Welcome to Lesson 2!

You are already to Lesson 2: Energy Supply and Demand. These energy supply and demand lessons will explore more about energy resources. Basically, you will be able to appreciate global and national consumption patterns. We will go over what kinds of energy we have been consuming, how much we have been consuming, and how we compare with the rest of the world, etc., over the past few decades. Based on those patterns, we can also deduce some information about how much energy we use to do a job; energy intensity. What kind of energy sources we will be needing, and how much we will be needing based on the past trends?

We will also look at energy reserves. Do we have those? Will we need more renewables, batteries, coal, more oil, or more gas? Can we (sustainably) use any of those resources? If we can, great, if not, what do we do? We will be doing those kinds of energy analysis. So, obviously, you are going to see a lot of numbers and statistics. One of the questions that I always get is: Hey, do I have to remember all these numbers? In 2023, petroleum and natural gas accounted for 77% of energy consumption in this country, and renewables accounted for 21% of the electricity generated by utility companies.

The most recent energy data is available from the EIA U.S. Energy Facts Explained.  

Do we have to remember these numbers? My advice is, you don’t have to remember everything but you need to get the main message behind these numbers. In other words, you have to know the fact that petroleum and natural gas are the main energy sources. Similarly, over 75% of our oil products or petroleum products are used for transportation. So, we need to know that transportation is basically run by petroleum; petroleum is mostly used for transportation. That is the message. You don’t need to remember the exact numbers. But if there is something that has very insignificant or significant quantities, you should note that. For example, renewable energy sources supply about 10% of our energy source. That is the message. You don’t need to worry about whether it is 9.2 or 9.5 or 8.5 or 11.2%. So just to give you a clue, you don’t have to worry about the exact numbers, but the message that is conveyed using these numbers is what you have to concentrate on. And we will also have one numerical type of problem in this lesson. That problem will be predicting the energy needed for the future. The problem follows an exponential function, and we will talk about that, and there will be a few numerical problems for you to practice.

See the Calendar tab in Canvas for due dates/times.

Questions?

If you have any questions, please post them to the General Course Questions forum in located in the Discussions tab in Canvas. I will check that discussion forum daily to respond. While you are visiting the discussion board, feel free to post your own responses to questions posted by others - this way, you might help a classmate!

In 2024, the world wide energy consumption was about 186,000 TWhs (or 635 Quadrillion BTUs). The energy mix used by the whole world is shown below in the figure from Our World in Data. This figure is interactive, so you can slide the bar across and see how that information changes over time. The largest energy source for the whole world is Oil, followed by Natural Gas and Coal. This means most of the world's energy comes from fossil fuels. If you slide the bar around, you can see how renewable has begun to steadily increase in the past decade or more.

Energy consumption numbers are always reported a few years behind, so we are always looking into the past before we plan for the future. As of 2024, The world's total primary energy consumption was about 186,000 TWhs (635 Quadrillion Btus).

The figure below shows how energy use is used per person (or per capita). You can see which countries have the highest energy use per person, in the dark red. The US is one of the highest consumers (but not the highest). Which country do you think is the highest user of energy per capita?

You can also explore this data, to see how it has changed over time. One major change over time is with China, which starts the time-laspe as about 1,000 kWh/ per person and ends the time-lapse at over 30,000kWh/per person.

• Do you expect this number to steadily increase?
• What do you expect to happen to India in the next 10 years?
• Do you think US energy use has increased, decreased or stayed the same over time?

Please click on the "Explore the data" for more analysis of each country over time.

The productivity of a country is measured by the total value (dollars) of goods and services, called Gross Domestic Product (GDP), produced by its people. Therefore, the average value of goods and services produced by each person - the GDP per capita of a country - is an indicator of the quality of life. The chart below shows the relationship between GDP and energy use per capita. While there are some outliers, the trend tends to have an upwards diagnonal shift. Click on the explore the data and you can filter the data by income group or country.

• What do you notice about the countries in the upper right corner of the chart?
• What do you notice about the countries in the lower left corner?
• Do you notice any similarities between the countires (Qatar, Brunei, Bahrain, Kuwait and Oman) at the very top of the chart? Where are they located?

Global Energy Consumption and GDP per person

In general, as the GDP (Gross Domestic Product) per person of any country increases, the amount of energy that is consumed is also expected to increase.

