As indicated in the previous section, many feedstocks, in addition to energy crops, can be used as energy sources. For example, agricultural waste, such as corn stover, orchard waste, open pasture waste and manure, can be used in bioenergy production. Ref. [28] show that some of them are not economically feasible because of the high collection and transportation costs, and this problem may be solved if they can be pyrolyzed in a small, locally built bioenergy processing plant. However, the probability of a stable supply of the feedstock must be taken into account. Sweet potatoes, which can be cultivated continuously on idle land, and rice straw, which can be obtained from the rice paddy, also have stable cultivation patterns. The collection of other agricultural waste may be interpreted by the rotation of different crops. Therefore, the quantity and quality of feedstocks cannot be guaranteed, causing a serious problem in bioenergy production. In addition, different crop residuals may require different pre-processing process, which increases the risk of both cost fluctuation and the amount of electricity generation. Therefore, to develop the bioenergy industry, finding alternative feedstocks and ensuring the stable supply of feedstocks must be considered simultaneously.
Feedstocks with a stable supply can come from other sources of waste. Municipal solid waste is a potential feedstock that not only produces renewable energy but also alleviates the pressure on landfill spots. Pulp sludge is a typical municipal solid waste than can be pyrolyzed. However, it usually contains substantial heavy metal and toxic components that must be removed, which could require additional equipment and increase pyrolysis costs. In addition, the energy content of various types of wastes is uncertain. Therefore, whether the municipal solid waste can be applied for bioenergy production on a large scale requires further analysis.
This study examines ethanol and pyrolysis based electricity production in Taiwan and shows that the development of the bioenergy industry can benefit Taiwan in terms of energy security and GHG emission reduction. Rice straw is also incorporated into the analysis. It provides significant energy supply and carbon sequestration in certain cases. Potential feedstock alternatives are discussed, and the most important concern regarding the alternatives, the stability of their supply, is uncertain. To what extent bioenergy can enhance the net emission reduction also depends on which type of bioenergy (ethanol or electricity) is emphasized. Social factors such as job opportunity and unemployment rate may also have a great influence on governments’ decisions and policymaking. To better explore how social factors affect bioenergy production requires considerable work in integrating social, economic, environmental and regional issues, which is beyond the scope of this study.