There are a number of slightly different definitions of renewable energy. The US Energy Information Administration (EIA, 2005) defines renewable energy as 'Energy obtained from sources that are essentially inexhaustible (unlike, for example, fossil fuels, of which there is a finite supply). Renewable sources of energy include wood, waste, geothermal, wind, photovoltaic, and solar thermal energy'. The definition presented by the Texas Renewable Energy Industries Association (TREIA, 2005) carries a more detailed description: '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.'
There are no reasons why the food processing industry could not use electricity generated by any renewable energy source. However, a very specific potential offers a co-product recovery from food processing that can use photosynthetic energy stored in biomass. In addition to the previously mentioned bagasse from sugar cane, the use of straw, grass and similar organic by-products from food processing is increasing.
The UK Department of Trade and Industry (DTI, 2005) classifies the biomass-dependent resources as those that include the by-products and waste generated by agricultural, industrial and commercial processes. This includes forest products, waste wood, straw, slurry, chicken litter, and industrial and municipal wastes (e.g. from food processing). For example, for every tonne of wheat harvested, a certain amount of 'waste' straw is created. Similarly, for every tonne of processed food, a certain amount of (mostly biological) waste is created. These by-products can be used as biomass fuels. In 2004, biomass accounted for 84% of renewable energy sources in the UK and this figure includes biomass used for both heat and electricity generation. Most of the energy was generated from landfill gas (33%) and waste combustion (14%) (DTI, 2005).
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