Extracting energy from biomass is an ancient practice, dating back to when people first burnt wood to provide heat and light. But just because the idea is old doesn't mean there's no scope for novel technology. Scientists are continuing to find new and increasingly efficient ways to extract energy from biomass, to a point where it is now being taken seriously as a future energy option. What is biomass? Biomass is a general term for living material – plants, animals, fungi, bacteria. Taken together, the Earth's biomass represents an enormous store of energy. It has been estimated that just one eighth of the total biomass produced annually would provide all of humanity's current demand for energy. And, since biomass can be regrown, it is a potentially renewable resource. One of the most appealing things about biomass energy is that it doesn't contribute to the enhanced greenhouse effect, provided that the biomass is harvested sustainably (Box 1: Biomass and greenhouse). Coal, gas, oil and other fossil fuels – the main greenhouse culprits – don't qualify as biomass, even though they are derived from living material. The time required for the formation of these fuels – millions of years – means that they can't be counted as renewable. Where does the energy come from? The original source of the energy present in biomass is the sun. Small 'factories' in plant-leaves called chloroplasts use solar energy (in the form of light energy, or photons), together with carbon dioxide from the air and water from the soil, to manufacture a range of compounds. These compounds include sugars, starches and cellulose – collectively called carbohydrates. The original solar energy is now stored in the chemical bonds of these compounds. Some of this stored energy is passed on to animals when they eat plants (or eat other animals). So plants, animals and animal excretions – biomass – can be seen as storehouses of solar energy (Box 2: Introduction to food chains). How biomass is used Scientists are busy developing different ways of converting biomass into a form that meets our energy needs, while making best use of the available energy. There are five different ways of extracting biomass energy: solid fuel combustion, gasification, pyrolysis, digestion and fermentation. Research into each of these is producing dramatic advances (Box 3: Ways of extracting biomass energy). Making haste with waste One source of biomass material is waste. Human society produces a veritable compost heap of organic waste. Kitchen scraps, sewage, the leftovers of the food processing industries, paper, sawdust, lawn clippings...the list is long. One of the reasons that energy from biomass is receiving so much attention is that it represents an opportunity to convert waste into something very valuable. In Australia, the potential value of organic waste as an energy source is only just starting to be tapped, with the sugar industry leading the way. It burns the residual fibre waste from raw sugar processing – called bagasse – to produce steam, which in turn is used to work the machines that process the cane and to drive electricity generators. The present installed electricity generating capacity of all the sugar mills in Australia is about 250 megawatts, 60-70 megawatts of which is sold to the electricity grid. According to the Sugar Research Institute, this is only a fraction of the potential capacity should more efficient systems be installed. One way of improving efficiency is called cogeneration, the practice of producing both electricity and useful heat. Some sawmills, for example, uses excess heat from boilers fired by sawdust to supply energy to their kiln-drying operations. But excess heat can also be used to gasify the biomass fuels so they can be used in a gas turbine, which is more efficient than a simple boiler that produces steam. Combined cycle technology can produce extra savings by using any additional waste heat from the gas turbine to power a steam-driven turbine. Landfill waste is a largely untapped resource in Australia. According to the Department of Industry, Science and Resources, the present installed capacity for landfill gas in Australia is about 72 megawatts from just over a dozen council tips. The scope for expansion is considerable. Nor is sewage so much on the nose any more, as we start to make use of it as a biofuel. The Department of Primary Industries and Energy estimates that the installed electricity generation capacity of sewage farms around Australia is about 7.5 megawatts - electricity production from this source could triple by 2010. Biomass farming Making better use of our waste could contribute significantly to our energy needs but it won't satisfy them completely. Some analysts have suggested that we should grow biomass specifically for energy production. One has even suggested that by committing about 2.5 per cent of the world's land area to energy crops (as well as by improving the recovery of energy from waste) we could meet about half of the world's current energy needs. In Australia, the Landcare movement is currently engaged in a large-scale tree-planting program in an attempt to arrest environmental degradation. Some of these plantations may produce valuable timber, but the commercial value of others is questionable. Perhaps some of the plantations could be used to generate electricity, thereby helping to meet the country's energy needs while also making a dollar for farmers. In Esperance, on the south coast of Western Australia, such a scheme has already been suggested. A power company there is considering plans to generate electricity by biomass gasification, using locally grown plantation trees as its biomass material. In suitable regions, biomass could be grown close to existing coal-fired power stations and used to supplement the fossil fuel supply. Future growth Ultimately, the success of biomass as an energy alternative will be determined by economics. Industries that use their waste biomass for energy simultaneously solve a waste disposal problem and save money on their energy needs (and, sometimes, earn money by selling excess electricity). As biomass technology becomes more efficient, the chances of biomass energy competing in the wider market place will increase. The government has announced that an additional 2 per cent of electricity (about 9500 gigawatts) will be provided by renewable energy sources by 2010. Biomass is likely to provide about half of this increase. Boxes 2. Introduction to food chains 3. Ways of extracting biomass energy Related Nova topics: Harnessing direct solar energy Enhanced greenhouse effect – a hot international issue
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Posted June 1999.
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This topic is sponsored by the Australian Government's National Innovation Awareness Strategy.
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