The Differences Between Clean Energy, Renewable Energy, and Alternative Energy

To many people, the differences between “alternative energy,” “renewable energy,” and “clean energy,” might not be obvious. But each term is unique and has its own individual definition. These three terms are not all exactly the same.

Alternative Energy

When we speak of alternative energy, we refer to sources of usable energy that can replace conventional energy sources (usually, without undesirable side effects). The term “alternative energy” is typically used to refer to sources of energy other than nuclear energy or fossil fuels.

Throughout the course of history, “alternative energy” has referred to different things. There was a time when nuclear energy was considered an alternative to conventional energy, and was therefore called “alternative energy.” But times have changed.

These days, a form of “alternative energy” might also be renewable energy, or clean energy, or both. The terms are often interchangeable, but definitely not the same.

Renewable Energy

Renewable energy is any type of energy which comes from renewable natural resources, such as wind, rain, sunlight, geothermal heat, and tides. It is referred to as “renewable” because it doesn’t run out. You can always get more of it.

People have begun to turn to this type of energy due to the rising oil prices, and the prospect that we might one day deplete available sources of fossil fuels, as well as due to concerns about the adverse effects that our conventional energy sources have on the environment.

Of all the different types of renewable energy, wind power is one which is growing in its use. The number of users who have some form of wind power installed has increased, with the current worldwide capacity being about 100 GW.

Clean Energy

“Clean energy” is simply any form of energy which is created with clean, harmless, and non-polluting methods.

Most renewable energy sources are also clean energy sources. But not all.

One such example is geothermal power. It may be a renewable energy source, but some geothermal energy processes can be harmful to the environment. Therefore, this is not always a clean energy. However there are also other forms of geothermal energy which are harmless and clean.

Clean energy makes the less impact on the environment than our current conventional energy sources do. It creates an insignificant amount of carbon dioxide, and its use can reduce the speed of global warming – or global pollution.

As you can see, alternative energy, renewable energy, and clean energy are very similar. But it is important to know that there are differences.

There are many actions which can be taken, to help reduce the greenhouse gases in our atmosphere. Some of these steps can be taken in your own home. Many clean energy solutions can can be easily installed, and some kits are quite affordable.

Carbon emissions and other forms of pollution are not only created by heavy industrial factories. They are created in the common household as well. Energy efficiency has become an important aspect of our lives.

It’s important to start making changes now; if we want to save our planet for our children, for the flora and fauna of the Earth, and for the future of mankind. Clean energy, to be exact, can make a big difference.

Commentary Robert Bryce, 05.11.10, 02:55 PM EDT

Hint: It’s physics.

The growing oil spill in the Gulf of Mexico has, predictably, resulted in a new chorus of voices calling for increased use of renewable energy sources. But over the past five decades renewables have actually been losing market share.

In 1949 nearly 91% of America’s total primary energy came from coal, oil, and natural gas. The balance came from renewables, with hydropower being a dominant contributor. By 2008 the market share for coal, oil and natural gas, along with nuclear, had grown to 92.5% of total primary energy in the U.S. with the remainder coming from renewables.

In other words, despite these huge investments, renewables’ share of the energy market has been shrinking. What’s happening? While conspiracy theorists may want to believe that Big Oil, Big Coal and Big Nuclear are stifling the growth of renewables, the simple truth is that coal, oil, natural gas and nuclear can satisfy the Four Imperatives: power density, energy density, cost and scale.

The Four Imperatives provide a simplified way to analyze the physics and math that rule our energy and its delivery, the latter better known as power. Before going further we must differentiate between energy and power. If you recall your high school physics, the definitions are straightforward: Energy is the ability to do work; power is the rate at which work gets done. Put another way, energy is an amount; power is a rate. And rates are more telling than amounts.

The first of the Four Imperatives, power density, is the most telling of the rates. Power density refers to the energy flow that can be harnessed from a given unit of volume, area or mass. Common metrics of power density include: horsepower per cubic inch, watts per square meter and watts per kilogram. And given the current infatuation with renewable energy sources like wind and solar, the essential metric for power density is watts per square meter (W/m2), which shows how much power can be derived from a given piece of real estate. It is also the metric that exposes the inherent weakness of sources like corn ethanol, wind energy and solar energy. If a source has low power density, then it will likely require too much real estate, material or space to provide the power that we demand at prices we can afford or in the vast quantities that the world needs.

The production of corn ethanol is a loser for many reasons. Just a quick glance at corn ethanol’s power density–just 0.05 W/m2–shows why the fuel makes no sense from a physics standpoint. Corn ethanol’s low power density is inherent in all biomass, which leads us to the second of the Four Imperatives. Energy density refers to the quantity of energy that can be contained in a given unit of volume, area, or mass. And the low energy density of biomass–corn, switchgrass, wood, etc.–makes it difficult to produce sufficient amounts of energy without occupying huge swaths of land.

