(RHIE) Renewable Resources Lesson

Renewable Resources

A renewable resource is a natural resource which can replenish with the passage of time, either through biological reproduction or other naturally recurring processes. Renewable resources are a part of Earth's natural environment and the largest components of its ecosphere. A positive life cycle assessment is a key indicator of a resource's sustainability.

Renewable energy sources including biomass, hydropower, geothermal, wind, and solar provide 8% of the energy used in the United States. Most renewable energy goes to producing electricity.

 

See description of diagram Links to an external site.

What role does renewable energy play in the United States?

The use of renewable energy is not new. More than 150 years ago, wood, which is one form of biomass, supplied up to 90% of our energy needs. As the use of coal, petroleum, and natural gas expanded, the United States became less reliant on wood as an energy source. Today, we are looking again at renewable sources to find new ways to use them to help meet our energy needs.

In 2012, consumption of renewable sources in the United States totaled about 9 quadrillion Btu — 1 quadrillion is the number 1 followed by 15 zeros — or about 9% of all energy used nationally. About 12% of U.S. electricity was generated from renewable sources in 2012.

Over half of renewable energy goes to producing electricity. The next largest use of renewable energy is biomass (wood and waste) for the production of heat and steam for industrial purposes and for space heating, mostly in homes. Biomass also includes biofuels, such as ethanol and biodiesel, used for transportation.

Why don't we use more renewable energy?

In the past, renewable energy has generally been more expensive to produce and use than fossil fuels. Renewable resources are often located in remote areas, and it is expensive to build power lines to the cities where the electricity they produce is needed. The use of renewable sources is also limited by the fact that they are not always available — cloudy days reduce solar power; calm days reduce wind power; and droughts reduce the water available for hydropower.

The production and use of renewable fuels has grown more quickly in recent years as a result of higher prices for oil and natural gas, and a number of state and federal government incentives for renewable energy. The use of renewable fuels is expected to continue to grow over the next 30 years, although EIA projects that we will still rely on non-renewable fuels to meet most of our energy needs.

Biomass - Renewable Energy from Plants and Animals

Biomass is organic material made from plants and animals (microorganisms). Biomass contains stored energy from the sun. Plants absorb the sun's energy in a process called photosynthesis. The chemical energy in plants gets passed on to animals and people that eat them.

Some examples of biomass fuels are wood, crops, manure, and some garbage.

Converting Biomass to Other Forms of Energy

Burning biomass is not the only way to release its energy. Biomass can be converted to other useable forms of energy, such as methane gas or transportation fuels, such as ethanol and biodiesel.

Methane gas is the main ingredient of natural gas. Smelly stuff, like rotting garbage, and agricultural and human waste, release methane gas — also called "landfill gas" or "biogas."

Crops like corn and sugar cane can be fermented to produce ethanol. Biodiesel, another transportation fuel, can be produced from left-over food products like vegetable oils and animal fats.

How Much Biomass Is Used for Fuel?

Biomass fuels provided about 5% of the energy used in the United States in 2012. Of this, about 45% was from wood and wood-derived biomass, 44% from biofuels (mainly ethanol), and about 11% from municipal waste. Researchers are trying to develop ways to burn more biomass and less fossil fuels. Using biomass for energy may cut back on waste and greenhouse gas emissions.

Wood & Wood Waste

Burning Wood Is Nothing New

The most common form of biomass is wood. For thousands of years people have burned wood for heating and cooking. Wood was the main source of energy in the United States and the rest of the world until the mid-1800s. Wood continues to be a major source of energy in much of the developing world. About 80% of the wood and wood waste fuel used in the United States is consumed by industry, electric power producers, and commercial businesses.  The rest, mainly wood, is used in homes for heating and cooking.

Waste-To-Energy

Energy from garbage

Garbage, often called municipal solid waste (MSW), is used to produce energy in waste-to-energy plants and in landfills in the United States. MSW contains biomass (or biogenic) materials like paper, cardboard, food scraps, grass clippings, leaves, wood, and leather products, and other non-biomass combustible materials, mainly plastics and other synthetic materials made from petroleum.

See description of diagram Links to an external site.

Waste-to-energy plants make steam and electricity

MSW is burned in special waste-to-energy plants that use its heat energy to make steam to heat buildings or to generate electricity. There are about 86 waste-to-energy plants in the United States that generate electricity or produce steam. In 2011, waste-to-energy plants generated 14 billion kilowatt hours of electricity, about the same amount used by 1.3 million U.S. households. The biogenic material in MSW contributed about 51% of the energy of the MSW that was burned in waste-to-energy facilities that generated electricity. Many large landfills also generate electricity with the methane gas that is produced as biomass decomposes in the landfills.

Waste-to-energy plants also dispose of waste

Providing electricity is not the major advantage of waste-to-energy plants. It actually costs more to generate electricity at a waste-to-energy plant than it does at a coal, nuclear, or hydropower plant.

The major advantage of burning waste is that it reduces the amount of material that we bury in landfills. Waste-to-energy plants burned about 29 million tons of MSW in 2011. Burning MSW reduces the volume of waste by about 87%.

Biogas

Collecting gas from landfills

Landfills can be a source of energy. Anaerobic bacteria that live in landfills decompose organic waste to produce a gas called biogas that contains methane.

Methane is the same energy-rich gas that is in natural gas, which is the fuel used for heating, cooking, and producing electricity. Methane is colorless and odorless, and a very strong greenhouse gas. Natural gas utilities add an odorant (bad smell) so people can detect natural gas leaks from pipelines. Landfill biogas can also be dangerous to people or the environment. New rules require landfills to collect methane gas for safety and pollution control.

See description of diagram Links to an external site.

Some landfills simply burn the methane gas in a controlled way to get rid of it. But the methane can also be used as an energy source. Landfills can collect the methane gas, treat it, and then sell it as a commercial fuel. It can then be burned to generate steam and electricity.

Landfill gas energy projects

As of July 2013, there were 621 operational landfill gas energy projects in the United States. California had the most landfill gas energy projects in operation (77), followed by Pennsylvania (44), and Michigan (41).

Using animal waste

Some farmers produce biogas in large tanks called "digesters" where they put manure and bedding material from their barns. Some cover their manure ponds (also called lagoons) to capture biogas. Biogas digesters and manure ponds contain the same anaerobic bacteria in landfills. The biogas can be used to generate electricity or heat for use on the farm, or to sell electricity to an electric utility.

Biomass & the Environment

Using biomass for energy can have positive and negative impacts

Using biomass for energy can have both positive and negative impacts on the environment. For example, burning biomass may result in more or less air pollution depending on the type of biomass and the types of fuels or energy sources that it replaces. Biomass, such as lumber mill sawdust, paper mill sludge, and yard waste in household trash, used for energy may avoid the use the fossil fuels coal, petroleum, or natural gas. Burning fossil fuels and biomass releases carbon dioxide (CO₂), a greenhouse gas, but when the plants that are the sources of biomass are grown, a nearly equivalent amount of CO₂ is captured through photosynthesis. Sustainable cultivation and harvesting of biomass can result in no net increase in CO₂ emissions. Each of the different forms and uses of biomass impact the environment in a different way.

[CC BY 4.0] UNLESS OTHERWISE NOTED | IMAGES: LICENSED AND USED ACCORDING TO TERMS OF SUBSCRIPTION