• For high income countries, the correlation is much stronger.
• For low income countries, the correlation is weak.

For example, Iceland, Denmark and the United States all have with similar GDP per capita. However, they each have significant differences in energy consumption per capita. In other words, to produce one dollar's worth of goods and services, the U.S. uses twice the energy of the Denamrk. Similarly, Iceland uses five times the energy of the Denmark.

Energy Consumption Differences

The differences in energy consumption among countries are the result of:

• efficiency of industrial, transportation, commercial, and residential energy,
• climatic and geographical areas of a country,
• lifestyles (use of more gas guzzling cars and SUVs and bigger sized houses), and
• the nature of the products produced by the nation's industries.

Credit: Superheros and Villains by Andreas Komodromo is licensed under CC BY-NC 2.0

Credit: Signs on the river bank by abrinsky is licensed under BY-NC-SA-2.0

Look at the Global Average Change in Energy Production by Fuel site and determine production of energy which energy sources decreased over the last 5 decades.

The world energy requirements are projected by several energy companies such as British Petroleum and Exxon Mobil and international agencies like International Energy Agency (IEA) and US Energy Information Administration (EIA). The International Energy Outlook is published every two years and looks at the long term energy outlook. This edition of the International Energy Outlook explores expected energy use through 2050. Global energy related CO₂ emissions are expected to increase through 2050, however the projections expect a shift from fossil to non-fossil energy sources.

• International Energy Agency
• British Petroleum
• Exxon Mobil
• US Energy Information Administration (EIA)

According to International Energy Outlook 2023,

• Global electricity generation will increase by 30-76% by 2050. Most new geneartion will be zero-carbon technologies. Electricity generation by fossil fuels are expected to decrease through 2050.
• Electric vehicles are expected to account for 29%-54% of all new vehicles sales (globally) by 2050.
• Population growth in African, India and other Asia-Pacific countries will drive energy growth.
• Global average annual GDP is expected to grow at 2.6% from 2022-2050.

Asia is heavily populated and continues to grow at a rapid pace. As a result, industrial growth has also increased, requiring a need for more energy. The world population is expected to reach 9.6 billion by 2050.

The figure below shows the per capita energy consumption for each country. The energy sources are also split out, so you can see where each country gets their energy. The US consumes the most energy per person. Interact with the graph and answer the following questions.

• What country is #2 energy consumer per capita?
• What is the average energy consumption per capita for the average citizen of the world?
• What source of energy is the highest for a citizen of China?

The figure below shows the Global Primary energy consumption by souce. This shows how the world wide energy sources have changed over time. As you explore the data, answer the following questions.

• What was the primary world-wide energy source prior to 1860s?
• What is the primary world-wide energy source today?
• In what year do you see Nuclear become an energy source?
• What renewable energy source is the largest percentage of world-wide energy?

Fossil Fuel Consumption

Energy Consumption and Electricity Projections

According to the International Energy Outlook (2023), global electricity genration will increase through 2025, however most of generation will be produced from renewable (zero carbon) technologies. The combined share of fossil fuels (coal, petroleum and natural gas) is expected to decrease. They also predict that electric vehicles are expected to account for 29%-54% of all new vehicles sales by 2050. China and Western Eurpoe are leading the switch to Electric Vehicles.

Credit: “Primary Energy Consumption by Fuel, World.”
US Energy Information Administration, International Energy Agency. 2020.

Credit: “Primary Energy Consumption, World and Consumption by Fuel for Power Generation, World.”
US Energy Information Administration, International Energy Agency. 2020.

As can be seen from the figures, the role of renewables is expected to change dramatically in the coming years.

Nuclear Power

Worldwide, electricity generation from nuclear power is projected to remain largely unchanged into 2040. However, some advancements in small modular reactors (SMRs) may drive an increase in nuclear energy production in the upcoming decade.

In 2025, five countries account for more than 2/3s of the world's total nuclear electricity generation.

In a nuclear plant, heat is produced by nuclear fission (splitting of an atom's nucleus into many new atoms) inside uranium fuel. As a result of fission, heat energy is released and the steam spins a turbine generator to produce electricity.

Renewables

Sizable growth in the world’s consumption of renewable energy resources is projected over the next 25 years. Much of the projected growth in renewable generation is expected to result from the completion of renewable energy installabtions all throughout the world. In 2020, 90 % of all new electric power generation installations were renewable across the globe.

