Availability: Fossil Fuels

These two maps show where coal (on the left) and natural gas (on the right) come from. These are the natural resources we use most to make electricity in the United States today. The U.S. has a lot of coal, which is found in many states. In fact, the coal here makes up one-quarter of all the coal in the world. The amount of known natural gas has been growing almost every year since 2000.

For an energy source to be used in a city’s power grid, there needs to be a lot of it available. Fossil fuels, which include rock (coal), liquid (crude oil), and gas (natural gas), are taken from the ground to provide energy. This energy has helped build many of the big economies in the world today.

In the past, coal was the main source of electricity in the United States. But in April 2015, natural gas became more popular than coal for the first time. We are using natural gas more and more because new methods, including one called fracking, make it easier to get natural gas from the ground. Natural gas is also better for the air than coal because it puts about half as much CO2 into the atmosphere.

Availability: Renewables

According to the U.S. Energy Information Administration, there is enough coal to last about 250 years and natural gas to last about 90 years, based on how much we use now. This means we might need to find new ways to get energy that don’t run out so quickly. Two ways to get energy from the Sun are leading the way

Wind Power

Wind is made when the Sun heats the Earth's surface unevenly. As long as the Sun is shining, the wind will keep blowing. Wind turbines have big blades that spin on a tall tower. Inside the turbine, a generator changes the energy from the moving air into electricity. This electricity travels through power cables to homes and buildings.

Sometimes, many wind turbines are put together in places called "wind farms." These farms work like power plants to create a lot of electricity. In 2015, wind turbines made 5 percent of all the electricity used in the U.S. Experts believe that wind could make 10 times more electricity than what people in the U.S. use now.

Solar Power

Solar energy can be changed into electricity and sent to a power grid, or it can be used right where it is made, like in a house, an apartment, a store, or a factory. This works through special devices called photovoltaic ("foh-toh-vol-tey-ick") cells. Many of these cells can be connected together to make solar panels.

Photovoltaic (PV) cells take in sunlight and turn the energy of moving electrons into electricity. In 2015, solar power made less than 1 percent of all the electricity in the U.S., but it can make even more energy than wind power in the future.

Cost: Fossil Fuels

Understanding the cost of power plants involves more than just fuel prices; it also includes construction, maintenance, and operational costs, such as machinery and electrical distribution systems. Fossil fuel power plants typically utilize boilers that convert fuel into steam to generate electricity, with coal and natural gas currently supplying about one-third of the country’s electricity. The cost of these natural resources can fluctuate based on availability and global events, making natural gas currently cheaper due to its abundance. Consequently, power plant managers often opt to modify existing boilers to use the least expensive fuel available, as this is generally more cost-effective than building new plants.

Fossil fuels are not just about their prices; they also have hidden costs that hurt the environment. When we mine, drill, and move these fuels, it can hurt plants, damage the land, and make the air and water dirty. Working in the ocean can also harm sea life. Accidents can happen, and cleaning them up can be very expensive and can cause long-lasting problems for nature and people's health.

Some people worry about wind and solar power because they might not look nice or could affect local plants and animals while being built. However, once they are up and running, they have a much smaller impact on the environment.

Cost: Renewables

Wind and solar power come from natural energy that is free. You might think that this would make the electricity they produce cheap. However, right now, wind and solar power are often more expensive to create and use than energy from fossil fuels. This happens for a couple of reasons. First, starting new technologies can be very costly at first. Second, the best places for making large amounts of wind and solar power are usually far away from cities. This means it costs a lot to connect these energy sources to the places that need electricity. One way to lower the cost is to make renewable energy production work better.

Reliability: Fossil Fuels

More cities are using information from watching how energy is used. This helps them decide how to share energy better. A system that uses this information is called a “smart grid.”

Electricity is very important for our daily activities. We need a good source of energy to keep everything working. If we don't have enough energy, we can have outages, or blackouts. This happens more often when everyone is using a lot of electricity, like during busy times.

Fossil fuels, like coal and natural gas, are mainly used to power big cities during these busy times. They are reliable because we can transport them easily using trucks and trains. We can burn fossil fuels anytime to make electricity. Also, we can store fossil fuels for later, which helps us have a steady supply of energy.

Reliability: Renewables

Engineers are working hard to make solar and wind power more reliable. This is important because more people are using these types of energy, and the costs are getting lower, especially in cities. One big area they are studying is how to create better batteries. This helps solve a main problem with renewable energy: it relies on weather.

When the sun is shining, special panels called photovoltaic cells make electricity. Wind turbines generate power when the wind is strong. But when the weather is bad, there might not be enough energy produced.