In the U.S., over the past several years, average net capacity factors (CF) for natural gas combined-cycle (NGCC) plants, utility-scale solar photovoltaics and wind farms have been increasing.
Driven by increased gas supply and attractive prices, NGCC power plants are running on average around 50% CF – up from around 40% CF at the beginning of the decade. During the same period, steam generators, primarily coal-fired, have declined from above 50% CF to near 40% today1.
Utility-scale solar farms have increased CF from below 19% to near 25% today, while wind farms have grown from around 29% to just under 35% on average1.
Nuclear is the generation source with the highest overall CF in the U.S. Over the past decade, nuclear has averaged 84% CF while generating one-fifth of the countries power. Because of its zero-emission status, nuclear is often described as the “renewable” with the greatest CF.
Power plant CF is the ratio of actual electric output over a period of time, to the plants potential output if it operated at full nameplate capacity continuously over the same time period. There are several reasons why a plant’s CF varies including; planned maintenance and unscheduled outages, disparate fuel costs and fuel availability.
Cloudy days inhibit solar and calm days inhibit wind turbines from generating electricity. Natural gas is most affected by volatility in fuel prices and pipeline constraints.
Wind
For wind, increasingly improved technology, like higher towers and larger turbine blades, have contributed most to higher levels of electric output over the years.
Recent improvements in the average wind CF can be attributed mostly to increased development in the Great Plains states and Texas where the wind blows harder and more consistently. Going forward there are additional factors that will affect wind output both positively and negatively. Wind turbines down for maintenance on windy days CF lower, while growth in wind with higher platforms and bigger blades will improve overall average CF of the wind fleet.
Solar
Most of the recent improvements in solar CF can be attributed to projects built in areas with the highest solar irradiance like Arizona, New Mexico, Nevada and California.
Going forward there are additional factors like the implementation of tracking panels to follow the sun during the day and deployment of new technologies like energy storage that are expected to lead to higher CF overall.
Natural gas
Combined-cycle’s recent improvement over steam generation CF is primarily driven by the sustained relatively low natural gas prices and the addition of a large number of new more efficient NGCC plants.
Over the past decade there has been 79 GW of new gas-fired combined cycle power plants built in the U.S., while over the same period, 120 GW of coal and older natural gas steam facilities have been retired, the majority of closures have been older coal units (74 GW)1.
Energy storage
Integrating energy storage technology with solar and wind farms will improve capacity factors. Storing power when the market price for electricity is low will ensure higher levels of output per unit of capacity when it’s most needed.
Texas wind capacity is primarily night-peaking and California solar output is highest at high noon even though higher power demand and market prices occur during the early evening peaking period.
Adding new storage technology makes it possible to generate power when the sun is shining and the wind is blowing, store it, and use it during peak periods when the grid is constrained. Though there are a number of key drivers supporting increased utilization of intermittent resources like solar and wind, don’t expect exponential growth since the sun doesn’t always shine and the wind doesn’t always blow. Driven by an unprecedented run of relatively low fuel prices, natural gas fueled combined-cycle generators will continue to replace older coal and steam units in the power fuel mix.
Some market facts
Over the past decade, power generation from steam driven power plants has declined precipitously from just over 2 billion MWh in 2010 to under 1.4 billion MWh in 2017. During the same time period, gas fueled combined-cycle units have moved from generating around 0.75 billion MWh to 1.1 billion MWh. Both wind and solar are contributing more today but still represent a relatively small amount – only 0.25 billion MWh in 20171.
Solar and natural gas driven combined-cycle CF’s are higher in the summer months while wind tends to generate higher during the winter and shoulder seasons. Nuclear is steady with dips reflective of maintenance and refueling schedules. With solar contributing more to the grid in recent years, the swings in actual output have become far greater between the seasons. In January, solar output totaled 3.3 million MWh, only 41.7% of the 7.8 million MWh recorded in June1.
1Source for all data within the article: ABB Ability™ Velocity Suite, 2018
ABB Ability™ Velocity Suite software solution provides analysts with the ability to quickly evaluate the activities of market participants and industry dynamics across commodities using a single integrated solution. Using Velocity Suite, analysts can look at coal production, daily gas prices, plant capacity factors, weather normalized loads and transmission all at the same time. Velocity Suite includes an easy-to-use query tool with interactive output grids, charting and mapping capabilities.
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