In this video, we'll discuss biomass as a source of renewable energy for electricity and heat. Biomass is harvested from forests and cropland as organic waste collected from agricultural or municipal resources. The attraction of biomass is that it may be cost-effective and maybe carbon neutral since carbon dioxide released by burning biomass is reabsorbed by the growth of new biomass. Formally, biomass is organic matter used as fuel for heat, light, and electricity. Humans have used biomass for heat and light ever since early humans mastered fire and continue to use biomass for energy today. Types of traditional biomass include; wood and charcoal, such as this woman carrying wood for cooking in Africa, dried animal waste such as these women preparing cow dung paddies in India and peat, the surface level precursor of coal, such as this man harvesting peat in a peat bog in Scotland. Contemporary sources of biomass for electric energy and fuels include; agriculture and forest waste, municipal waste, wood pellets, anaerobic digesters, landfill gas, and biofuels from biomass. Let's examine each of these. A significant source of biomass is forest and agricultural waste collected to burn in electricity generating plants. Sources of this type of biomass include; forestry trimmings, sawdust, crop waste, and sugarcane bagasse. Challenges of forest and agricultural biomass are that the supply is often seasonal with long periods without supply. This type of biomass is usually bulky with low volumetric energy density, creating difficulties in expenses for resource gathering, transportation and storage. Finally, using foresting and the agricultural waste for energy is carbon neutral at best. While the carbon released by burning may be replaced by new growth, this growth can take many years to develop depending on its source. Further, the gathering, transportation, storage, and handling of waste biomass consumes energy and increases carbon emissions, which are now replaced by new growth. Most logical use of forests and agricultural waste for energy, is immediately adjacent to lumber mills and agricultural processing plants. While waste fuel is readily available in large quantities and in steady supply, such as the sawdust fueled power plants shown to the right. Similar to forest waste, are wood pellet plants where trees are processed into wood pellets to burn in power plants. Trees are grown and harvested in commercial forests and transported to the pellet plants. The trees are then ground and processed into wood pellets for easy handling and transport. The pellets are then shipped to power plants where they are typically combined with coal to reduce the carbon footprint of the plant. There is a substantial trade in wood pellets from North America to Europe and elsewhere. The challenges of energy from wood pellets are creating the pellets is energy intensive. Transportation to foreign markets is expensive and energy intensive. Wood pellets as fuel are carbon neutral at best and only over many decades as new forest grow. Another stream of waste that can be used to generate electricity and heat is, municipal solid waste that is burned to power as steam turbine generator. Suitable municipal solid waste includes; paper, garbage, trash, agricultural products, and clean industrial waste. MSW is often supplemented with natural gas to smooth supply variation. MSW waste streams must be sorted before use to remove metals, glass, non-combustible, and any toxic metals. Then MSW is burned to create steam, which powers the steam turbine generator to produce electricity. Depending on the location of the plant, steam may be piped into town for heat and air conditioning. The only difference between an MSW power plant and traditional coal plant is the fuel for the plant as indicated by the yellow square to the right. Hollows is the same. Another means of extracting energy from solid municipal waste is with anaerobic landfill gas, where municipal landfills are kept to capture methane that is then used to generate electricity. Methane naturally occurs in large landfills, which then escapes into the atmosphere. By sealing a landfill with an impervious cap, the naturally occurring methane can be captured and then used to generate electricity in a natural gas power plant. This technology is widely used in many countries to generate electricity and to convert methane to CO2, which is a much less potent green-house gas than is methane. The challenges of landfill gas are that there are a limited number of landfill sites. The economics acquired large landfills. It's more expensive than traditional landfills, but the cost may be offset by gas sales and low natural gas market prices. Another means of producing methane for energy production is anaerobic digestion where methane is captured from animal manure and dairy cattle, hog, or chicken facilities. An anaerobic digester is a tank filled with manure that is sealed from oxygen in the air, that's the anaerobic part. Anaerobic bacteria ''digest'' the waste to produce methane gas and solids. The solid waste can then be used as a fertilizer. The methane gas is collected and can be used for lighting, heating, and to power an electric generator, usually onsite for local use. One benefit of anaerobic digesters is that the technology is basically simple. Digesters are practical for both large and small applications, as shown in the picture to the right. Anaerobic digesters are environmentally beneficial since they prevent water pollution and reduce green-house gases by turning potent methane into less potent carbon dioxide. These charts show that the current cost of constructing a biomass plant is about $2,100 US per kilowatt hour of capacity. The level ice lifetime cost of biomass energy is six or seven cents per kilowatt hour. Quite competitive. Biomass plants operate with capacity factors of about 75 percent. This next graph shows that biomass energy has almost doubled in over the last decade, from about 65 gigawatts of installed capacity to over 120 gigawatts. Looking forward, biomass is forecast to continue to grow over the next decades to 2050, but we'll have a relatively small part of the overall picture of renewable energy technologies. Biomass energy has several important advantages. Biomass energy uses renewable resources which can directly replace fossil fuels, such as coal and electricity and heat generation. The use of biomass can reduce waste and pollution, and can reduce carbon emissions, or can be carbon neutral depending on the technology and processes used. Biomass production also has its challenges. Since biomass resources are by definition, hydrocarbons, they release CO2 when burned. In addition, other use of biomass can produce other undesirable emissions, such as nitrous oxides and other volatile organic chemicals. Some biomass technologies can promote deforestation. Transportation, storage, and processing of biomass can be costly and create ancillary carbon dioxide emissions. Supply of biomass may be seasonal and variable and the energy efficiency of biomass energy may be low, meaning that the energy required to produce bioenergy, maybe almost as large as the energy obtained. Despite these challenges, biomass energy technologies can be environmentally and economically attractive when used to the right circumstances in the right way. In next video, we'll review concentrating Solar Energy. Will see you there.
