The electricity that arrives at your home or business comes from the many electricity generating facilities that are used in your region of the country. Think of several streams feeding into a pond from which you draw your water. The several streams are different generating plants delivering power to the pond, or "power pool". And just as one stream might be clean and another polluted, so different generating facilities may use different fuels and technologies to make electricity, and have different environmental effects: Carbon dioxide (CO2) and other emissions from coal, oil and gas plants; radioactive waste from nuclear plants, and so on. From this common pool, power lines transmit blended power to your home.

How your electricity is generated depends on where you live and what mix of energy resources are in your utility's power pool. In the United States, the majority of electricity that we use is produced through burning fossil fuels. Contact your utility to learn more about the generation sources for the electricity that you receive.

Making electricity by burning fossil fuels is the largest industrial source of air pollution in the country. The American Lung Association reports that air pollution from electricity production costs the nation $20 billion per year in health care impacts.

In addition to smog and acid rain, burning fossil fuel is a major contributor to global climate change (or "global warming"). Human activities are now adding about 7 billion metric tons of carbon into the atmosphere every year. This is enough to knock the natural system of our planet out of balance. The oceans and land vegetation are absorbing about half of these emissions. The other half remains in the earth's atmosphere for 100 years or longer. This is what is causing the rapid buildup of CO2, a buildup that surpasses nature's ability to take CO2 emissions out of the atmosphere and dwarfs natural fluctuations.

Most scientists feel that the warming trend caused by the CO2 buildup affects our everyday activities through disruptive weather patterns, such as drought in some areas or floods in others. Furthermore, the problems of air pollution and climate change are bigger than our own community. What we do in one area affects the whole planet. So, how we make electricity is important to our families, our communities and everyone around the world. That is why the Bonneville Environmental Foundation (BEF) makes its BEF Offsets available to anyone, no matter where they live.

Many environmental and nonprofit organizations, like BEF, are committed to changing and improving the energy mix in the country. That means first using our energy resources efficiently by using energy-efficient equipment and appliances, and insulating businesses. It also means building additional facilities that produce renewable energy, like wind turbines, solar projects and other types of cleaner burning projects, such as landfill gas. It also helps when consumers state their preference for renewable energy by calling their utility and communicating with their elected representatives. As more people commit to saving energy and using renewable resources, the energy mix will begin to get greener. See responses to "What is a BEF Offset?" for a more detailed description of how BEF Offsets help to remedy this electricity generation issue.

Electricity is the leading industrial cause of air pollution in the United States. BEF calculates the carbon dioxide equivalents (CO2e) created by your electricity use. Traditional power sources like coal create serious air pollutants, including sulfur dioxides (SO2), which cause acid rain, and nitrogen oxides (NOx), which cause smog, and of course, CO2, a gas that causes global climate change. Generally, the new renewable energy facilities that BEF supports do not generate any of these pollutants.

When a renewable energy facility sends electricity to the grid, less electricity needs to be generated from fossil fuel plants. Those plants then burn less fuel. The obvious result ought to be that less pollution overall is generated. This is true nationally for CO2 emissions, for example. At least in the western United States, it is also true for many other pollutants, such as NOx, mercury and carbon monoxide.

But for one major pollutant -- SO2 -- it's not that simple. This substance is regulated under out-of-date laws which do not recognize the value of renewable energy as a way to reduce this pollutant.

The problem with sulfur oxides (SO2): Sulfur oxides (SO2) are regulated under what is called a "cap and trade" system. The amount of SO2 that can be emitted by all the utilities in the U.S. is capped. Utilities and other polluters are given "allowances" (basically permission slips) that allow them to generate a certain number of tons of SO2. If we add a new, renewable energy facility to the system, the number of allowances does not change, so the amount of SO2 that utilities are permitted to emit does not change. (It makes no sense to us either, but that's the current law.) The utilities can either emit more pollution for each unit of energy they create, or they can sell their allowances to other entities that can use those allowances to pollute more.

The result is that a dirty coal facility may have the right to put, let's say, 1,000 tons of SO2 into the air each year, and even if the amount of power they generate is reduced by a new wind facility, the amount of SO2 the utility can emit stays the same.

The Good News: Buying green power or Offsets does reduce the amount of greenhouse gasses emitted, and, in most places, reduces the amount of pollutants other than SO2 that are emitted. CO2 is the best example of how this works.

