"Renewable energy: Any energy resource that is naturally regenerated over a short time scale and derived directly from the sun (such as thermal, photochemical, and photoelectric), indirectly from the sun (such as wind, hydropower, and photosynthetic energy stored in biomass), or from other natural movements and mechanisms of the environment (such as geothermal and tidal energy). Renewable energy does not include energy resources derived from fossil fuels, waste products from fossil sources, or waste products from inorganic sources." - Texas Renewable Energy Industries Alliance
The term biomass refers to organic matter such as plants, residue from agriculture and forestry, the organic component of municipal and industrial wastes, and animal waste. Some types of biomass can be burnt or decomposed to produce energy. A good example of this is the burning of wood; for thousands of years it has been used to provide heat.
Biomass is a renewable energy source because plants can re-grow over a relatively short time for use as an energy source. By the process of photosynthesis, chlorophyll in plants captures the sun's energy by converting carbon dioxide from the air and water from the ground into carbohydrates (complex compounds composed of carbon, hydrogen, and oxygen). When these carbohydrates are burnt, they give off carbon dioxide and water, and release the energy they captured from the sun. Biomass is, therefore, a form of solar energy since it receives its original energy from the sun by photosynthesis.
Unlike fossil fuels, such as coal, oil or natural gas, the carbon emissions from biomass become part of a carbon cycle. Biomass carbon emissions are taken up or recycled by subsequent plant growth within a relatively short time, resulting in low net carbon emissions. This is because, through photosynthesis, plants absorb roughly the same amount of carbon dioxide (CO2) as is given off through the burning of them. On the other hand, the burning of fossil fuels add new and additional carbon to the atmosphere.
Biomass Energy Sources
WOOD
A very common source of biomass energy is wood. For thousands of years it has been burnt to produce heat, cook food, and more recently, produce electricity. For electricity production, wood can be burnt to use the heat to raise steam to drive steam-turbines, or the wood can go through a gasification process. By heating wood in a carefully controlled amount of oxygen and under pressure, it can be converted into a mixture of hydrogen and carbon monoxide called syngas. This syngas is often refined to remove contaminants. The gas produced can be used in a gas turbine or a steam turbine to produce electricity.
WASTE-TO-ENERGY
A large portion of our garbage that we dispose daily contains biomass matter that can be converted to energy. Paper, cardboard, grass clipping and scraps of food are all examples of biomass energy sources. Such wastes can be burnt in waste-to-energy plants to produce electricity.
BIOGAS
Biogas comes from microorganisms that digest (break down) organic waste and produce a mixture of methane gas and carbon dioxide. This is called anaerobic digestion. Manure and human waste are also goods sources of biogas. An anaerobic methane digester is used to trap large amounts of waste with limited oxygen and high temperature to induce bacteria into digesting (breaking down) the waste.
Biogas can be a renewable substitute for natural gas. According to the Renewable Energy Information Center, biogas can be used for any purpose that already uses natural gas such as heating, cooking, lighting, steam production, electrical production, and can even be used as an alternative fuel in natural gas vehicles.
BIOFUEL
Organic materials can be used to produce fuels such as biodiesel and ethanol. These fuels can be used on the own to power engines, or can be blended with coventional fuels as a green supplement.
Biodiesel is usually made from materials such as animal fat, recycled grease, and vegetable oil. It is made by separating biomass into fatty acid methyl esters (FAME) and glycerin. The methyl esters are what make up the biodiesel. The glycerin is a byproduct that can be used in cosmetics, pharmaceuticals, soaps, and food additives.
Biodiesel is compatible with most diesel engines; no modification to the engines are necessary to utilise biodiesel. It can also be blended with regular diesel in any amounts for use in diesel engines. Specific labels are used to indicate the ratio of biodiesel used in a blend. For example, a B20 label indicates 20% biodiesel and 80% petroleum diesel.
Ethanol is made from crops such as corn and sugarcane. When these crops undergo yeast fermentation they release ethanol.
Most gasoline engines can run on a ethanol/gasoline blend of up to 10% ethanol. However, more flex-fuel cars are being manufactured that are capable of running on E85 fuel (85% ethanol, 15% gasoline), or on gasoline alone.
References:
- "How Biomass Works," Union of Concerned Scientists, accessed July 11, 2015, http://www.ucsusa.org/clean_energy/our-energy-choices/renewable-energy/how-biomass-energy-works.html#.VbI7l_ke3KA.
- "What is biomass energy and how does it work?" Renewable Energy Information Center, accessed July 25, 2015, http://www.poweredbymothernature.com/what-is-biomass-energy.