Now let’s consider the power density of wind energy, which is about 1.2 W/m2, and solar photovoltaic, which can produce about 6.7 W/m2. Both sources are superior to corn ethanol (nearly everything is), but they are incurably intermittent, which makes them of marginal value in a world that demands always-available power. Nor can they compare to the power density of sources like natural gas, oil and nuclear. For instance, a marginal natural gas well, producing 60,000 cubic feet per day, has a power density of about 28 W/m2. An oil well, producing 10 barrels per day, has a power density of about 27 W/m2. Meanwhile, a nuclear power plant like the South Texas Project–even if you include the entire 19 square-mile tract upon which the project is sited–produces about 56 W/m2.

Simple math shows that a marginal gas or oil well has a power density at least 22 times that of a wind turbine while a nuclear power plant has a power density that is more than 8 times that of a solar photovoltaic facility. Those numbers explain why power density matters so much: if you start with a source that has low power density, you have to compensate for that low density by utilizing more resources such as land, steel, and ultra-long transmission lines. Those additional inputs then reduce the project’s economic viability and its ability to scale.

That can be understood by comparing the land use needs of a nuclear plant with those of a wind energy project or a corn ethanol operation. The two reactors at the South Texas Project produce 2,700 megawatts of power. The plant covers about 19 square miles, an area slightly smaller than the island of Manhattan. To match that output using wind energy, you’d need a land area nearly the size of Rhode Island. Matching that power output with corn ethanol would require intensive farming on more than 21,000 square miles, an area nearly the size of West Virginia.

Environmental groups and many politicians in Washington insist that the U.S. must lead the effort to develop renewable energy sources, with wind, solar and biomass being the lead components. But doing so will mean replacing high-power-density sources that are reliable and low cost with low-power-density sources that are highly variable and high cost.

Wind energy manufacturing continued to grow in 2009, albeit at a slower pace than in 2008, according to the annual U.S. wind industry market report released in April by the American Wind Energy Association (AWEA). AWEA says that despite a slowdown in turbine manufacturing compared to 2008, 10 new manufacturing facilities came online last year, 20 were announced, and nine were expanded. The report also found that more than 10,000 megawatts of new wind power generating capacity was installed in 2009, which is enough to power the equivalent of 2.4 million homes. In state rankings, AWEA says that Iowa leads in percentage of electricity from wind power, with 14 percent of the state’s power derived from wind energy sources. Iowa also has the highest number of wind industry jobs in the private sector. More information is available online at www.awea.org.

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The National Renewable Energy Laboratory’s (NREL) web site features a free map tool that shows real-time photovoltaic (PV) panel installation activity in the United States from 1998 to 2009. The tool also provides access to a database including graphs and charts of the size, location, capacity and cost of the panels. Geographers in NREL’s data analysis and visualization group accept data uploads from utility companies, local and state governments and the public. Since going online last October, the project, called the Open PV project, has catalogued more than 67,000 PV systems with an approximate capacity of 785 megawatts. NREL reports that it is exploring the creation of additional open databases for wind, solar, hot water and geothermal installations. Learn more about the project at
openpv.nrel.gov.

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On April 10 the Alaska Senate passed Senate Bill 220, the Alaska Sustainable Energy Act, an omnibus bill to stimulate the state’s economy by attracting investment in renewable energy. Sponsored by Sens. Bill Wielechowski and Lesil McGuire, the bill would set energy efficiency and renewable energy goals, dedicate state funds for renewable and alternative energy projects and testing, and establish a renewable energy tax credit of 15 percent of the retail rate for each kilowatt-hour of electricity produced from renewable sources. Upon adoption by the Senate, the bill was transferred to the House for consideration.

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A group of 19 governors sent a letter to President Barack Obama in March urging expansion of the Section 48C Advanced Energy Manufacturing Tax Credit under the American Recovery and Reinvestment Act. In January, $2.3 billion in tax credits was awarded to recipients in 43 states to support manufacturing energy projects. The governors report that these federal resources have leveraged more than $5.4 billion in private investment. In the letter, the governors discuss the success of the tax credit and describe the economic benefits that would come with an expansion. A copy of the letter, and more information about the Section 48C tax credit, can be found online at www.energytaxcredits.com.

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In early March, Delaware Gov. Jack Markell announced the introduction of the Clean Energy Jobs Act, legislation that calls for the potential installation of approximately 300 megawatts of new solar PV systems by 2029. Markell says the bill could lead to the installation of more than 1000 megawatts of utility-scale generation in the form of offshore wind power, which would result in the creation of 1,000 construction jobs and 150 long-term operation and maintenance jobs by 2029. The bill proposes a market-based method for financing renewable energy projects under the state’s Green Energy Fund. Supporters say this would resolve the long wait time and inadequate overall funding for the current grant program. A fact sheet about the Clean Energy Jobs Act is available at governor.delaware.gov.

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Sen. Mark Udall, D-Colo., introduced legislation in March that would offer a tax credit for homeowners who invest in community solar projects. Senate Bill 3137, or the Solar Uniting Neighborhoods (SUN) Act of 2010, would expand the tax code to enable taxpayers to claim federal solar investment tax credits (ITCs) when purchasing a share of a community solar project. The current tax code requires solar panels to be installed on the taxpayer’s actual residence. A copy of the bill is available online at www.energytaxcredits.com.

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