Offsetting CO2: Ironically, because there is no regulation on CO2, it is the easiest pollutant to offset with new renewable energy facilities. Utilities are not trying to reduce their CO2 contributions by installing new technology and they are not trying to meet any caps on CO2, because there aren't any caps. This means that if we reduce the amount of coal or natural gas burned, we are actually reducing the amount of CO2 in the system. The utilities do not have any limits on the amount of CO2 they can emit, so they do not benefit by emitting more or by selling their allowances to other entities that can use those allowances to pollute more. There are no allowances. When less dirty fuel gets burned, less CO2 is emitted and the story ends there.

Offsetting Other Pollutants

As you can see, the BEF calculator only calculates the carbon dioxide equivalents (CO2e) created by your electricity use. We do not calculate the SO2 your purchase offsets because under current law and regulatory practice, we cannot guarantee that there is a real, physical offset of SO2. The Pacific Northwest Electric Power and Conservation Planning Council is currently performing calculations to determine the amount of air pollutants other than CO2 that will be offset by new renewable energy facilities in the region.

There are many other reasons to support new renewable energy facilities:

• They help diversify our power supply
• They help reduce our dependency on imported fuels
• They often help local communities
• They are an important export technology for the United States
• You are showing support for the development of resources that do not pollute
• You are helping the renewable energy industry to maintain competition and to continue to grow and improve its great products.

So, buying Offsets or green power is a very good thing. Global climate change is a serious threat to the health and well-being of our planet. We must act to protect our children and grandchildren (and their grandchildren). Buying BEF Carbon Offsets is a great way to reduce our personal contribution to global climate change and to support a great industry that is changing dirty business-as-usual practices. However, be wary of claims made by some marketers that sulfur oxides (SO2) emissions are being reduced as well.

Contact your utility company or your state utility regulatory agency, or energy office and ask for information on your utility's generating sources (often called the fuel mix), and the pollution created from those generating sources. Many utilities are required by state environmental disclosure laws to provide this information.

Electricity is used as it’s generated. There is very little ability to store electricity in our nation’s grid. Because of this instantaneous nature, the electric power system must constantly be adjusted to ensure that the generation of power matches the consumption of power. On continental U.S. power grids, roughly 150 Control Area Operators serve this function by using computerized control centers to dispatch generators as needed. To help the Control Area Operators, electrical generators are divided into three categories:

• Baseload power plants, which are run almost full-time to meet minimum power needs
• Peaking power plants, which are run only to meet the power needs at maximum load (known as "peak load")
• Intermediate power plants, which fall between the two and are used to meet intermediate power loads

Baseload technologies are any resources that can produce a continuous, or baseload, amount of electricity, and can be controlled to adjust the amount of electricity they’re producing. Think of them as a giant water storage tank with a faucet on it -- when you need a little water, you open the faucet a little, and if you need more water, you open the faucet more. Examples of baseload technologies are hydro, biomass, and geothermal.

Non-baseload technologies are resources with electricity output that is not continuous, and cannot be completely controlled. Using the water analogy again, non-baseload technologies are like rain. If you want a glass full of water, you can set it outside to fill up, but it might take several days before it rains, and even then it might not be enough to fill your glass. Examples of these non-baseload technologies are wind and solar power.

Build margin is the region’s estimated emissions based on its current facilities and new facilities planned through 2010. Operating margin is the "non-baseload" emissions of currently operating grid-tied generating facilities in the region. These are the facilities that will actually reduce their output in response to an increase of electricity from renewable resources entering the grid.

For illustration, consider this example: there is a neighborhood of 400 homes in North Dakota, which currently gets its electricity from a coal-fired power plant.

Let’s say the electric utility installs a wind turbine that has the capacity to serve 400 homes when the wind is blowing at a given average speed. However, any time the wind is not blowing, or is blowing less than average, the wind turbine is not producing enough electricity. If the wind turbine were the only source of electricity for those 400 homes, some or all of them would be without power whenever the wind slowed down or stopped blowing. Another scenario is that on a hot day, a large portion of those 400 homes could try to run their air conditioning at the same time, thus pushing the total demand higher than the wind turbine alone can supply. To avoid these situations, the electric utility needs to keep a backup power plant on standby to deliver electricity to the homes whenever the wind turbine slows down or when the total electric load increases beyond the turbine’s capacity. While the wind turbine clearly reduces the amount of electricity that the backup plant needs to produce, it cannot entirely eliminate the need for the backup plant.