In hydroelectricity, mechanical energy from the water being pulled downward by gravity is converted to electrical energy. More specifically, a hydroelectric generator directs the flow of water through a turbine, which extracts the kinetic energy from the movement of the water and turns it into electricity through the rotation of electrical generators. Hydropower is the largest single renewable electricity source today, providing 16% of world electricity at competitive prices. It dominates the electricity mix in several countries, developed, emerging, or developing. However, wind and solar are quickly catching up.

For a long time, growth in the world and the U. S. energy consumption as a function of time, follow what is known as exponential function. Now it looks like we have switched to linear growth, but time will tell if this is a permanent change. The exponential increase is characterized as follows. The amount of change (increase in energy consumption) per unit time is proportional to the quantity (or consumption) at that time.

$$\frac{\Delta N}{\Delta t}\propto N$$

or

$$\frac{\Delta N}{\Delta t}=\lambda N$$

Where Greek letter Δ(delta) is the change or increment of the variable and λ (lambda) is the growth rate. After some mathematical methods, it can be shown that the equation changes to the form

$$N=N_0{e}^{\lambda t}$$
where e is a constant = 2.71

We can determine how long it takes for N0 to become 2N0 (twice its original number or double). That time period is called doubling time. After some mathematical steps it can be written as:

Fossil Fuels account for a large portion of the world's energy sources. These fossil fuels are non-renewable fuels with a finite lifetime. So, the question is: Will we have enough supply for future energy requirements?

The answer to this question depends on the quantity of fossil fuels we have in the ground. Energy sources that have been discovered but not produced cannot be easily measured. Trapped several feet below the surface, they cannot be measured with precision. There are several terms used to report the estimates of the energy resources. The most commonly used terms are “reserves” and “resources.”

• "Reserves" represent that portion of demonstrated resources that can be recovered economically with the application of extraction technology available currently or in the foreseeable future. Reserves include only recoverable energy.
• “Resources” represent that portion of the energy that is known to exist or even suspected to exist, irrespective of technical or economic viability. So reserves are a subset of resources.

Coal

While much of the world has decreased their use of coal over the past two decades, both China and India have been increasing their use of coal.   Push the play button below to show how coal usage has changed since 1900.   The US was the #1 producer of coal until the 1980s, when China became #1.   Since then, China's coal production has continued to increase with the exception of a small dip during COVID. 

As of 2025, total world proved recoverable reserves of coal were estimated at 1139 billion short tons. In many countries, such as the US, coal consumption has been decreasing. However, in China and India, coal use has increased significantly in the past decade.

Five countries have nearly 73% of the world's coal reserves:

• United States—28%
• Russia—18%
• China—13%
• Australia—9%
• India—7%

Petroluem

Based on data from OPEC (Oil Producing and Exporting Countries), the highest proved oil reserves including non-conventional oil deposits are shown in the graphic below. This shows which regions of the world have the highes amounts of oil reserves. You can interact with this figure to show the historical change of proven reserves or create different types of charts to separate by country.

The top countries for oil resereves are Venezuela, Saudia Arabia, Canada Iran and Iraq. The US does have considerable about of oil resources and lands in the top 10 of oil producing countries.

Based on data from BP (British Petroleum), proved gas reserves were dominated by three countries: Russia, Iran and Qatar, which together held nearly half the world's proven reserves. According to the US CIA The World Factbook, the US has the 4th largest reserves of natural gas. Due to constant updates about the shale gas estimates, these are difficult to say with certainty.

How Long Will the Reserves Last?

How long these reserves do last depends on the rate at which we consume these reserves. For example, let’s assume that we have $100,000 in the bank (reserves) and if we draw 10,000 dollars every year (consumption) the reserve will last for 10 years (\$100,000/\$10,000 per year). However, in this case, we are assuming that we do not add any money to our deposit, and we do not increase our withdrawal.

This is generally not true in the case of life of an energy reserve. We may find new reserves, and our energy consumption or production can also increase. In the case of energy reserve, although we know that we might find new resources, we do not know how much we could find. But the consumption can be predicted with some accuracy based on the past rates.

Lifetime of current reserves at constant consumption

We can calculate the life of current petroleum reserves by dividing the current reserves by current consumption.

