If you’ve read Climate Change 101, then you already know that greenhouse emissions are a problem, and that the vast majority of emissions in the U.S. are from fossil fuels.

Here’s how clean energy can help.

What is Clean Energy?

In the U.S., 82% of our energy is generated by burning fossil fuels. These fossil fuels cause 85% of our GHG emissions. Clean energy refers to methods of power generation that do not emit GHGs.

The fastest-growing sources of clean energy are wind and solar. Nuclear power and hydroelectric dams are also considered clean energy from a climate-change perspective; however, they adversely impact the environment in other ways.

Clean energy methods are only able to generate power in the form of electricity. Unfortunately, most of our energy-related emissions are from burning oil and gas directly for transportation, heating, and industrial processes. This means that in order to meaningfully reduce GHG emissions, we will need to convert these sectors to electric power and convert our electricity production to overall clean sources — at the same time.

GHG Emissions in the U.S.

The U.S. emits 6,872 Mt (megatons, or millions of metric tons) of CO2e each year — more than every country except China. Here’s where the GHGs come from:

U.S. GHG Emission Sources (as percentage of total)

The coloring in the chart above is based on how feasible it will be to reduce emissions for each source by using clean energy:

  • Electricity generation is by far the “easiest”. Clean energy sources present challenges, but the vast majority of GHG emissions can be eliminated with today’s technology.
  • As electricity generation becomes cleaner, consumer vehicles and natural gas heating can be converted to electric power. Again, this is possible with current technology.
  • If we are able to decrease our overall usage of gas and oil, leaks during production and transport should decrease along with it.
  • Industrial energy and commercial vehicles require large quantities of portable and on-demand power. New technology will be required to convert these systems to electric.
  • Agriculture and chemical emissions are not related to fossil fuels; clean energy will not affect them at all.

It will be a monumental task to meaningfully reduce our emissions. And it’s obvious that the place to start is with electricity generation.

Electricity Generation in the U.S.

Electricity is generated from five main energy sources: coal, natural gas, nuclear, hydroelectric, and wind/solar. The chart below shows their relative usage and emissions:

U.S. Electricity Sources % of Usage and Emissions

Coal

Coal is the most widely-used energy source, accounting for 37% of our electricity. It is also the dirtiest fuel by far, emitting more than twice as much as natural gas for the same power output. Mining operations for coal are also a major environmental problem.

Coal’s great advantage is that it is cheap to produce, and has been for a long time. However, its use is beginning to decline.

By Stephen Codrington, CC BY 2.5

Natural Gas

Natural gas is the #2 source of U.S. electricity, at 30%. It is a much cleaner fossil fuel than coal, but it still emits a large amount of CO2.

In recent years, the price of natural gas has dropped significantly. This, along with environmental concerns, has resulted in many coal plants converting to natural gas operations.

Nuclear

Nuclear power is in widespread use today, accounting for 19% of electricity production in the United States. It emits no greenhouse gases, but there are other problems associated with nuclear power: radioactive waste disposal, risk of meltdown, and nuclear weapon proliferation.

Stringent regulation based on these concerns has made nuclear plants very expensive to build and operate. As a result, nuclear power has not increased in usage since the 1990s.

Hydroelectric

Hydroelectric power (from dams) is the “original” clean energy - it supplies 9% of our electricity without producing GHG emissions. However, building new dams is very difficult due to environmental concerns and a lack of suitable locations. As a result, production from hydro-power has not increased since the 1970s.

Dams do have a major advantage relative to other power sources: they store energy by blocking the flow of water. This allows them to easily generate power on demand.

By Chintohere - Own work, Public Domain

Wind

Wind power currently generates 4% of our nation’s electricity, and is growing rapidly. It is extremely clean, and it is cheap to produce.

Wind has two major disadvantages: it is inconsistent over time, and large parts of the country don’t have enough wind to make generation viable.

Solar

Solar power generates less than 1% of our electricity. There are two types of solar power generation: photovoltaic (PV) panels, and solar concentrators. PV panels convert sunlight directly to electricity, whereas concentrators focus lots of sunlight on a single target to generate heat.

Like wind, solar is intermittent. It is much more widely usable than wind power; each of the lower 49 states gets enough sunlight to meet its electricity needs. The main disadvantage to solar has been its price — but current solar technology is nearly as cheap as coal and gas (especially with government tax subsidies).

Overcoming Intermittency

The biggest challenge to integrating large portions of wind and solar energy is that neither produces consistent power. When the sun isn’t shining and the wind isn’t blowing, we still need electricity.

There are a few ways to work around this problem:

Fossil Fuels as Backup

The most effective near-term solution to solar and wind intermittency is to use our other power sources to make up the difference. Solar and wind conditions can be predicted ahead of time to give traditional fossil-fuel plants time to ramp up their production.

Fossil fuels are extremely flexible and reliable as a power source; we will need to use them (at least a little bit) for a very long time to come.

Smart Consumption

A portion of our electricity usage can be coordinated based on current supply and demand conditions. Some water heaters, HVAC systems, and industrial processes already do this to save money on electricity. Electric cars will be another great candidate for this sort of technology as they become mainstream.

Long-Distance Transmission

If we were able to transmit power freely across the country, we could utilize excess sun or wind in one region to power others. We have the technology to do this, but it would require major investments to build the infrastructure.

There is some controversy about how effective transmission would be - conditions for solar and wind power are sometimes poor across the entire country.

By Sue Jones, CC BY-SA 2.0

Energy Storage

The ideal long-term solution for intermittency is to store excess energy when there is ample sun or wind. Unfortunately, we do not yet have technology for large-scale, cost-effective energy storage. Hydropower and batteries can meet some of our storage needs today, but they are limited and expensive.

New technologies will be required to make energy storage work for a grid powered primarily by wind and solar.

The Future

If we let it continue unchecked, climate change will have massive consequences for our country and the world. The first step in stopping it is to transition our country’s energy production from fossil fuels to clean sources such as solar and wind.

By TAFE SA TONSLEY, CC2 License

U.S. Clean Energy Fund is working to accelerate this transition by developing construction of new clean energy. If you’re interested in our progress, sign up for our email list below!

Further Reading

As with climate change, you can spend hours learning about clean energy. Here are a few sites that I’ve found particularly helpful: