In recent years, the established capacity factor and capacity of US coal fleets has been declining. The main reason for the decline is the economic capacity caused by the low cost of natural gas and the cost of compliance with different environmental standards for coal generators. Both types of natural gas have a competitive advantage over coal in electricity generation.
The renewable energy sources covered in this article are mostly wind and solar. Hydropower is a strategic element of the US electricity generation plan, but in recent years the country’s installed capacity (about 80 GW) has hardly changed. Nuclear power remains an important part of the US energy structure. Although several nuclear power plants have been decommissioned in the last five years, only one new reactor has been operating since the mid-1990s. The installed capacity of nuclear power in the United States is still around 100 GW.
The 6.5% decline in coal burning capacity in 2015 was related to the date of compliance with the mercury and air toxic substances standard (MATS) and the decline in natural gas prices. Over the past 10 years, coal installed capacity has decreased by 71.5 GW, while natural gas and renewable energy installed capacity have increased by 69.0 GW and 110.9 GW, respectively. At the same time, as demand for electricity stagnated, the US energy industry increased capacity. However, due to transmission or pipeline restrictions, additional capacity is required in some areas. The US Energy Information Administration (EIA) reports that the energy industry produced 4,119 TWh in 2009. The average annual electricity production for the ten-year period was 4131 TWh, which was more than 2% of the average for one year only.
Power factor is the ratio of the electricity produced by a generating unit during the reporting period to the electricity that can be produced by continuous operation of full power during the same period of time. For many years, the price of natural gas used to produce electricity has been at its lowest level in history, and the power factor of coal-fired power plants continues to decline, leading to an increase in the number of cycles, while the combined cycle and the production of natural gas over a simple cycle. During this period, the installed capacity of the nuclear power fleet remained stable at about 91%. There is a direct correlation between the reduction of installed capacity and the power factor of coal plants and the price of natural gas.
Viewing the annual data does not give a clear idea of the importance of coal plants and other technologies for the everyday generation. If we analyze January 30, 2019 as the coldest day of the year and July 19, 2019, as the hottest day of the year, it is better to understand the significance of coal production and the mix of electricity generation Generated in the lower 48 states. In January 2019, natural gas used to generate electricity amounted to 834.116 million cubic meters. In July 2019, one of the highest monthly natural gas consumptions for electricity generation was 1,267,083 MMF, which is one of the lowest average prices for gas.
Sometimes coal production is actually the equivalent of gas production. This winter, solar energy has little effect on total electricity production, with wind energy reaching about midnight, while overall load decreases. Hydropower can optimize production to meet peak demand. Nuclear power generation is a base load of nearly 20% of total energy generation.
On January 30, 2019, the coal power factor was 68.4% higher than the annual average and the natural gas power factor 38.5% lower than the average. If coal is completely replaced by natural gas this winter, assuming that the capacity of renewable energy production is optimized, then 3 871 GWh of energy will be required to produce natural gas. Without reducing housing and commercial needs, an analysis should be conducted to determine whether natural gas is sufficient. In the next 48 states, only 1% of electricity is generated by solar energy and 5.3% by wind on the coldest day of the year.
The power generation profile on July 19, 2019 is the hottest day of the year. Load curves and fuel costs are significantly different from January 30. On January 30, the daily total system load was 12,619 GWh and the peak load was 568 GWh, while on July 19, the total system load was 13,747 GWh, of which the peak was 692 GWh. In July, the natural gas used by residents was the least, so a large amount of natural gas can be obtained for power generation at a lower cost.
In January 2019, the average monthly cost of natural gas used to generate electricity was $ 4.16 per thousand cubic feet. The average price in July 2019 was $ 2.62 / McF. The rise in natural gas prices in January had a direct impact on the growth of coal production. Total monthly natural gas consumption in January 2019 was the highest since 2001. However, natural gas used for electricity production has only slightly increased. More wind energy was produced on July 19 than January 30, and natural gas was used to absorb most of the energy. Similarly, hydropower can optimize electricity production by providing peak and baseline coal reserves.
On July 19, the coal fleet utilization rate was 61.9% and natural gas was 48.0%. Increasing coal power factor confirms its importance in times of high demand
For a different view of the US energy regime, consider weekly high temperature data. During this period, large fluctuations in the load of natural gas and coal were demonstrated. Nuclear power was installed as usual. Peak of solar energy in high season. Hydroelectricity regulates their load to meet demand and optimize revenue, while wind energy reaches maximum demand. During this period, there is a daily peak.
Large fluctuations in the electricity production of gas and coal units have a negative effect on the thermal efficiency (efficiency) of these units. The rate of heat is directly linked to the economy and the production of carbon dioxide. Cyclic loads increase thermal efficiency (Btu / kWh) and CO2 emissions. For example, as the annual capacity factor for coal parks goes from 64% to 54%, the heat rate goes from 10,100 Btu / kWh to 10,200 Btu / kWh. Lower thermal efficiency means lower operating efficiency, which means higher fuel consumption per MWh, higher maintenance costs and more carbon dioxide emissions per MWh.
Dr. Robert K. Smith of the Department of Energy reports that the power plant cycle has had an impact on costs in the western region. The analysis shows that the cost of the entire system went from $ 0.14 / MWh to $ 0.67 / MWh, which represents 2% to 7% of the total cost of production. As the capacity factor of coal decreases, the capacity factor of single cycle gas turbines increases considerably. Due to the variability of wind and solar power, gas-fired single cycle power plants are used to heat quickly to fill the electricity production gap.
During this August 2019, the average capacity of the coal fleet was 54.8%, but the hourly power factor ranged from 37.1% to 72.7%. In addition, during this period, the percentage of energy produced by coal remained relatively constant every hour. The average utilization rate of the park was 46.3%, and hourly data ranged from 29.3% to 64.3%. These large-scale factors not only affect the heating rate, but also significantly increase the cost of operation and maintenance of equipment.
In winter, there are different maps of coal and natural gas distribution. For example, between January 25 and 31, 2019, there are two peak loads per day. During these periods, coal and natural gas provided, on average, most of the power generation capacity. Nuclear power remains constant and hydropower reaches peak demand. In winter, the amount of solar energy is different. It peaks when demand is insufficient. During this period, wind generation is more random.
The high price of natural gas for electricity generation in January led to an increase in coal-fired power generation as it is more economical. In addition, electricity production from natural gas is restricted in some regions due to limited pipeline capacity and the use of residential heating. For example, in Edison’s integrated service area in New York, gas plants will switch to very low sulfur when the temperature drops below 20 ° F. During this period, the average power factor of the coal fleet was 60.0%, but the hourly power factor was 48.2% to 73.5%. The average capacity factor for natural gas parks is 32.8%, with hourly data ranging from 23.4% to 45.0%. The conversion of gas turbines from gas to fuel increases the rate of heat and air emissions
Another important aspect of the American network is the regional impact. In some areas of the United States, wind and solar power is not as technically / economically viable as others. The use of wind power in the southeastern United States and Florida is limited, while the potential for wind power in Texas, North Dakota and California is very large. In regions with limited wind and solar power, coal-fired power can fill some of the gaps in power generation.
For example, on July 19, the Texas Electricity Reliability Commission (ERCOT) accounted for 27.8% of wind energy, while Florida’s wind energy was 0% and solar energy was only 1.3%. On the hottest day of the year, solar in California is 22.4% of total power, while solar in many other regions is less than 1%. Please note that in July 2019, the price of natural gas for electricity production was approximately $ 2.20/Mcf, which was about the same price as in 1998. Natural gas consumption in July was about 12% in January, which means that natural gas is easier to use to generate electricity. Low nuclear power in some regions has had a significant impact on energy production. Coal is a major source of electricity generation in the Midwest and Central United States.
ERCOT provides additional hourly data that is not available in the EIA database. ERCOT solves the problem of gas consumption between the combined cycle and other gas power plants. ERCOT also provides biomass production data. ERCOT data shows that on July 19, 15% (91.8 GWh) of natural gas used in the ERCOT system came from sources other than the combined cycle unit. Based on this information, we can assume that most of the second generation is simple gas turbines that are used for rapid warming to compensate for changes in wind and solar power generation.
Most simple gas turbines have been tested with a thermal efficiency of about 11,300 Btu / kW / h, which is above the average thermal efficiency of 10300 Btu / kW / h for coal-fired power plants. An important environmental issue is that most simple gas turbines do not have selective catalytic reduction to control NOx. In addition, additional infrastructure work must be undertaken in US transmission systems to allow the transfer of energy from renewable sources to areas where renewable sources are limited.
The analysis shows that, on a daily and regional basis, coal, natural gas, nuclear, solar, hydro and wind power play an important role in US energy plans. Do not rush to shut down coal, nuclear or other technologies without evaluating existing data and supporting infrastructure. Political factors, technological changes, the design of transmission and distribution systems, fuel costs and utility are added to the equation, and hybrid power generation decisions are complex.
Over the past decade, coal-fired electricity production has declined under economic, political and environmental pressures and is likely to continue to decline, but remains an important part of the US energy base. The impact of coal in the electricity mix should be evaluated on a micro (daily or seasonal) basis, rather than annually. During the two extreme weather days (the highest peaks in winter), no electricity was produced on coal on January 30, 2019. This is due to the fact that the polar vortex occurred in most parts of the country, and a heat wave swept the entire country on July 19 (peak summer day). The unstable demand for electricity in the US system will have serious consequences.
In this fast-growing world of electricity generation, more and more renewable energy sources are producing electricity, and it is still important to have a ready-to-use base load, and coal is still a key component of the portfolio. Electricity generation systems in the United States should be flexible in adapting to extreme weather events such as polar storms, hurricanes, droughts, and other local issues, including power outages.
To maintain its economic leadership, the United States needs an energy and electricity system independent of international tensions, the costs of which can stimulate economic growth. Tax credits can cause artificial balances in the electrical system. The United States needs a balanced energy policy that takes into account environmental, economic, regional demand, security of supply, and system capacity. In addition to improving the transmission, other work needs to be done in the coal-fired power plant to increase its heat production during the cycle. If the performance of coal-fired power plants does not improve, there will be more shutdowns.