• At the current rate of consumption, the approximate lifetime of the world’s petroleum, natural gas, and coal reserves is 47.1 years, 52.4 years, and 133 years, respectively.
• At the current rate of consumption, the current U. S. petroleum, natural gas, and coal reserves will last approximately for 6.3 years, 21.5 years, and 919 years, respectively.

It is important to note that the entire U.S. petroleum consumption is not coming from the U.S. reserves because we import more than one half of the consumption. Because we import more than one half of the consumption, the petroleum reserves at the current rate will last about 11 years. If the consumption increases in the future, the life will be less. However, there is also a chance of adding more reserves with more exploration and discoveries. The increase in consumption can change depending on the price of petroleum and other alternative fuels. Likewise, us moving to electric cars and harnessing unconventional oil reserves can extend the lifetime of these reserves.

Therefore, these lifetimes are not carved in stone. It can be debated whether the U.S. reserves will last for 6 years or 10 years or even 20 years, or we may never run out! But there is increasing consensus that we must change our lifestyle. Even if we won't run out, the environmental consequences of continued use are pushing us to change anyway, but more on that later...

The R/P ratio can change from year to year, similar to our bank balance. We can add more if we make more or consume more. That changes the time we can draw on the balance.

Therefore, we must conserve, innovate (get more with less), or learn to live without these resources.

US Energy Supply and Demand

When focusing on the energy supply and demand, it can be helpful to see where the energy is going. Below is a sankey diagram showing the total amount of energy consumed in the US and where it is going. Where does most of our energy go? Does this surprise you to see over 65% of our energy is rejected in the form of waste?

Image description: Estimated U.S. Energy Consumption in 2023

The image is a Sankey diagram illustrating the estimated U.S. energy consumption in 2023, totaling 93.6 quadrillion BTUs (Quads). It shows the flow of energy from various sources to different sectors and highlights the amount of energy that is ultimately rejected or used. Energy sources are color-coded and include solar (yellow, 0.89 Quads), nuclear (red, 8.1 Quads), hydro (blue, 0.82 Quads), wind (purple, 1.5 Quads), geothermal (brown, 0.12 Quads), natural gas (light blue, 33.4 Quads), coal (gray, 8.17 Quads), biomass (light green, 5 Quads), and petroleum (dark green, 35.4 Quads). The energy flows into categories such as electricity generation (orange, 32 Quads), residential (pink, 11.3 Quads), commercial (pink, 9.3 Quads), industrial (pink, 26.1 Quads), and transportation (dark green, 28 Quads). Finally, the diagram shows rejected energy (gray, 61.5 Quads) and energy services (gray, 32.1 Quads). The logo of Lawrence Livermore National Laboratory is in the top right corner.

Source: LLNL October, 2024. Data is based on DOE/EIA SEDS (2024). If this information or a reproduction of it is used, credit must be given to the Lawrence Livermore National Laboratory and the Department of Energy, under whose auspices the work was performed. Distributed electricity represents only retail electricity sales and does not include self-generation. EIA reports consumption of renewable resources (i.e., hydro, wind, geothermal and solar) for electricity in BTU-equivalent values by assuming a typical fossil fuel plant heat rate. The efficiency of electricity production is calculated as the total retail electricity delivered divided by the primary energy input into electricity generation. End use efficiency is estimated as 65% for the residential sector, 65% for the commercial sector, 49% for the industrial sector, and 21% for the transportation sector. Totals may not equal sum of components due to independent rounding. LLNL-MI-410527

Source: Lawrence Livermore National Laboratory (LLNL): Energy Flow Charts

Globally, many interesting transitions are occurring. While the U.S. was once the top consumer of energy, China claimed this title in 2009.

Fossil Fuels

Fossil Fuels still remain a major component of energy use in the US. As shown in the figure above, over 80% of US energy use is produced from fossil fuels.  The three fossil fuels are coal, oil and natural gas.

As a result of innovations in oil and gas extraction, U.S. imports have dropped considerably. While the US still consumes a lot of oil for transportation, a lot more oil has been discovered and produced domestically.