Now, let’s look at the same neighborhood, but instead of a wind turbine, we’ll say the electric utility has installed a new, low-impact, hydroelectric power plant. This plant also has the capacity to power 400 homes when a specific amount of water is flowing through the turbines. In this case, the flow of water through the turbines will neither increase nor decrease unless a plant operator makes a change. In other words, there is a continuous, reliable supply of electricity. Now let’s say that half of the 400 homes decide to turn on the air conditioning again, increasing the total power demand by 25%. The operator in the hydro plant can increase the flow of water through the turbines to produce more electricity and meet the increased demand caused by the air conditioning. In this case the hydro plant is actually capable of supplying the electricity needs of the 400 homes on its own. There is no need for the coal plant in this scenario.

As a nation, our power demand is increasing. That means we continue to build new power generation facilities. In fact, the electric utilities across the country are continually developing and refining their plans for how they will meet this increasing demand and how to address the fact that existing power plants, at some point, need to be replaced.

Let’s now change our two scenarios slightly to see how renewable resources might affect the utilities’ plans. Let’s say that instead of an existing neighborhood with an existing power plant, the 400 homes are in a new development, which the electric utility needs to provide power to.

In the hydro example, we saw that a hydro plant could meet the demand of a neighborhood of 400 homes on its own and therefore a new coal plant would not need to be built. When renewable energy is added to the grid in sufficient amounts to prevent the construction of new polluting resources, the emissions that are avoided are referred to as "Build Margin." The Build Margin reflects the emission rates of the planned capacity additions in the United States. If the planned capacity additions included nothing but coal plants, the Build Margin would be very high. If the planned capacity additions were mostly cleaner natural gas plants, the result would be a lower Build Margin.

In the wind turbine scenario, we saw that we could meet most of the demand of the 400 homes most of the time. For reliability, we would need power from somewhere else to fill in the gaps in power generation of the wind turbine, but when the wind blows, the "backup" plants can produce less energy and therefore collectively release fewer greenhouse gas emissions. We can say then, that when the wind turbine operates, it is displacing the emissions caused by the operation of currently existing power plants on the grid. These displaced emissions are called the "Operating Margin".

However, wind energy is becoming very popular and many new wind turbines are being added to the nation’s electricity grid, sometimes as part of large wind farms. This is good news and, in fact, this trend is beginning to affect the actions of utilities and regulators as they try to stay ahead of our nation’s growing power demand. Over time, the output of wind facilities can become sufficient to prevent the construction of new polluting resources. So wind energy, and other non-baseload resources, affect both currently operating facilities (Operating Margin) and planned facilities (Build Margin). To represent this combined impact, we use the average of the Operating Margin and the Build Margin emissions, which we call the "Combined Margin."

To summarize, over time, Baseload Renewable Technologies reduce the need to build other power plants and therefore offset the Build Margin. Non-Baseload Renewable Technologies reduce the need to operate other power plants in real time (the Operating Margin) and over time, also reduce the need to build other power plants (the Build Margin). Therefore these resources are deemed to offset the average of the Build and the Operating Margin, which is called the Combined Margin.

The Bad News: Electricity from a wind turbine looks no different and acts the same as electricity generated from a coal facility. Electricity cannot be stored efficiently, so when a generator makes electricity it is directed to where it is needed at that moment in time. Once the energy leaves the generator and goes into the electricity mix or grid, it is all the same, and the grid cannot deliver electricity from a particular generator to you. You are going to get electricity from the same mix of generating plants as your neighbor gets regardless of whether you choose to buy green power.

The Good News: There may be no difference between one bit of electricity and another, but the way electricity is generated has very different environmental impacts. If we use more wind turbines and fewer coal plants, we produce less air pollution. All the electricity will continue to look the same, but the environment will look better - and be healthier. The important goal is to change the mix of the plants generating the electricity that goes into the grid. BEF, a nonprofit organization, is committed to doing just that. When you and others purchase BEF Carbon Offsets equal to all or a portion of the energy that you are using, your contribution helps build more wind turbines, solar facilities and other forms of renewable energy.

Renewable energy is still generally more expensive to generate than is electricity from polluting fossil fuel facilities. On the other hand, renewable power is a much higher quality product. Most of BEF's customers would pay a little more for a car that would run cleaner, quieter, more reliably and more safely. And they'll do the same for the electricity they buy.

For more information on air pollution, we suggest that you begin by visiting the Web site sponsored by the American Lung Association: www.lungusa.org.

For more information on global climate change issues, we suggest that you visit the following Web sites:

Climate Solutions: www.climatesolutions.org

Environmental Protection Agency: www.epa.gov/climatechange/index.html

Natural Resources Defense Council: www.NRDC.org