solar facilities, averaging 2 years.
The PJM Interconnection and ISO New England regions both had an average fleet age of 29 years. PJM was home to the youngest hydroelectric facilities, averaging 48 years, and gas-fueled combined-cycle units, averaging 11 years and reflecting the addition of gas-fired capacity in recent years. ISO-NE had the oldest oil-fired steam-turbine units, at 46 years, and coal-fired facilities, at 53 years, while the average age of gas turbines was 15 years.
Overall average fleet age was at 28 years for the Southwest Power Pool, 23 years for the California ISO and 21 years for the Electric Reliability Council of Texas Inc.
Average fossil fuel plant retirement ages
Gas-powered steam turbine units had the highest age upon retirement among fossil fuel plants that shut down in 2018, an average age of 56 years, exceeding the 2000-2018 capacity-weighted average of 47 years. Gas-powered gas turbines and combined-cycle units retired at 36 years and 30 years, respectively, compared to 2000-2018 averages of 25 years and 27 years.
With an average retirement age of 25 years, other gas-powered plant types had the lowest age upon retirement, below the 2000-2018 average of 30 years.
Non-steam turbine oil-fueled plants had the second-highest retirement age, at 44 years, versus the 19-year average of 37 years. Coal-fired facilities retired in 2018 at an average age of 41 years, below the 2000-2018 average retirement age of 50 years.
Fleet age of investor-owned utilities
Avista Corp., with about 2,000 MW of owned generating capacity, had the oldest overall fleet, with an average age of 44 years, and the oldest renewables fleet, aged 35 years. About half of the company's generating capacity is hydroelectric, and its owned renewables are comprised of a single biomass-fueled facility.
At the end of 2017 New England utility Eversource Energy had the oldest average generating fleet, but in early 2018 it completed the sale of its fossil generation portfolio. A smaller New England utility, Unitil Corp., has an owned power generation fleet that consists of a 1.3-MW solar facility in Fitchburg, Mass., that began operating in late 2017.
The oldest gas-powered facilities were steam turbine units aged at 65 years on average attributed to ALLETE Inc., Ameren Corp., and Consolidated Edison Inc. Public Service Enterprise Group Inc. had oldest coal-fired fleet, aged 49 years, comprised of partial interests in two large plants in Pennsylvania and a 385-MW plant in Connecticut. Otter Tail Corp. had the oldest hydroelectric fleet, aged 101 years on average. The company's six hydro units, the oldest of which began operating in 1907, are all less than 1 MW.
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