Image description: U.S. energy net imports by major source, 1950-2023

The image is a line graph titled "U.S. energy net imports by major source, 1950-2023," measured in quadrillion British thermal units. The horizontal axis represents the years from 1950 to 2023, while the vertical axis measures energy quantities ranging from -10 to 25 quadrillion British thermal units. There are four colored lines, each representing a different energy source. The brown line shows crude oil imports, peaking around 2005 at over 15 units before declining to approximately 2 units by 2023. The maroon line indicates petroleum products, with fluctuations around 5 to 10 units until it declines to negative values in recent years. The blue line for natural gas remains relatively stable from the 1970s, eventually dipping below zero after 2000. The black line represents coal and coal coke, consistently near zero, slightly fluctuating around the mid-20th century. Each energy source is identified with corresponding colors in the legend below the graph. At the bottom left, the "eia" logo is visible, along with a text box citing the data source.

Credit: EIA Energy Explained

Looking at the U.S. Energy Profile, It can be seen from the imports profile that the US Crude oil imports have significantly reduced between 2005 and 2019 from a peak of 25 Quadrillion BTUs. Another significant change that can be noted is that the US is now exporting natural gas (below zero on the y axis) instead of importing it. Although crude oil is imported, US exports finished petroleum products resulting in less net imports. As a matter of fact, US total energy exports exceeded the imports in 2019 since 1950.

The top five countries (sources) of US total petroleum in 2019 were Canada (49%), Mexico (7%), Saudi Arabia (6%), Russia (6%) and Columbia (4%).

The U.S. also ranks:

• first in worldwide reserves of coal;
• sixth in worldwide reserves of natural gas;
• eleventh in worldwide reserves of oil.

US Energy Consumption by Source and the chart of the US Energy consumption by source and user sector shows each energy source and the amount of energy it supplies in British thermal units (BTU). Petroleum is the leading source of energy in the US in 2019 with 36.72 quadrillion BTUs. Next is natural gas with 32.10 quadrillion BTUs. Coal supplies 11.31 quadrillion BTUs of energy. Renewable energy and nuclear power are responsible for 11.46 and 8.46 quadrillion BTUs respectively. Of the total petroleum consumption, 72% is used for transportation and another 23% is used by the industrial sector. Similarly, 35% of the natural gas (largest fraction) is used for power generation. On the other hand, 76% of the residential and commercial energy needs are met by natural gas. The actual percentages are not required to be memorized but answers to the questions such as: Which fuel is most used by power plants for power generation? Which sector uses petroleum the most? Approximately what fraction of the electricity is generated by renewable energy? (10, 25, 50 or 90) What is the primary purpose of coal use? etc. need to be answered.

US Energy Consumption by Source and Sector

The graph shows how dependent the U.S. is on our petroleum supply, as it accounts for almost 37% of our energy. Our next two highest sources of energy, like petroleum, are non-renewable and include natural gas and coal. Only about 11% of our energy comes from renewable energy sources such as wood and water (hydroelectricity). According to Energy Information Administration, US renewable energy consumption surpassed coal for the first time in over 130 years in 2019. Of the 4.12 trillion kWh of electricity generated in the US, 38% was from natural gas, coal accounted for about 23% and nuclear adding another 20%. Renewable sources contributed to 17% of the total electricity generated.

Image description: U.S. Energy Consumption by Source and Sector, 2024

The flow diagram illustrates the U.S. energy consumption by source and sector for the year 2024, measured in quadrillion British thermal units (Btu). On the left, the energy sources are listed with corresponding percentages: petroleum (35.3, 38%), natural gas (34.2, 36%), renewable energy (8.6, 9%), nuclear (8.2, 9%), and coal (7.9, 8%), totaling 94.2 quadrillion Btu. The lines connect these sources to various end-use sectors on the right: transportation (28.1, 38%), industrial (26.1, 35%), residential (11.2, 15%), and commercial (9.5, 13%) with a total of 74.9 quadrillion Btu. In the center, a section is dedicated to the electric power sector, splitting into electricity sales (13.5, 41%) and energy losses (19.3, 59%), with a total of 32.8 quadrillion Btu. Different colored lines represent energy flow from each source to sectors, indicating the percentage allocation.

Credit: Energy Review Monthly, April, 2025 by EIA

In 2023, fossil fuels made up 84% of total U.S. energy consumption, the lowest fossil fuel share. The greatest growth in renewables over the past decade has been in solar and wind electricity generation. Liquid biofuels have also increased in recent years, contributing to the growing renewable share of total energy consumption. 2020 was the first year that renewables surpassed coal consumption in the U.S.

US Energy Consumption Over Time

Image description: U.S. Primary Energy Consumption

The image is a line graph displaying energy consumption trends in the United States from 1950 to 2024, measured in quadrillion British thermal units (Btu). The horizontal axis represents years from 1950 to 2024, while the vertical axis represents energy consumption in quadrillion Btu, ranging from 0 to 50. Five colored lines represent different energy sources. The green line indicates petroleum consumption peaking around 40 quadrillion Btu in the early 2000s. The brown line, representing natural gas consumption, steadily rises, nearly intersecting petroleum consumption in 2020 and again in 2024. The blue line shows coal consumption, peaking around 1990 but sharply declining thereafter. The red line, depicting total renewable energy consumption, shows a gradual increase. The yellow line, representing nuclear electric power, rises sharply around 1970 and stabilizes. A legend at the bottom specifies the color coding for each energy type.

Credit: US EIA, Energy Monthly Review Apr. 2025

The most significant decline in recent years has been coal: US energy consumption from coal was at a high of 37% in 1950 to only 9% in 2023. Biomass, which includes wood as well as liquid biofuels like ethanol and biodiesel, remain relatively flat, as wood use declines and biofuel use increases slightly. In contrast, wind and solar are among the fastest-growing energy sources in the projection, ultimately surpassing biomass and nuclear.

US Energy Consumption History

The plot of US energy consumption shows the relative amounts of each type of energy that was consumed for each year. The history of the energy consumption profile of the United States indicates that petroleum makes the largest part of the energy demand over the past seven decades. Natural gas has taken the second over the past decade with the production of gas from shale. Coal has been replaced by renewable energy and natural gas for electricity generation. Among the renewable energy sources, biomass has the larger share followed by wind energy. Wind energy and solar energy are the fastest growing energy sources.

Credit: US EIA

Credit: EIA Annual Energy Outlook 2021

Answers to the following questions need to be looked for in the material presented above.

• Of all the renewable energy sources, which renewable source is used most?
• Which of the renewable sources is used most for transportation?
• Approximately what fraction of the electricity is generated by nuclear energy? (10, 20, 50 or 90)

Electricity

Electricity demand is expected to grow in the future. Visit the webpage US electricity explained - Sources and profiles

Examine for:

• Sources of U.S. electricity generation
• What are the notable changes in the major sources for electricity generation between 1950 and today?
• Role of renewable energy in the electricity generation.

Growth in electricity use for in the residential and commercial sectors is partially offset by improved efficiency. However, increases in demand from electric cars and data centers are causing a expected increase in electric demand. In 2023, Fossil Fuels accounted for 60% of US electricity generation, with natural gas accounting for most of that.  

Most capacity additions over the next 10 years are expected to be renewables.

Review

Watch the following 4 minute 50 second video Review for Lesson 2.

Test Yourself

The questions below are your chance to test and practice your understanding of the content covered in this lesson. In other words, you should be able to answer the following questions if you know the material that was just covered! If you have problems with any of the items, feel free to post your question on the unit message board so your classmates, and/or your instructor, can help you out!

1. Is energy use in the world increasing, decreasing or staying the same? Does it depend on where you live? Why?
2. The United States, with 5% of the world's population, uses about 25% of the world's energy and contributes 25% of the world's greenhouse gas emissions. Explain.
3. List the reasons why the United States per capita energy consumption is one of the highest. What other countries have high per capita energy consumption? Why?
4. List reasons why the United States energy consumption per dollar of GDP is higher than most of the industrialized nations.
5. What is the difference between reserves and resources?
6. List the changes that you would make in your personal lifestyle if you were mandated to reduce your energy consumption by 25%.
7. What variables determine the lifetime of a nonrenewable resource?

Extra Resources

For more information on topics discussed in Lesson 2, see these selected references:

1. Hinrichs, R., Wade, R. H., & Clemons, J. L. (2024). Energy: Its use and the environment. Cengage.
2. Energy Information Administration, Annual Energy Outlook, DOE/EIA 0383 (2025), U.S. Department of Energy, Washington D.C., 2025.
3. Energy Information Administration, International Energy Outlook, DOE/EIA 0484 (2023), U.S. Department of Energy, Washington D.C., 2023.